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Old 09-21-2016, 06:46 AM   #1
Mini-Skoolie
 
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VERY touchy brakes

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
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Old 09-21-2016, 08:25 AM   #2
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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,
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Old 09-21-2016, 09:47 AM   #3
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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!
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Old 09-21-2016, 10:00 AM   #4
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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.
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Old 09-21-2016, 01:56 PM   #5
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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
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Old 09-21-2016, 07:40 PM   #6
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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
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Old 09-22-2016, 09:01 AM   #7
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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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Old 09-22-2016, 09:14 AM   #8
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Quote:
Originally Posted by cadillackid View Post
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.
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Old 09-22-2016, 10:43 AM   #9
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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
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Old 09-22-2016, 04:02 PM   #10
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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.
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