| Author | Message | ||
| Michael Lewis (Puffbus)
Rating: |
Let me first say that while anything is possible, I'm not sure even the most determined types would want to convert air to "juice" or hydraulic brakes. The idea seems interesting, however. No issues with moisture, compressor issues, leaky air lines and what we all fear, total shutdown of the system and roadside assistance, etc. Before you bash me for this hare brained idea, here's a quote I picked up on the Open Roads Forum regarding (Canadian?) converters actually making this conversion: "- people are even converting MCI and Prevost coaches to juice brakes so they don't need the air brake endorsement. Now if you'd said that any rig that big "should" have air brakes, I'd agree with you." I understand that Canada requires an air brake endorsement as a prerequisite to licensing drivers of air brake equipped coaches. This post was a response to avoiding that requirement. If nothing else, it probably will make for some interesting arguments. Michael | ||
| Ron Walker (Prevost82)
Rating: N/A |
Michael ...yes it is a prerequisite to licensing drivers of air brake equipped coaches in Canada, and in my mind should be south of the border too, for safety reasons. I have not seen or heard of anyone with a coach (bus)(BC Busnut's) change their system from air to hydraulic, god the test isn't that hard, the wife ace it the first time and she's not mech. inclined. And what do you do with the air suspension?, if you rip the all the air components out!! This makes no sense at all, for the cost of it, so you don't have to take a 4 hr course, write a test and run a air system and brake test....shaking my head.... A have seen some air over hydraulic systems on RV's that you don't need a air ticket but not on a bus conversion | ||
| David Dulmage (Daved)
Rating: N/A |
Hydraulic brakes require some type of assist to multiply the force exerted by the driver - braking force is proportional to force applied to the brake pedal, not a very suitable arrangement, in my mind for large vehicles like highway coaches (although air over hydraulic could work). One of the concerns I would have is the proper engineering of a hydraulic system, or for that matter any system that deviates significantly from that which was designed for the bus and which met federal motor vehicle safety standards (FMVSS or in Canada CMVSS) that were in effect at the time of manufacture. If I were an insurance underwriter I have likely not be willing to provide coverage for such a vehicle. The course I took in Ontario was a good one, well worth the cost and time to me. Considered against the overall money I have spent so far on my conversion it hardly rates mention and is certainly no where near the cost of making any conversion to the braking system. FWIW Dave Dulmage (MC-8) | ||
| john w. roan (Chessie4905)
Rating: N/A |
This question should be saved for April 1st. | ||
| Marc Bourget Rating: N/A |
Air or safety brakes have a significant failure mode advantage over hydraulic If the application side of the system fails, the brakes will "apply" and stop the vehicle. I have hydro-boost brakes on the Dually I tow the race car with. I lost a fan belt on the Golden State Fwy (LA), which took out the belt to the hydraulic pump and there went, for all effective purpose, the brakes. I had 7000#+ on the trailer and I hit the brakes with both feet, pulling on the steering wheel enough to lift my rear off the seat, I wasn't gonna make it, but the light turned green and the cars stopped at the bottom of the off ramp pulled away mere feet in front of my gradually slowing sled. I don't think you want to switch to "juice brakes" | ||
| Buswarrior (Buswarrior)
Rating: N/A |
Hello. I'd like the writer of that piece to identify who and how many of these brake converters there really are. I am skeptical of the source. A point of clarification, here in Ontario, if there is air pressure used in some way to apply the service brakes, you need an air brake endorsement. So air-over-hydraulic still needs an endorsement in these parts. happy coaching! buswarrior | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
And as far as I can see, everyone who has posted on this subject has ignored a principal reason for the use of air; to prevent losing your brakes when the temperatures inside the drum take the brake fluid above boiling. I imagine at those temperatures, all the rubber parts would be at risk, as well. With heavies, the temperatures do get up there. I know some of the linings are rated to work with very little loss of braking into the 400 to 600 degrees fahrenheit range. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| John MC9 Rating: N/A |
Most of the "schoolies" I drove back a whole bunch of years, were hydraulic. They were vacuum assist, and we had to know what the vacuum pressure should be, and what to do if it wasn't right... Those school buses were used to full capacity, with standees, and luggage. Probably 9-10 or so tons at the least? The hydraulic brakes worked fine! ---------------------------------------------------------- Specifications: Blue bird buses gmc 2000 up to 2002. Catepillar 3126 engine, manual transmission.72 passengers, hydraulic brakes and spring suspensions. Blue bird buses ---------------------------------------------------------- Do a "google" for more examples! | ||
| John MC9 Rating: N/A |
Michael - They guys are absolutely right. The bus was designed to have air brakes, and the driver was to have air brake certification. Hell man, it's the least costly, and least time-consuming thing you'd be doing on your dream RV! Just study up, take the test, and move on. It's just not worth the hassle to re-engineer what's been engineered and built. | ||
| truthhunter@shaw.ca Rating: N/A |
While I can not imagine converting Air Brakes to Air-over-hydraulic or Vacum-hydraulic or belt driven pump-hydraulic (both often have a electric backup pump and pressure accumulator when used on schools bus which also operates the park brake) as being worth considering; those hydralic systems do work very well as factory installed on large school buses. They do of course require proper and expensive maintenance/repair just like every thing on heavy vehicles. | ||
| FAST FRED Rating: N/A |
From what I read in the truck mags we are not far from electic disc brakes for class * trucks. Weather the goodies will simply be a junkyard run & bolt on is still an open question. Disc brakes would probably be easier to service than our antiques with slack adjusters , and might allow the wheels to lock up (or have ABS) for better breaking , with out installing a full pressure treadle valve. FAST FRED | ||
| John MC9 Rating: N/A |
I dunno FF, but I was taught that a locked up wheel was an out of control situation. The last thing I'd ever want, is my wheels skidding when I'm trying to make a quick stop. The "ABS" system attempts to duplicate what we were taught to do when the wheels skid during a panic stop... We got off the pedal long enough to get the wheel rolling again, pumping the pedal to insure no wheel skids. (To tell ya' the truth, I don't remember ever skidding a bus wheel on dry pavement.. I think I would have been fired, if I did) | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
After my new (amazing) experience with the Telma retarder, I'm not surprised that trucks are soon going to have electric disk brakes. If they do it smart, they'd incorporate eddy current braking with disc shoes in a single unit. You've got the rotating disc, all you need is some extra magnet coils added to the system. That would be awesome. For starters, an eddy current brake would self-limit and never lock up. Well then, it may not be practical since the Telma works on the driveshaft which is 3-5 times faster in RPM than wheel discs, which has a lot to do with making it work well... We'll see. I never underestimate detroit engineers... | ||
| niles steckbauer (Niles500)
Rating: N/A |
My bus HAS air/disc brakes w/ ABS - the tech already exists | ||
| Buswarrior (Buswarrior)
Rating: N/A |
Hello brakers. I think Fast Fred was reading about electronic control of air disc brakes. Brake by wire. Takes the split second delay out of the stopping distance equation. The delay in air brakes is waiting for the volume of air sufficient to make the necessary pressures to travel to and fro between tanks and the brake pedal and the relay valves and the brake chambers. Electronic braking will replace the hoses on the brake pedal with wires, and the tanks will be plumbed directly to solenoid valves at the axles. The government is afraid to allow it, without requiring the redundancy of a fail safe mechanical/analog system that meets the current regulations. We don't have a problem trusting "throttle by wire". Been around and quite reliable for many years now. As for locked up brakes... All things being equal, there are precious few on-the-road conditions in which a sliding tire will not produce the shortest stopping distance. In other words, a skidding tire makes for shortest stopping distance, almost all the time. The reason we might want the tire to stay rotating at the threshold of sliding is so we may make the compromise between directional stability and as much stopping as we can get while keeping the former. A skidding tire doesn't maintain any directional control. Once the tires are sliding, the vehicle will react to where its centre of mass chooses to go. The vehicle might rotate, or follow the contours of the road towards the downhill direction, etc. Whatever the slope, camber, or varying friction of the road surface under each tire influences it to go. ABS systems automatically keep the wheels turning at close to skidding so the vehicle doesn't change direction, and so the driver may steer under heavy and/or low traction braking. However, of most importance: ABS DOES NOT SHORTEN STOPPING DISTANCES! ABS, in fact, LENGTHENS STOPPING DISTANCES, sometimes grossly. For instance, try to panic stop an ABS vehicle on a gravel road. When the history of this time is written, the misunderstandings about ABS systems, and the horrible misinformation about them will no doubt be noted. In order to have directional control, we give up stopping distance. no free lunch. Rats. happy coaching! buswarrior | ||
| Bob Wies (Ncbob)
Rating: N/A |
FF touched on a subject I've been discussing with a couple of (former) OTR trcuk drivers over the weekend and the topic has been on my mind since last week with a near mishap with an idiot driver in a roller skate.... Do the treadle's on MCI (and perhaps other) buses have a "full volume" or "full pressure" treadle on the braking system. My brakes are adjusted to the T's and I can't lock 'em up to save my soul. Last week, fortunately for all concerned, the left lane was open for me or the driver of that little 'roller skate' I referred to realier would have been in a world of hurt. NCbob | ||
| Ron Walker (Prevost82)
Rating: N/A |
Bob, I don't think you are alone, I can't lockup my brake either, and all the brake components are 100%. Just give yourself lots of room to maneuver and hope for the best, always going to be idiots on the road that will test you and your bus... | ||
| Richard Bowyer (Drivingmisslazy)
Rating: N/A |
I only had one requirement in many thousands of miles on my 80 Eagle to do a panic stop. (And yes I know you are supposed to only apply enough brakes to just the point of skid). However when you are traveling down the FL interstate at 75 MPH and you suddenly see a lumber truck, without brake lights, pulling off the road the only time you have to do anything is hit the pedal and try and see if the left lane is still clear. Fortunately I missed the truck by only inches, but I left a cloud of blue smoke that completely obliberated the freeway behind me. So yes, at least on that model coach, you can lock the wheels. It really does leave flat spots on the tires though. Richard | ||
| Jack Conrad (Jackconrad)
Rating: N/A |
A couple thoughts. I am not sure about the GM buses but on our MC-8, the brake application valve is mounted on the bulkhead below the driver's seat. There is an adjustable rod from the brake pedal to the valve. When I replaced the floor in the driver's area, I had to re-adjust this rod. I had not paid attention to how much play was in it prior to removing it. When re-installing it, I adjusted it to about 1/16" clearance. This made a big difference in the how stongly I could apply my brakes. Second thought, I put a brake application pressure gauge in our new instrument panel (because I had an extra air pressure gauge). With an E1 brake application valve, I get about 75-80 PSI max. pressure with a full, hard brake application. I have been told that an E3 brake application valve will boost this to full air pressure available. I have not tried this, so I can't confirm this. A normal "slow down" brake application on our bus requires about 15-20 PSI. Brake air pressure X surface area of brake pancake = braking force applied to brake shoes. (A 24 brake can is 24 square inches, a 30 brake can is 30 square inches, etc). Hope this helps, Jack | ||
| Bob Wies (Ncbob)
Rating: N/A |
You might have lost me there Jack, but let me give this a try. My discussions with the OTR drivers (who are understandably living with 'split'systems..because of the duty of the tractors they drive.. tell me that 20# (PSI of applied pressure) on the dash guage is enough to cause them to PANIC! At this point I don't know where I am on this curve. I will talk to my bus mech this week and trust me...we'll sort it out. One of the things I learned years ago is that to apply the brakes (on any vehicle, without an ABS system) is to the MPR... (maximum point of retardation) that point just the infantesimal point BEFORE the wheels lock..is the most ideal.. because a skidding tire (or tires) have virtually much less traction on dry pavement..call it a river of slippery rubber if you will. Now, where do we go from here? Perhaps FF had the answer...while I'm inclined to trust his judgement and years of expertise..I'm willing to listen and learn. NCbob | ||
| Bob Wies (Ncbob)
Rating: N/A |
Might I add, I can live with some flat spots on my tires if it means that a tragic situation was avoided and I don't have to go to my grave knowing that I might have responsible for the taking of the lives of someone's children or grandchildren. Tires can be replaced...people can not! I have no problem taking out some cretan who violates me or mine...but that's a different situation. Highway situations which cause pain and suffering for which I can take precautions to avoid might be something I might wish to do something about. Apologize for the double post. An afterthought. NCbob | ||
| FAST FRED Rating: N/A |
Jack has the only answer that actually works , a pressure valve in the line with the STD treadle valve replaced with a full pressure one , if you dont get full line PSI. Many folks unfortunatly think a coach should stop like an auto. The folks building and purchasing your coach when new didnt think so. 6 or 8 tires to change because a driver got slopy and stomped on the treadle valve was not to their liking. While changing out to get line pressure works , YOU may be stuck with 6 or 8 tires with the flat spots. The usually unwanted advice is to LIGHTEN UP !, when building the camper intereior and the amount of "Stuff" you carry aboard. That 1 1/2 marble wall system may look great but it needs to be accelerated , hauled up every hill , and STOPPED at the bottom. Light weight IS the way to go! FAST FRED | ||
| Bob Wies (Ncbob)
Rating: N/A |
FF, your point (and Jack's) make sense. What peeved me the other day was that I had difficulty stopping and the interior of the bus was NEAR STRIPPED! The only items left in were the Galley cabinets, shower, closet and upper cabinets. I'd removed all the furniture to make it easy to re-build the bedroom area. And, yes I'm definitely keeping an eye on weight. No marble and the only ceramic tile is in the shower. The slack adjusters had been adjusted and air was 110#'s. I'm going to speak with David (the mech) this AM. Thanks guys, NCbob | ||
| Buswarrior (Buswarrior)
Rating: N/A |
Hello brakers. One problem that doesn't get talked about is the condition of the linings and their relationship with the drums. All the linkage may be great, but the linings might not be making the friction they should be. Only way to tell is to put it on a brake dynometer. There are more and more fleets putting these into operation and discovering all manner of problems they didn't used to find. Basically, the axle is put on a set of rollers, the rollers are driven by an electric motor and then you put on the brakes. The dyno is able to measure the amount of force it takes to stall the rollers. In moments you can find weak spring brakes, and know if you are generating the proper brake force at each wheel. And we've been lied to: A sliding tire makes the shortest stopping distance. Remember who tried to tell you it was bad: the owner that was going to pay for new tires if you locked 'em up. I wonder what else we were told when we were learning that is wrong? happy coaching! buswarrior | ||
| John MC9 Rating: N/A |
A myth? A sliding tire makes the shortest stopping distance <---- a link! We always were taught the opposite! Is it different in Canada? From "The Discovery Channel" in Canada: "The other issue was skidding versus non-skidding. You actually don't want to skid. If you start skidding it will take you much longer to stop. That's because the friction force between something that's sliding over something else is actually smaller than it is when something is not moving. And a tire rolling down the road without slipping is actually not moving on the road. Therefore it will take you a lot further to stop if you're sliding and can't steer. " USA? : The University of Michigan did a nice study, and I believe it claims that a sliding tire gains no de-acceleration (loosely spoken) It's a PDF that's worth a read! Or: The University of Tennessee Department of Physics and Astronomy "Suppose you are driving a car along a highway at a high speed. Why should you avoid slamming on your brakes if you want to stop in the shortest distance? That is, why should you keep the wheels turning as you brake? Solution: When the wheels are turning, friction between the surfaces of the brake pads and the disks or drums of the wheels is responsible for decelerating the car. When the wheels are locked, friction between the tires and the road decelerates the car. The brake pads are designed for the job, and the coefficient of kinetic friction between the brake pads and the disk or drum is large. " But hey... Although I'm sure there's a ton we've been taught that is as wrong as red wine with fish, anything regarding the greater stopping distance of a sliding tire, vs the non-sliding tire, should be simply taken for granted. There's been enough studies to prove the point, and probably enough real-time experience, to make those studies a redundant waste of cash. Gimme a non-slider any day. | ||
| truthhunter@shaw.ca Rating: N/A |
Many variable dynamic factors determine the coefficient of friction (how stuck to the road the wheel is) between the road and your wheel. Hydroplaning in the wet or snow increases with wheel lock up and reduce that coefficient of friction as well as loss of directional control. This will normally increase the stopping distance with most tread patterns. On dry pavement and asphalt, a skidding wheel has a drastic rise in temperature at the point of contact(hot enough to leave a skid/vaporize the tire/grease/dirt on the road and oil in the asphalte) which causes a drastic drop in the initial maximum coefficient of friction and which will take longer to stop the vehicle under more conditions than a wheel the has not locked up. Consider that the condition imposed on that tire's contact with the road changes between the initial point of lock up (with reducing kinetic energy factored in) and the final point of lockup. As the speed reduces (reduction in kinetic energy transfer/conversion or E=MC2 if you like) the temperature rises at the point of contact between the tire and the road. Yes this seems to contaradict what goes on at the drag strip , but those are different variables. On lose gravel or mud a lock up tire also has less potential coefficient of friction and will take longer to stop the vehicle under most conditions. Under MOST driving conditions a wheel lockup is LESS effective at stopping the vehicle. The most effective braking practice is the cardinal rule "of adjusting your speed/following distance according to the conditions" (distance you need to stop before you can collide with the visible as well as the unexpected). A rule that is always violated prior to any collision . | ||
| Bruce Larsen Rating: N/A |
I'm hoping to adopt a converted, homeless '68 GM 4107 pretty soon, and have been reading this forum for quite a while now (first post). This discussion on Brakes and Braking reminds me of a couple of things I learned quite a while ago about braking a large vehicle: 1. The Three-Quarter Second Rule: No matter how much coffee you drink, simple physics limits your ability to get your foot from over the accelerator to mashing the brake to about 3/4 of a second, max. In that 3/4 of a second, you will travel 55 feet at 50 mph, 66 feet at 60 mph, 82.5 feet at 75 mph. The easy way to figure it is times the mph by 10%, and add together. (70 plus 7 = 77 feet in 3/4 second @ 70 mph). (You fellows with the calculators can jam the "proper" math to this - you'll see it works every time!) You WILL travel that far at that speed before you even BEGIN to stop! 2. The Egg Drop. Drive you rig, holding an egg out the widow. Have your passenger catch you un-awares and yell "STOP!". Drop the egg and stop at the same time. (Try this at different speeds, but save enough eggs for breakfast) After the rig / coach has stopped, get out and walk back to the egg. You will be truly amazed at how far it actually took you to stop. My guess is you'll be rather humbled. Drive Safe! | ||
| Gus Causbie (Gusc)
Rating: N/A |
Michael, I have a bunch of antique cars and trucks. The number one problem with them is rusted/stuck hyd brakes. I have two Army trucks, one is air/hyd one is vac/hyd. Right now one has a rear brake locked up and the other has a grabbing front brake. I have a '53 five ton GMC 633 with a locked up rear brakel (vac/hyd). I have two trucks, a fire truck and the 4104 with air, no problems with any of them-ever. I have a '31 Chevy 1 1/2 ton grain truck with straight mechanical brakes, no problems. Air brakes are simple mechanical systems with air as the pushing force. No hyd fluid leaking on brake linings and causing grabbing, no wheel cylinders boiling over and catching fire from hot brakes or wheel bearings, and no sticking wheel cyls from stale hyd fluid. I've had all of these problems. Moisture, contrary to your post, is the major problem in hyd brakes. I wish all my trucks had air brakes. | ||
| FAST FRED Rating: N/A |
"Moisture, contrary to your post, is the major problem in hyd brakes." Brake fluid is "hydroscopic" , it loves to absorb water. When the brakes are used in much RV downhill work the fluid temp can climb over the boiling point of water. As steam IS compressable (brake fluid is not) NO brakes is the result of the fluid heating. OF course most car , truck & even motorcycle mfg. recomend flushing out the brake fluid every 3 years or so , but many never bother.( Like replacing antifreez & flushing , few bother till the system dies) At least the air brakes will usually allow a stop , even after overheating. FAST FRED | ||
| Marc Bourget Rating: N/A |
Gusc said: No hyd fluid leaking on brake linings and causing grabbing, . . [and] and no sticking wheel cyls from stale hyd fluid. How do these examples work? In first case, does the leaking fluid swell the linings or??? In the second, does the brake fluid actually get "stale"? What goes away, (like moisture from bread?) to make the fluid stale? | ||
| Stan Rating: N/A |
Marc: snip In first case, does the leaking fluid swell the linings or??? snip We have to depend on you to explain the molecular changes that occur when brake fluid comes in contact with brake lining material, and the resultant change in friction characteristics between cast iron and the now changed brake lining. In the meantime, we change the lining because experience tells us that is the correct approach. There are several reasons why vehicle manufacturers recommend the changing of brake fluid at specific intervals. One of these is that brake fluid absorbs moisture. This does not make it fresh like bread losing moisture and going stale so the comparison is not applicable. | ||
| RJ Long (Rjlong)
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What's the matter, Stan. . . not had your morning coffee yet? The attitude displayed in your response to Marc's questions was exactly the type of remark you were complaining about in "My View of the BB". | ||
| R.C. Bishop
Rating: N/A |
 ...RJ is Back!!! and amen. RCB | ||
| johnwood
Rating: N/A |
Back to hydraulic brakes on a big rig......... there is one mfg of motorhomes that installs air over hydraulic disc brakes on their rigs. Alpine Coach. Asked rep why and he replied that it reduced the latency..... time between application and effect. And the motorhome is 40' DP with a respectable gross. FWIW One thing air gives you is slop in the system. You can have a leaky, yet usable brake system. Try that w/ hydraulics! Electric? I always think of utility and camp trailers.......... I hope Class 8 rigs are higher quality when electrified. |
