Stuck parking brake on 1980 GMC fishbowl transit

[herarmwashisleg]

 

   I have a 1980 GMC transit bus that I am working on as a hobby...  The parking brake seems to have a mind of its own...  Maybe i am doing something wrong?

I cant seem to get it disengaged!  Four days ago I had the same problem, but then after a bit of messing with it (on/off more than a few times), it popped off and off down the road
I drove.  Now it is parked at my farm and will not budge.   I dont think it is rust, since I had it disengaged 4 days ago, and maybe a few days before that..

Any info would be appreciated as i need to move it, and its not going anywhere with the parking brake stuck ON!

cheers

[Dreamscape]

What was the air pressure?
Somethimes the shoes stick on the drum if it has been cold and there has been moisture.
I had that happen to me on our Eagle, just put it in first and broke the shoes free.
I don't know much about transits, but someone on this board will be able to better answer you question.

Happy Trails,

Paul

Dreamscape

[tekebird]

some systems once the parking brake is released you must make a full service brake application.

[NJT 5573]

dear cheers, I think the rules are something like this. full air in the tanks. release valve. hold brake pedal all the way to the floor for 30 seconds, good to go. sometimes the shoes stick to the drums because they want to. the anchor pins and shoes are mounted avoid brake lockup in emergency situations. trying to drive foreward normally won't free a stuck shoe (common). put her into reverse and put some torque on it and they will come loose. If its freezing and you don't have an air dryer there may be other issues. If the rear air tanks are loosing air on application, there are other issues.

[RJ]

Chances are real good that this coach has DD3 parking brakes on it.  Look underneath and see if it's got three air lines going to each of the rear brake cans.

If it does, then the parking brake release procedure is as follows:

1.  Build coach air pressure to 120 psi.

2.  Release parking brake (push down on the button)

3.  Make a full service brake application AFTER releasing the parking brake.  Hold for about 5 seconds.

4.  Coach should roll after this.  If not, repeat. 

If it still doesn't release, after steps 1 - 3, try putting coach in reverse and giving it some throttle.

OTOH, if the weather outside is really cold, as others have mentioned, the rear shoes may be frozen to the drums.  If that's the case, other procedures are called for.

Good Luck, and HTH. . .

[Sojourner]

I believe your GM transit is equipped with DD3 cans. It has 3 air lines to DD3 can but if only 2 lines then it a spring (parking) can or actuator. After full air build up...90psi or greater....with parking push in...It should unlock roller cam in DD3 can...however it may still be lock by tension from applied brake shoes to drum....so by applying full brake pedal at stand still will release or over come wedge's tension between steel balls & main's piston's shaft or rod via small "releaser" piston.

Sometime it small "releaser" piston force alone is enough to release roller cam...which mean it unnecessary to apply full brake pedal at this time.

Some DD3 may have grease fitting (on DD3 can close to mounting bracket) to grease roller cam department...my MIC 8 does. It may be dry or lack of lube to cause sticking condition. From factory it is packed with grease.

FWIW

Sojourn for Christ, Jerry

[Buffalo SpaceShip]

If the other fixes here don't get you rolling, you'll have to look into your inversion valve and/or the aux. diaphragms on your DD3 cans. DD3's can be tricky to diagnose. BTDT.

I got a call from Cliff (FL Cracker) last week and he's going to attempt a DD3 diaphragm replacement with the can on the coach. I'm sure he'll post about his success (or failure) in doing so.

Keep us posted, herarmwashisleg (scariest screen name I've seen in awhile  )
Brian B.

[herarmwashisleg]

        Woot thanks for the quick answers...  I gave it full pressure to the brake for 10 seconds after releasing the brake then put it in reverse, rocked it back a tiny bit, then 1st, and it disengaged...


It seems now that with a 5 second of pressure full to the floor on the brakes after 120psi builds up it releases as it should..

now my only problem is getting it out of the mud, so much snow/rain here in oregon

Thanks all for the quick answers!

cheers!
herarmwashisleg