Zj Brakes

I know this has been discussed before, but after reading multiple threads and multiple pages without a straight answer, I figure it might just be easier to ask...


I have a 93 XJ, no ABS, 8.25 rear, running 33's and my brakes suck. There's a 94 ZJ at the junkyard. What could I strip from it to make my braking situation better? If I took the rear discs would I need to take the master cylinder and booster as well or just the brakes/proportioning valve?
Is this pretty much bolt on with the 8.25? All the writeups mention either the D35 or the D44...

I don't really want to know about WJ stuff because I'd need to buy that new since there's none in the junkyards. I'm looking for a cheap(ish), fast(ish) upgrade for some better brakes. Mine aren't horrible, but I'd just like a little more grab for DD'ing.

grab the prop valve, but you don't need the master cylinder and booster if you don't want (but you might want to check if it is an upgrade over what you currently have)

it's a pretty simple bolt-on with just a little bit of modification

my writeup here: http://www.myxj.net/blog/?p=35

HTH

Installing discs on the rear requires a change in MC for 2 reasons. One, the rear discs require more volume than the disc/drum set-up you're replacing. If you look at your MC, you'll notice the reservoir for the rear brakes is smaller than for the front. Although it's not absolutely required to have a larger reservoir for the disc, it's a good idea--that's why disc/disc factory systems have near-equal reservoirs. Number 2 reason to change MC's is the piston size should also be increased to accommodate rear discs.
The '94 ZJ, with 4-wheel discs uses a 1.00 inch MC; your YJ has a 15/16 MC, so a you should change out the MC. If you don't, your pedal will be much lower when you engage the brakes. Some (all?) '94 ZJ's have dual diaphragm boosters. That means their MC's wont fit the '93 XJ booster. If you don't want to change boosters, you could bolt in a '76 Mercury Grand Marquis MC intended for hydro boost, 4-wheel discs. It has a 1.125 bore, and is a direct bolt in for the early XJ with a single diaphragm booster.

IntrepidXJ said:

grab the prop valve, but you don't need the master cylinder and booster if you don't want (but you might want to check if it is an upgrade over what you currently have)

it's a pretty simple bolt-on with just a little bit of modification

my writeup here: http://www.myxj.net/blog/?p=35

HTH

Click to expand...

So all you did is basically bolt on the ZJ stuff and throw in the proportioning valve? How much did that whole setup end up helping you out?

If the ZJ has a dual diaphragm booster, should I grab it and the master cylinder as well? If it has the single then I'll stick with my existing mc/booster...

xjbubba said:

The '94 ZJ, with 4-wheel discs uses a 1.00 inch MC; your YJ has a 15/16 MC, so a you should change out the MC. If you don't, your pedal will be much lower when you engage the brakes. Some (all?) '94 ZJ's have dual diaphragm boosters. That means their MC's wont fit the '93 XJ booster. If you don't want to change boosters, you could bolt in a '76 Mercury Grand Marquis MC intended for hydro boost, 4-wheel discs. It has a 1.125 bore, and is a direct bolt in for the early XJ with a single diaphragm booster.

Click to expand...

So if I swap in the ZJ discs, prop valve, mc and booster that's the best way to go?

If I use my existing mc and booster you say the pedal will engage lower, but it should still grab more right? So less pedal travel but still better braking? Doesn't seem too bad to me...

ert01 said:

So all you did is basically bolt on the ZJ stuff and throw in the proportioning valve? How much did that whole setup end up helping you out?

Click to expand...

I still haven't swapped in the ZJ prop valve yet, but I am hoping to get around to that soon. I'm very happy with the performance so far.....plus the fact that I don;t have to deal with drums anymore

I kept all the XJ stuff and only bolted on the brakes. Mine works great. My pedal actually grabs higher up, and noticably harder. The first time my wife drove it after the swap (I didn't say anything to her about it) she noticed a huge difference.

I was told that they would drag if I didn't remove the spring in the valve, but I don't have that problem. The only problem I have now is that occasionally my rear end wants to pass my front end under hard braking when it's wet. I can live with that!

Lack of proper proportioning between front/rear brakes result in rear brakes engaging first, and locking up, while the fronts don't. Problem is either bad/no/wrong proportioning valve, or front brakes not working, or fronts not bigger than rears.

yeah... I read about a cheap fix on here where you remove the prop valve spring. I did that and the rears got mushy and unimpressive. I kept the spring in because I don't mind the back engaging first / harder. It really helps on the trail vs. stock.

just installed a set yesterday. went fine. had to slightly enlarge the bolt holes on the backing plates. make sure your bleeder is in the top position or you won't be able to bleed the rears. You can remove the spring from the valve and cut off 1.5 threads, put it back in and it works great.

Will dicss from a D35 fit my 8.25 ?