Brake failure or something else?

[nthach]

A 1998 Chevy Tahoe I maintain for a friend had a weird thing that happened to it - he was driving it and had to brake for a speed bump. He texted me and said he heard a rubber band like sound, a low-sounding boing and can't get the "truck out of brake". I asked him about the pedal feel, he said it was stiff, not the usual softness associated with GMT400 trucks, and that the truck jerked to the stop afterward.

I asked him to apply the parking brake and try to move it into gear and he reported the parking brake pedal felt fine and the shift lever moves, to rule out broken drum brake springs or shift lock.

My guess is the power brake booster failed or something else has happened, if the brakes did fail to release I'm certain there would be lots of brake drag - my research on this led me to the brakes being the achilles heel of the GMT400s - a few guys have swapped in the GMT800 master cylinders, but those trucks were 4-wheel disc. What else could be a culprit here?

 

[Johnny2Bad]

I think the problem is whomever is attempting to fix the truck is looking at a computer screen instead of a brake system. No brake work should ever be done without a complete inspection of the entire system. Since that means possibly buying new parts unrelated to whatever issue the truck is having, there isn't much point in trying to pre-diagnose the issue. Get dirty and fix everything that's broken or worn.

The one thing that should be done online is to search out and buy the Service Manual for the specific vehicle. If you want to DIY repairs you have to consider that as a necessary Parts Budget item.

 

[SnowDrifter]

Actuator rod?
Go through the system piece by piece and see. Check inside the brake drums, check the shoes, the hardware, springs, cables, adjusters, etc
Check the front disc brakes, verify the piston and slide pins aren't seized
Check brake lines. Soft lines should be free of any cracks/fraying/leaks. Hardlines should be free of leaks and excessive rust
Master cylinder should move freely, but require a bit of effort to push in. There's a return spring in there that exerts ~20ish pounds of force. It shouldn't have any leaks either. An external leak will dribble down/into the brake booster. An internal leak will cause some weird issues. You can lack pressure in either front or rear or both.

 

[supton]

I wonder if a pad delaminated and got sideways, or otherwise something else got stuck in there. I'd probably tell him to jack each wheel up and see if it will spin freely, to see if it's one or all wheels that is a problem. If it's all then I'd think master cylinder or in that area, if it's one well then that's the area to tear apart.

 

[bullwinkle]

One trick is to loosen the nuts holding the master cylinder to the booster, pull it loose, bet the brakes release. Something has failed in the booster or the pedal linkage.

 

[Merkava_4]

There's no springs on the front disc brakes, so you'll be looking at the back drums and the parking brake/cable assembly. Don't forget there's springs in the parking brake pedal too.

 

[spasm3]

Originally Posted By: supton
I wonder if a pad delaminated and got sideways, or otherwise something else got stuck in there. I'd probably tell him to jack each wheel up and see if it will spin freely, to see if it's one or all wheels that is a problem. If it's all then I'd think master cylinder or in that area, if it's one well then that's the area to tear apart.


That's where i would start as well. After that noise you really need to inspect each wheels caliper/wheel cylinder. Put it on jack stands.

 

[nthach]

I've found the PDFs of the official GM service manual, and I did notice a leak at the master cylinder between the reservoir and the body itself. I'll proceed with checking the wheel-end brakes and ABS sensors.