New Brake Information

[TomC]

Once again, we have the Government intervening into truck equipment and instilling new braking standards on trucks. Most big rigs (and a lot of buses) use 15"x4" front brakes and 16.5"x7" rear brakes. On over the road trucks (with sleepers) the brakes have been increased to either 15"x5" or 16.5"x5" in front and 16.5"x8.625" in the rear.

I had an interesting conversation with one of our Meritor factory brake reps.  He said most still want to stay with the larger brake drums then going with the more expensive disc brakes (mainly because the disc brakes we use are made by Bendix).  He then said-besides, with the new bigger brakes, we've been able to get our stopping distances down to within 20ft of disc brakes.  To which I said-that means that a disc brake truck would stop in time and a drum brake truck would continue 20ft more and plow through a car.  The rep had nothing more to say.

The amazing point to all this is-even with self adjusting slack adjusters, anti-lock braking, traction control, lane guidance, tip over avoidance, crash avoidance, intuitive cruise control, etc systems available on trucks, with the exception of better braking materials on the brake shoes, the braking system is much the same as invented around WWII.  Personally-if I were buying a new truck today, I would only choose disc brakes. 

When I started my truck conversion, I called Eaton/Spicer (maker of my axles and brakes) to see if they had a conversion kit to disc brakes I could use.  So far none is being made.  Good Luck, TomC

[robertglines1]

? why do I have disc on tag and steer and drum on drivers? 98 prevost XLE curious  Bob.   

[Lin]

Very interesting information.  Bob, disc brakes came to the front first on cars also.  I assume there are extra issues on a drive axle.

[Ralph7]

 When I worked big trucks with front disc brakes, yes you got lots of miles on pads an rotors compared to drums, BUT you threw away the rotors every time you changed pads. BIG cracks!
Remember the drive axle/axles do most of the stopping.

[artvonne]

  So if I understand the jist here, im supposed to go out and blow untold thousands of $$$$$$ upgrading my 35 year old Bus to disc brakes so I can "maybe" stop 20 feet shorter?

  BS. Within a week of learning to drive I learned to compensate and adapt. I have never gotten into any vehicle that I couldnt figure out how it stopped, and compensated for its particular idiosyncrocies. What happens when you load your disc brake equipped Bus with 5000 pound of extra crap, because you have such way more awesome brakes, and you have a left rear hang up? Whoa, are your plowin through the guy in front of you now?

  When I learned to fly I learned the Pilot is "in command" and all decision making rests on his/her shoulders. If your coming in with a wheel up and an engine out, making a dead stick landing, and wreck the plane, kill someone, etc., the FAA accident report will say the Pilot "in command" failed to maintain control. It may then go on to list extenuating circumstances that existed, but you still lost control.

  If you plow into someone with your antique Bus propelled with an antique motor and transmission (seems anything non four cycle/non computerised is an antique now) with antique drum brakes, dont blame anyone but the NUT behind the wheel. It has nothing to do with the level of technology. It has everything to do with your competence as a driver (Pilot), to compensate and react.

[Seayfam]

In most instances, you are correct. But the problem I have always run into driving commercially and driving my bus is... When I am in a city, I always leave plenty of room between me and the car in front of me to stop. But it never fails, someone always has to squeeze in between me and that car right before the light changes to red. (Many of pucker factors there) "IT Will BE YOUR FAULT" That is where the extra braking power is nice! All your newer cars on the road today stop much faster than they did 35 years ago. That makes us with older buses very vulnerable. And you are right, we need to be in control. This is just a example of one place where I wish I had better brakes.

[robertglines1]

You drive what brakes you have and don't over drive them. I mentioned the 98 had disc on two axles. Just wonder why? I will  still drive it like the 89 all drum brake coach. Just would be nice to have a little in reserve for those close moments..   I didn't know it had disc till I took the wheels off.   Bob

[belfert]

Read Tom's post again.  Only the new larger drum brakes stop 20 feet longer than disk brakes.  Old smaller drum brakes will probably stop in a much further distance than disk brakes.

[bevans6]

Slowing down 5 mph probably decreases stopping distance more than the 20 feet.  In fact I found a chart that says 39 feet shorter comparing 55 mph to 60 mph (car or light truck, 15 FPSPS).  That's part of the equation, and I drive slow anyway these days...

On the "why does my bus have disc's on the tags and steers and not on the drives" question, probably because disc's for that application, being lighter and less stopping capability required that drives need, were cheaper and more available.  The heavy stopping power of the drives was better served by drums. 

Brian

[artvonne]

  Im not arguing that we shouldnt have good equipment, but there does appear sometimes the implication that if your not driving the latest and greatest, and most expensive stuff, your not driving a safe vehicle and you shouldnt be on the road.

  Mercedes has more often than not led the automotive world in safety and innovation, but I would hate we mandate everyone own and drive a Mercedes simply because they are the safest vehicle. I would rather accept there are always going to be older, less technological vehicles with lower capabilities, and trust the Nuts behind the wheels drive them appropriately.

[Iceni John]

Tom,

Those brake sizes you quoted seem really small  -  according to my bus's axle specs it has 16.5 x 6" on the front and 16.5 x 10" on the back.   Do most buses and trucks really have that small brakes?   Even without a tag axle I can almost launch myself through the front window if I'm not careful braking, and I'm at about 26,000 lbs now.

John

[RJ]

Those brake sizes you quoted seem really small  -  according to my bus's axle specs it has 16.5 x 6" on the front and 16.5 x 10" on the back. 

John -

Crown's have always had the biggest brakes available.

The old 40-foot Twinkie 10-wheelers could throw a high school kid from the back seat through the front windshield in a panic stop from 40 mph.

FWIW & HTH. . .

[prevosman]

While Bob's (and mine) bus has discs on the steer and tag, and drums on the drive, newer Prevost coaches are disc all around. I don't think we can say drums are better than disc or vice versa because the effectiveness of each type is dependent upon the size of the drums and shoes or the discs and pads.

The stopping ability of our buses is lousy compared with the average car and no matter what kind of brakes we have we just have to back off a little to protect the fools from themselves. Can anyone guess cars pulling in too close is one of my pet peeves?

[HB of CJ]

Good information.  Guess that is why nearly all fire apparatus have disk brakes all around...so they can stop all that over load.  My old 1974 Crown Supercoach 40-foot 3-axle 10-wheeler had 16.5 brakes on all three axles.  The rears were 10" wide but I have forgotten how wide the front brake shoes were...had a 16K front end.  Yeah; she could really stop.  HB of CJ (old coot)

[Mex-Busnut]

Slowing down 5 mph probably decreases stopping distance more than the 20 feet.  In fact I found a chart that says 39 feet shorter comparing 55 mph to 60 mph (car or light truck, 15 FPSPS).  That's part of the equation, and I drive slow anyway these days...

Brian

A big amen, Brian! I cannot believe how many brag on these awesome forums of driving their 400-year-old 200,000-pound buses at 80 miles per hour. Seems totally ridiculous to me.

In Mexico, by federal law, all buses are restricted to 95 kilometers per hour (aprox 58.6 miles per hour for you gringos.) it makes a lot of sense to me to keep a very heavy older vehicle in top mechanical shape, but also at a far more controllable speed. Plus you will consume a lot less of that really cheap $4.00 diesel fuel you so enjoy buying.

My two pesos' worth.