'97 Tahoe RR Brake Sticking - Won't Bleed

[wirlybird]

Hi all,
I have a 1997 Tahoe LT 4X4 2 Dr.
The right rear drum brake sticks. Has been doing this for a long time.
Some years back I had the rear brakes done with all new parts including wheel cylinder and drums. Problem is still there.
Pulling away from a stop light or sign, for instance, you step on the gas and feel a slight resistance in the truck moving forward then a "clunk or thump" from the rear and it starts to roll. After driving some the RR wheel is quite hot compared to the left one.
Another thing to note is the dealer, after adjusting rear brakes and trying to replace brake fluid, said they could not bleed the RR but had no further diagnosis of that issue at the time.
So my question would be - what do you think the most likely cause is for this?
Master cylinder would seem unlikely.
ABS components? Something else?

Thanks for any ideas.

[Stealthee]

Its possible you have a bad proportioning valve. While a different car, my 3000GT was going through its "restoration" and I was flushing and bleeding all the brakes. I had set everything up to gravity bleed while I did other things and was closing bleeders as they started to dribble. The right rear was taking forever, and knowing its furthest away from the master I kept letting it go.

Finally, I got annoyed enough to look deeper. I set up my one man bleeder and with the bleeder wide open stepped on the brake pedal and it was hard as a rock. I stomped it, and same thing. Absolutely no fluid was coming out. I took the line off, and no fluid was coming out. I got to the prop valve and took the line off there, stomped the pedal, and it was hard as a rock, and no fluid came out.

I replaced the prop valve, and everything worked as it should after that.

[wirlybird]

Thanks. I was wondering about this. Figured it could be that or an ABS system component.
I think considering the age of the truck I might just do some parts replacing anyway to get new parts on it. Brakes are no area to skimp!

[wirlybird]

It is looking like the proportioning valve is part of the ABS unit.
Anyone know for sure?

Maybe a part number for the ABS unit?!!!

[Blue Bowtie]

It is possibly a Kelsey-Hayes ABS unit, and would need to be cycled to bleed the brake lines to each wheel caliper/cylinder. That will require a scan tool capable of bi-directional communication. There is also a prop valve bolted to the face of the ABS unit, and it may be shifted and stuck. Cycling the ABS under pressure may relieve that, or it may have to be physically shifted.

It is also important to verify that the bleeder screw is not rusted shut. It may be necessary to completely remove the bleeder and run a small drill bit or pick through the cross-drilled holes to insure they are open.

After that, it's all just lines and the ABS unit.

http://www.askatech.com/AskATechLive...9.pdf#G1081872

[wirlybird]

Originally Posted by Blue Bowtie

It is possibly a Kelsey-Hayes ABS unit, and would need to be cycled to bleed the brake lines to each wheel caliper/cylinder. That will require a scan tool capable of bi-directional communication. There is also a prop valve bolted to the face of the ABS unit, and it may be shifted and stuck. Cycling the ABS under pressure may relieve that, or it may have to be physically shifted.

It is also important to verify that the bleeder screw is not rusted shut. It may be necessary to completely remove the bleeder and run a small drill bit or pick through the cross-drilled holes to insure they are open.

After that, it's all just lines and the ABS unit.

http://www.askatech.com/AskATechLive...9.pdf#G1081872

Yes it is a Kelsey Hayes unit.
I had the truck at the dealer recently for a rear brake adjust and flush and fill fluid.
They told me they couldn't bleed the RR. I tried to ask questions but got vague answers about bleeding the RR.
The main reason I am wondering about the ABS unit is that the "sticking" brake was an issue before replacing the rear cylinders and all rear brake components. This was NOT done at the dealer so brake bleed may not have been done correctly with the scan tool.
I need to verify if there is one brake line running to the rear of the truck.
This ABS unit has a total of 5 lines. 2 of which are from the master cylinder.
This leads me to believe that there is only one line to the rear-end then it splits to left and right brakes cylinders.
If this is the case the the no bleed must be in the RR line or brake cylinder.

[j cAT]

probably a brake line has a leak to the rear .....
master cylinder probably has dirty brake fluid and must bleed the master cylinder .