Residual pressure valve? Or Proportional Valve?on the rear brake line coming out of the master cylinder there is a valve inline with the rear brake line that I’ve heard called two different names. I’m wondering if that valve will be necessary when I plan on switching to a rear disc brake conversion kit. I think it is. I also want to know if mine is bad or not, not sure how to tell.
this truck has RABS as well. I’ve bleed everything on the truck before, got great front brakes, and rebuilt the drums completely in the rear but I’m not impressed with the braking power or pedal feel. I’ve also replaced the master cylinder and brake booster.
I need to adjust the screw between the master and booster, I never did that when I installed it. I need to replace some brake lines cause they’re OLD. And then I need to bleed everything again. I’m wondering if anyone has any information on the best way to bleed these brakes, tools and or sequence. And if I’ll have to touch the RABS bleeder, and if I should just replace the Proportioning valve/residual pressure valve since I don’t know the condition of the current one I have now. I apologize in advance if I’m not being straightforward in this rushed write up, but I just want any and all information I can get from ya’ll about the RABS, residual valve, bleeding sequence, spongy pedal while driving, and screw adjustment between the master and booster.

thanks.

i should mention the spongy pedal does hold resistance at a certain point, meaning it doesn’t eventually go all the way to floor, but the initial travel before the brakes kick on seems excessive

 

First thing to do is post what you are driving or working on
Those residual pressure valves (maintain 10 psi) are required / used for some applications
The valve prevents fluid drain back into the master cylinder and makes the rear brakes apply quicker, and more evenly in conjunction with the fronts
If you search the internet for long enough, you'll get lost in terminology
That valve on the rear master cylinder port is a "residual pressure valve"
Like a pip sensor (distributor pickup) is a "stator"
It probably has a different name on the box if you ever get a new one from Ford

 

1990 F-250 XLT Lariat 4x4 5.8L
Do you happen to know what this Fords Residual pressure valve’s pressure should be? A quick search gives me a couple pressures to select from.

 

The residual pressure valve is used to keep pressure in the rear drums to prevent the lip seals in the wheel cylinders from leaking. With 10psi, the lip seals will have more tension on the cylinder bore. A side effect is that it would allow the brakes to engage fast, but that is not the primary reason.

Those valves should be removed if you have disc brakes. The seals are different and you do not want to have 10psi on disc brakes.

 

I've heard it was 10 lbs. but have never measured it

 

You want to know if the truck has RABS or you’re saying it has RABS? I don’t know if it does but it did from the factory.

You rebuilt the drum brakes but did you properly adjust the shoes? If not that would explain why there is so much travel in the pedal before it firms up.

No special tools are needed. The bleeding order is: right rear, left rear, RABS valve, right front and then left front.

 

The truck has RABS. I did rebuild the drums, everything brand new about a year ago. Haven’t touched it since.
I did adjust the shoes when I rebuilt the drums, but maybe not far enough out. I figured the star wheel would auto adjust the shoes so that I didn’t need to adjust the shoes perfectly.

I’ll try that, and I’ll bleed everything again in the correct order, as well as adjust the master to booster. Master to booster set screw gap is supposed to be 0.020” if I’m not mistaken?

 

Great information to know, thank you! When I found a rear disc brake conversion kit online for the sterling 10.25 axles, they have an option to include a residual pressure valve in your kit for $250! If I don’t need one I won’t put one on if/when I decide to switch to rear discs. I may double check with the manufacturer of the conversion kit out of curiosity as to why they include a residual pressure valve in their kit if they’re not necessary for disc brakes.

 

If you have RABS, you shouldn't have a residual valve or a proportioning valve. You should have an adapter on the rear port on your master cylinder. It's just a hexagonal steel tube with a straight hole through it. Check yours to see if its a one-piece adapter, or if it has a split-line on the hex that looks like it can be disassembled.

 

Interesting, I’m gonna take a look tonight, I’ll take a picture and put it in this thread. I’ll also snap a picture of the RABS.

 

No. You need to adjust the shoes so that there is a little bit of drag. You cannot rely on the star wheels to adjust themselves. Does the parking brake hold the truck?

 

parking brake holds the truck, unless there’s an incline then it’s useless. I see where you’re going with this. I need to adjust those brakes

 

 

Little bit of drag. The star wheels only adjust when you backup, in reverse and hit the brakes. Do that a few times.

 

If they are that far out of adjust that is not the best way to do it. Also, if you do not use the parking brake very often the brakes will get an out of adjustment.