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Old 02-13-2014, 04:25 PM   #1
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Air Brake Issues

Hey everyone,

I'm not sure who here is knowledgeable about air brakes / air systems but I am having some issues with mine. Last night I started my bus up for the first time in a month or so to move it out from under a tree, because there was going to be (and was) heavy snow and freezing rain. I warmed it up for 15 minutes orso to let the air pressure build and so the trans would get warm enough to be able to shift (these allisons have a minimum fluid temp to engage). It started fine, built up air pressure, and I tried to release the brakes, I heard air move, but they didn't release. I pulled the switch back and pushed it in to try and unstick them, as well as press on the pedal hard and let go, air moved then too, but nothing moved. I put it in gear and it wouldn't budge, but I could tell it did engage successfully.

Anyone ever had this issue? I don't know what could be causing it.

Thanks
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Old 02-13-2014, 04:44 PM   #2
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Re: Air Brake Issues

I've had the pads stick to the drums pretty bad on mine, but it always broke free. Could you have somebody crawl under and there and see if the rod is actuating?
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Old 02-13-2014, 05:37 PM   #3
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Re: Air Brake Issues

Sounds like shoes rusted to drums

Block all the tires front and rear...bus will try to move when brakes get free

Have air up engine off and "park brake" released, bus will be held by the chocks

Front will be fine, crawl under bus from in front of rear tires with a big azz hammer and drift, place drift on the verticle shoe metal and hit with a hammer...hard this will break the shoes loose

A flashlight will let you see which shoes are touchy drums....gap or no gap....bus will rock/move so make sure it is chocked good....and if you pee a little first time you knock the stuck shoe loose....it,s okay

You want to hit the part that is up and down, don't hit the metal part with the shoe attached and the pad

I can take a picture of were to hit if needed

Most school buses had semi metallic shoes since they never really got hot and they rust to drums
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Old 02-13-2014, 06:17 PM   #4
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Re: Air Brake Issues

Quote:
Originally Posted by bansil
Sounds like shoes rusted to drums

Block all the tires front and rear...bus will try to move when brakes get free

Have air up engine off and "park brake" released, bus will be held by the chocks

Front will be fine, crawl under bus from in front of rear tires with a big azz hammer and drift, place drift on the verticle shoe metal and hit with a hammer...hard this will break the shoes loose

A flashlight will let you see which shoes are touchy drums....gap or no gap....bus will rock/move so make sure it is chocked good....and if you pee a little first time you knock the stuck shoe loose....it,s okay

You want to hit the part that is up and down, don't hit the metal part with the shoe attached and the pad

I can take a picture of were to hit if needed

Most school buses had semi metallic shoes since they never really got hot and they rust to drums
You know, this is probably it. Last time I drove it (4-5 weeks ago) I drove it nearly an hour, and in the pouring effin rain the entire time. Backed it into where it is now, set the parking brake and haven't moved it since. They're probably totally rusted to the drums.

Once the 15" of snow and ice we just got / are still getting is gone and it is above 20 degrees out, I'll get under there and try the hammer-sh!t-your-pants trick.

Would it work if I used the t-bolt things to manually release the brakes, or could that bend / break something since already ~125psi won't break it loose? I just don't like percussive maintenance

Thanks!
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Old 02-13-2014, 06:37 PM   #5
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Re: Air Brake Issues

You say you have below freezing weather, I would take a propane torch to the spring brake control valve see if it lets the brakes off,When I used to drive tractor trailer we used to have to take a road flare to it sometimes in freezing weather to get the brakes to release
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Old 02-13-2014, 07:20 PM   #6
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Re: Air Brake Issues

Quote:
Originally Posted by allwthrrider
You say you have below freezing weather, I would take a propane torch to the spring brake control valve see if it lets the brakes off,When I used to drive tractor trailer we used to have to take a road flare to it sometimes in freezing weather to get the brakes to release
Isn't there a rubber diaphragm in there? I don't want to melt that...not disagreeing with you I just don't know a ton about air brake systems.

Also, I have an issue with what I believe is the "unloader" on the compressor, or the clutch or whatever...sometimes it is slow to rebuild pressure...like nothing nothing, then it surges from 100 to 125 psi.
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Old 02-14-2014, 08:32 AM   #7
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Re: Air Brake Issues

If they were wet when you parked it and it went below freezing right away, they are probably just froze, happens to semi's all the time. If you've seen trucks with big white stripes painted on the tires, it's so you can see in your mirrors if your tires are going around. Quickest way to unstick is hit the edge of the drum HARD with a BIG hammer.
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Old 02-14-2014, 11:08 AM   #8
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Re: Air Brake Issues

Happens to me a lot. Release the brakes and them apply foot brake pedal hard, then release them. That has always done it for me. You might have to press and release the foot pedal a few times.
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Old 02-18-2014, 11:45 AM   #9
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Re: Air Brake Issues

Quote:
Originally Posted by opus
Happens to me a lot. Release the brakes and them apply foot brake pedal hard, then release them. That has always done it for me. You might have to press and release the foot pedal a few times.
I tried this but it didn't do anything. Once the snow melts I will try releasing and then tapping them with a hammer.

Thanks.
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