All brakes stuck on

[Dan]

After 10-15 mins of around town driving it seems like the brake system is building pressure and not releasing the brakes. It eventually gets to the point where the engine wont move the truck. The brake pedal becomes increasingly harder, I can feel the system is pressurized. If I let it sit for a few hours the pedal returns to normal feel and the brakes are relaxed.

Im thinking master cylinder. Any other ideas? What is that black part behind the master cylinder that has some hoses running from it to the power steering pump etc??

Its not the e-brake causing the issue, its all 4 wheels.

Any thoughts??

- Dan

[Xotik H3]

I vote master cylinder as well. If it affects all 4, it has to be common to all four. Also, isn't that piece you speaking of the brake booster? I have not gone out and looked at mine, just going from memory.

[Dan]

Yeah Im assuming its a booster. Im just used to seeing the big vacuum pancake ones from the old days. And wasnt sure if that thing could be the issue somehow.

[Scarsman]

How do you know it is all 4 wheels? Did you jack it up and try to turn them all? It sounds to me like a bad brake hose. What happens is the inner liner of the hose collapses and becomes an impromptu check valve. You step on the brake and fluid goes into the caliper activating the brake. Then the flap of liner wont let the fluid flow back out of the caliper when you let off the brake. And so it just keeps getting tighter and tighter as you drive. Then when you park it and it sits it has time for the fluid to slowly bleed back past the blockage, releasing the brake until you use it again.

To locate the culprit jack up each wheel after it has been sitting and see if it turns. Then start it and press the brake hard a few times and then try to turn the wheel again. The one with the bad hose will be stuck now. Locate the bleeder on the caliper and crack it open. It should give a little high pressure squirt and the caliper should release.

Another way is if you have just driven it to the point where you can feel it dragging and is not wanting to go, get out and feel each hub. The one or ones that are sticking will be much hotter than the others. Be carefull, as it can be very hot.

Hope this helps!

[Dan]

I had a friend stand next to the truck and he could hear both front & rear brakes dragging. My fronts squeak so that was easy to figure out, and the rear was smoking last time it happened yesterday afternoon. And the only way I could move the truck was in 4Lo. 4Hi couldnt overpower it so thats more than 1 wheel braking I'd guess. Im gonna go back out soon and see if the pressure has come off and I can sneak it home and stay off the brake. I'll check out the MC bleeder too, that could help me if I have to stop a couple times and bleed off pressure. Its only a few miles away...

Thanks for the suggestions!
- Dan

[Dan]

Update -

Last evening I went to where I left the truck sitting for a few hours. Started and put into gear and it rolled freely. So the pressure buildup slowly released itself during that sitting period. I was able to get it home without using the brake pedal, just a couple times on the e-brake at intersections and then just rolled thru. Once home I checked the rotors. The front two were cold. The back two were both hot to the touch. Evenly, both about the same hotness. Today Im going to recreate it and see which wheels are stuck so I'm 100% sure of that and go from there.

Still thinking master cylinder. Its not the e-brake because thats mechanical and should have no effect on the line pressure and the pedal becoming rock hard.

[Scarsman]

...just a couple times on the e-brake at intersections and then just rolled thru. Once home I checked the rotors. The front two were cold. The back two were both hot to the touch. Evenly, both about the same hotness.

Just a thought, not knowing how long it was from when you used the e-brake till you got home, but the rears being warm could be normal from using the e-brake, as it only activates the rear brakes. Maybe still warm from that? Just a thought.

[Xotik H3]

Just a thought, not knowing how long it was from when you used the e-brake till you got home, but the rears being warm could be normal from using the e-brake, as it only activates the rear brakes. Maybe still warm from that? Just a thought.

Let it go Dan... it's ok. :jump: :fdance:

[IRA51]

First off there is no vacume booster ,you have hydraboost . Your power steering and brakes are run buy the power steering pump . If you unplug the ABS unit and the brakes work again ,you have an ABS problem .

[fusionH2]

Did you ever figure out what the problem was? I'm having the same exact problem with my 2006 H2.

[starkey188]

It's the hydrabooster, just happened to my 2005. There was a recall on it in 2005 but GM wouldn't honer mine because it wasn't the correct vin number. They quoted 726.00 for a new one. I priced one at a auto store and got it for 200.00. I think they priced the whole master cylinder at GM. My hydrabooster was leaking a little. It took about 3 hours to change out. The hardest part is working under the dash. I'm still bleeding air out of the steering pump system. Hope that helps a little.

[IRA51]

Gm had big problems with the hydraboost units in 05 Avalanches ,my brother had his brand new 05 truck in to the dealer 6 times ,and they never could fix it in the 6 months he owned it . he traded it in on a ford after 5600 miles. As it turns out he likes his 05 Ford supercrew Lariat better that the Avalanche any way .