Brake rotor fitment, 1990 MJ

Hey fella's. Ran into an interesting problem this weekend. Doing my front brakes, and purchased NAPA ultra premium rotors for the 1990 MJ 4x4. Slid them on the hub and they are Waaay to deep and hit the calipar mount. They are both deeper than stock, and not as thick at the hub end which makes the problem even worst.

Brought them back, compared them to 1990 premium rotor and same deal. Checked out an 89 rotor and bingo for the thickness and depth, only problem is its about 3/4 inch in diameter too small and won't slide over the hub?

Anybody else run into these problems? This is a stock dana 30 front axle that came on the truck. To my knowledge nothing is differnt that would be causing my problems with rotor fitment.

NAPA has ordered me some composite rotors that have slightly different measurements...will that be the ticket? Cause all these other rotors they have for my rig, which seem to be the same for many many year of the xj, don't seem to be workin.

Thanks guys!!

~Mark

Best I can figure is..

1. Napa has part number confusion and doesn't know what they're talking about, like 90% of parts stores.

2. You have 2wd Calipers (yes, they're different from the 4wd ones, or at least they are 91+)

3. The D30 on your truck is not a 90, but another year someone swapped on.

Best I can figure is..

 

1. Napa has part number confusion and doesn't know what they're talking about, like 90% of parts stores.

 

2. You have 2wd Calipers (yes, they're different from the 4wd ones, or at least they are 91+)

 

3. The D30 on your truck is not a 90, but another year someone swapped on.

Hey thanks for the reply. I agree with you with the parts number confusion part...problem is, is I have looked them up too. We tore open several boxes to see if I had mis boxed parts....and no luck.

The calipars really arent the problem at all. Its the rotors being over 1/4 inch too deep and sliding on WAAAAAY to far that results in hitting the calipar mount. If the calipar mount wasnt there, then it would be hitting the shield in the back. They are just plain to deep. Also the thickness at the hub is off by about 1/8 on an inch, which adds even more depth to the already to deep rotor, haha.

The Dana 30 could be from another year yes. I have checked the 89 rotors and they are waaaay to small, won't come close to sliding on, off by about 3/4 inch. he told me the 90, 91+ were coming up with the same part number....

Ive heard something about 90's having a composite rotor...I'm hoping that will be the difference, as the NAPA guy said they do have slightly different measurements. We'll see.....

Did everything that was already on the truck match up?

Yes there were several different rotors throughout the years, and the bearings were changed in 91.

Does your axle have a CAD?

Yeah, everything that was on the truck matched up perfect.

I did ask about the 91 rotors and he told me they were the same part numbers...I can check again though.

Not sure what CAD is, sorry. haha ..damn newbee ;)

I think its time to go to a different parts store.

..probably end up with the same exact problem, haha. Ive read that if my truck came iwth composite brake rotors, that they are indeed a different fit than standard. Guess I'll find out when these come in. They are on order.

Not sure how you are suppose to know this when shopping for brakes

While it's awesome that we have interchangeable parts with several other Jeep vehicles for such a long time span, it can come back to bite us in the kiester. Since our trucks are so old, unless you're the original owner, you have no idea what POs have done, wether it was right or not, etc etc. Your truck may very well have originally been 2wd, so the axle on it could be a variety of years. Or it could have a mismatch of wrong brake stuff on it. AFAIK, there's no stamp anywhere on the D30 the denotes year.

As for the CAD, it's the Central Axle Disconnect. It's located under the right side UCA(Upper Control Arm). If you have a CAD, there'll be a large cast housing there, with a vacuum actuator bolted to it. If there's no CAD, it'll just be a straight tube from the diff housing to the knuckle C.

CAD:

No CAD:

(axle's upside down but you should see what I mean)

Thanks for all your help man!

I am not the original owner unfortunately. However, according to the VIN and title it has always been a 4x4.

As for the CAD, I just went out and double checked, and mine does not have that. Its straight tube.

What transfercase do you have? NP 231 or NP 242?

NP 231 is part time. You'll have: 2HI - 4HI - N - 4LO

Np 242 is full time/part time. You'll have 2HI - 4HI Part time - 4HI Full time - N - 4LO

If you have a 231, then chances are really, really good that's not the original axle, therefore not a 90 axle. The only reason a 90 D30 should be without a CAD is if it came with an AWD(Full time 4wd) Transfer case.

I also seem to remember seeing that the only factory full time MJs were in 86 with the 228 or 229.

ahh sweet, you are onto something. Its a 231 TC

Ive also noticed in rotor listings that 90-92, and 93-98, and 99-01 are all the same for cherokee 4wd's. Perhaps I should bring in my stocker and check out the 99's? not sure what else to do at this point...I know its not a 89 axle and napa is one of the few that have the same rotor all the way from 90-98....

I have posted this before, but I guess it's time to repeat. As before, this is taken from a book I am writing and it IS copyrighted. In posting it here, I am NOT granting permission to reproduce it anywhere besides here. Please respect my copyright:

In general, the parts to be concerned with in keeping the front brakes compatible are the steering knuckles, the hub/bearing assemblies, the rotors, and the calipers. (There is a more complete enumeration of the interrelationship of these parts in Chapter 6, Axles.)

 

• Only two steering knuckle designs were used: 1984 through 1989, and 1990 through 2001. Left and right side knuckles are different part numbers within each group.

 

• Three different hub/bearing units were used. The hub/bearing units are the same for both sides of the vehicle. The different years for hub/bearing assemblies were: 1984 through 1989; 1990 through mid-1999 (composite rotors); and late-1999 through 2001 (cast rotors).

 

• Three rotor types were used: 1984 through 1989; 1990 through mid-1999 (composite); and late-1999 through 2001 (cast).

 

• Only two caliper types were used: 1984 through 1989, and 1990 through 2001. Left and right side calipers are different part numbers within each group.

Eagle, that only includes the D30, right? The 2wd beams with spindles have their one calipers. At least my 1991 2wd calipers were different than the ones on the 94 D30 I put on.

Thanks for posting eagle, I sure appreciate it. However, I am confused why folks at brembo and powre slot think there is a difference somewhere after 92. They only list for cherokee's 90-92. No years after that?

Napa lists the same part number on all of their rotors, untill 99.

I'm really thrown on what the heck to do, to put brakes on my rig..haha. Obviously there IS a rotor out there that fits whatever year my dana30 axle is, cause they are on there right now..just worn out and needing replacement....

I guess according to your post, the only thing I havent tried is 99+ rotors....

Napas 1990 rotors fit the hub, and slide right on, just way too far. The 89s are the correct depth, but won't slide on my hubs. Thats only leaving me with 99+ to try out?

Thanks for posting eagle, I sure appreciate it. However, I am confused why folks at brembo and powre slot think there is a difference somewhere after 92. They only list for cherokee's 90-92. No years after that?

You sure you didn't have them look up Comanche? 1992 was the last year the Comanche was produced, but the Cherokee continued through 2001.

Napa lists the same part number on all of their rotors, until 99.

Obviously, NAPA is incorrect. The hubs AND the rotors changed between 1989 and 1990. And since the steering knuckle and calipers also changed at that point, and the caliper mounts to the knuckle, it is critical to keep ALL the parts within the same "generation." You cannot mix and match, or you get an interference fit (like you did), or no brakes.

I'm sorry eagle, I didnt clarify that enough for you..my bad. I'm the one that looked at brembo and powerslot. I put in cherokee. I thought the same as you that because 92 was the last year of the manche, that I was mistaken...but I was searching under cherokee.

Napa does have the 89-90 swap correct, I was referring to napa having them all the same part number from 90-99.

I tried out a set of 89 rotors as I thought they were the ticket cause the depth was right on them, never thought to check the diameter of the hub...as the 89's are clearly much different and won't even slide on.

This leaves me with only the later 99+ rotors to try out, in hopes that I have a 99 axle/hub bearing assembly under my comanche...otherwise I don't know what to do..lol, besides take the 89's to a machine shop and have it turned out..lol. The 90-99 napa rotors are just waaaaay to deep on my hubs.

guess I should have checked to see if my rotors are cast or composite. I'm assuming you can tell the composites are of two different materials? That would clear this all right up right?

Also check to see if there is a listing for a police package cherokee that year. I work at an advance auto and I had to order in some calipers for a guy because he had the police package. IIRC, the rotors were the same as the regular cherokee, but ya never know. Its not unknown for cars to have the wrong model or year's parts on em. Sometimes I'll have to look back a couple of years to find the right parts. Or in the case of one 2001 Toyota Corolla, I had to look back to a 94. That was weird. When the guy found that out he brought the car back to the Toyota dealership and they gave him a 2002 Corolla instead.

Check your production date. 90 was an change year for many parts in the XJ/MJ. If your production date is late 89 for the 90 model year (like mine) you need 89 rotors as they switched rotor types between 89 and 90. Some of the early 90s still had 89 axles. I had this exact problem with mine before I switched to the 94 XJ D30. I needed the 89 rotors to make it work.

:popcorn:

Screw it, pull the whole axle and swap in a front 44.

Maybe you have some WJ spindles with the earlier hubs with the correct bolt pattern for our trucks. Just a guess!

:popcorn: :popcorn:

:popcorn: :popcorn:

Hungry there bud?

Thanks very much for all the replies there fellas. I def don't have 89 hubs, as I said before, I have tried the 89 rotors and my hubs are much bigger. I have tried the 90-early 99 rotors now too. I am going to try the late 99-01 rotors next. They sound like the correct depth :)

Another question... is your axle a low pinion or a high pinion?

High Pinion on the right, Low Pinion on the left: