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i have a 1990 gmc pick up, replaced front brake pads because the pedal was going almost to the floor. still have problem, bleed system using about a quart maybe more of brake fluid, still have problem any ideas were to go next, when you pump the brakes with the vehicle off two pumps and pedal is rock hard

Submitted: 567 days and 18 hours ago.

Category: Chevy

Value: $15

Status: AWAITING CUSTOMER ACTION

Optional Information:
1990 GMC 1500 5.7

Already Tried:
bled brakes,new pads,new master cylinder

Accepted Answer

First of all let me tell you that the brakes on your truck will feel different than other vehicles you have driven.The brake pedal can be pushed past the point where the wheels will be locked up during braking while driving,quite easily.That makes it seem like there is air or a leak in the system.If the truck is not stopping properly "after" putting on the new pads you probably forced debris into the isolation valve located under the master cylinder.It can't be cleaned and will need replaced if that is the case.If the pedal drops slowly while holding a light pressure on the pedal the master cylinder is most likely bad.I will take it for granted you have checked for leaks.

Accepts:
Expert:	Davo
Pos. Feedback:	97.7 %
Answered:	5/4/2008

Master technician

ASE Master Technician also L1 Advanced Engine Performance Specialist

567 days and 16 hours ago.

Reply

i put a new master cylinder on thinking that it was the problem. the truck will not lock up the brakes it will stop but not that good

Posted by Davo 567 days and 15 hours ago.

Answer

I have replaced quite a few dump valves on those for poor stopping.Before I replace them I bypass the valve as a test to confirm proper brake application because they are big bucks.The brakes would need bled again after bypassing the valve.

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Optional Information: 1990 GMC 1500 5.7Already Tried: bled brakes,new pads,new master cylinder