I have an 8.8 that I just slapped under the jeep and have been researching the proportioning valves.

So far the opinions are completely mixed.

They're mixed because Jeeps don't all respond the same and even if they did, owners don't always understand what they are seeing or experiencing. Factor in all the BS on the internet purported to be fact and you have a perfect recipe for a confusion.

What I've understood is...
-Disc/Drum has a spring to hold a slight pressure (10psi) on the rear drums.

Nope. Not even remotely true.

This could cause excessive wear on the rear brakes if swapped to a disc.

If you put a 10 psi residual pressure valve inline, maybe.

-Some people have squishy brakes (even when completely bled)

Some pee poles don't know how to bleed brakes. In fact, most pee poles are a bit poor at it.

-The volume to actuate drums is much less than discs, therefor you're getting less brake for the press when swapping to discs.

If you run the volumes, they are so close as to be interchangeable. Most folks look at a wheel cylinder and figure because it's such a smaller diameter that calipers must take more volume.

What they fail to take into account is the wheel cylinder is actually double for starters, because there are two pistons that move much further than the caliper piston does. A caliper piston only moves a very slight amount from foot off the pedal to full lock-up.

I just wanna get some firsthand knowledge. Did you swap your proportioning valve when you went from a disc/drum to disc/disc combo?

For this, you need to create your own first hand knowledge. Run it with the stock combo valve, if you like it leave it alone. If you want to change something about the way it performs, then get a combo valve from a ZJ and swap it in.

 

With WJ brakes on the front and Ford 8.8 axle disc brakes on the rear, I removed the "O" ring from the metering shaft in the OEM proportioning valve. For my Jeep, I couldn't ask for a more balanced setup…

 

Removing the O-ring worked great for me also.:tea:

 

My first hand experience is that I hooked the 8.8 brakes up to the stock brake system and ran with it. No changes were made to the TJ brake system other than installing the 8.8 axle. It works well, is balanced, and stops me when I want to stop. What more could I ask for. There is no residual pressure in the system forcing the pads to ride on the rotors. The amount of fluid required to move the pads is going to be pretty equal to what is required to move shoes if the drum brakes are adjusted properly. If the drum brakes are not adjusted properly, which seems to be the case on a lot of Jeeps, the drum system will probably require more fluid to make the shoes contact the drums than the rotor system will require.

 

What I've understood is...
-Disc/Drum has a spring to hold a slight pressure (10psi) on the rear drums.

What you are reffering to here is the residual pressure check valve. I can't speak as to the actual pressure it holds on the wheel cylinders, but I seem to remember it being around 2psi. I'm not even sure that is enough to move the piston in the caliper, I have asked this question before and gotten no response. It can be in a lot of different locations in the system; in the master cylinder, in the proportioning valve, or somewhere in the lines to the rear (like at the "T"). Some systems may not even use one. It's purpose is to keep the cup seals on the wheel cylnder pstons slightly inflated.

I know it was said above that this is not even remotely true, but if that's the case it means that all of the tech schools and the college that I went to are teaching all of their students a bunch of rubish.

Seeing as how the rear line "T" is part of the rear hose, why not compare part numbers of the rear center hose (I believe the Rubicons have three rear hoses, if not forget that part), master cylinder, and proportioning valve between an X model (rear drums) and a Rubicon (rear discs).

You could always run it and see what happens, or you could switch over to Rubicon master cylinder and proportioning valve.

 

What you are reffering to here is the residual pressure check valve. I can't speak as to the actual pressure it holds on the wheel cylinders, but I seem to remember it being around 2psi. I'm not even sure that is enough to move the piston in the caliper, I have asked this question before and gotten no response. It can be in a lot of different locations in the system; in the master cylinder, in the proportioning valve, or somewhere in the lines to the rear (like at the "T"). Some systems may not even use one. It's purpose is to keep the cup seals on the wheel cylnder pstons slightly inflated.

If it was a check valve, the pistons would never release. However, you are correct that the original purpose was to keep a slight amount of pressure in the system to keep the cups expanded to stop weeping.

It's a very common myth that discs use a 2 psi residual pressure valve and with drums you need a 10 psi to keep the shoes expanded closer to the drums so they don't have to move as far when you apply the brakes. That's continually perpuated by those that also happen to sell the valves.

What's never explained is the springs that hold the shoes at rest on the anchor pin generate over 100 lbs of force. If you run the numbers on the force at 10 psi x the diameter of the wheel cylinder, you get nowhere near enough hydraulic pressure to move the shoes. The reason the springs are so strong is to overcome the self actuating nature of drum brakes. They are shoe return springs and have to have the force to bring the shoes back to rest when you release the pedal.

Also, todays modern mold making and polymer technology has improved to the point where cups don't weep any more and that has pretty much removed the need for a residual pressure valve and what little need there may be is easily accomplished by the hydrostatic pressure developed by the weight of the fluid.

I know it was said above that this is not even remotely true, but if that's the case it means that all of the tech schools and the college that I went to are teaching all of their students a bunch of rubish.

There's a brake tech bible written by one of the sharpest tech guys I've ever seen over on POR. Even he repeats the myth about 10 psi valves.

Seeing as how the rear line "T" is part of the rear hose, why not compare part numbers of the rear center hose (I believe the Rubicons have three rear hoses, if not forget that part), master cylinder, and proportioning valve between an X model (rear drums) and a Rubicon (rear discs).

You're inviting a 400 dollar experiment that will not get you a RPV.

You could always run it and see what happens,

Best advice yet.

or you could switch over to Rubicon master cylinder and proportioning valve.

With the exception of the 05 and 06 IIRC, all the combination valves are the same part number.

 

Thanks for the input guys. Keep em coming. I plan to have my WJ setup in before the end of the month.

MrBlaine: Bleeding brakes, loosen bleeders, press pedal down firmly with some speed, tighten. Repeat. Correct? I understand the concept of putting some force into the pedal so it creates turbulence in the line and removes air from any high spots. I picked up some speed bleeders for my setup to help make this an easy 1-man job.

 

Correct and frankly, you don't need any more input. How can you fix something until you know whether or not it's broken?

 

Do NOT remove the o-ring. There is no benefit, and any leak will result in complete system failure.

The prop valves, disc/drum OR disc/disc are identical part numbers. All older part numbers supercede to the same number. In other words they are the SAME PART! ZJ is NO improvement, just missing a port.

Almost all folks who left the prop valve alone report perfect funtionality. Leave yours alone, drive it a while, see if further work is needed. (PS... if anyone reused the old calipers, pads, or rotors that came on the 8.8.... it's FAR more likely to be bad parts than the prop valve causing their issues. Few who reuse the old parts bother to completely rebuild them.)

 

Do NOT remove the o-ring. There is no benefit,

I don't know what your experience is working with this setup. When I installed my Explorer disc brakes on my 9" rear axle, the braking was severely lacking. I removed the "O" ring and the braking improved noticeably, so much so that I didn't need to do anything else. As far as I'm concerned, this was (and still is) the answer to balancing my front (WJ) and rear brakes. Works for me...

 

When I did my 8.8 swap several years ago, I purchased a new Rubi Proportioning valve. I have yet to install it. Sooner or later, I'll install it just because I have it. However, if I had never purchased the Rubi valve, I never would even mess with it.

 

Just keep it for a spare. It's the same as you have now.

 

I was only refering to the presence of a 2psi valve on drum systems. I've never heard of a valve on disc systems. I didn't mention it, but I am fully aware that 2 or even 10psi isn't nearly enogh to overcome your shoe return springs. I also was unaware that these valves are now unescessary due to improved manufacturing prcoesses. So, it looks like it's a moot point on newer vehicles.

You're inviting a 400 dollar experiment that will not get you a RPV.

I was only suggesting to compare part numbers to see if there were infact any differences between the parts. There may very well not be.

With the mass amount of people that install these axles without any other brake system modifications, I would still just run it and see how it works.

 

I was only suggesting to compare part numbers to see if there were infact any differences between the parts. There may very well not be.

My point is there is a difference in part numbers and that difference doesn't reflect the RPV, it reflects the higher pressure the ABS on the Rubicon puts out. That makes the rear hard line, a 400 dollar brake line from the dealer. Normal versions are about 10 percent of that.

 

I've removed the spring, removed the o ring, but I finally got a 1 ton master cylinder and the tj brake booster and I love it.

 

Which 1 ton master?

 

My buddy had it laying around his garage. I can ask if he remembers exactly but all I remember is that it came out a 1 ton dodge truck.

 

Why do you think you have better brakes now?

 

Well, I have my 8.8 under the jeep and it brakes fine with the valve untouched. Other than the fact that the tires are 35" and I don't expect much from my stock brakes.

Within the week or so I plan to put my D30 w/ WJ stuff in there. I'll post up the results with braking.

 

Does anyone have the schematic where this o ring is located in order to remove it. I just put in an 8.8 everything is tide up but I want to try and remove the o ring for the rear and see how it performs it I like how it works, I will go no further but if not I will upgrade as some of you already have.

 

O Ring is on the combination valve. I never messed with mine. Works fine as is, so I just never saw the need to mess with it.

 

Do you have any picture of the combination valve? So what you are saying is that you swapped in an 8.8 and never messed with the porportioning valv and you are getting a good response from it. How do you know that it will not respond better if you remove the o-ring as a lot of people have indicate that it make a big difference?

 

The Combination valve and the Proportioning valve are all one unit. The O Ring is on the plunger rod (for lack of better word). I have heard a lot of guys say that never noticed a difference when the removed the O Ring so I just never did anything to my proportioning/combination valve. If it's not broke........

 

I got to tell you lil jeep, coming from a guy that only had 2 front brakes for about 6 years, I just removed the little so called 0-ring from the plugger rod as you called it and bled my brakes and to my jeep for a ride around the block for the 1st time in about a year.....All I have to say is WOW...WOW...WOW..it feels better then My Cadillac CTS and that car is brand new...Man what a difference..but you are right if it is not broken.....I agree..however if you ever get the urge....I can confirm it for you...it is like night and day for me...Thanks for the feed back..

 

I wonder if this is a YJ / TJ thing as I honestly can't imagine my brakes being any better than they currently are.

 

Been riding on my 8.8 for a while now. Didn't touch the valve. Stops great with minimal pedal effort. Will stop on a dime.

I was driving down a res. street on my way home from work, and some kid sprayed the side of my TJ with a water hose. I thought about it for a split second and was ganna let him go on it, but I though what if he had sprayed Me, my wife, or my daughter.:nono:
So I slammed on the brakes (locking up front, not sure about the rear) and scared the crap outta the kid.:laugh:

 

Did anyone have a problem with the 'BRAKE' light coming on when they messed with the proportioning valve? When I did my 8.8 swap, the light came on, and it turned out my booster went bad by coincidence at the exact same time, so I replaced that and removed the o-ring on the proportioning valve. I had the battery disconnected for 15 minutes and the computer reset, but the 'BRAKE' light remains on even though my brakes work fine again.

Any ideas on this?

 

Swapped in an 99' 8.8 over two months ago and don't have any problems. Don't mess with the brakes unless you actually notice problems. Otherwise you are going to make a mess for no reason. Oh and be sure not to get any brake fluid on your paint... it will eat it off.

 

This WJ front conversion that you speak of, what is it, what are its benefits, what axles will it work on?