Front Rotors

[Manny]

Hello everyone in this forum. I'm not mechanic but i star to restore my comanche 87 buying parts here and there. i have a quetion : anybody knows if front rotors from cherokee 94 fits on my comanche 87? . Thank you!

[87MJTIM]

It depends....

 

Is your axle original to your truck?  If so, then no.  The front brakes/hubs changed on later model MJs/XJs.

[eaglescout526]

Also 2wd is different than 4

[MiNi Beast]

no. 

[FrankTheDog]

1 hour ago, eaglescout526 said:

Also 2wd is different than 4

Again it depends. 1/21/92 and later built 2wd and 4wd have the same slip on rotors.

1/20/92 and older 2wd’s have a spindle mounted rotor.

[eaglescout526]

3 minutes ago, FrankTheDog said:

1/20/92 and older 2wd’s have a spindle mounted rotor

Fun fact. 84-86 2wd is the slip on rotor type. 87-91 2wd were those all in one units. Then they switched back. Really weird. 

[FrankTheDog]

10 minutes ago, eaglescout526 said:

Fun fact. 84-86 2wd is the slip on rotor type. 87-91 2wd were those all in one units. Then they switched back. Really weird. 

Really? Never had contact with pre 1990 2wds so I wouldn’t know for sure.

[eaglescout526]

20 minutes ago, FrankTheDog said:

Really? Never had contact with pre 1990 2wds so I wouldn’t know for sure.

Yup! I thought all 2wd were those all in one rotor assemblies until I got a free 2wd axle from an 86 and it had the tradition slip on rotor. It was an interesting discovery. 

[ghetdjc320]

The only substantial change on the unit bearing was in 99.5+ when they went to longer studs and a different shoulder height. The pre 90 unit bearings also had a different bearing design. The pre 90 knuckles had bolt on calipers with thick lugs cast into the knuckles. The pads were held in only by the calipers and they also had a ball joint “preload” insert in the lower knuckle flange. In 90 they added the “wings” onto the knuckles to retain the pads and the caliper mounts are itty bitty compared to the older knuckles. The rotors in 99.5 also went to a cast design. 
 

 

[Eagle]

On 3/4/2021 at 8:52 PM, ghetdjc320 said:

The only substantial change in the unit bearing was the 99.5+ when they went to longer studs and a different shoulder height. The pre 90 unit bearings also had a different bearing design but are interchangeable the newer styles.

 

 

Not correct. They don't interchange -- the old style and the new style have a slightly different offset. People who tried to swap have found the brakes locked up when installed.

 

I've posted this before, but I'll post it again. As before, this is material from the book I never finished writing. It is copyrighted, and by posting it here I am NOT releasing it into the public domain. Any Comanche Club member is given permission to copy it for your own use, but I am not granting anyone permission to distribute copies in any format or form.

 

Quote

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.

 

Quote

Steering knuckles:  There are two designs of steering knuckle, and within each design the left and right sides are mirror image and carry different part numbers. The early knuckles were used from 1984 through 1989. The late knuckles were used from 1990 through 2001.

 

Hub/Bearing:  Three different hub/bearing assemblies were used. The hub/bearing assembly is the same for both sides of the vehicle. The first type was used from 1984 through 1989, and must be mated to the early steering knuckle from the same range of years. The early hub/rotors used tapered roller bearings, which are available as individual replacement parts, and in theory can be rebuilt. In practice, removing the old bearings and installing new ones requires a large arbor press and bearing splitter, equipment not available to the average owner. In practice, even dealerships simply replace the entire assembly, because the labor cost to rebuild would exceed the cost of a replacement assembly.

 

The second type of hub/bearing assembly was used from 1990 through mid-1999. This hub/bearing assembly mates up with the newer style steering knuckle and is used with composite rotors. Certain years of XJ with composite rotors were subject to a safety recall if they were located in northern “rust belt” states, because of problems with the rotors (see below). When replacing hub/bearings in vehicles within this range of years, unless the vehicle recall history is known it is wise to call a dealer or DaimlerChrysler customer service to determine whether or not the vehicle has undergone the brake rotor recall. If so, confirm which hub/bearing assemblies should be used as service replacements..

 

The third type of hub/bearing assembly was used from mid-1999 through 2001. This hub/bearing is also used with the new style steering knuckles, and is mated with the newer style cast rotors.

 

Rotors:  Three types of rotors were used. Rotors are the same for left and right sides. The first style of rotor was used from 1984 through 1989. The second style of rotor was used from 1990 through mid-1999. This second style rotor was a “composite” design—the braking surface disc was separate from the center “hat” section, which was stamped from comparatively thin sheet steel. After several years of service, it was found that in states and localities where salt is used on the roads in winter, corrosion of the “hat” section could result in the disc portion separating from the assembly, causing a loss of brakes. A factory recall was issued to correct this problem. The recall affects only vehicles within a range of years, and only in certain states. Anyone owning a Cherokee or Comanche in the range from 1990 through 1999 is advised to call a dealer or DaimlerChrysler customer service with the VIN number to determine if the vehicle is subject to this recall.

 

Mid-year in the 1999 model year the front brakes were changed to an all cast rotor design. Although the original, early style rotors were also all cast, the new rotors are different from the early ones and carry a different part number. The new cast rotors were used from mid-1999 through 2001. Because 1999 was a transition year, owners of 1999 Cherokees will need the VIN number to determine the correct parts to order when servicing the front brakes or hub/bearing assemblies.

 

Calipers:  Two styles of caliper were used. The calipers are mirror image for the left and right sides and carry different part numbers within each group of years. The early style caliper was used from 1984 through 1989. The later style caliper was used from 1990 through 2001 and is used with both the composite rotors and the newer cast rotors.

 

As previously noted, a complete front axle assembly from any year Cherokee or Comanche can be installed in a Cherokee or Comanche of any other year. It is only when attempting to swap components among different years that the above parts differences become critical.

 

[ghetdjc320]

1 hour ago, Eagle said:

Not correct. They don't interchange -- the old style and the new style have a slightly different offset. People who tried to swap have found the brakes locked up when installed.

I’m just referring to it fitting on the knuckle. The correct caliper and rotor combo would be needed. It makes perfect sense though that for the old bolt on fixed position calipers (pre-90) they would need the rotor located at a specific depth to center it in the caliper. That would be accomplished through the unit bearing shoulder height. So that makes sense as you mentioned that the pre-90 brakes would lock up with a different unit bearing shoulder height. 

When installing a different brake setup though (Wilwood, big brakes etc.) I normally use the 99.5+ unit bearings on the pre-90 knuckles since there is less offset to compensate for and the wheel studs are longer. They work just fine in the earlier knuckles.