| Author | Message | ||
| Stan Rating: N/A |
Several posts recently about brakes and air leaks indicate that a lot of people have no idea of how this brake system works. A majority of the buses owned by people on this board use DD-3 brakes. When someone asks a question they have every reason to expect answers that are, at a minimum, based on knowledge of the system. Everyone using this brake system (or giving advice) should use the book and understand how the rear brake cans, the inversion valve and the regulator feeding the inversion valve operate in conjunction with the foot valve and the the push-pull valve. It is not the same as the spring brake system used on trucks. A lot of the question indicate that this is not undrstood and a lot of answers are totally wrong. PROPERLY OPERATING BRAKES ARE CRUCIAL BEFORE TAKING A BUS ON THE ROAD. | ||
| Ian Giffin (Admin)
Rating: N/A |
Hi Stan, Are you up on your DD3 brake knowledge? If you are, we'd be happy to get a new "Article of Interest" on this subject matter. I agree with you, and it can't be overstated, that everyone in this hobby should have at least a fundamental knowledge of their braking system before setting out on any jouney. As a matter of fact, in many jurisdictions, it is the law that you do a complete circle check of your bus, including a check of the brakes and braking system, before moving the bus. Ian www.busnut.com | ||
| TWODOGS (Twodogs)
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yeah Stan...tell us everything you know about dd-3 | ||
| Ian Giffin (Admin)
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Two Dogs, Stan has already been in touch with me via email with a detailed outline and I have a writer who is completing the article, as I write this message. Stay tuned... it'll be in the "Articles of Interest" by the end of June. Ian www.busnut.com | ||
| niles steckbauer (Niles500)
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ROTFLMMFAO , I@N | ||
| Buswarrior (Buswarrior)
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|@N Good estimate, proper research and technical writing takes lots of time! And you didn't indicate which year, good for you! Always got a contingency plan! I bow down low in your presence! happy coaching! buswarrior | ||
| Artis Rating: N/A |
Maybe the "Article of Interest" by Two Dogs about electric fan conversions for buses will be right there next to Stan's article......hahahahahah!!!! | ||
| TWODOGS (Twodogs)
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would take up too much room.... | ||
| J.B. Rating: N/A |
At BusnUSA this year was a custom coach built in Auburn, Wa. it was cooled by two 40amp refridgeration fans. One came on at one temp and the second came on at 5* higher. I spoke to the owner/builder for 1/2 hour and he claimed they worked well for him. J.B. | ||
| TWODOGS (Twodogs)
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elec. fans WILL work...rideing TWO DOGS doesn't  | ||
| Ian Giffin (Admin)
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Yeeeeeahhhh, giddyap!!!!!!!!!!!!!!!!! I used to just like you, Two Dogs, but now I really loves ya, baby!! Two Ians www.busnut.com | ||
| TWODOGS (Twodogs)
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I think of you often dad | ||
| Stan Rating: N/A |
Nobody is rideing Two Dogs. You can't ride a dead horse. BTW Two Dogs: Check your facts when you tell somone that you apply air to release A DD-3 brake. There is always a chance that someone might think you know the answer. | ||
| TWODOGS (Twodogs)
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teach us stanley | ||
| Ian Giffin (Admin)
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Now, now, kids, let's do try to be civil, hokay? Thank you. Ian www.busnut.com | ||
| niles steckbauer (Niles500)
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Ian - did you take a funny pill today - your freakin hilarious - keep 'em com'in | ||
| Jim Bob Rating: N/A |
I just signed onto the Two Dogs team on this one, (AND ONLY THIS ONE) Stan. Tell us how you release a DD3 without applying air. Jim-Bob | ||
| gusc Rating: N/A |
It appears to me that the link http://www.mcicoach.com/parts-service-support/serinfo/serinfo0700.htm provided by Davidinwilmingtondl under "The du-u-uH valve" tells just about all one needs to know about DD-3 brakes. | ||
| gusc Rating: N/A |
Correction; it is "DavidInWilmNC" not dl. It is also "the duhh valve". I should be a newspaper editor after all these corrections!! | ||
| Craig (Ceieio)
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"I should be a newspaper editor after all these corrections!!" Aim lower, try the evening news. | ||
| Buswarrior (Buswarrior)
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Hello all. Using MS Word, if you highlight and paste the MCI Service Info that gusc gave us the link for, http://www.mcicoach.com/parts-service-support/serinfo/serinfo0700.htm it works properly if you change the page setup to landscape. It didn't paste properly for me into a portrait orientation. happy coaching! buswarrior | ||
| john w. roan (Chessie4905)
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For anyone that rebuilt their dd2 chamber(s) and got the parts from mohawk...could you get all you needed in one" kit"? or did you need several items? | ||
| Brian Brown (Blue_velvet)
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John, I rebuilt a DD3 on my old MC8 with Mohawk parts. About $100 instead of the $400 for a rebuilt can. I dug into mine to see what was broken or worn out, then ordered the parts I needed. There's like 70 pieces to them, so it's hard to know what you need until you do that. Dunno what's in their kits, though. I'd advise to replace a lot of the cheapest parts in 'em, because it's a LONG job you don't want to have to do again. HTH, bb | ||
| john w. roan (Chessie4905)
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Thanks... One of mine started leaking after sitting for the winter, so I'm going to just rebuild them both and be done with it. I wish someone would make a nice short Maxi that would fit in it's place.I measured it and it's too much work to modify the body to make any of the current Maxi's fit. | ||
| Brian Brown (Blue_velvet)
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John, although the DD3 gets some bad press on the Boards, it's an impressive device. Once you dig into it, you'll be amazed at the engineering that went into it. The rub is that the accompanying air plumbing makes them so confounding to troubleshoot. And they cost LOT$ more than equiv. spring brakes. But, the aux. diaphram will stop your bus much more rapidly in an emergency situation than any spring brake could. And stop it will. I liked to have never gotten my MC8 rolling again... until I fixed the can. Sounds like a good safety device to me! BTW, make sure the dust shield and breathers get put back on right. Mine were missing and clearly led to its demise. HTH, bb | ||
| gusc Rating: N/A |
John, There is a short maxi that fits buses. At least I was told this by a very savvy bus converter/mechanic. I was about to buy a bus from him and was going to have them installed. It is very common. This was a GMC, don't know about MCIs. I don't think there is a better emergency/parking brake made than the maxi. All trucks that I know of use them, they weigh 80,000lbs +. All air brakes are actually mechanical brakes so the spring application is the only completely foolproof system I know of. Depending on air for emergency application is not so hot an idea to me. I wouldn't want my wheels locked up in an emergency and air will certainly do that. A locked up wheel is a wheel out of the drivers control. Maybe DD3s don't lock up, don't know much about them. | ||
| Brian (Bigbusguy)
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As far as I know the DD3 will lock up your wheels at hwy speed if you plug it. Not to hard to rebuild . One thing I found out from Bendex was that oily wax type stuff on the rubber is Murfeys Oil soap. I needed to put something back on my older diphrams after I cleaned them. On mine I just needed a 0.50 cent 0 ring. and a good cleaning and greasing. Brian 4905 Klamath Falls Oregon (Kanasas City) | ||
| Stephen Fessenden (Sffess)
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And a bad DD3 can fail to mechanically lock and release the parking brake when there is no air. The reserve air pressure sets the parking brake, but it is held by a mechanical device that can rust and fail occaisionally. Thank God I learned that in flat Florida, not in Tennessee. So occaisionally, bleed off the air in your bus (if it doesn't self bleed like many of ours) and see if the DD3s are still holding ( on flat, flat land only). | ||
| jim Bob Rating: N/A |
Steve, once the park feature is set, the DD3 locks the actuator shaft with a handful of steel balls that wedge against the shaft, preventing it from retracting. (If in poor condition, it might stick that way when you try to release it.). But... to release DD3s, you have to have air for 2 functions. First, when you push in the button to release them, air is applied to a piston which tries to push the balls back away from the shaft. But it intentionally does not have the necessary force to do that. Releasing them requires a full 120 lb brake application. Here's why: The park diaphragm is about 80-90% as large as the service diaphragm, so it doesn't generate as much force from a given air pressure. So when you apply full pressure to the larger service diaphragm, it pushes the rod a "scosh" farther. When the rod moves, the park release piston can push the balls away from the shaft & hold them away. It's a pretty cool design that prevents the bus from being moved at all if there's not full air pressure. It also takes full air pressure & two operations to release the park brakes so it's harder for the dog to make your bus roll halfway out of your site at the campground. (Don't ask how I know this!!) As far as the guys who rightly are fearful about the emergency brake being air actuated, the system has a separate tank for the park/emergency brake with alarms on each tank for loss of pressure & inversion valves that activate & direct air from the highest pressure source if any of the tank pressures drop while in operation. My 4905 has split front & rear service brakes with DD3s in the back, making it a really safe system for it's day, even for today. Also, as for sticking DD3 cans, there is a release toggle on the brake arm that you whack with a hammer to release the brake on that side so you can get the bus moved. (But it's a real bear to get to it without jacking up the bus!) The big thing that spring brakes have going for them is that you can fill them up with water & mud & they'll still work. The DD3 will fail if it is not periodically serviced/overhauled. It will usually stick in parked position (Gets your attention though.) I recently overhauled mine & found that someone had installed a left hand can on the right side, putting the exhaust & vents pointing up so it got full of water & stayed that way. (GM has L & R, MCI does not seem to.) It was so ruined that I bought several more used ones trying to get a rebuildable core. My experience was that 4 out of 6 working cans taken off running buses had internal damage & badly needed overhaul. Some had deteriorated oil soaked diaphragms and others had rusty components. My (and "Da Book's") advice is due to the age & mileage of our buses, these should be routinely overhauled as soon as you get a chance just to be sure your brakes are right. The money & time you spend dealing with the brakes in your driveway is a lot less than you spend if you are on the side of the road. Jim-Bob | ||
| pipes Rating: N/A |
SNIP from my web page http://members.tripod.com/Pipesusmc/Kaykay.htm My German Sheperd dog ...... had stepped on the DD3 brake button while we were in a restaurant and as result had his first driving test in Oregon. I had to jump in the rolling bus and slapped my hand on the foot brake just as it rear ended a car and almost shoved everything into the front of the restaurant. | ||
| TWODOGS (Twodogs)
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I remember reading that....just doesn't seem possible... | ||
| Jim Bob Rating: N/A |
Pipes, are you SURE the bus has DD3s? Spring brakes will allow your dog to release the brakes but DD3s in proper operating condition will not release without a full pressure brake application. Interestingly, I have a later Eagle that requires the same full brake application to release but they do it with spring brakes & a tricky Bendix valve setup. | ||
| Jim Ashworth (Jimnh)
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If you still have the same air pressure that applied the parking brake, it will release without a brake pedal application. If the brakes are applied with low air pressure, and then the bus is started and air built up to full pressure, the brakes will release without a pedal application. My MCI would hold air almost forever and I didn't always have to apply the service brake to release the parking brake. My current Prevost has the spring brakes and they need nothing but a push on the button to release them. Jim | ||
| Jim Bob Rating: N/A |
If the park LOCK mechanism is operating correctly, DD3s will not release without a brake application. If you go to the Bendix website, the DD3 service data will confirm what the bus manual states. If they WILL release without a brake application, then the bus is being held in Emergency/Park mode BY AIR ALONE which is very bad. If that is so, the brakes need immediate service because if the air bleeds away, the bus can roll off (without a dog.) But as I said above, I bought 4 used cans & all needed overhaul even though they had been operating. | ||
| gusc Rating: N/A |
After reading all this I'm sorry my bus had the mechanical parking brake removed. I've decided to install a guard around my spring brake button. It would be a lot safer if it were plumbed to apply when pushed in so it would be very difficult to release accidentally--except by busy little hands. | ||
| Stephen Fessenden (Sffess)
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On my 4905 (H8H) the little balls and shaft were very rusty and the brakes were being held on with air. I did not know that you could diagnose that by trying to release the parking brake without a foot brake application. In that case, I would recomend that any one with DD3 brakes do this test regularly. It still frightens me to think that I could have converted that coach, stopped somewhere for a nap and awakened to a rolling sensation with no air to stop with until the engine is turned on and built up some air pressure. If the test is that simple, add it to the check list. I have spring brakes now and they do not lock as firmly as the DD3s did. I was even able to drive with them on once. I liked the DD3s once they were repaired. | ||
| Artis Rating: |
I chock my tires when I'm parked. Isn't that proper proceedure with big vehicles? | ||
| Jim Ashworth (Jimnh)
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On the DD-3's, the balls are only pushed, not locked, between the taper and the shaft when the brake is applied. It is only when the air to the park diaphragm decreases and the shaft moves ever so slightly that the balls get locked between the taper and the shaft. If the shaft doesn't move, the balls don't lock. Try releasing the brake immediately after application and you will see what I mean. I have commercially driven 30+ MCI's, they all act the same, new ones, old ones, it doesn't matter. Chocking the brakes is standard procedure on spring brake vehicles because the springs can break without warning, even in the middle of the night. It is a rare sight to see a bus with chock blocks. If it were a problem with DD-3 brakes releasing unexpectedly, Greyhound would certainly have this as standard procedure. Jim | ||
| Jim Bob Rating: N/A |
Point well taken, Jim. The balls don't actually lock when the park brake is activated. They lock when the rod moves back. If you push the park valve back in before there's been any air loss, I guess they could just retract. I have not experienced this but my bus leaks down a bit when shut off. I'm thinking this would happen way easier on a commercial coach that frequently parks with the engine running for AC or heat. When running, the air pressure would increase significantly if park was applied and then the compressor cycled on. Murphy's law applies flawlessly in my life so I will be fabricating a flip up "dog preventer" for my bus & my nephew's 4905 just in case. (I don't think it will work on Two Dogs.) You know, many times I don't jump into a thread because sometimes it's easier not to argue with anyone. But I see that it can be pretty important because Jim Ashworth's hands on experience is not as "Da Book" says. And not just what most of us have experienced. Thanks for taking the time to make us see this possibility. | ||
| Brian (Bigbusguy)
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A lot of bus operators will pump down the air after motor shut down using the foot valve so there will not be air to release the brakes. My DD3 will some times relese with out a full aplaction if the air is not bleed off in the can. And yes you all should rebuild you DD3 or at least take em apart and clean and grease em. Brian 4905 Klamath falls | ||
| gusc Rating: N/A |
Stephen, If your spring brakes didn't hold they weren't adjusted properly or one spring was broken. They can be backed off for moving when the vehicle is disabled. Wrecker drivers do this all the time. I doubt that there would ever be a case of both springs breaking at the same time, the odds are in the zillions. | ||
| Stephen Fessenden (Sffess)
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I hadn't learned to adjust the slack adjusters yet, so they were loose. It sounded daughting to me at first, then a friend pulled one out of a junk box and showed me how. Now I can adjsut them in 10 minutes. | ||
| gusc Rating: N/A |
Stephen, If my memory is correct the slack adjusters are only for the service brakes. I believe the spring brakes have a completely separate adjustment that essentially compresses the spring to release the parking brake, the same thing air does when available. | ||
| Tom Caffrey (Pvcces)
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Spring brake and service brakes work on the same pushrod; there is only one normal service adjustment and it's the slack adjuster. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher | ||
| Brian (Bigbusguy)
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Its easy to adjust them I tighten then up till they stop tight up to the drum and back them off until they are just off the drum .You need to find the adjusting nut a round spring cover the wrench will push down when you put the wrench on the nut. It holds the nut from turning by it self. You can tap the drum and you will hear when they are touching or not by the sound the drum makes when its ringing like a bell they are not touching. Now if you want to get fancy you can spin the wheel and back em off till the drag is just off the drum you will hear the high and low spots some times. Also make sure the parking brake is not on. You dont want them to lose and I would have some on step on the brake to see how much travel the rod has when your done to make sure you did not do it wrong , Too much and you can lose you brakes going down a hill.Or have none going out your drive way. This is somthing every one needs to know how to do or pay to have it done. Im in Overland park (Kanasas City) if any one is close I will show you how. Just drive by big parking lot easy in and out. Or come and get me no car here with me. Brian 4905 Klamath Falls Oregon(Kanasas City) | ||
| gusc Rating: N/A |
Tom, You're probably right for some systems, they aren't all the same. I have no experience with DD-3s at all, never heard of them prior to this string. On some spring brakes there is a nut under the dust cover in the center of the spring brake chamber used to release the spring brake when there is no air. This shortens the brake push rod without touching the slack adjuster. I watched a wrecker driver do this to my '59 American LaFrance fire truck a long time ago but I have never had the occasion to do it myself. There is another type that has a small air reservoir tank isolated by a check valve so spring brakes can be released to allow some emergency movement and to prevent the spring brakes from applying suddenly. In other words this gives the driver a bit of control over the otherwise automatic spring brake. I've never seen one of these but it sounds a bit like a DD-3 to me. | ||
| Tom Caffrey (Pvcces)
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Gusc, the nut or bolt in the middle of the spring chamber is for collapsing the spring; it doesn't do anything to the pushrod but keep the spring from pushing on it when there is not enough air pressure to do the job. We have most of the parts for the emergency air release system. We bought them when we were setting up the spring brake system. We didn't install it because it added quite a bit of complexity to the system and the people we had install the spring brakes thought that it wasn't worth the effort and expense. One argument they made is that tow trucks that can tow heavy rigs are equipped with the required connections to air up the tow. If there was a bad leak in the system, the spring pots would have to be released or the leak fixed prior to the tow, so the emergency release system would only help you move a short distance. We don't have any plans to use that system, for the time being. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher |
