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?
1. The master cylinder is faulty.
2. The proportioning control valve is faulty.
If ABS, need to check the ABS master pump.
June, 24, 2008 AT 2:00 PM
Is there a way to tell if its the master cylinder or the proportioning control valve?
June, 24, 2008 AT 2:07 PM
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.
June, 24, 2008 AT 2:28 PM
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.
June, 25, 2008 AT 8:08 AM
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.
June, 25, 2008 AT 11:17 AM
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.
June, 25, 2008 AT 12:13 PM
Use the individual pipes connectors to test.
June, 25, 2008 AT 2:16 PM
Will do thanks for all of the help! You guys are awesome!