Got A Work Van On GovDeals Today!

[Tango]

I have always been told that the pressure bias on big rigs, buses and such heavy haulers is adjusted to favor the rear instead of the front as it is on passenger cars and motorcycles. With tractor-trailers it makes sense, because otherwise the mass of a loaded trailer would simply overrun the tractor if it tried to stop faster than the trailer. Not sure on buses, but have "heard" they are often set to a similar bias as big rigs (?)

Any experts out there?

[Kubla]

Pressure on a semi tractor is equal if you have a trailer hooked up but biased to the front if the trailer valve is not pushed in, also the front brake chambers are smaller because there is only a single tire up there

[EastCoastCB]

Originally Posted by Mountain Gnome

Passenger vehicles take about 80% of the stopping force on the front tires, 20% on the rear. I think you are mis-conceiving the physics. When a car stops, the rear-end lifts, the front end lowers, as the vehicle tries to rotate around the front tire. This is why disk-brakes are found on the front of almost any modern passenger vehicle (they work better), while the rears may be left as drums. Having the motor up-front also gives them more traction.

Its the other way around on a bus.

https://www.youtube.com/watch?v=-R7J9BIjNEw

at about 3:30 it explains that the rear provides around 80% of the stopping power.

[Twigg]

Originally Posted by EastCoastCB

Its the other way around on a bus.


at about 3:30 it explains that the rear provides around 80% of the stopping power.

I guess the RE's have an advantage then, with much of the weight bearing on the rear axle.

[Robin97396]

Mine actually has a bunch of stacked steel pates bolted between the frame rails in the back. I'm told it was for traction when the bus was empty.

Sounds like a nice place to put batteries, but to hard to access them there.

[EastCoastCB]

Originally Posted by Twigg

I guess the RE's have an advantage then, with much of the weight bearing on the rear axle.

I think the reasoning behind why buses brake with the rear is that it keeps the bus straighter. They're so long, if you ever locked up the front end that would be all she wrote. But if you lock up the rear its gonna still pull it all straight, more or less.

[Twigg]

Originally Posted by EastCoastCB

I think the reasoning behind why buses brake with the rear is that it keeps the bus straighter. They're so long, if you ever locked up the front end that would be all she wrote. But if you lock up the rear its gonna still pull it all straight, more or less.

I can see that. It would only help if the rear wasn't already sliding though. In that situation it will just keep on sliding and never straighten.

There is twice as much rubber on the rear too, and that might factor into the brake balance.

[EastCoastCB]

I've got no complaints about the brakes on any bus I've owned. Three air one hydraulic. All stopped/stop fine.
This new one's brakes feel a bit different than I'm used to. Less feel, slightly wooden feel at the pedal. But awesome bite. Stops on a dime!

[cadillackid]

Originally Posted by EastCoastCB

Its the other way around on a bus.

at about 3:30 it explains that the rear provides around 80% of the stopping power.

mine on DEV must ne miosadjusted even though the auto slack adjusters are in Spec.. its EASY to lock up the rears. while I still can step harder on the oedal and gain more stopping power from the fronts.. redbyrd has ABS so I dont have that issue and it feels much more balanced when I hammer the brakes.. its also hydraulic..
-Christopher

[Robin97396]

I didn't know these had antilock breaks. I felt something strange while downhill breaking on a gravel road this past summer. It felt like antilock breaks but I thought that would be unlikely. I've been looking for something wrong in the front end ever since then. Otherwise there is no indication of any breaking frontend problems.

And I limited my trips this past summer because of this.

[cadillackid]

when you start the bus you dont get an ABS light on the dash for a few seconds? I never k new school busses had them (at least not 99/00 ones).. iuntil I got this bus and noted the ABS light pops on as a test for a couple seconds when I start it... then I found the ABS module underneath about midway back.. all the brake lines for front and rear were going backwards first.. not siure why the module is mid-ship but it is.. I took the bus out when we had some snow last winter and sure enough I stabbed it hard.. the familiar ABS pulse.. found a J1708 port on the ABS module, plugged the computer into it and sure enough no codes..

if you crawl under and find brake lines going to a biox with a thick column of wires plugging into iot than chances are its an ABS module..
-Christopher

[2kool4skool]

Originally Posted by Robin97396

Mine actually has a bunch of stacked steel pates bolted between the frame rails in the back. I'm told it was for traction when the bus was empty.

Sounds like a nice place to put batteries, but to hard to access them there.

Took 3 of the 4 out, they weighed 900 plus lb. And yes, the 2000 TC1000 has ABS.

[Brewerbob]

Originally Posted by Mountain Gnome

Passenger vehicles take about 80% of the stopping force on the front tires, 20% on the rear. I think you are mis-conceiving the physics. When a car stops, the rear-end lifts, the front end lowers, as the vehicle tries to rotate around the front tire. This is why disk-brakes are found on the front of almost any modern passenger vehicle (they work better), while the rears may be left as drums. Having the motor up-front also gives them more traction.

That's what I was thinking. Bus is going to do the same. Rear engine less so. The engine weight would be transferred to the rear axle since the engine is behind the axle instead of mid engine.

Front engine bus especially a shorty is going to nose dive like a car.

[Brewerbob]

Originally Posted by EastCoastCB

I think the reasoning behind why buses brake with the rear is that it keeps the bus straighter. They're so long, if you ever locked up the front end that would be all she wrote. But if you lock up the rear its gonna still pull it all straight, more or less.

You guys are forgetting why brakes work. There's twice the rubber back there too.

Charlie, for a long bus yes. Wranglers have no towing capacity when they have the same engine as the Cherokee; short wheel base. It's going sideways.

For a shorty, single rear I bet the bias is that of a car.

[cadillackid]

Originally Posted by Brewerbob

That's what I was thinking. Bus is going to do the same. Rear engine less so. The engine weight would be transferred to the rear axle since the engine is behind the axle instead of mid engine.

Front engine bus especially a shorty is going to nose dive like a car.

see thats the physics im missing somewhere is how I have 80% of my braking in the rear on ALL busses.. as I still feel like there would be a huge weight transfer to the front.. just like a car or van..

I spent lots of hours on this weight transfer stuff with Drag cars.. to get just the right amount of squat at launch (rearward weight transfer).. since I was only ever racing streetable cars.. we had normal car brakes on them.. at the end of a pass you hauled ass on the brakes in the shutdoiwn lane and it wasnt abnormal at all to make smoke with the front discs at some tracks with short lanes..

why would it be any different in a bus? does the exyra long wheel base create less of a lever for the weight transfer? and since the rear is often heavier it creates the ability for more friction between the rear tires and ground? my DEV bus sure acts like a car.. or the treadle valve is Jacked...


someone explain this to me..
-Christopher

[Robin97396]

Again, if it ain't broke...

No I haven't noticed an ABS light specifically, but if I'm not wearing my glasses it might as well be an oil light. I'm usually watching the air and oil pressure gauges. I'll have to make it a point to look at all the pretty flashing lights.

I finally finished my rather lengthy radiator flush and got back to a 50/50 mix. I can't see the fins in this radiator. The water didn't look very dirty though.

Chris, I'll have you know this is the first time I've used distilled water to refill a radiator.

We had one self thinking truck driver in Korea that filled his cooling system with straight undiluted antifreeze. He figured if a little bit was good, more was better. The block survived somehow in the sub zero temps overnight but the radiator didn't.

[Brewerbob]

Originally Posted by cadillackid

when you start the bus you dont get an ABS light on the dash for a few seconds? I never k new school busses had them (at least not 99/00 ones)..
-Christopher

Mine stays on even after changing out the speed sensor for the wheel it said it was (PF). Haven't gone any further than that in troubleshooting. The brakes seem fine even when some jackass stops short in front of me. I've had various **** on the dash ever since I've gotten it home so I've never stood on the brakes.

[cadillackid]

did you put the SCA's in your coolant mixture? I believe your CUmmins needs those like the other diesels do..
or did you use an ELC coolant?

I never used to use dustilled water till I got started with diesels and learned its actually a bigger deal with the chemical balance in a diesel...
-Christopher

[Brewerbob]

Originally Posted by Robin97396

Again, if it ain't broke...

No I haven't noticed an ABS light specifically, but if I'm not wearing my glasses it might as well be an oil light. I'm usually watching the air and oil pressure gauges. I'll have to make it a point to look at all the pretty flashing lights.

Orange and says ABS on mine.

[Brewerbob]

Originally Posted by cadillackid

did you put the SCA's in your coolant mixture? I believe your CUmmins needs those like the other diesels do..
or did you use an ELC coolant?

-Christopher

The 5.9L does but the 8.3L does not. Or something like that. My bus doesn't. I quoted/pasted the FSM in a comment somewhere on here months ago.