The Stovebolt Site Forums The Parking Lot Big Bolts unsticking air brakes

I am now the proud owner of a 1974 GMC COE w/427 & Spicer. The seller says the brakes might be stuck since the truck has sat for 15 years. Question is: Are there any tricks to unsticking air brakes? I've unstuck regular truck drums, but not air brakes. I might be able to get the truck running. The seller said the motor was running when parked but now the motor won't turn over. I'll soak the cylinders & replace ignition parts and see what happens.
Thanks,
Scott

well, how much ya know about big trucks? a good start might be to apply some grease to the s-cam tubes. NOT ALOT OR YOU WILL SQUIRT GREASE OUT OF THE TUBES ONTO THE BRAKE SHOES. are the brake backing plate still on? alittle p-blaster or kroil to the rollers where they meet the shoes will help.

then there's the hammer. don't go crazy with it. brake drums are plenty expensive.

by the way, remember to back off the slack adjusters. grease them BEFORE YOU try to back them off. oh yeah, how ya gonna put air to the truck to back off the emergency brakes.

like i said. how much do you know about big trucks??? hang with us. we will help you all we can!

Hope theyre not wedge brakes either... and depends on whats stuck...the s cam,,or the shoes to the drum??? Might mean he means all the valves stuck too..??? in that case,, alot of alcohol and taking them apart or replacing.... oh i meant alcohol for the brakes not the mechanic...hehehe..

UncleScoot,

To answer koolkar's question..I don't know much! This is what I think I know...unless this rig has a spring brake, then the service brake has long since pulled the linings away from the drum. If it has a spring brake then you pop the little plastic access cover on the back and compress the spring using a socket? This pulls the linings back too. Doing this allows you to move a truck that has no air in the system.


Stuart.

using the tool to "cage" the spring brakes is a good idea. and yeah, that's how you move a big truck with no air. just because the brakes are caged does not mean the shoe will pull away from the drum. now we are back to the backing plates and the hammer.
i'm pretty sure that the brakes on that year are s-cam, unless they were special ordered with the wedgies.

ya know, for a reasonable fee i could make a service call---------------.

Sorry about disappearing. I was called in to work. I don't know much about big trucks. I mainly want the 427 & spicer for my '51 4400. This truck might be too good to part out. Then I'd have to sell it. But, I could use a lot of those parts.
Anyway, the seller probably doesn't know that there has to be air pressure to release the brake. I didn't know til last night when I asked the truck driver at work. I think I can get the motor running, but I don't know about the air system. I will print this out & take with me.
Thanks for the info, guys!
Scott

You might consider breaking the output line from the compressor and fitting it with a coupling to connect it temporarily to a shop compressor or air tank,just to see if the brakes will function. If that's a go,it might be a good idea to incorporate the air hose coupling into the system for such emergencies in the future. (Not to mention it'll be useful for filling a low tire or blowing all the dirt out of the cab a couple of times a year.)
Speed

Koolkar & Speed,
The issue on air supply: I'm betting that I can get the truck running. Is the compressor run off the engine or a PTO? I'm guessing engine. I wouldn't think it's electric or exhaust driven. I will lube what I can & check fittings before firing engine. I'll also pull the wheels & brake drums(wish me luck!) to see what I have.
If I can't get the truck running, I have a little compressor that might work. I'll have to buy a power converter. I might need that anyway to run lights to see. I'm nocturnal & won't meet up with the seller til 5pm. I won't be going til Monday, so I have time to prepare.
Man! This is gonna be fun!
Scott

with a gas engine of that vintage the compressor is likely belt driven. If so you may want to loosen belt ant try spinning compressor by hand to make sure it isn't stuck. If you get the engine stated and the s -cams release but the shoes are still tight to the drum put it in reverse and GENTLY ease up on the clutch just enough to rock it and see if they will release. Do not do this if the s cams aren't releasing. Do it gently so that if they are bad stuck you don't tear the linings off the shoe. If useing a hammer try to remove dust covers and tap on side of shoe rather than downward on shoe or directly on drum as Koolkar said they are expensive. .After you get airpressure built up bleed the air tanks ( there should be petcocks on the airtanks) to remove any accumulated crud then build pressure and put air to your brakes it doesn't take much crud to cause a airvalve to stick some times.

Thanks for the help again, everybody. Hopefully I can get this baby up & running without breaking anything. It's always better to gain knowledge from those with experience than by the old trial & error method. I'll update with results & pictures on Tuesday.
Scott