VERY touchy brakes

[HealthyPetsBus]

Hello!
My two older buses, which are '82 Waynes, have very nice control of brakes when driving, very similar to a car or truck. However, my '96 Thomas has brakes that I would describe as slow but VERY touchy. What I mean is, that I seem to have to push down harder than I would expect when braking, but then when the brakes engage, they grab so hard I feel like I'm slamming on the brakes. There is no middle ground. Are there any suggestions on how I can adjust the brakes for soft, more consistent braking? Im almost afraid to take this bus on the highway once converted due to how extreme the braking is.
Thanks
Virginia

[bansil]

Virginia
Does the 2 waynes have hydraulic brakes and the Thomas have air brakes?

The air brakes take some time to get used to, remember all you are doing is moving a switch to bleed air off, you are not moving fluid

Make sure the pedal is not binding on flooring or rusty etc,

[GreyCoyote]

My first encounter with air brakes sorely tested their anti-lock capabilities. Like you, I thought something was very wrong. Turned out my foot just needed re-training. If you are used to hydraulic brakes, there is definitely a learning curve!

[turf]

i had a brake problem a year ago. air compressor wasn't making enough air to hold all 4 brakes open. the last brake shoe on the line would stay shut. that brake / wheel overheated a lot.
a new air compressor, air governor, and air dryer fixed it.

if they are air brakes, i'd try a new air governor first (cheap), then service or replace the dryer. if you still have problems then the compressor.

[cadillackid]

air brakes are touchy.. there is not a lot of pedal movement.. so when you press on the pedal it feels like you press and theres no pedal movement... and it feels hard.. your bus is not braking alot at this point.. so you step harder.. enough to feel pedal movement? if so you will stand that bad boy on its nose!..

with hydraulic brakes you have much more pedal movement as you press down.. more like a car..

now if theres something wrong.. you can get some ideas maybe?

there is also a distribution valve near the back of the bus, if it goes bad it wont properly distribute the air to the 2 rear brakes evenly so you'll feel a Grab on one wheel or a tendancy to lock one rear wheel..

slack adjusters that are not correctly set are also a possibility..

wioth air brakes (unlike car brakes) 70-80% of oyur braking comes from the Rear, not the front.. this makes it drive differently.. and in the rain it really makes things touchy in an empty bus as the rear wheels lock Very easily...

you can have the slack adjusters and the pad health chacked faiurly cheaply at a commercial tire shop.

in Most bendix air brake systems there are THREE complete sets of brakes.

1. front brakes.. - activated by APPLYING air to the air cylinders.
2. Main rear brakes - activated by APPLYING air to the main section of the rear air cylinders.

3. Aux / Parking rear brakes (also called spring brakes) - activated by RELEASING air from the aux section of the rear air cylinders.

in normal braking only sets 1 and 2 are used.

when you park and pull the park lever and hear the "whooosh!" you are releasing air from the aux section of the rear air cylinder and letting the springs apply brakes to the rear wheels (brake set 3)..

if you have an air pressure deficiency to the rear of the bus your spring brakes will automatically apply.. this is an emergency action in case you blow and air line or the air compressor stops working.. you bus WILL STOP!

if you have partially blocked air line or a defective valve you could possibly have your spring brakes applying causing a lurch...

-Christopher

[HealthyPetsBus]

Hello All!
Thanks for the input. Yes, all three buses have air brakes. And yes, while the old Wayne buses brake easily, they are different from the feel of my hydraulic brakes on my truck or car. The newer Thomas bus just feels so terrible. I initially chalked it up to "I dont know how to drive a bus", because I purchased the Thomas first. But then, after I purchased and drove both of the old Waynes, the brakes on the Thomas seem terribly wrong.
NOT being a mechanic, I guess the reall answer to swing the bus by a mechanic as suggested. I know NOT how to mess with air governors, etc. But is sounds like getting them checked is likely the best bet.
Thanks for everything. If you have other comments, please feel free to post. I am here to learn!
Thanks
Virginia

[Whiskeyjr]

To me, it sounds like your slack adjusters are out of spec. Have a good look at them, there are a number of YouTube videos on this.


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[jazty]

Originally Posted by cadillackid

with air brakes (unlike car brakes) 70-80% of your braking comes from the Rear, not the front.. this makes it drive differently.. and in the rain it really makes things touchy in an empty bus as the rear wheels lock Very easily...

For completeness, I'm going to add to this statement. It's not just air brakes that mostly use the rears for braking, but buses and other vehicles with any braking system that have the majority of their weight resting on duallies.

Incoming anecdote! 3.. 2.. .1...
I did the front brakes on my bus a couple years ago. The entire time I was awed by the size and weight of the calipers, pistons and pads. This summer I did the rear brakes. Those suckas were easily 1.5x the weight and size! The brake pads alone were at least 8" long! I knew that the rears did most of the braking, but seeing the hardware put it all into perspective.

[cadillackid]

I agree.. while I havent had my brakes apart yet.. i did see the bus with all the rims off when i got 6 new tires.. and the size of the drums on the rear was massive!..

the only issue with busses ..esp empty ones as the weight shift in a hard stop is real.. (except maybe an RE).. where the rears lose traction easier than you might want.

ive played with the braking on mine in the rain .. and when going downhill a fast stop, its pretty easy to lock the rear wheels solid..

a little more playing and I found if i reduce pedal pressure to get al lthe wheels spinning again my stopping distance increased..

if I stayed the course with the pedal just at the point where the rears locked.. my stopping distance was shorter but the bus wanted to get sideways..

if I went down harder on the pedal, to the point of just keeping the steers spinning, my stopping distance was shorter yet and short enough that the rear end of the bus most times stayed the course..

if i went on the pedal hard and off the pedal enough so i was basically pulsating the rear tires, I had good stopping distance (but a little loinger than the last scenerio).. and the bus stayed straight on.. (and I didnt run out of air... ever)

mind you, this is all testing in an empty dog-nose air-brake All-drum short bus (7 row)..

stopping distances on flat ground were greatly reduced in general as was the tendency for the rears to lock.. the weight transfer is greatly reduced, along with the gravity downhill pull.. my guess is that all brake power distribution is set up to assume flat ground an at least a certain % of weight in the rear...

I see a lot of bus conversions where alot of the weighty stuff is closer to the front... tanks, generators, etc.. and the back of the bus is a lightweight master bedroom and general family sleeping area... I dont know how much affect that has on the weight shift during a stop???

-Christopher

[Dragonpop]

It sounds like you could have oil or other lubricants on your brake shoes.
If you have leaking axle seals the oil gets on the surface of the friction
material (brake shoes) and allows the drum to slide past the shoes until
enough pressure is applied to overcome the slippage and then the brakes
grab violently. I would look for oil on the inside of the brake drums. Just
another possibility.

[Mountain Gnome]

Aloha! I just bought my first skoolie, a 1999 BlueBird TC1000 HandyBus. I, too, had the same impression with my brakes. I had to practically jump down from a ladder onto the petal to get it to stop, then it would lurch to a halt. Nothing in between. I test drove several buses, and none were like that, but I can't say if they were hydraulic or air...they were big Thomas buses with International motors. I kinda remember the brakes being "different," but not almost dangerously uncontrollable.

I took it to the repair shop that originally sold the bus new to the school system I bought it from used (auction, unseen, undriven) and told them of my concern (and lack of experience) and asked them to check it out, and check the whole system for problems, leaks, worn parts, etc. I got it back for $250, with paperwork that says "visual inspection - no air leaks". I drove it out of there with it still lurching to a stop. Note this was Tucson, AZ in August, 105°F, and I drove it to NorCal during the heatwave from Portland, OR, so it was near 100°F there also.

With time, I got better at it, so it seemed; though it still seemed like I had to press unusually hard to get it to stop, and keep it stopped at a light. Like if I was a small-framed frail(er) older man/woman, I wouldn't be a safe school-bus driver. Only those with strong legs and good endurance for all the stop-and-go.

I drove it 3 days, mostly on the highway, and parked it for 2 months. I just got back to it, and noted immediately how much easier it was to control the application, so it seemed. I could slow down in a parking lot without stopping to a lurching halt, and I didn't feel like I was panic stopping on freeway off-ramps. I drove it 2 days, and noted my air pressure would leak down completely overnight, and even noticeably (into the red zone) when I stopped for an hour or more. Note now it is cooler than when I first bought it and drove it, especially at night.

Then the "actuator control valve" blew out this afternoon, and the warning buzzer went off as I pulled into a parking lot riding the brakes (the idle at 800rpm will pull the bus faster than I want in a parking lot). No pressure to the front now. This valve unit sits directly under the brake petal, under the floorboard, accessible from under the front of the bus.

Now I am thinking that has been my problem with the brakes the whole time. I am an auto mechanic for passenger vehicles, but without tools right now. And I have no air brake experience. I will be starting another thread on fixing this problem, but for now, I am wondering what others with experience have to say about the original symptoms. I think the valve was not working correctly due to a crack, worn rubber seals, or something I am not imagining, and now the crack is worse and/or the rubber seal is shot. Air is leaking out of the bottom of the round main body of the unit.

Comments?

[bluebird90]

There seems to be a misconception of how air brakes work. Air does NOT hold the brakes off,( except for the spring brake)
air does not bleed off to apply. Air is the force that applies the brakes. Other than just needing to get used to air brakes, there may be an issue with the brake treadle valve or a relay valve holding some air in the system causing an uncontrolled apply.

[Mountain Gnome]

So I replaced what they call the "foot switch" (I called it an "actuator control valve" in my previous post). That fixed both of my problems.

I no longer leak air at a critical volume, my warning signal does not go off anymore, both front and rear build to 120psi+. Also, it does not completely leak down overnight.

And my brakes now work like I would expect them to. No, they don't feel or work like hydraulic brakes. But I can keep the bus stopped at a light without wanting to shift into neutral from having to hold the pedal down so hard. I have subtle control of the stopping power now. It's not all or nothing like it was.

It wasn't particularly hard, just tedious; it was just hard to track down the 13/16ths-inch crows foot wrench. But NAPA came through with it all...just a half-day order away....

$60 for the part. $93 dollar taxi ride when it broke down Sunday night and all rental car companies were closed. $120 for 3 days of rental car. $225 for 3 days of hotel (not bad for the SF Bay area in a place that is not a dump). Hours and hours of driving through smog - the worst of the cost.

So if you seem to have the same hard to stop - very touchy brakes, perhaps think about a new foot switch while you are parked where it is convenient...

[Brad_SwiftFur]

I learned to drive in an OLD IH Transtar cabover which had a similar touchy-brake/stiff-pedal issue. It was, indeed, the "foot valve" as some folks call it (it has other informal names). It's not much more than a few diaphragms and rubber seals and springs. Time consuming, if not otherwise terribly difficult to replace.

[Rusty]

Originally Posted by Brad_SwiftFur

I learned to drive in an OLD IH Transtar cabover which had a similar touchy-brake/stiff-pedal issue.

ALL or nuthin' brakes. Keeps you alert at the wheel, and your passengers hangin' on.

The valve is actually called: a Treadle Valve.

[cadillackid]

is this valve what distributes or affects distribution between front a and rear main brakes?

on my DEV.. my rear wheels Love to lock up even when I dont feel like im into the front brakes that hard.. in fact I have a lot of front brake capabilities left yet my rears love to lock..

I realize part of it is weight transfer in a hard stop.. but seems like the balance is way off..
-Christopher

[family wagon]

My bus has a Bendix treadle-operated brake valve. I don't recall now whether it's the E-12 or E-15.. In any case, the service data for those is on the Bendix web site. It shows a schematic and gives some insight to how this particular valve operates the primary and secondary circuits, which often correspond to front and rear brakes. There doesn't seem to be any proportioning going on here. I think you'd have to go looking further downstream in your air lines to see whether maybe there are relay valves that can be adjusted to give a proportioning effect.

[golfersmurf57]

Also be sure to lubricate the brake cams.

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