moneyman380

Alright i have a 91 Z28 with 4 wheel disc but the rear brakes dont work. I had the car on jack stands tonight with the wheels off to test the new tranny. But even at IDLE i couldnt stop the axles from turning when pressing the brake pedal as hard as i could, only slow them down. Im thinking the brake proportioning valve is messed up or maybe the master cylinder. Before i start throwing money at the problem i figured id ask the experts, so any ideas?

Stekman

How's the fluid level? If it's low, that would further support a leak theory. If it's full, I would look into a faulty master cylinder or prop. valve.

If it's low, I would check the integrity of the rear braking system (brake lines, around the calipers, etc), wherever fluid flows. You could end up be pressing fluid out a hole rather than to the pistons.

If it's full, I would look to the prop valve or master cylinder.

ebmiller88

iTrader: (7)

Also check the rear lines for fluid flow. Take the lines off at the calipers or bleed them to make sure the lines aren't clogged.

Ed

88IROCARMY

Okay before you start throwing parts at this. Do a search about "prop valve mod". This is a common problem with our cars. The fluid volume/pressure to the rear brakes is set very low from the factory. Due to the proportioning valve not allowing much rear bias.

Although you could have some failure of equipment causing this, i.e. check hoses, lines,etc. I would research the mod thread

moneyman380

I did a search and read that you are not suppose to do the mod if you have 89 or newer rear disc brakes, which i have. So is this true or should i go ahead and do it ?

ebmiller88

iTrader: (7)

Personally I wouldn't do it. Others will have different opinions but I don't like the idea...you can either install an adj prop valve or swap to a 1LE valve, IMO.

Ed

moneyman380

Tonight i replaced the master cylinder and reblead the entire system but it still doesnt feel right. Going to test drive it tomarrow and pray!

Stekman

I'm with him on this one.
How much fluid did you get out of the rears?

moneyman380

The rears didnt flow nearly as much as the fronts did. I test drove it and i can stop but the rears really dont do much. So im going to rebleed the back brake again sunday.