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Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
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1995 gmc: cargo van..front brakes work but the rear do not...booster

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I have a 1995 gmc 2500 vandura 4.3 cargo van. The front brakes work but the rear do not. Is it the booster?
Hello and thank you for using JustAnswer. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.

The problem could either be in the master cylinder or in the brake proportioning valve. Have someone hold pressure on the brake pedal, then crack the lines loose at the master cylinder. If you have good flow from both ports, the problem is in the proportioning valve. If there is not good flow from one of the ports at the master cylinder, replace the master cylinder.
Customer: replied 5 years ago.
Is the master cylinder by the brake shoes
The master cylinder is on the firewall. It is the part where you add brake fluid.
Customer: replied 5 years ago.
I have no rear brakes. I pumped the brakes up, then tried to bleed them Just a tricle of fluid came out. What is going on. Just the front blakes are operating properly.
Most likely the proportioning valve is stuck. This valve is down on the frame and controls brake fluid flow.

Some of these vans had a valve that was controlled by a lever to the rear axle and regulated fluid flow according to ride height (vehicle load)

Customer: replied 5 years ago.
Would this cause the dash brake lite signal to come on?
If the proportioning valve is off center internally, this will definitely cause the dash brake warning light to come on. One trick that sometimes works to unstick the valve is to drive the vehicle in reverse, then jab the brakes hard. Do this 3 or 4 times in a row, then try bleeding the brakes again. If this does not help, replace the proportioning valve.
Customer: replied 5 years ago.
When removing the lines connected to the valve, I am sure that the nut and the line is rusted together, causing the line to twist and brake when trying to remove them. How is this situation avoided.
Soak the brake line and fitting with rust penetrating spray like PB blaster for a day or two. Also try heating the fitting with a propane torch and tap on the fitting with a small hammer to break up the rust. If none of this works, then worst case scenario is that you will have to replace the brake line.
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