Differences-WJ vs. 97+ XJ MC/booster

I have searched this for a while now without a good answer.

What, if any, is the difference between a WJ and late model XJ master cylinder and booster (dual diaphragm)?

Both have a 1" diameter bore.
Is the WJ booster bigger in diameter?
My 2001 XJ's booster measure a little over 8 1/2" in diameter (27" circumference).

I know the WJ MC/booster is a great upgrade for the earlier XJs but is it an upgrade or more of the same for late model XJs?

I've always thought they were the same part. I too have a 97+ and was gonna do the "upgrade" but then realized its no upgrade for 97+.
Keepin an eye on this post.

from my reading, the 99-01 grand cherokees have the biggest out of the bunch, and people with the newer xjs swap them in for a small boost. I dont think the boosters physically larger, but I think its more powerful and the master cylinder is bigger as well

I went with a 95 xj booster in my 88 because I couldn't find the new grand cherokee in the junkyard.

to my understanding i htought it was 00-01 xj's and 99-04 wj had the same bigger brake booster and the 84-99 xjs had the smaller ones

so in your case. this wouldn't be an upgrade, more of a replacement seeing that your's is a 2000

97+'s have a different rod configuration and won't work with older XJ's. Thats the only difference I know of.

MTBracer367 said:

to my understanding I thought it was 00-01 xj's and 99-04 wj had the same bigger brake booster and the 84-99 xjs had the smaller ones.
So in your case. this wouldn't be an upgrade, more of a replacement seeing that your's is a 2000

Click to expand...

IslanderOffRoad said:

97+'s have a different rod configuration and won't work with older XJ's. Thats the only difference I know of.

Click to expand...

Thanks for the replies. I'm trying to separate fact from fiction.
Many on this site have recommend the WJ MC/booster as an upgrade, even for late-model XJs.
If the WJ setup does not offer any real improvements over the late-model XJ MC/booster, then why recommend it?
Looking at Rock Auto's site, you find that the WJ MC/booster cost about twice as much as the XJ.
Is it wasted money?

I'm curious as well but here's my input:
The WJ unit is designed for a V-8 vehicle with over 300 lbs more weight and was produced till 2004. The booster / MC combo was designed to power twin-piston front calipers & rear dics - a lot more fluid here than the single-piston / rear-drum combo that even the later XJs used. The parts were also, I think, designed in 98-99. The later XJ units were designed in 96 at the latest. Now maybe not much changed in those few years as far as parts design but hey - I look at three years in some technologies and it blows my mind how far they've come. Cell phones, anyone?
I've read in multiple posts that it is a HUGE difference in braking performance.
I suspect that the WJ unit is a lot more powerful than the 97+ unit... but I'm really hoping 5-90 or Dino or somebody will chime in here with solid knowledge.

supposedly the WJ is easier to swap into an older model XJ/MJ ie: pre 1990. The 95/96 XJ booster is a direct swap to the 91-1994 XJ/MJ for an upgrade. The master cylinder is the same part from 1997 on in both XJs and ZJs, but the V8 ZJ has a different prop valve.

The WJ might be a slight upgrade for a 97+ but I would not consider it worth the effort you will get more bang for less effort doing a rear disc swap or a WJ caliper upgrade on the Newer models. The older models will see an advantage from just swapping the booster and MC.

Bore size is exactly the same at 1" and also the diameter of the dual booster as the 95+.