Adjustable Proportioning valve ????

Ok, I can't get my Xj w/ disc's all around to to lock up my 35's on the pavement. It's a slow stop at best. I've been doin' some research, and I've come to the conclusion that I can use an Adjustable Proportioning Valve to send more fluid to the rear and get them to lock up or at least do more brakin' work. I just had a few ?'s about it first. If I understand correctly I want to run the front lines directly to the master cylinder and run the Adjustable valve to rear brakes only. Is this correct? Then I've read some stuff about people guttin' the combination valve to run adjustable proportion valves. I'm not sure this is something I want to do? Anyways I'm looking for someone that has already done this swap to chime in and clear some stuff up for me. Thanks in advance.

adam

Do you still have the factory proportioning valve in, or have you removed it allready? All i did when i went to rear discs is remove the factory valve, and now i can lock up all 4. The rears lock a little bit early, but i think that was mostly due to the massive brake dive and undloading of the rearend before i did my longarms.

i still have the stock valve in there. I've never heard about removing it all together??? I knew about removing the oring,and the success of it, but i'm a little leary about it just because of debri gettin' in there and losin' my brakes. What does removin' the whole valve do?

I forget exactly how its done, but its removing a spring and seal inside the distribution block for the brakes. It doesnt leave anything open for debri, but you do have to rebleed the brakes. If i remember right, a haynes manual will describe how to remove it.

Yes I did it, it's an excellent upgrade. Even with stock rear drums braking is much better. I got the Wilwood Brake Proportioning Valve from Summit racing (about $40).

Junk the stock Proportioning Valve (it's all front no rears) and just replace it with a three way block. I found a small hole in the fire wall to run a new line (for the rears) and mounted the adjustable valve to the center console. Just drill a hole in the plastic console for the knob to stick through and pop the line under the plastic.

Drill a small hole under the drivers seat and carefully fish the original line up to the outlet of the adjustable valve. Just make sure the line doesn't go up an down, you don't want to trap any air bubbles.

Really not a big job and I LOVE being able to adjust the brakes on wet roads!!! You can really feel a big difference and I can lock up all four tires simultaneously.

Rick

the stock valve is a proportioning valve jsut not adjustable. loosing the o-ring will not give you awsome brakes the only thing it will do is allow equal brakign to both front and rear. removing the whole valve is fine with no ill effects other than the rears locking up before the front (this is not good). no back to the origional question about why your brakes suck let me flip the q around and ask you what year xj you have and do you have abs. with that being said earlier xj's had a singal diaphram booster which was later changed to the superior dual diaphram booster (this should be your starting point for early model brake upgrades) next is making sure you are moving enough fluid to the brakes. Again you need to fill us in on what brakes you have how could we possibly guess at what disks you have in the rear.

I have a 96 w/ ABS, I swaped in a 87d44 in the rear and I replaced the drums w/ 97ZJ discs. Since I swaped the d44 in, I no longer have ABS. I hope this helps

run your stock master straight to the fronts, take the rear single line leading aft from the master and place an adjustable prop valve somewhere in line. Adjust brakes till the fronts lock up a little before the rears (this keeps ya going straight when your tires lock up)

mmmkay325 said:

I have a 96 w/ ABS, I swaped in a 87d44 in the rear and I replaced the drums w/ 97ZJ discs. Since I swaped the d44 in, I no longer have ABS. I hope this helps

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mmmkay325,
Quick off topic question for you. Did your braking get better with the larger D44 drums verses the smallish D35 drums or did you do the disc swap at the same time as the axle swap?

I installed an adjustable. It was pretty tough, took me a while to find the right fittings and everything, but it was worth it. Basically, you can have slightly tighter and more powerful brakes with all juice going to the rears, but safety is compromised. If you have to slam them in an emergency, you are highly likely to spin out of control, so it is a tradeoff.

I would like to add the following

Never have two proportioning valves in a brake line, i.e. if fitting an adjustable proportioning valve you must remove the original one.

Secondly I don’t think enough has been mentioned about sending too much braking pressure to the rear. This is very dangerous and I cannot emphasise it enough. The reason is as follows.

Maximum braking force is just before the tyres lock up (I.E. abs braking). Now if you send too much braking pressure to the rear and the rear lock up first, then the rear of the car will be very “light” and try overtaking the front of the car. This situation is far more dangerous than mediocre brakes. I believe 70% of braking is done with the front brakes so it’s a fallacy if you think your car will stop faster of the rear can lock up. In saying that your brakes must be able to make the front lock up.

Locking up the back (With the front wheels still turning) is the same as doing a handbrake skid; this is the last thing you want in an emergency situation when the back tries to over take the front.

If all 4 wheels lock up, its not a major problem, as long as the front lock up first.

So what im saying is this is one area to be VERY careful focus more on the front brakes not the back, just because they don’t seem to lock up is a very good thing and has been designed to do so.



http://www.4x4wire.com/jeep/tech/brakes/

http://www.wilwood.com/Products/005-PedalAssemblies/Pages/techtip/pedaltech.asp

http://www.wilwood.com/Products/006-MasterCylinders/001-PV/index.asp

Ray H: I swapped the disc right onto the 44 before it went under my jeep. So i don't know the difference, I switched to 35's w/ the 44 so I don't know how the d35drums would have done w/ 35's either.

I appreciate everyone's help, but i'm still just a bit comfused. I understand why it's dangerous to if the rears lock up first. But I can't get anything to lock up. I"ve got new shoes and calipers in the front. At best it's just a slow/quick stop. There was one time I had too stop very fast because of a guy slammin' on his brakes....and I just stood up on hte paddle and it just kept on rolin'...so i had to switch lanes very fast to kept from slammin' into him. My big problem is, around town my brakes are find, but for stoppin' in an emergency situation, I want the puppies to lock up! Is there bigger brakes I could swap on a d30/d44 combo??? Thanks again for the help everyone, but keep the ideas following

I have just had new front disk pads put in my Jeep, but after putting in these pads the brakes were shocking. The Jeep just went into “Glide” mode whenever I stomped on the brakes.

I can’t remember the brand of pads but they were a reputable brand. I have just had the Brake Shop exchange the pads and put in a set from the Jeep agents. All I can say is what a difference I can now lock up the front to the point where the ABS kicks in.

So try changing the pads to those supplied by the agents, the price will be double but I found it to work. I was very surprised with the improvement.

The fact that u have disks on the rear means thet it is unlikely that you have a volume transfer problem with the brake fluid as disks require less volume transfer than drums. It is for this reason I think you may have a friction problem, i.e. not getting enough friction between the pad and disk at the front end.



Good Luck

mmmkay325 said:

Ray H: I swapped the disc right onto the 44 before it went under my jeep. So i don't know the difference, I switched to 35's w/ the 44 so I don't know how the d35drums would have done w/ 35's either.

I appreciate everyone's help, but i'm still just a bit comfused. I understand why it's dangerous to if the rears lock up first. But I can't get anything to lock up. I"ve got new shoes and calipers in the front. At best it's just a slow/quick stop. There was one time I had too stop very fast because of a guy slammin' on his brakes....and I just stood up on hte paddle and it just kept on rolin'...so i had to switch lanes very fast to kept from slammin' into him. My big problem is, around town my brakes are find, but for stoppin' in an emergency situation, I want the puppies to lock up! Is there bigger brakes I could swap on a d30/d44 combo??? Thanks again for the help everyone, but keep the ideas following

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Ultimately, you have to learn to adjust your driving style. Your stock tires were approximately 28 inches in diameter. Now you're on 35s. That's a difference of approximately 3-1/2 inches in radius, which translates to a 25% increase in the leverage the tires exert against the brakes when you try to stop. If you really want to be able to lock up 35s, you need bigger brakes. It is highly unlikely that any incremental changes you make to stock XJ brakes (even with ZJ rear discs) will lock up 35s.

Berrill: You tryin' to say my good ol' $20 EverWears pads aren't good enough??? LOL....The whole "glide" stopping is exactly what i'm experiencing....I think i'm gonna try my luck w/ a higher better brand name pads and see if that makes a difference like yours. Thanks for the thought, let me know if you happen to remember the name of those pads.

Eagle: Your totally right, I mean common sense told me something designed to stop 28's aren't gonna do the same for 35's at 100%. I just had some wishful thinkin' that there might be some quick easy fix out there that wouldn't break the bank and fix my braking problem. But thanks for your nice break down of physics and brakin' principals,I thought that was pretty cool and i'm gonna write that down.

Well, with all you guys helpin' me out...I think I've come to a conclusion. I need to by a ford focus and quit bein' such a weenie hasta Naw....really I think i'm just gonna try to swap in a ZJ proportioning valve so I can have a setup intended for disc's all around, switch to a better brand pads all around, and stop tryin' to draft off of all the lil' ricers around town and complainin' when they slam on the brakes, why i can't stop as quick as they do. Thanks again for all you guys inputs and experiences. :wave:

Would a prop valve off of a 4 wheel disc TJ work?