• Notice for iPhone users: DO NOT use the image size reduction option when uploading photos to the forum. This causes portrait images to post as landscape. We have added a warning to the image insert pop-up as well.

What's going on with my rear brakes

I

Ifster

Member
City
White Rock
State
NM
Hi,

I have changed the master cylinder, new flex lines, rear wheel cylinders and a new proportioning valve. Booster appears to be working properly. Brakes are blead, pedal feels good. Rear pads are adjusted.

I currently have the Jeep on jack stands with the wheels off. Did some stop tests today with the engine running and found the rear drums will not stop rotating no matter how hard I stand on the pedal. I readjusted the pads to where they were pretty much riding against the drums and still no stop. A buddy who came by said he could just barely hear the pads scraping when I was trying to stop.

I removed the drums and applied the brakes, the secondary pad moved just like it should.

What's going on? Maybe the proportioning valve? This is the one I got.
Thanks.

 
Right now, I'm leaning to the PV being set to cut off the rear brakes. I'm looking into this.
 
Sounds to me more likely there is either air in the rear braking system somewhere or the master cylinder is faulty.
Air would allow the brakes to move freely when there is no drum and therefore no resistance there but just compress when under load?.
If it is air related and the lid is off the master cylinder then you will likely get a geyser effect at the master cylinder when releasing the brake pedal as the air decompresses and rapidly shoves the brake fluid back rather than it flowing back slowly.

If you have a brake clamp handy you could try clamping the rear hose to the axle which will prevent fluid getting to the rear brakes and see if it stiffens the pedal up at all. Make sure to remove it afterwards though!
 
I did bench bleed the MC and it looked fine. I am getting a geyser from the rear MC chamber.
Just now, I removed the rear, residual valve from the proportioning valve and manually pushed the plunger forward. This did allow the rear to bleed better, for a second than again nothing. I think the piston reset to shut the rear off during the bleed.
The proportioning valve is still in the return window, so I have a new one coming. The pedal is nice and firm, but not getting fluid to the back. It's gotta be the plunger...........

I'm gonna try another test. I'll remove the plunger and re-bleed, see how it goes. Will report back.

Thanks again.
 
Nope, didn't work.
Pedal is good. Still just front brakes only, so now it's either the pressure residual valve, or the MC.
I did a "bench test" on the MC while it's still on the jeep. Both chambers flow fine.
I did flush out the lines before installing the new parts, all looked well, no leaks. There are still no leaks. I did have to re-nut and re-flare a few of the connections when removing the old lines, but all are good.
Now I'm out of ideas, other than replace the new MC and the new proportioning valve.

I can not pinch off the rear line, it's steel braded.
 
To bleed the brakes you need to disable the proportioning valve slide by holding the “button” depressed at the front. If you don’t do this, the valve thinks there is a problem and will shut off flow to the ‘leaking’ line.
 
did you use one of these to keep the proportioning valve from wigging out?
 

Attachments

  • Screenshot 2025-05-19 205327.png
    Screenshot 2025-05-19 205327.png
    39.8 KB · Views: 12
I put a new proportioning valve on when I rebuilt mine a few years ago, and had nothing but trouble with the brake warning light staying on. Bled the thing a dozen times - tried the tool shown above and also the factory style tool for the front piston, no joy. So eventually i took the new PV off and replaced it with the old one - no issues since. On disassembly i believe the problem was caused by a misplaced seal in the valve that was blocking the rear port. The center seal in the left hand picture.
 

Attachments

  • PV1.jpg
    PV1.jpg
    298.3 KB · Views: 10
  • PV2.jpg
    PV2.jpg
    1.1 MB · Views: 10
I did not use that tool, yet. Learned about it after I removed my PV and MC to send back for replacements. I do have the tool coming in the mail also. I'm hoping that's all it'll need and work out. But if not, I'm going to put in a manual proportioning valve and an in-line residual valve, and be done with the OE type PV forever.
 
I could never get that tool to work. I had better results holding the front button in.

tom keyes

Post in thread 'brake adjustment?'

One other thing I thought I should mention. When I got my tool I had to do a slight modification for mine to work. The newer Proportioning valves installed in cars today (or maybe just my jeep?) have a larger gap to slide the tool onto. I had to take my belt sander and thin the bottom side down until I could fit it onto the gap or grove it slides onto. Here is a sight that has a fair image of the components from front to back:

http://www.allstate4wd.com/p8-7286.htm

Here is a little write up I found informitive:

Proportioning Unit Operation:
The proportioning valve section operates...
 
ag4ever said:
I could never get that tool to work. I had better results holding the front button in.

tom keyes

Post in thread 'brake adjustment?'

One other thing I thought I should mention. When I got my tool I had to do a slight modification for mine to work. The newer Proportioning valves installed in cars today (or maybe just my jeep?) have a larger gap to slide the tool onto. I had to take my belt sander and thin the bottom side down until I could fit it onto the gap or grove it slides onto. Here is a sight that has a fair image of the components from front to back:

http://www.allstate4wd.com/p8-7286.htm

Here is a little write up I found informitive:

Proportioning Unit Operation:
The proportioning valve section operates...
Click to expand...

Man, this thing is way too fidgety to mess with for too much longer. And I don't see the necessity for the block off piston........If you have a single chamber MC, then it makes sense, but with a dual chamber, you can't loose the fluid in the opposite side of the MC anyway.
So I'll give it a shot, but if it's a pain, out it comes and in goes one of these.


 
Got the new MC and PV in place. I did use the little bleed tool this time, (since I now learned about it).
Everything blead out just fine.
While bench bleeding, I did notice the MC front chamber/for rear brakes was pumping fluid much more smoothly as compared to the last one, so I'm still not sure where the problem actually was. Specially since before I still could not get fluid out the back, even with the PV piston removed.
One more step close to the first drive.
Thank you all for the help.
 
You must log in or register to reply here.
Back
Top