| Author | Message | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 150 Registered: 10-2003 Posted From: 66.165.176.60  Rating: N/A |
I suspect this will start a bit of debate but here goes. I need to retrofit my coach with a better parking/Ebrake than the old drum on the driveshaft. If you were going to upgrade rear pots to a newer style is there an advantage of one style over the other? I see that spring brakes are cheaper but there must be a reason other coaches use DD3. Assuming you could fit either type which would you use and why. Tim | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 110 Registered: 1-2007 Posted From: 208.81.157.90  Rating: |
Spring brakes. Work great. Cheep. Simpler. Parts available everywhere. Service at any truck shop. No expert and I am sure others will respond with reasons for DD3s in buses, but I think it was a way to keep passengers from releasing brakes by pushing parking brake knob. Nothing wrong with DD3s. I have no plans to change unless parts become unobtainable. Don 4107 | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1005 Registered: 10-2003 Posted From: 71.58.48.5  Rating: |
If you don't already have dd3's use spring brakes as the others have extra air valves and piping over maxi's, plus a ridiculous cost for the chambers. Figure about $450 each exchange. New ones are not available. Maxi's are about $50 each, plus maybe another $100 for release valve and lines, fittings. One thing that DD3's do have is not having a large spring to hold the coach stopped. The possibility exists for a maxi to have a broken apply spring and not be able to hold on a grade parked with just one working. This is rare and spring brakes are used on all the otr semis for years with few problems. A lot of our coaches couldn't be changed from dd3"s to maxis even if we wanted to because there isn't enough room to install them. Plus involves removing or changing some valves and rerouting lines. DD3'3 are expensive because Bendix is the only company that made them afaik and they charge a lot for the parts or rebuilt units because there aren't competitive comparable units.Figure about $225 or $250 to rebuild two of them yourself. Not too hard to do; just get a Bendix service manual or one from a 4905. You can get the parts from Mohawk or others. That price estimate is only approx if the case halves are reuseable. You would need to disassemble and clean/inspect. Go with Maxi's and test them occasionally. Make sure the units are the same size as the old chambers. Should be either 30-30's 36-36's AND you can buy them at most truck stops/service areas or truck parts dealers. | ||
| Laryn Christley (Barn_owl)
Registered Member Username: Barn_owl Post Number: 326 Registered: 10-2006 Posted From: 153.2.247.31  Rating: |
I don’t think you will start much of a debate with that one. Put on the springs. | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 151 Registered: 10-2003 Posted From: 68.158.244.12 Rating: N/A |
I'm actually relieved there has not been much debate. The springs are much more cost effective but it's always good to find out if there is a downside | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1007 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
just remember, it's only been 8 hours since you started this post. Everyone else is out trying to fill up their coaches before fuel prices go up again. Crude hit $112 today so pumps will HAVE to go up tomorrow morning as it gets from the ground to the pumps so much faster nowadays. Credit technology? | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1245 Registered: 12-2000 Posted From: 76.68.120.191  Rating: |
I'm a DD3 guy, but I'll throw my support to install a spring brake system, if the chambers will fit. While DD3 is a fine system, it will be far more expensive and somewhat more complicated to properly plumb either a single or a dual circuit style system. If you are going to switch to spring brakes, go that little extra and refit to a dual circuit style system. You'll have to do a bit of plumbing and change out to a newer brake treadle valve. Read a lot and check back here to be sure you have it figured out. Measure twice, cut once. happy coaching! buswarrior | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 226 Registered: 3-2007 Posted From: 76.4.151.87 Rating: |
I am like BW, I love dd3 too. If you can put spring brakes on DO IT>>. I have an 4104 that was converted from hand brake to the spring brake and they work great. my 2cents gomer | ||
| Ed Brenner (Epbrenner)
Registered Member Username: Epbrenner Post Number: 33 Registered: 5-2007 Posted From: 64.12.117.73 Rating: N/A |
I used to have a 4106 and I added the spring brakes to it . I added the newer brake treadle vavle. They will not fit without cutting off the old brackets and welding on new ones and braces. I bought all the items brackets and all with instructions from Dean's Coach. I did it myself and it worked out great. Haven't talked to them in years but I believe Garys son still runs the business.He had a kit air line everything needed. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 286 Registered: 10-2006 Posted From: 66.90.226.172 Rating: |
"I need to retrofit my coach with a better parking/Ebrake than the old drum on the driveshaft." The brake on the driveshaft is only the parking break , your emergency break is the ICC valve. It works as well as either the springs or DD3 , as they all only work in the rear drums. In an emergency your coach can be pushed off the road , or towed with the existing setup , with the "modern " stuff you need a huge wrecker with an air supply to unlock your locked breaks. I would simply suggest relining the mechanical parking break and maintain the existing setup with in my opinion is superior in RV operation to the new stuff. In a breakdown I would prefer to stay mobile , rather than be prey for the Road Pirates. FF | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 152 Registered: 10-2003 Posted From: 66.165.176.60 Rating: N/A |
FF, While I respect the advice another reason I want to install spring brakes is to have another option than the ICC valve should I experience a catastrophic failure in the air system. as you know if there is insufficient air pressure and ICC valve isn't going to do anything for you. As to the road pirates thats why I carry full towing coverage on it. Now it's time to read up on a dual circuit system | ||
| Jim Wilke (Jim Bob) (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 277 Registered: 2-2001 Posted From: 69.77.153.238 Rating: N/A |
Tim, you can install a small air compressor in a bay like used for nail guns. This can supply kids water toys & bikes as well as air the bus up before you leave a campground so you don't have to idle the Detroit and fog/annoy your neighbors. If you have a genset or BIG inverter on board this rig can also temporararily supply your bus systems if you had a main compressor failure. | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 153 Registered: 10-2003 Posted From: 66.165.176.60 Rating: N/A |
Jim, That's a really good idea. I have a 15KW gen so power isn't an issue. | ||
| Kyle Brandt (Kyle4501)
Registered Member Username: Kyle4501 Post Number: 406 Registered: 9-2004 Posted From: 65.23.106.193 Rating: N/A |
My spring brakes have a cage bolt to release them. A true PITA if you have to use it . . . But still leaves options if no air is available . . . | ||
| Mitch Wright (Gyrocrasher)
Registered Member Username: Gyrocrasher Post Number: 13 Registered: 5-2006 Posted From: 68.102.119.87 Rating: |
FWIW, here's a video test, created by Brian Brown, comparing the emergency stopping power of the two types of brakes. I know which I'd rather have. Mitch http://www.thefamilybus.net/videos/parkingbrake.wmv (Message edited by gyrocrasher on April 10, 2008) | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1011 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
Some have an additional air tank to only be used to release the spring brakes in an emergency to move the coach. My 4905 has a small Sears oil less compressor with about a 12 gallon tank that can be run to air up without running the engine or in an emergency. In middle center of one bay and is pretty quiet. Nice for morning in campground- air up, block heater on for a couple of hours using the electricity you paid extra for. Start up, run for ten to twenty seconds for oil pressure and ease out. Helps fuel mileage as idling time is cut way back. At $1.00 a gallon, few cared about wasting fuel. Oh, and useful for finding air system leaks too. That drive shaft drum is a pita when you need to do differential, transmission, u-joint repairs. Also that big lever is somewhat in the way up front. Also removing and related parts and linkage will eliminate a few hundred pounds to keep that sports car light. | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 111 Registered: 1-2007 Posted From: 208.81.157.90 Rating: N/A |
'FWIW, here's a video test, created by Brian Brown, comparing the emergency stopping power of the two types of brakes. I know which I'd rather have." I think this video was made in response to an old thread about what happens if you apply parking brake at speed and to dispel the myth that things come to a very sudden halt. Emergency brake or parking brake? I vote for parking brake. The emergency brake in my busses is my right foot. I want to be able to determine how fast I stop in an 'emergency' and I don't want it to be an irreversible action. If the ole right foot fails to get the desired response, then I might consider pulling the knob. If you have a sudden catastrophic air system failure trucking down the road at highway speed do you want a tire smoking, rear-end crash causing, heart stopping event that leaves you sitting in the middle lane of a freeway, or do you want a nice controlled stop that lets you know you have a (serious) problem and gives you some options? Don 4107 | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1247 Registered: 12-2000 Posted From: 76.68.134.95 Rating: N/A |
Mitch, hold on... Don't be making decisions about which style you want to have from that video. The stopping performance of the DD3 equipped bus was not acceptable. It should have stopped much more like the spring brake equipped transit. Don, when you lose the air pressure in this catastrophic failure, how do you plan to make this nice controlled stop? In the good old days, no air meant no brakes.... happy coaching! buswarrior | ||
| Moe Hollow (Moehollow)
Registered Member Username: Moehollow Post Number: 31 Registered: 12-2007 Posted From: 71.102.34.199 Rating: N/A |
My '65 MC5a has DD3's and my '67 Superior has spring brakes which I believe were added since there is the remnants of a hand brake system. I have not had to use either in an emergency and both serve their daily functions well. Wasn't there some reason that passenger buses were mandated to have DD3's? I had to replace mine recently, and it was quite expensive, but I do not think I will ever have to do it again. Transforming the system to springs would not have been cheap, and may have had other complications. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 401 Registered: 8-2006 Posted From: 76.91.197.153 Rating: N/A |
Maybe an easy answer to the question? DD3s came about 20 or 30 years before springs/maxis. That's why most of our busses have DD3s, because they fall into the right age range. DD3s have a separate application reservoir which charges the parking chamber of the brake system when the knob is pulled. They remain applied after air leaks off because of a mechanical "latching" system that has to have air applied to it to release. If I had a handbrake type parking brake, and wanted to upgrade it, it would be maxis, even though my bus has DD3s. I won't change them out, only because it would be a lot of work. FWIW, George | ||
| Mitch Wright (Gyrocrasher)
Registered Member Username: Gyrocrasher Post Number: 14 Registered: 5-2006 Posted From: 68.102.119.87 Rating: N/A |
Hi guys Here's the thread that precipitated that video. http://www.busconversions.com/bbs/index.php?topic=1489.0 And to quote Brian in that thread: "In my post, by emergency, I meant an air-loss emergency, not a traffic-induced one".I agree with Don 100%, in that I'd MUCH rather have control of braking w/the treadle valve. However, sometimes I don't get my 'drathers' Buswarrior, I hadn't considered that those particular dd3s may not have been up to par. I have lot's of experience with springs, but VERY little w/dd3s The one such equipped bus (30K lbs?) I test drove (a whole 20 miles) would not stop as well as my 80K lb semi. Perhaps the system was not up to snuff. No offence intended to the owner of that bus-just speculating.In retrospect, I don't see why the SERVICE application of both types would not be equal. Of course the semi has 5 axles braking instead of 2. (4106) Wait...what was the topic?:-) And Tim, I drove that entire 20 miles w/the hand brake on. She pulled just fine, but the seller was (politely) less than happy about it! Mitch (Message edited by gyrocrasher on April 10, 2008) | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 112 Registered: 1-2007 Posted From: 208.81.157.90 Rating: N/A |
What I was trying to get across, probably not well, is that the only time I would consider using the parking system while under way is if the service brake system failed completely and you should not expect it to bring your rig to a screeching halt. If I have a air system failure and have failed to recognize things are going south, when the system applies the brakes I would not want and it will not stop the bus like a max application of the service brakes. If for no other reason only the rear brakes are applied. I at least want a shot at getting to the side of the road. I know what the old bus that has spring brakes does, have not tried the new (actually older) bus with DD3s when rolling, yet. To chicken to play with the (very) short wheelbase day cab I move the boat with. Nothing on the fifth wheel probably equals flat spotted tires. Don 4107 | ||
| Mitch Wright (Gyrocrasher)
Registered Member Username: Gyrocrasher Post Number: 15 Registered: 5-2006 Posted From: 68.102.119.87 Rating: N/A |
I agree with all of that, Don. Especially the part about the flat spots. I suspect that day cab would get real interesting real fast. I can assure you an empty 48' trailer does! Witnesses behind me said I was using most of 3 lanes in OKC when I lost air to the trailer.(road debris) From what they could see through the smoke, anyway. M | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1013 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
Tim, remember back at the beginning of this thread that you were glad there wasn't much debate on this. See... they all got back from filling up their coaches.  | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 290 Registered: 10-2006 Posted From: 66.90.226.187 Rating: N/A |
as you know if there is insufficient air pressure and ICC valve isn't going to do anything for you. Not very likely, Read your book and you will find the brake air is well protected , and not likely to be lost when an air bag or feed line blows. On startup if you watch the gage and listen to the low air buzzer , you will hear the alarm stop long before much pressure exists in the rest of the system. Thats why you service 3 air tanks,not 1. FF | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 403 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
FF, Lets consider a very real situation! Either a rear diaphragm ruptures, or a rear hose breaks, with the resulting large air spillage. Now you have your foot on the pedal, the low air alarm is on, and you are not stopping. Flipping the ICC switch will add more air to the leaking system for a few seconds, depending upon just where the leak is. If the combination of foot pedal, ICC switch, and handbrake stops the {low air pressure bus,} and the handbrake holds it, great! Now a question: Have you looked at the size of the handbrake drum on your bus and compared it to the size of ONE rear brake drum lately? (After you do this, you will understand why a better method of emergency stopping was invented!) Before you fall all over yourself to post back, I am well aware that most buses, including yours and mine have protection valves, and check valves, which will prevent brake reservoir pressure loss when a failure occurs in the auxiliary portion of the air system!!! The problem with your comment is that it absolutely does not address what happens when the failure is in the treadle valve, the relay valve, the brake reservoir, any of the piping and hoses front to back, or the brake diaphragms! DD3s have a FOURTH tank, which is also check valve protected, and applies a completely separate pair of diaphragms on the large rear drums. Maxis accomplish the same thing with springs instead of the fourth reservoir. AND, both of these systems remain applied with no air in the bus! Bottom line? With either DD3s or Maxis, popping the knob will give the same amount of braking force ON THE DRIVE AXLE as a full foot pedal application, with no air at all in the rest of the bus. All of us DD3 and Maxi owners know that won't happen, because the inversion valve will initiate an emergency application by itself at about 75 pounds. George | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 157 Registered: 10-2003 Posted From: 68.158.244.12 Rating: N/A |
It also may surprise everyone but Flx has only two tanks....a wet and a dry. George that is exactly the scenario I am trying to mitigate. Tim | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 158 Registered: 10-2003 Posted From: 74.244.14.221 Rating: N/A |
For anyone curious here is a shot out of the service manual of the entire system (Message edited by timb on April 12, 2008) (Message edited by timb on April 12, 2008) (Message edited by timb on April 12, 2008) | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 159 Registered: 10-2003 Posted From: 74.244.14.221 Rating: N/A |
let me try again http:\members.tccoa.com\timb\air.jpg so what's the trick to getting HTML to post it is automatically removing one of the slashes and the file size is larger than the 50 kb allowable to attach (Message edited by timb on April 12, 2008) | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1016 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
George, you're right on on this. One thing about that drive shaft brake drum though is you are multiplying that braking force times the axle ratio or 4.11 times the force or so. Which would help the available stopping power. But, get rid of it and the associated linkage and put on the maxis. Then we can move on and talk about other important issues like electric cooling fans. Those old systems were good in their day, but technology keeps marching ahead. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1249 Registered: 12-2000 Posted From: 76.66.18.200 Rating: N/A |
A correction to one of George's points, for the benefit of those who will read this in the archives: A spring brake or DD3 parking/emergency application is not as strong as the full service application, and was never intended to be. It only takes somewhere in the neighbourhood of 60 lbs of air to fully cage a good spring brake, and a DD3 has somewhere around 85 lbs applied to a diaphragm that is smaller than the service diaphragm. Both styles of parking systems are considerably weaker than the squeeze that the brake pedal is able to transmit via the service portion of the same chamber with a healthy air supply behind it. A parking brake stop with spring brakes or DD3 in a coach style bus is just another moderately aggressive stopping event. On a good traction surface, with a bit of speed on, there won't be any wheel lock. Let's keep it in perspective, the parking brake needs to be strong enough to keep it from rolling away on a steep hill, and may be employed in an attempt to stop when regular methods have failed, hence the use of the word "emergency". Over the years, the performance of parking brakes has been mandated to improve, and their role in performing a more "automatic" back-up to the service brakes is more formal and designed to be somewhat fail safe. Updating from one of the older systems to a newer one has advantages, should the coach suffer the wrong air system disablement while under way. happy coaching! buswarrior | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 292 Registered: 10-2006 Posted From: 66.90.226.60 Rating: N/A |
"Have you looked at the size of the handbrake drum on your bus and compared it to the size of ONE rear brake drum lately?" Yes, it is more similar to a single front brake . But the assumption that an air failure will occur at the Exact same time that HARD breaking is required is not ,to me realistic). If normal slowing and modest breaking is required , the hand break will do it. I have sucessfuly stopped the coach from cruise (70 mph) on entering a turnpike parking area the normal way.Some slowing some coasting and lots of moderate breaking with only the hand break. "Updating from one of the older systems to a newer one has advantages, should the coach suffer the wrong air system disablement while under way." And perhaps some operational disadvantages too, do it Your Way, FF | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 405 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
FF In my opinion, hard BRAKING is exactly when a failure will occur, because that is when the diaphragms and hoses are under the most pressure! That is when a BRAKE hose, or a BRAKE diaphragm will BREAK, if you get my drift. In that situation, the handBRAKE will not stop the bus short of a collision. Either DD3s or Maxis will provide much more stopping power than a handBRAKE. Please tell us how much BRAKING force is applied to the rear drum slack adjuster arms by a pair of #30 cans, at 120 psi. Then take a guess at how much effort you can apply to your one parking BRAKE drum with your handle. This isn't a trick question either! I'll post the answer in a couple of days, and I welcome answers by others also. In my opinion, after the low air warnings start, I can get to the side of the road, or out of the way, before a penalty application occurs. Having a bus stopped by a low air application, is a LOT better than one stopped by a rear end collision, where I am at fault. Do it your way, after you do the math. George | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1022 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
You getting all this Tim? | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 160 Registered: 10-2003 Posted From: 74.244.14.221 Rating: N/A |
just sitting back eating popcorn and watching the show | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 406 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
You notice the silence is deafening? ROTFLMAO, thanks to Kyle. G | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1025 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
Thanks a lot Kyle! | ||
| JR Lynch (Njt5047)
Registered Member Username: Njt5047 Post Number: 230 Registered: 7-2006 Posted From: 69.132.233.230 Rating: N/A |
My feelings are that almost anything is better than a driveshaft handbrake system of old. From my perspective, limited it be, if any catastrophic air loss presents, I just want to stop...preferably without my having to reach for anything. Rear end collision or whatever...just let the brakes apply. I'd be happy to find myself sitting in the middle of an interstate...stopped. I'll keep my DD3s. One point no one has mentioned is the size (length) of most spring brake cans. Some coaches don't have room for spring brake retrofit. Some MCI models don't have room for spring brake chambers Spring brakes appear to be more desirable than DD3s. Much less complicated. I've heard that DD3's softer emergency stops were considered desirable on a bus. Less potential for injury with a softer application? I also notice that some newer MCI "D" series have spring brakes as standard equipment. JR | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1251 Registered: 12-2000 Posted From: 76.69.141.132 Rating: N/A |
Ummm.. George, what power are you intending the spring brake or DD3 to have to stop the coach by itself? It isn't related to 120 lbs. This comparison of potential stopping power with the driveshaft drum handbrake will not be as far apart as some suspect. I concur, the chamber diaphragm tears or the hose bursts with a pressure applied. The most inopportune time! It is unfortunate that drivers, then and now, do not have very good guidance for their thoughts as to what they should do upon seeing the air gauge dropping rapidly. In the rare circumstance of experiencing a fast dropping air gauge while driving, this requires the driver to take immediate action. No thinking. STOP, NOW, QUICKLY, with whatever air is left. Head for the shoulder. You may think and wonder about why this has happened later, if there is a later. Preventive Maintenance is key to leaving this experience to others. Busnuts are notorious in their ignorance/negligence to do proper regular inspections and maintenance on these tired and worn out chassis. In a union shop, big fleet, for a stock, in-service MC7-8-9, a full preventive maintenance inspection, lubed, adjusted, tested, measured, everything in the book done, took two mechanics a 40 hour week to do. How many hours a year do we put into all the various systems? Back to our current issue, in this instance, testing of the brake system to check for air leaks. Aired up, engine off, parking brake released, brake pedal to the floor. Watch the air gauge, and listen for leaks. Easily done every day just before you pull out. Easily done at every stop light, when the compressor is cut-out. If you get any pressure drop in one minute, best to get under there and find out what is leaking. If you do not know how old your brake chamber diaphragms are, best to change them. Same for the rubber brake lines. It may be cheaper in time and effort to replace the whole chamber. Price it both ways. Cheap insurance, good reliability and a fine example of due diligence. Tim, good going, we'll have every aspect of brake design, performance and maintenance covered on here by the time we're done! happy coaching! buswarrior | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1252 Registered: 12-2000 Posted From: 76.69.141.132 Rating: N/A |
The Double Diaphragm 3 Airline Safety Actuator came along popularly just ahead of spring brakes. The fact they stopped the bus "automatically" under a loss of air, with the isolated second air supply, and stayed parked when the air leaked away, were their major selling points. The effectiveness of the stop was irrelevant at the time, as the alternative handbrake application required human intervention, and thus was less safe. The story about smooth stopping is a fabricated explanation in the intervening years. Remember that the rubber diaphragms of that day were no match for today's, they failed more easily, so this automatic feature was an attractive consideration versus the handbrake. Frankly, with the isolated parking supply, the DD3 system was matching the safety a decade and a half earlier of the government's mandated dual air system of 1975. As the years have gone by, MCI staunchly supported the DD3 when everyone else gave up, finally succumbing to the economic pressures and switched to spring brakes due to their lower costs only a few years ago. happy coaching! buswarrior | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1188 Registered: 5-2001 Posted From: 71.59.182.58 Rating: N/A |
Buswarrior, I think that your posts really hit the nail on the head! A good job, all around. We changed to springs when we found that the hazard of a blown rear chamber was not covered by the ICC valving. Making room for them was not very difficult. I noticed that no one brought up the oiled handbrake drum from a leaking pinion seal. I seems too commmon to be ignored. The handbrake does not stop the coach very well when oiled up! A handbrake is kind of handy when manuevering over a pit or adjusting brakes. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 166 Registered: 2-2007 Posted From: 207.200.112.102 Rating: N/A |
Guess those dd3s been around along time! I drove a 48 KW that had factory maxi brakes. When dd3s came along I asked why they didn't just use maxi brakes and was told USDOT would not approve them for passenger use. Maxi/spring brakes are applied when there is no air present. If you are parked they are on and when you build air and compress the spring they are off. The reason USDOT would not approve spring type brakes for so many years is that if you have a bad diaphram (leaker) on the emergency side it will not hold enough air on the diaphram to keep that brake spring from applying as you are driving down the road. The shoes get cherry red, the drum gets cherry red and since a bus does not have the air flow under it and around the brake drum that a truck has, a bus will burn to the ground. Not a good senario for passenger service. Over the years it was proven that with regular service (changing diaphrams often) spring brakes could be acceptable to USDOT. USDOT allowed spring brakes starting sometime in the 80s on passenger buses but you have to know what to watch for or you will burn your bus if you loose a diaphram on the emergency side and continue to drive. I change mine every couple of years on the buses and usually change them on the trucks when they start smoking. dd3s will not drag the brakes and that is why they were invented for passenger use. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1031 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
The driveshaft drum brakes usually have a passageway or tube to allow leaking tranny oil from the rear seal to escape without getting on the lining or drum surface.BTW, if a Maxi has a broken emergency apply spring, there may not be enough force to stop the coach quickly with only one properly operating spring brake. And we haven't even gotten into oil lubed rear hubs leaking onto the rear lining, loosing 40 percent of the braking capacity. Some prefer synthetic grease lubed hubs to mostly prevent this possibility. Time for more popcorn Tim. While you're there, get me some; light on the butter. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 409 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
B W has thrown it all out there really well, and there really wasn't a debate to start with, everybody said put on maxis, except the guy with a handbrake. To answer the question, and it wasn't a trick, I was just trying to get one person to think, and we did get an answer that a driveshaft drum is approximately the size of a front drum. We all know that our rear drums are twice that size, which makes the driveshaft drum approximately 1/4 the size of the total area of the two rear drums, right? Now, cans are sold by their square inches of diaphragm area, so a number 30 can has 30 square inches of diaphragm area, times 120 psi gives 3600 pounds of force on ONE adjuster arm, times two = 7200 pounds of total effort on the arms! I don't want to go into the length of the arms, S cams, etc, all I want to ask is how much effort can one of us put on a driveshaft drum? The handle is about 3 feet long, but the effective length is less by the amount below the pivot to the yoke on the rod. Then we have to know how much is gained by bell craks, etc, and lost by mechanical binding, etc, and I don't know how much clamping travel there is on the constricting shoe, versus how much the lever moves. Bottom line, I don't think it is anywhere near 7200 pounds, and one small drum is going to get hot in a hurry if the bus is going any speed. A comment on "dragging maxis." They are equipped with low air pressure protection, just the same as DD3s, somewhere between 70-80 pounds, the parking valve will pop up, and you get a full application of the springs. If the leak is large enough to prevent the diaphragm from holding the spring off, the bus/truck will lose reservoir pressure, and a "penalty" application will occur. Then we need to ask "What happens when one DD3 parking diaphragm ruptures?" Well, half the stopping power again, and lets hope there was enough application made that the locking system can hold the bus, before all the emergency air leaks away! I really like John's comment about oil lubed rear hubs, because that was the way my bus came to me, only it was the left tag. Enough, George | ||
| joe padberg (Joemc7ab)
Registered Member Username: Joemc7ab Post Number: 233 Registered: 6-2004 Posted From: 66.38.159.33 Rating: N/A |
George Driving home one day when this post first got started it occurred to me that nobody had factored the multiplication or division of the rearend into the equation. Well John R beat me to it. I think him and I think alike in many areas!! I donot know whether you overlooked that fact in your last post, but I think it is very relevant and would change some of the figures. Having said that, my personal preference would be to go with the maxxis Joe. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1259 Registered: 12-2000 Posted From: 76.66.17.97 Rating: N/A |
Hello George. You need to cut the force by more than half. The spring in a spring brake is fully caged by 60 lbs of air, so it is weaker than that. And the effect of the differential gearing, as noted by others has to be considered as an advantage of sorts to the handbrake. The handbrake will be stressed in the comparison, but not by that wide a margin. Maintenance and condition of both systems will be critical out in the real world as to what really might happen in each of our conversions. No matter the type of brakes each of have, have we inspected them, and tried using them as we might if we had a failure in the service brakes? happy coaching! buswarrior | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 410 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
B W, Lets kick three or four things around. What I asked for was braking force from a #30 can at 120 psi. That is 3600 pounds of force, I was not asking for either DD3 or spring application force. With two drums on the rear, there is a TOTAL force applied to the rear adjuster arms of 7200 pounds. The length of travel of the adjuster arm, compared to the movement of the shoe by the S cam is 3 or 4 times, I never measured when I had drums off, and it doesn't really matter whether it is two or five either. Lets just say for the sake of discussion that the adjuster arms and S cams double the pushrod force, ok? Now, in that case, which is probably a little conservative, we have 14,400 pounds of force applied to the ends of the shoes. The way I THINK I understand lever multiplication, is it is a direct result of the difference in distance traveled??? So, we can probably pull a handbrake lever a foot, which will move one end of the shoes, or constrict a band an inch? If so, and we put a hundred pounds of force on the end of the handle, we would apply 1200 pounds to the drum. I also agree 100% with the comments about the HOLDING POWER of the handbrake being multiplied by the differential ratio. Would we then get the EQUIVALENT of about 5000 pounds of force on a STOPPED bus driveshaft drum with a 4.11 ratio? Yep! NOW, we're going down the road at 70 mph, and the handbrake drum is being turned four times faster than the rest of the brake drums, and we apply 1200 pounds to it. It IS being turned four times as fast as the other drums, so it will produce FOUR TIMES THE BRAKE HORSEPOWER it would if were being turned at axle speed, with the same amount of force applied. My point is that we are asking that one "smaller" drum to provide braking horsepower equivalent to 5000 force pounds, I'm pretty sure, while a full pedal application will produce 14,400 force pounds on the rear drums, with at least FOUR TIMES the surface area. Then, how much effort do the front brakes supply? My whole point is that a properly maintained handbrake is not going to provide much braking effort, and is going to go up in smoke quickly either at speed, or on a grade. Next point, and I agree with you, but I just want to get it out for reference. Springs are supposed to provide stopping effort in proportion to the diaphragm size. So if a #30 can is fully caged at 60 psi, thats 1800 pounds of force, ON ONE ARM, times two, equals 3600 force pounds on the rear brake ARMS, and about 7200 on the rear DRUMS. I also like your term of "moderately agressive stop." It describes a DD3 application perfectly. I pop the knob at 3-5 mph once a week or so, when I am going to park the bus someplace where a couple of feet one way or the other doesn't matter, as a test. The stop is (and should be) pretty quick, but not jamming a car in park. KUTGW, George | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1036 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
Don't forget to add the self energizing effect of the drum brake shoes on the drive shaft. The rotation of the drum tries to rotate one shoe that in turn adds more force to the other shoe as in drum car brakes. This does mot happen in air braked shoes, as the bottom of the shoes are against stops and can't assist the other shoe. AND don't forget the pucker power addition that can be added to that emergency brake handle in an emergency! Sorry, had to keep this going- not out of popcorn yet. I have experience with this; the first coach I had was a 1948 ACF Brill with nice sized but a little greasy rear brakes, no maxis and a good working emergency brake. Back then, I was working with a shoestring and hadn't cobbled up enough to rebuild the brakes to proper condition. I drove easy, kept lots of room and watched for possible problems. The brakes worked, but just not as well as they should. Did have to use that emergency brake once, because of some idiot two cars ahead. Stopped with 6 foot margin and an adrenaline rush. One time I had vapor lock on a mountain and had to pull off on the side of the road. The grade was steep enough that the emergency brake wouldn't hold the coach. Had to hold the foot brake on while sister in law went out and looked for rocks to put behind tires. That convinced me that however nice that em. brake was, I was going to go for spring brakes as soon as I could afford them. Anybody that wants to stay with a driveshaft brake instead of dd3's or spring brakes is an idio.....uhhh naive. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1261 Registered: 12-2000 Posted From: 76.69.140.108 Rating: N/A |
Hello John. There's a chance that had you had spring brakes with your oily linings, they might not have held on the slope either!!! Theoretically speaking, the handbrake/driveshaft drum system has a redundancy that the spring/DD3's don't. It is a completely seperate system from the service brakes. With springs/DD3, whether foot brake or parking knob, the chamber acts on the same linkages and squeezes the same shoes...if that brake is out of adjustment, contaminated with oil, linings glazed, linings powdered from overheating, cam bushings worn, allowing squirm instead of twist,...if the brake is ineffective with one part of the chamber squeezing, it will be ineffective with the other. George, try popping the parking brake at 25 mph or better, on a good road, with no one following you, of course! At a couple of mph, there is very little braking demand; broken springs, brakes out of adjustment and even oil contaminated ones will feel like they are working, and give you a false sence of security. DD3's with improperly set pressure regulators on the park portion will also expose themselves with a bit of load put to them in a stop. happy coaching! buswarrior | ||
| joe padberg (Joemc7ab)
Registered Member Username: Joemc7ab Post Number: 235 Registered: 6-2004 Posted From: 66.38.159.33 Rating: N/A |
Fred's handbrake probably works quite well.The only thing that is left on mine are some linkage pieces, so I have no way to compare. He strikes me as being a fastidious guy that makes sure that his stuff is up to snuff. Now fred being on the right coast and george on the leftcoast it would be kind of difficult to arrange a side by side runoff between the light 06 and the heavy mc6 from say 35 mph. If that could be arranged , I would willingly volunteer to suply some good canadian beer. Joe. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 413 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Do we get the beer before or after the test? John, I think you left out the hole in the seat? BW should talk to the seller of my coach, (charter company) after finding all of the brake troubles it had when I bought it! I really need a high powered beer now! George | ||
| Laryn Christley (Barn_owl)
Registered Member Username: Barn_owl Post Number: 366 Registered: 10-2006 Posted From: 72.66.181.54 Rating: N/A |
The PO of mine converted to springs, but for whatever reason, also left the working hand brake. I think in a panic situation it would be awkward at best. | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 161 Registered: 10-2003 Posted From: 74.244.14.221 Rating: N/A |
john roan, What year did you have the brill. My folks had one as well back in the 70's in CA. Ended up being stolen by the broker who was selling it for us. | ||
| joe padberg (Joemc7ab)
Registered Member Username: Joemc7ab Post Number: 236 Registered: 6-2004 Posted From: 66.38.159.33 Rating: N/A |
George A couple before, none during, and more after. Joe. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1039 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
1948 IC-41 | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1264 Registered: 12-2000 Posted From: 76.66.18.98 Rating: N/A |
I'll have a beer or two with you.... All in the pursuit of higher understanding, of course! Drinking as an educational tool...hmmmm this could catch on.... happy coaching! buswarrior |
