Proportion valve delete?

[mpbannon]

Hey everyone,

Having some issues with my rear brakes. I have a 97 tj sport with the zj rear disc conversion. The jeep has been sitting for a few years and I just finished swapping the tub. While the tub was off I did all new brake lines, calipers and rotors, and then pressure bled the system.

I tried taking it to the DE DMV for inspection and registration, but failed for 0 rear braking power.
When I have the rear lifted off the ground I'll hit the brakes, which will stop the wheel, but then the rear will just start rolling again. The front brakes lock up and the pedal does stay firm. I pulled the prop valve cleaned everything up and reinstalled it but still the same issue.

My brother sent me this
https://leedbrakes.com/i-23439389-r...-calipers-dana-35-dana-44-chrysler-8-1-4.html

I've since pulled the prop valve spring and gasket as it says in the installation instructions and regained full stop on the rear, but would rather have it to avoid locking the rear.

If anyone has any advice or input on this situation, I would highly appreciate it, so I can finally put the ol girl back on the road.

 

[Chris]

Let's ask the brake wizard, @mrblaine.

 

[mrblaine]

Hey everyone,

Having some issues with my rear brakes. I have a 97 tj sport with the zj rear disc conversion. The jeep has been sitting for a few years and I just finished swapping the tub. While the tub was off I did all new brake lines, calipers and rotors, and then pressure bled the system.

I tried taking it to the DE DMV for inspection and registration, but failed for 0 rear braking power.
When I have the rear lifted off the ground I'll hit the brakes, which will stop the wheel, but then the rear will just start rolling again. The front brakes lock up and the pedal does stay firm. I pulled the prop valve cleaned everything up and reinstalled it but still the same issue.

My brother sent me this
https://leedbrakes.com/i-23439389-r...-calipers-dana-35-dana-44-chrysler-8-1-4.html

I've since pulled the prop valve spring and gasket as it says in the installation instructions and regained full stop on the rear, but would rather have it to avoid locking the rear.

If anyone has any advice or input on this situation, I would highly appreciate it, so I can finally put the ol girl back on the road.

View attachment 639290

You don't have pull the spring, simply removing the odd little cup seal defeats the proportioning aspect of the combo valve. You can experiment a little to see if you can drive up the rear stopping ability some. Find a shim washer to put on the plunger to preload the spring. That will bring up the pressure in a panic stop and get you more rear braking. Only works if you get the cup seal facing the correct direction so hopefully you remember how you took it apart.

Have you tested it with full pressure and know it will lock up when it shouldn't or are you guessing it will?

 

[mpbannon]

I haven't road tested it yet, only with the rear lifted off the ground and hitting the brakes. I worry it'll lock up from what I've been reading throughout the forums, and intermittently I'll have my kids in the back.
I plan on taking it through inspection with it out in the morning, but I was thinking of replacing the combo valve, maybe the spring was bad, and if that doesn't work I'll try to shim it unless there is an aftermarket spring that is stiffer.
Thanks for the insight!

 

[kmas0n]

You don't have pull the spring, simply removing the odd little cup seal defeats the proportioning aspect of the combo valve. You can experiment a little to see if you can drive up the rear stopping ability some. Find a shim washer to put on the plunger to preload the spring. That will bring up the pressure in a panic stop and get you more rear braking. Only works if you get the cup seal facing the correct direction so hopefully you remember how you took it apart.

Have you tested it with full pressure and know it will lock up when it shouldn't or are you guessing it will?

You say find "a shim washer" ... Where? Can I make one. How would you do it?

 

[mrblaine]

You say find "a shim washer" ... Where? Can I make one. How would you do it?

I've used the copper washers for rivets before.

 

[Danno4x4]

Wilwood makes an adjustable proportion valve that you can plumb inline with the rear brake line that lets you incrementally reduce the pressure to the rear brakes. The one I have has an adjustment knob that lets me tune the rear lockup to come after the fronts lock up.

They also have a ratcheting lever style with 6 “click” positions that makes it so you don’t have to keep track of the number of turns.

https://www.wilwood.com/MasterCylinders/MasterCylinderValves

This lets you adjust rear pressure based on the rear weight in the Jeep. The idea is that you have one setting for empty (around town) driving and one setting for the jeep loaded up with gear (or people).

Of course you can set it for empty weight and leave it there if you don’t want to fiddle with it, but the rear brakes will perform slightly less than optimally when it’s loaded.

@mrblaine have you had any experience with the Wilwood valve? Good or bad? For me it’s been installed for 10+ years without any major issues.

 

[mrblaine]

Wilwood makes an adjustable proportion valve that you can plumb inline with the rear brake line that lets you incrementally reduce the pressure to the rear brakes. The one I have has an adjustment knob that lets me tune the rear lockup to come after the fronts lock up.

They also have a ratcheting lever style with 6 “click” positions that makes it so you don’t have to keep track of the number of turns.

https://www.wilwood.com/MasterCylinders/MasterCylinderValves

This lets you adjust rear pressure based on the rear weight in the Jeep. The idea is that you have one setting for empty (around town) driving and one setting for the jeep loaded up with gear (or people).

Of course you can set it for empty weight and leave it there if you don’t want to fiddle with it, but the rear brakes will perform slightly less than optimally when it’s loaded.

@mrblaine have you had any experience with the Wilwood valve? Good or bad? For me it’s been installed for 10+ years without any major issues.

Adjustable prop valve is a bit of a misnomer. The factory version is proportional in that once the pressure in the rear circuit reaches a certain point, it stops rising at a 1-1 rate with the front pressure and kicks over to rise at a lower proportional rate. Wilwood et al, are just reducing overall pressure at whatever circuit they are plumbed into and that generally stops at about a 30% reduction. Yes, more experience with them that I want and I won't use one if the factory is available.