Brake problems

Ken Kidder · September 11, 2021

HELP Started with having to replace brake lines. One blew and they were all rotten and rusty from salt up here. So got kit and had them install all of them. Mechanic got it it wrong and had them all wrong going to ABS module. Finally got that right and got it back with brakes and ABS bled. Brakes after a few uses locked up and would not release. Took it back. Said needed new master cylinder. Did that and had them re bleed brakes and ABS. Got it back and front brakes STILL slow to release and heating up. Checked calipers and shoes. Pistons and rubbers and shoes ruined from getting to hot. So I replaced all calipers and shoes in case that was it. NOPE !! Replaced ABS module! Still slow to release after getting brakes and ABS module bled again. So replaced both front rubber hoses on front in case they had collapsed inside. NOPE Still slow to release. If it sits for awhile the brakes act normal. But if you sit and pump on them the pedal slowly gets firm and won't release brakes for quite awhile. So after replacing all brake lines, master cylinder, calipers, brakes shoes, ABS module and front rubber lines I have nothing left to replace. Truck has only 170,000 km or 106,200 miles.

dna9656 · September 11, 2021

Well, since you have replaced just about everything... Does your truck have a hydro-boost? My 06 Avalanche does. I used to a ASE certified brake qual. but it didn't cover hydro-boost so I'm making an educated guess here ok?

I appears the brakes are being applied by some force that's not your foot. The hydro-boost is a a hydraulic power brake vs. a conventional car/light truck power brake that use engine vacuum to provide 14.7 lbs. + of assist. so I think you have a hydro-boost issue.

You mentioned salt "up" where you live. Usually salt is along the ocean or on the roads in East and many Mid-West states in the US. So I am unsure of your general location; I grew up in that part of the US but never heard of corrosion directly linked to brake issues unless the car has sat for a long time. I would also suggest you check all brake control electrical connections in the brake system for faulty grounds.. Also, do a internet search for GMs brake system trouble shooting charts and see what you can learn there.

I'm thinking after you've gone through all this you will be the forum's go to guy for brake issues.

Edited September 11, 2021 by dna9656

Ken Kidder · September 11, 2021

I actually was thinking after seeing many posts of same problem of maybe putting a couple of washers on both bolts between the booster and master cylinder in case the rod in booster is not retracting all the way. But like I mentioned the pedal starts out normal but can be pumped up till it is hard at the top. It then takes quite awhile to release on its own. I have discounted an electrical problem by pulling the ABS module fuse. That should give me straight mechanical brakes. As far as salt. It is used in winter up here to melt ice and snow off the roads. I am around 800 miles north of the Alberta and Montana border.

Ken Kidder · September 11, 2021

The vacuum booster passes all tests that it is working properly but when I pump up brakes till hard and with front wheel of ground and not moving I backed off 2 bolts holding master cylinder to booster. After it separated a little way the brakes released and I could spin wheel. Tried the 2 washers between master cylinder and booster. It releases brakes but not enough travel now as have way less brakes. When I road test it it slowly starts applying brakes and vibrating and getting hot. If I go out and just crack master cylinder line to front brakes they release. Had to put back to original. So I guess only thing left is to try another booster.

Ken Kidder · September 12, 2021

Have tried all the self tests for vacuum booster on you tube and it passed them all. But maybe it is not 100% or why would brakes release when I detach Master Cylinder from Vacuum Booster. With out cracking a brake line anywhere and that happening it seems logical that is all there is. Have another refurbished vacuum booster from Amazon on the way and will update findings in a week when it gets here.