Mechanics

DON'T HAVE MUCH REAR BRAKES.

1996 Nissan 240SX

Brakes problem
1996 Nissan 240SX 4 cyl Two Wheel Drive Automatic 110000 miles

I just did my safety inspection and was told that the front brakes are working really well but the back brakes barely passed. Front was 120% back was 49% I checked the pads and they are fine. I have noticed that if you hit the brakes hard the front will lock up but the back won't. I thought there might be some air in the rear brakes so I started bleeding them with a friend. The back brakes had enough pressure to dribble brake fluid into the bottle but that was it(no air either). The front shot lots of fluid out. I checked the rear brake lines and didn't find any pinched lines. What would cause this?
Avatar
96silvia
June 24, 2008.



Hi 96silvia,

Possible causes

1. The master cylinder is faulty.
2. The proportioning control valve is faulty.

If ABS, need to check the ABS master pump.

KHLow2008
Jun 24, 2008.
Is there a way to tell if its the master cylinder or the proportioning control valve?

Tiny
96silvia
Jun 24, 2008.
Hi 96silvia,

Try the bleeding technique at master cylinder, if one is weaker than the other, then master cylinder is faulty.

Btw, if the rear wheel brakes have too much clearance, it might also cause the problem.

KHLow2008
Jun 24, 2008.
So your saying bleed the master cylinder and if the pressure on the master cylinder is different than the back brakes then the master cylinder is bad? The proportioning control valve is on the master cylinder though. Shcould I rotate the proportioning valve to try and give more pressure to the back? I was looking at the fsm and my mc is on the opposite side. There is an f and an r mark but do you go clockwise or counter clockwise?
I am willing to bet there is a difference in the pressure because the front works so well
Sorry I did forget to mention I don't have abs on my car. Thanks for the input I really appreciate it.

Tiny
96silvia
Jun 24, 2008.
Hi 96silvia,

If the pressure of master cylinder and rear are same, the master cylinder is bad.

The PCV is not supposed to be adjusted. You should test pressure before and after PCV, any difference means the PCV is not accurate. F = front and R = rear.

The most accurate way to test the master cylinder is to attach pressure gauges.

KHLow2008
Jun 25, 2008.
Thanks for the reply. If there is only one bleeder valve how do you test before and after the PCV? I am glad that you told me not to adjust the PCV. I thought that untwisting the PCV would change the pressure on the back.

Tiny
96silvia
Jun 25, 2008.
Hi 96silvia,

Use the individual pipes connectors to test.

KHLow2008
Jun 25, 2008.
Will do thanks for all of the help! You guys are awesome!

Tiny
96silvia
Jun 25, 2008.
Hi 96silvia,

You are welcomed, glad that we are of help.

Good luck.

KHLow2008
Jun 26, 2008.