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Old 06-19-2019, 07:28 AM   #1
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Air brake not releasing

Iím not sure Iím even doing this right?🥴 I have a 2006 International that we are converting. My husband disconnected wires to lift gate, emergency exit doors and outside flashing lights. Now, parking brake wonít release. Have put jumpers back on all wires he disconnected and still nothing. All air working properly through the system just will not disengage. Anyone have any advice?? My husband is very mechanically gifted but this time, because itís a bus heís stumped.
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Old 06-19-2019, 09:19 AM   #2
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How long has it been sitting in one place? Could just be rust on the drums holding it still.
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Old 06-19-2019, 09:39 AM   #3
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How long has it been sitting in one place? Could just be rust on the drums holding it still.
Very likely. I second WarGear's suggestion.

However, are you absolutely positive this bus has air brakes? Not to be condescending, but some still do have hydraulic brakes, and most assume they have air when they may not.

The reason I ask is that many older Ford and some Navistar chassis skoolies (the older, the more likely) have the dreaded Lucas-Girling system, which is known for a slew of problems, hard to service, and even harder to find parts for, let alone find a shop that will touch them. My previous Ford B-700 bled down the parking brake chamber after sitting for too long and had to be scrapped due to inconvenient timing.

If you have THIS to (dis)engage the parking brake, it is air brake.
Air Brake Knob.png
If not, you have hydraulic...

If they are indeed air, first order of business is to check system air pressure on the gauge. If it is below 60, that is likely causing the problem. Air-brake buses engage their spring brakes much sooner (60 psi) than trucks (20-40 psi). Their low-pressure warnings come on sooner, too, at 85 psi vs the 60 psi that trucks are set for. System pressure should hold between 90-120 psi on most systems, there is a blow-off valve to keep it from exceeding 150. Slow leaks are quite common in older air systems, which will cause them to bleed down slowly when sitting. I've seen severe leaks lose pressure completely in a matter of a couple hours. Leaks will also allow more moisture to enter the system, which is not good for it.

If air system pressure is not at least 60-80 psi (which still indicates a problem), start the engine and let it run for about ten minutes. The system should build air pressure back up within a few short minutes, but if it has bottomed out, it will take longer. Especially if there is a moderate leak to start with. If air system pressure is sufficient, generally only two things will keep the parking brake from disengaging -- chamber / linkage malfunction, and brake linings rusted to the drums.

If you are not aware, it is necessary to open a drain cock on the air supply tank periodically. If I remember correctly, DOT rules state once a day -- reason being that compressing air always results in a bit of moisture in the system, and a small bit of oil from the compressor can make its way to the tank as well. Hopefully THIS is not your problem, if the lines are clogged with oil and water, it will take a bit of work to purge. Even worse if it has made it to the chambers. However, if it was working fine when it was parked, I doubt this is likely.

One of you will have to get under the bus and watch the brake chambers when attempting to disengage. CHOCK THE WHEELS FIRST! If the chamber is releasing and moving the brake linkage, then it is likely rust on the linings and drums.

I do not recommend attempting to service a brake chamber, if that is the problem. Many reasons behind this, all for safety.

On both air and hydraulic systems, the semi-metallic brake linings will indeed rust and bond with the drums. Clearing rust on the drums and linings is a bit of a job, as removing the wheels and drums will be necessary, but it is something the average person can do. Keep in mind the wheels and drums will be much heavier than anything you are used to. Standard 2 - 1/2 ton floor jacks and jack stands are not going to safely support your bus for very long, either.

Only undertake this if you think you can handle it. Make sure any jack / jack stands used are rated for the weight of your bus (likely at least 6-8 ton). DO NOT ATTEMPT THIS WITH JACK STANDS OR JACKS THAT ARE NOT APPROPRIATELY RATED - IT IS NOT SAFE. Start by properly chocking both wheels on the other axle, and release the parking brake. Then begin lifting the rear. Chase the axle housing tubes with your jack stands, which is to say every time to you can raise them and latch them, do it. It will minimize the fall if your jack slips.

Once the wheels are removed, you can heat the drums with a propane torch, tapping on them with a hammer to work them loose. Brake cleaner may help with this, I recommend wearing some sort of mask or respirator to prevent inhaling brake dust -- it can cause cancer.

Spray the brake linings well with brake cleaner, lightly sand the friction surface, as well as the drum contact surface. Reinstall and you should have no problem.

If you don't have the proper equipment for this, or do not feel comfortable tackling it, you might call a truck repair shop and see if they have a road service available. It's cheaper than towing (usually $100 hookup and $10 a mile).
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Old 06-19-2019, 11:29 AM   #4
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Or, if it's simply the linings stuck to the drums (somewhat common), just make sure you have full air pressure, push in the knob to release, drop it into low gear, and give it some throttle. Might have to use reverse a couple times. It's how I've always unstuck stubborn brakes.


Side note - it's not always rust that causes this. Setting the brake while the shoes/drums are hot can cause this too.


I have crawled under and used a hammer/chisel to separate the shoes from the drums but *MAKE SURE* it's chocked to prevent movement if you try this. In my case I was driving a tractor trailer and used the trailer parking brakes to prevent movement. More than one driver has found themselves pinned under a truck that moved after attempting this.
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Old 06-19-2019, 11:43 AM   #5
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*snip* make sure you have full air pressure, push in the knob to release, drop it into low gear, and give it some throttle. Might have to use reverse a couple times. It's how I've always unstuck stubborn brakes.

Side note - it's not always rust that causes this. Setting the brake while the shoes/drums are hot can cause this too.

I have crawled under and used a hammer/chisel to separate the shoes from the drums but *MAKE SURE* it's chocked to prevent movement if you try this. In my case I was driving a tractor trailer and used the trailer parking brakes to prevent movement. More than one driver has found themselves pinned under a truck that moved after attempting this.
Yup! Never trust those trailer brakes, m'boy! I had a trailer once that just kept rolling when I tried to slide the tandems. Never trust a 12,000-lb bus either!
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Old 06-19-2019, 12:18 PM   #6
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Yup! Never trust those trailer brakes, m'boy! I had a trailer once that just kept rolling when I tried to slide the tandems. Never trust a 12,000-lb bus either!

Had one that had "No Brakes" - and BossMan was like "well, have the shop adjust the brakes". No. I did not say "The brakes are out of adjustment. I said it has no brakes. Missing brake shoes and rollers and springs and who-knows-what else." Literally. I always tested trailer brakes before anything that unsafe. Yes, we had a couple that were difficult-to-impossible to slide when heavily loaded, the brakes simply weren't strong enough. One would work fine until you used heavy brake application, after which the brakes were weak. Slack adjusters were shot and wouldn't hold position under heavy application.
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Old 06-19-2019, 02:11 PM   #7
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Originally Posted by Brad_SwiftFur View Post
Had one that had "No Brakes" - and BossMan was like "well, have the shop adjust the brakes". No. I did not say "The brakes are out of adjustment. I said it has no brakes. Missing brake shoes and rollers and springs and who-knows-what else."
Angry Duck.jpg
I remember one time I had someone pop over a hill when I was about to make a left turn onto a ramp. They were doing 70 in a 55, easy. Not wanting to cross their path and be at fault, I came to a stop, which made me overshoot the ramp slightly and swing onto the shoulder making the turn. The truck sunk in and apparently cracked the PlastiCrap oil pan (thanks, Detroit!), though I didn't realize it at the time.

Brand-new truck with 40k on it, mind you. Of course, it began leaking slightly, but with the oil matching the color of the pan, I couldn't tell where the leak was. I told the company about the leak, but I didn't think the above incident had caused it, as I never felt anything hit. It was coming up on an oil change, and they put me in a spare truck for a week. When I came back to pick up my assigned truck, I told the shop supervisor, IN FRONT OF THE SAFETY DIRECTOR, that the brakes needed adjusting on the spare truck, because it would move with the parking brake set.

The safety director proceeds to grill me about the oil pan, accusing me of not doing pre-trip inspections. Wait a minute -- I just PROVED that I did! It was pretty clear they intended to fire me no matter what I said at that point. To which I replied...
Does It Hurt To Be That Stupid.jpg

Incidentally, the same company hired me back and put me in a truck that had a frame bent so bad it was tap-dancing on the steer tires above 55 under load. I argued with them for 8 weeks and 10,000 miles. Even took it to a DOT station, where it was confirmed that running the steer tires lock-to-lock caused the frame and cab to 'dance' even at a stop. I drove that POS straight the yard, dismounted the trailer, got a rental car and cleaned out the truck.

Anyways, sorry to hijack the thread...
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Old 06-24-2019, 05:31 PM   #8
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Iím not sure if yíall have resolves this issue yet but I know with my bus, if the button is engaged for the lift, it wonít let me release the parking brake. During my build, I didnít disconnect the wiring for the lift after seeing how this worked on my bus and the bus at work. I think you are dealing with part of the safety feature to keep drivers from moving the bus with the left deployed. I know your lift and wiring is out but somehow, your bus doesnít know that.

Also, another issue that the tire guy experienced when getting my tires balanced was he couldnít release the parking brake. If you donít fully engage the service brake (brake pedal) and you press the parking brake it, it will lose air as if it is releasing the brakes but never do until you press the pedal all the way down.

Those are 2 safety features that Iíve seen on both International and Thomas built buses. I hope that itís just you arenít fully depressingly the brake pedal fully!!!
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