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97+ Brake uprade? Disc swap done....

J

joshv98xj

NAXJA Forum User
Location
Bozeman, MT
98 XJ. About 2 years ago I swapped in a D44, and did the ZJ disc swap at the same time, as well as the ZJ prop valve. I did no alterations to the proportioning valve.

I would say that I saw basically NO change in my braking performance. I replaced my pads and rotors all the way around. I swapped to synthetic brake fluid. I bled, and re-bled, and bled the brakes again.

Finally I called it quits because I was so sick of bleeding the brakes.

Well, recently I've been driving my XJ a lot more, and it's becoming apparent that I need to do something. I'd also like to move to some bigger tires in the future, and that's going to make things worse.

I don't have a lot of financial resources at hand, so Vanco is out. Sorry, I'd love to do it, but no-can-do.

What I'd like to know is, will I see a difference from a WJ master cylinder AND/OR brake booster swap? Has anyone done this?
 
a adjustable prop valve could help...... WJ fronts are the biggest improvement in brake mods and can be picked up with some looking for about $100
 
If I recall, they won't fit into my stock steel rims either.

Knuckles + calipers + master cylinder + pads + rotors + steering + rims + tires = Affordable? Not so much.
 
i got my knuckles, calipers, and used (but only had like 20 miles) for 100 bucks. could have got the steering with it but i went with heims.
 
joshv98xj said:
What I'd like to know is, will I see a difference from a WJ master cylinder AND/OR brake booster swap? Has anyone done this?
Click to expand...

No, you already have a dual diaphragm booster in your '98. No need to go through all that work for nothing.
 
Okay, good for you, I'm glad you got a deal. I don't have the money or the time to do an entire front end swap and buy new tires and wheels.

That's why, in my original question, I asked about upgrading the master cylinder- can we go back to the original question? I'm trying to be specific so others can find straight answers in searching, rather than having to read through 12 pages of "Simplified WJ Brake Upgrade." Yeah, simplified all right.


Thanks, I understand the dual diaphragm booster is what I have.
 
Installed disc brakes in 2000 on the Corp 8.25 for my '98 XJ and the master cylinder and vacuum booster have worked well with this setup..
The only modification that I did was remove the rubber seal from the proportioning valve internal shuttle valve; this provides full pressure to the front and rear calipers.
 
So I've been doing some research, and these are the master cylinders I've been looking at and the bore sizes I've found. On the other hand, I haven't been able to find anything on stroke length, so I'm not sure how much bore size matters without that... These specs are per NAPA's website.

1998 XJ - 1.0625" or (1 1/16)
2003 WJ - 1.0"
2003 Durango - 1.125" or (1 1/8)
2001 Ram 1500 - 1.25 or (1 1/4)

I have no idea on the bolt pattern for the two bolts of the master cylinder to the booster. Anybody know where I might at least be able to find out some more of this info?
 
Josh -

The answer that isn't quite being given is
NO
a new booster / MC isn't going to change much with your setup.
You already have the dual diaphragm booster.
The Durango MC is favored by some guys who have gone to larger front calipers because it pushes more fluid and gives you a better brake pedal feel. On your setup it is probably going to feel very stiff and reduce your light-touch control. You might stop faster, you might not.

Try EBC yellow brake pads, a lot of guys seem to like them.
Without going to dual piston front brakes or hydroboost, you can't do much more than upgrade your pads.
 
Thanks Yoss, that makes sense. I guess if guys are doing the WJ caliper upgrade and not doing any MC swap, then it isn't the MC that's the problem.

So I'm going to take this into a whole new direction- but to do that I'll start a new thread and eventually link it to this one. Thanks guys-
 
CharlesS said:
Installed disc brakes in 2000 on the Corp 8.25 for my '98 XJ and the master cylinder and vacuum booster have worked well with this setup..
The only modification that I did was remove the rubber seal from the proportioning valve internal shuttle valve; this provides full pressure to the front and rear calipers.
Click to expand...
Have you tried this?
 
Yes, I removed the rubber seal. With it in, I could not lock the rear wheels even on the jackstands.

Edit- and yes, I bled the brakes. Three times.
 
joshv98xj said:
Yes, I removed the rubber seal. With it in, I could not lock the rear wheels even on the jackstands.

Edit- and yes, I bled the brakes. Three times.
Click to expand...

There is definitely something wrong somewhere.
You running 31s you should be able to lock up the rears no problem.
Years ago after I installed the TeraLo in the NP231 I couldn't slow down in first and second gear while running in 4low. After installing the rear discs I can gently rest my foot on the brake pedal and stall the engine. Yes I have a manual transmission.
 
Last edited:
I think something is wrong as well...

I have 31's on my rig at the moment, COMPLETELY stock setup ('99), and I can easily lock up the rears if I jam on the pedal. Fronts as well, but they take more effort.

How are your brake lines? All rubber? Original? Could they be worn out and expanding?

Also, you contradicted yourself. Which is it?
and did the ZJ disc swap at the same time, as well as the ZJ prop valve. I did no alterations to the proportioning valve.
Click to expand...
Yes, I removed the rubber seal. With it in, I could not lock the rear wheels even on the jackstands.
Click to expand...
 
Dan- you got me there. I mis-spoke. I mentioned in another spot that I did this axle swap about 3 years ago, around the same time I was doing an axle swap and brake MC swap in my old MJ. I seem to be getting them mixed up a bit.

I did install the ZJ prop valve, but being unable to lock the rear wheels was with the XJ valve, not the ZJ valve. I don't remember if I did pull the rubber washer. At this point in time I was sick of bleeding the brakes.
 
Not trying to be a dick, but you do have the calipers on the correct side? The bleed valve should be above the brake line input.
 
No offense taken- I just checked, they're on correct.

I just ran out to my chiropractor, and just to be sure, I made sure that I can't lock up the tires. Not on dry pavement anyways, I know I've done it in the rain, but that takes a lot less.
 
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