I've got a rear disk conversion on my xj with stock d44/30 and 36's and my pedal is getting bad..I planned to swap in the '96 xj 7" dual diaphragm booster, drop the prop valve and get an adjustable for the rear..I'm wondering if this will be enough boost or if I should try'n squeeze an 8" booster in there?? And should I be looking for a 1 1/8" MC like the E-350? Is a 1 1/4" ok and just overkill or shouldn't I go that big?

(Anyone with xj specific booster/mc/valve pics is very much welcomed also)

I run a '93 booster with the vette master and an adjustable prop. valve. Pedal is great and it stops my 36" tires well.

A later model booster won't seal up with the vette master so I'd try it with the single diaphram booster first.

Edit: This is with Ford 1/2 ton brakes on the front and 1/2 ton Chevy parts on the rear.

Has anyone else had experience with this setup or the one i'm looking at??

You don't say what year XJ you have, but it it's older than a 96, then any tire 31" or larger and your braking will suck big time. I swaped in a 97 booster into my wife's 89 Cherokee....fantastic improvement.

I think your first plan is a good way to go. It might be worthwhile giving Inline Tube a call regarding the adjustable prop valve. Those guys have a lot of experience with conversions since most street rods will have rear disks.

I have a 90 XJ with explorer rear disc brakes on my 9", and stock in the front on the D30. I have swaped in the 96 booster and master, along with a wilwood adjustable prop valve. I like it and I am running 32's going to 33's soon. If your really worried about the stopping get in touch with VANCO.. they make some of the best stuff out there..

On my friends XJ after an exploder disc conversion, his pedal was very soft and the brakes sucked ass. We took the proportioning valve apart, removed the valve o-ring, and re-bled the brakes and that did the trick. Brakes worked great after that, if that does'nt work and you still have a soft pedal, than I would go for a larger MC. On my own XJ the only stock brake component is the pedal, I'm also running hydro boost, that was the best 50 bucks I've spent on that jeep.

I've been doing a HELL of a lot of research on this type of topic over the last several weeks. On monday, my rig goes to Otter for a rear disk conversion and MC swap on my rig with waggy f/r 44's.

Instead of getting an adjustable prop valve for the rear - why not consider swapping in a combination valve from a 94-98 ZJ with disc/disc configuration?? http://go.jeep-xj.info/HowtoZJvalve.htm
Try this first and see what happens.

Or - do more research and you'll discover that some of the folks remove the 'metering' pin and/or spring and/or the o-ring out of the YJ combination valve.

Personally - I liked the ZJ prop valve idea.

I just purchased one from First Class 4x4 for $25 including shipping.

http://www.firstclass4x4.com/

The only reason to mess with the prop valve is if you have a difference with braking power front vs rear. If you can't lock up at least one of the axles, the prop valve is not your problem.
Soft pedel? Fix that first.
Pedel hard? And you can't lock up any of the wheels? Upgrade the MC and booster.

Instead of getting an adjustable prop valve for the rear - why not consider swapping in a combination valve from a 94-98 ZJ with disc/disc configuration?? http://go.jeep-xj.info/HowtoZJvalve.htm
Try this first and see what happens.

I'd rather spend the extra $10 and get one that I know will work because it's adjustable. If your brakes ever change again you'll still be able to use it and it won't require re-plumbing when you need to make a change or your wild guess at a fixed valve doesn't work.

Everytime one of these threads comes up people always guess, assume and half ass some sort of proportioning valve. I'll never understand why people would be doing that when you can just get one that's guaranteed to work.

I'm looking to really upgrade all areas of the braking system. I'm not looking to spend a fortune but I do have 36's on my DD..

I have no problem spending the $ on this 8" dual diaphragm booster & 1 1/8" MC..

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8037521962&sspagename=STRK%3AMEWA%3AIT

http://pics2.spoonfeeder.com/AieFTPFiles/AIEUser/K7F9VPHZ8LHP/88QJCQV9QBGB.jpg


I've been told a 8" booster would be ideal for 4 wheel disks..I'm wondering if anyone with a cherokee has swapped in an 8" booster? Obviously its not going to just bolt right up but it looks pretty tight in there an I'd like to know if anyone has already made this fit?

The only reason to mess with the prop valve is if you have a difference with braking power front vs rear. If you can't lock up at least one of the axles, the prop valve is not your problem.
Soft pedel? Fix that first.
Pedel hard? And you can't lock up any of the wheels? Upgrade the MC and booster.

The stock prop valve is actually a combination valve. Metering & proportioning. These combination valves are different for disc/drum setups versus disc/disc setups. Drum brakes need residual pressure (residual valve within a disc/drum master cylinder) and metering (within the combination valve, allows initial pressure to go to the drum brakes before the discs).
If you think I'm full of BS....that's fine. Read this:
http://www.mpbrakes.com/mpfaqvalving.htm

He's running the stock combination valve AND stock master cylinder.
The reason I suggested changing out the combination valve - is because the ZJ combo valve is specifically for disc/disc setups. He could try this and see what happens. It's cheap and easy to do to and keeps it closer to factory.

Unless there's something wrong with his overall setup somewhere - he really doesn't need to upgrade the MC for a bigger BORE since his brakes are still stock size. He could change out the MC to get a DISC/DISC master cylinder.

A bigger bore MC might be too much on both ends. THEN - you'd need separate proportioning for both front lines and the one rear line.

Ok so a better/cheaper solution might be to swap in the 7" dual diaphragm booster from a '96 xj, and a MC/prop valve from a zj with 4 wheel discs..(?) Do you know if the zj mc will bolt right up? I have an '88 xj by the way but I don't think it matters.

I have a 95 ZJ and am trying to upgrade the brakes.I've been told to run an XJ booster/69 vette MC and adj. proportion valve,how does this sound.
Here is another write up on Kung-fu brakes
http://www.akextreme4x4.com/tech/brake/master_cylinder.htm