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Fron Brake Rotor Delima

FitchVA

NAXJA Forum User
Location
Roanoke, VA
Front Brake Rotor Delima

i have searched for threads about this issue and i still have a few issues/concerns.

background:

soon i will be doing a brake job on the front of my white dd'er '98 XJ. while installing by 2" bb this past weekend, i noticed that the rotor was different on this '98 than the other '98 XJ that i own. the rotor on my white dd'er xj is the correct composite style rotor while the rotor on my green offroad toy xj is the incorrect cast type rotor.

oops. looks like i messed up the brake job on the green one when i did a brake job on it in january of '06. i looked at old pictures from when i installed the lift on the green one (put on before the brake job) and sure enough, the rotors that were on it then were composite! :dunce: so i put on the wrong type of rotor that time.

here's my delima:

i didn't have any issues with the green one (with the wrong rotor). i daily drove it for about a year and never noticed an issue.

i am currently planning on putting ceramic pads in the white dd'er xj because i don't want to deal with the heavy brake dust that i have to deal with it now.

however, i have read that the ceramic pads are harder on the rotors. i have also read that the composite rotors are a little more prone to warping. so it would make sense that i'd want the tougher cast rotors with the harsher ceramic pads, right?

...but my '98 calls for composite. ...but i've been running cast on my other 98 for a year w/ no issues. also, a coworker has been running with the same mix-up for over 50k miles with no issues either.


should i just put the rose-colored glasses down and just do the composite rotors?


oh, and the green xj that had the rotor mix-up is a non issue now because i have the warn hub kit installed with that special rotor setup.
 
Last edited:
Why does it call for composite?

If the dimensions are the same, just go with the cast. When I was doing my hub conversion the auto parts guy was telling me composite rotors are becoming less and less common because of quality issues, like the warping you mentioned.
 
that's just it. i'm not sure if the dimensions are the same. all of the threads on naxja talking about composite vs cast state that there is a difference in the hat height. and i wasn't aware of all of this at the time of my past brake work on the other xj
 
I found out the hard way that the composite rotor and full cast rotor are not the same size.

The 'hat' size is different...the composite rotor is about 1/8" taller than the full cast.

If you XJ was designed for the full cast, like mine is, you can only use the full cast.

If your XJ was designed for the composite, I believe you can use either...I, myself, am not 100% sure, but that's the info I got for the parts counter guys...
 
thebrick said:
If your XJ was designed for the composite, I believe you can use either...I, myself, am not 100% sure, but that's the info I got for the parts counter guys...
judging from my other brake job as well as my co-worker's brake job where we put cast rotors on xj's meant for composite about a year ago w/ no ill effects so far would back up that statement.
 
thebrick said:
I found out the hard way that the composite rotor and full cast rotor are not the same size.

The 'hat' size is different...the composite rotor is about 1/8" taller than the full cast.

If you XJ was designed for the full cast, like mine is, you can only use the full cast.

If your XJ was designed for the composite, I believe you can use either...I, myself, am not 100% sure, but that's the info I got for the parts counter guys...
Sorry to 'jack a somewhat old post but wanted to expound on this.
Went to Autozone to get new rotors for my '01. Present rotors were cast, so when I got the AZ ones I checked them. Both boxes were cast rotors; like what was on there. Put them on. Couldn' t move. Come to find out, the hat size can be different on the cast ones as well (the 1/8th inch). One rotor was right, the other wrong, same boxes, same part number.

Bottom Line: Regardless of construction, do yourself a favor and bring a measuring tape to compare to your old ones.
 
Get the cast steel rotors and pass on the composites. I have never run into a problem on front rotors for either 98XJ or the 97TJ's as far as 'hat size' goes. Everytime I do get new rotors which is every brake job, I just pick up wagner's from the parts store and take em home.
 
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