89 vs. 90 brakes

These questions have nothing to do with my jeep they are just for for personal information. I see that brake rotors for the XJ for 90-98. What is the differance between a 89 and a 90 rotor that it would interchange? Is it the caliper or the axle? If you swaped in a 90 axle in to a 89 could you use the 90 rotor? What would you need to fit a 90 on an 89? Also can you use a 4wd rotor on a 2wd jeep?

As always Thanks

Chris

from what i can tell the 4wd 90+ changed but 2WD stayed the same. not sure for rotors, I know the caliper bolts changed, dont think the axle would make a difference. not sure though.

Somewhere around 1990 the outer steering knuckle went to a once piece design in comparision to a two piece design found on the pre 1990. This change was accompanied by a hub depth change, caliper bore increase and rotor depth change.

I'm not positive on the exact time of the change.

So if you had an 89 could you swap in a 90+ axle (with knuckles/complete) and then also swap in 90+ calipers? and make 90+ rotors fit?

The reason I am asking all these questions is becaseu I am thinking of buying and older 2wd MJ (prerunner buildup). But I see there are more braking options for the 90+.

Thansk
Chris

Yes, a 90 or newer axle will work fine in an '89 XJ. Just be sure to keep the knuckles, hubs, rotors and calipers matched for year. (Or group of years)

Eagle said:

Yes, a 90 or newer axle will work fine in an '89 XJ. Just be sure to keep the knuckles, hubs, rotors and calipers matched for year. (Or group of years)

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So there is no way to fit a 90+ rotor on a 89?

bzdel2441 said:

So there is no way to fit a 90+ rotor on a 89?

Click to expand...

Maybe if you swapped everything from the knuckles out, but I don't think it would be worth it. Now if you swapped a complete axle with the '90+ brakes and rotors the only thing left to match up would be the brakelines which would work just fine.

OK here goes. My '91 ran for several years with pre 90 spindles and calipers/90 up hubs and rotors. I also ran the newer rotor on the old hubs but this required a spacer behind the rotor to make up the difference in the rotor flange thickness. The old rotors will not fit over the new hubs wheel flange. I know the setup with the spacers was far from ideal but the new rotor/hub and old caliper/spindle seemed to work fine.

As a side note I am now running a completely un-bastardized '87 front and rear brake system but my '91 master cylinder, should a swap in the '87 master cylinder as well?