Frozen Brakes-- Help!

[wb4hla]

    Help Welcome > Brake Lockup

Hi  I own an older GMC PD4108A         Its up here in Maine Where I am afraid last Winter & Spring , the Humidity has caused the Back brakes to Lock up and , Unlike Years past where I could rock or shake it loose then drive it---its no go

Have tried bleeding all air resevoirs of air while engine running    air pressure good at 120 pounds but no release

Have pulled tires and jacked & cribbed rear end and despite beating on rear drums with sledge hammers ( what a local truck garage suggested ) they are still locked up.

Depressing brakes does cause brake actuator do extend the threaded rod !

Any suggestions on how to release them would be welcome !   Thanks Ed Hammond WN1I
                                                                                                    Buckfield Maine ( pushing for Fla)

I moved this post to it's own topic so that it could get a larger audience-- Dallas

[gumpy]

Both sides or just one?

Can you back the slack adjuster off or is it too tight? 

I suspect it's not the shoes, but the cans sticking. If you can get the slack, you should be able to tell if the shoes are free. If they are, pull the pins and cans and have them rebuilt or replaced.

[RJ]

Ed -

Do your rear brake cans have two or three air lines going to each of them?  Being a 4108, chances are they're DD3s.

If they have three, then you've got DD3s, which release differently than spring brakes.

1. Build the air pressure up to the governor cut-out (about 120 psi).

2. Release the parking brake by pushing the button in.

3. Apply a full service brake application, and hold for 5 seconds.

4. Release service brakes, and see if the brakes are free.

If so, problem solved.

If not, besides what the others mentioned, if you've got DD3s, then the rollers may be "rusted" stuck inside the brake cans.  Translation: time to pull the cans and rebuild them, or exchange for rebuilts.

FWIW & HTH, somewhat. . .

[Ncbob]

Hi Ed,

So far, darned good advice.  I have an MC5  and it has the DD-3 brakes (with the 3 air lines going to the brake actuators) and I just went through my whole system...lines, actuators, shoes and drums.  One other item in the mix is the Inversion valve which actually releases the P/B's when you stomp on the Service Brake treadle.

If you have Da Book..it should lead you through the brake air schematic...or ..better yet...Buswarrior is our resident DD-3 Specialist.
You might try sending him a personal message...he's a great guy and much talented.

Best with your quest for a solution.

NCbob

[buswarrior]

Hello Ed.

You describe that when the brake pedal is pushed, the pushrods move.

Please let us know how many air lines are attached to your brake chambers.

All things being equal, I'm thinking the linings are rusted to the drums. Try to back off the slack adjusters to see if the linings will come away from the drum. There is no cure short of a fair degree of violence, carefully applied, or you will be spending a lot of money!!!! Whacking on the shoes is what you want, not whacking on the drums.

Get one of the mechanics to come out after work for cash or beer, or whatever, to have a look and to apply that violence for you.

Once free, you need to be worried about what the effect has been on the bus's stopping ability. What will all that rust will do to your brake adjustment when it comes out of there, not to mention the condition that the linings might be in?

And then, don't leave your bus parked for that long again without releasing the brakes and moving it a few inches forward or back!!! Once a month at least, move it back and forth in the parking spot, if you aren't going to drive it, and park it a little forward or back than it was.

happy coaching!
buswarrior