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Vibration when braking


NAXJA Forum User
Lomita, CA
I own a 99 XJ w/ 4WD, commandtrac.

When I step on the brakes, I get a vibration from the front end.
My Pirellis were getting pretty worn so I figured they might have something
to do with that. This past weekend I replaced them with new tires but the
vibration is still there.

My educated guess is that the front disks are warped.

Do you guys know of any way to make sure this is the problem without the use
of special tools?

Would the warping be bad enough that several measurements with a micrometer
around the disk would show this?

I'm leaning on getting new disks but would like to make sure before I spend
the money.

Which type of disk would be better? vented or solid?

What brand would you recommend?

What is a composite disk?
Is that one that is partially cast and where the rest of the body is made of sheet metal??

Any feedback is appreciated.
I think there is a response to your questions on the old forum. Anyway, a micrometer won't tell you if the rotors are warped. To check for warp, you'll need a dial indicator or some crude equivalent. For a crude equivalent, you can clamp a screwdriver to something on the suspension so that it just touches the rotor at the point of most deflection. You can then slowly spin the rotor around and see how much the gap varies. You can quantify it by measuring how much the gap varies by inserting a feeler gauge between the screwdriver tip and rotor. My XJs are too old to have composite rotors so I'm not sure what those are really all about. All the rotors on my various 6 vehicles are ventilated and several of them have had warped ones at various stages of their lifes.
Well, without even trying to measure anything, I'd almost bet money that the disks are warped.

Can anyone tell me what exactly a composite rotor is?

What is an ALL CAST rotor?

Can anyone suggest what to get?
I've seen a PG Plus Rotor for about $35 each on Rock Auto.com. I'll have to price them at the local autoparts store. I have noticed that the height of some of these varies by almost a quarter inch.

Would the various sizes listed for my Jeep fit?? Some say 21 31/32s, and another 3 3/16.
Would either fit?

No, they will not all fit.

It seems that over the years Jeep has used a couple of different hub/bearing assemblies. These appear identical on a quick look, but they actually have different offsets. If you mix the rotors for one year with the hubs for another year, you get an interference fit. Assuming your XJ has the correct hub assemblies, there should not be two different height rotors listed for your year.
On the Autozone.com site and rockauto.com site I was given a choice of disks of 2 different heights for my 99 XJ w/ 4WD.
I guess I won't know what it should be until I take the wheel off.

What's a composite disk?

Can someone enlighten me??


I have a 88 XJ with one piece rotors. My rotor slides onto my hub. It is a one piece casting.

On the composite rotor someone figured out they could save a few cents per rotor by stamping the center section out of sheet metal. Then they place this stamping into the mold and cast the braking surface. It saves them some machining time and may reduce the cost of materials used. It is called a composite because it is make of two parts.

I do not know if there is a one piece cast aftermarket rotor available for your application. I think I read on here Chrysler had some type of recall on composite rotors, maybe someone with your version of XJ can give you the details.


Avoid rotors from China. I haven't shopped for XJ rotors, but if you check at NAPA, you'll often find that the ones from China are less than half the price of the ones that come from just about anywhere else. You get what you pay for and I really do depend upon my brakes.
The store I buy parts from sells brembo replacements. I just installed them yesterday along with loaded calipers and the difference was amazing. Vented is the only way to go.
So are the Raybestos PG Plus the ones to get?

The other brand at the local autoparts store is AIMCO?

Anyone heard of them?
They were cheaper than the Raybestos.

Manuel said:
The other brand at the local autoparts store is AIMCO?

Anyone heard of them?
They were cheaper than the Raybestos.


Never heard of them. Where are they made? Remember -- they are probably cheaper for a reason, and that reason is not to do you a favor.
OK, I'll go with you wiser gentlemen and get the Raybestos PG Plus rotors.

I checked the prices for them at the local autoparts stores and was amazed and how much prices varied for the same rotors. There was quite a bit of difference in price between the 3 1/16 and the 3 3/16 overall height rotors.
I need to take one off of the XJ to figure out which size I have.