weak rear brakes, what could be the problem ?
 

Car has new pads, new disks, cylinders are not sticking, calipers are ok, but still rear brakes are almoust not working at all. I need suggestions, what else could be wrong ?

Thanks

Re: weak rear brakes, what could be the problem ?
 

Brake bleeding can be hard on these cars.

I am guessing but air in the Master Cylinder or the lines could do it. You also have two bleeders on the ABS unit.

The master cylinder could have failed, it has two circuits so if the rear is out then you could have problems there but good brakes at the front.

You might want to explain how you know the rears are not working. That might help people rule out some things.

Re: weak rear brakes, what could be the problem ?
 

Brakes were checked on brake test bench during the annual inspection (mandatory here in Europe). Both left and right were equally weak, but fronts were excellent.

I will try to bleed it once again, but as it has been done several times already, I don't think it will help much.

How I could check the master cylinder ?

Re: weak rear brakes, what could be the problem ?
 

If they pulled the brakes to test them on a bench then the master cylinder may have air in it. You might have to bench bleed the mastercylinder. I have heard but can not confirm that due to the angle the master cylinder sets at, it won't fully bleed when installed.

A good shop might have some gages that they could hook to the brake lines to test the pressure at each brake.

I think the most common test is to put another master on the car, hit or miss.

If you can't test then a step by step replacment may be your only choice.

I had my master cylinder loose to install some other parts so I flexed the lines until it was level and then used a "Mity-Vac" hand held vacuum bleeding system. First the right rear, left rear, right front, left front, then the two ABS bleeders Rear and then front. I then repeated the wheels and did the ABS a second time. That worked for me. I used a full quart of fluid to flush the system. You can't bleed air, only move fluid, so you have to move enough fluid and hope the air goes with it.

A damaged or flattened hard line could cause problems, but if you can get fluid to the rear bleeders then that rules it out. You have to have the ABS in the right setting also. You have to start the car and wait till the ABS light goes out and then shut the car down without tripping the ABS. Or use a Tech 1 to cycle the ABS to the right position.

To cause problems with both rear brakes it hav to be in a common componet. The rear brakes share the hard lines, ABS module, and the master cylinder. Air or a failure in any of these will impair both rear brakes.

You seem to be doing all of the right things, must be a detail some where that is fouling you up.

Re: weak rear brakes, what could be the problem ?
 

I had the same problem with the rear disc brakes on a 1989 Iroc, it turn out to be a bad proportioning valve.