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Unread 04-02-2011, 12:42 PM   #1
GOrton
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rotor size

I need to change the front rotors on my 2002 jeep wrangler and apparently they come in two sizes. How do I determine the correct size of 82mm or 78mm? Any help would be appreciated.

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Unread 04-02-2011, 02:02 PM   #2
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Quote:
Originally Posted by GOrton View Post
I need to change the front rotors on my 2002 jeep wrangler and apparently they come in two sizes. How do I determine the correct size of 82mm or 78mm? Any help would be appreciated.
You have the 78mm versions.
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Unread 04-02-2011, 04:12 PM   #3
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How about a 1999 Sahara?
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Unread 04-02-2011, 04:33 PM   #4
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Originally Posted by iceman1947 View Post
How about a 1999 Sahara?
The 99 is the split year. It can have either the 78 or 82 mm versions and it's too bad the manufactures use the overall height dimension which can easily confuse folks.

Here is the only correct way to measure the rotors for the TJ front applications.



That number won't correspond to the 78 or 82mm meaurements but you will be able to identify the rotor correctly with the measurement you get.

If the measurement is 2.75" like the picture or 70mm, you have the later 2000 and up rotor.

If the measurement is 3.00" or 76mm, then you have the earlier 97-mid 99 rotor.

The reason the dimension is so confusing is if you have the earlier and taller composite rotors on a 99 and measure the overall height, it's really close to the same height as the later and shorter full cast rotor due to how thin the rotor hat is.

Since the only dimension between the two rotors that matters is how deep it is because the unitbearings are different heights, they need to be measured like the picture.
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Unread 04-02-2011, 04:54 PM   #5
GOrton
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Thanks, seeing how this is my only vehicle I didn't want to have to buy both to be sure, you saved me a trip and the hassle of a return.
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Unread 09-01-2012, 05:54 AM   #6
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Is there a specific manufacturing date we can go by to determine which rotor we have? I got a coupon for $50 off a $100 order at advance and want to put the order through but I have no way to check the jeep's rotor size at this time.
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Unread 09-01-2012, 06:21 AM   #7
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Is there a specific manufacturing date we can go by to determine which rotor we have? I got a coupon for $50 off a $100 order at advance and want to put the order through but I have no way to check the jeep's rotor size at this time.
Not that I have found. My 99 was built in 3/00 and has the taller rotors. I've worked on earlier ones that had the shorter ones.

If you pull a tire and take a picture of the rotor, I can likely identify it.
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Unread 09-01-2012, 08:36 AM   #8
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We went through this with my sons 99 a few months ago. His was built 12/98 and has the shorter rotors. Autozone uses the same part number for my 98 and his 99 for the Duralast rotors.

2000 and up fit just fine.
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Unread 09-03-2012, 05:23 AM   #9
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Originally Posted by mrblaine View Post
Not that I have found. My 99 was built in 3/00 and has the taller rotors. I've worked on earlier ones that had the shorter ones.

If you pull a tire and take a picture of the rotor, I can likely identify it.
How do you identify which is which by looking? Taller or shorter hub center? Just curious....
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Unread 09-03-2012, 05:59 AM   #10
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I went to where my jeep was and took it apart real quick. I found that I have the 2.75" hat rotors which are the later 2000 and up rotors BUT my hub center (that sticks out) measures 3/4" out. Isn't the 3/4" hub for the taller rotor? I thought I saw a picture of the two hubs and the difference was 3/4" and 1 1/8" or something like that.

If I'm right, the shop that did the work on this jeep (before i owned it) put the wrong rotors on. I am noticing some weird wear on the rotors. The outside of the rotor is worn evenly and smooth while the inside only is worn in the middle about an inch and the rest of it is untouched. Rotors and pads look pretty new.

So am I correct that I have pre-99 hubs but post-99 rotors?
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Unread 09-03-2012, 06:28 AM   #11
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We ran the old rotors on his for about five miles before removing them. Iirc the inside had a groove in it from where it made contact.

The rotor didn't sit straight either, where it hit pushed it out some.

Not sure about the measurements its been a few months.
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Unread 09-03-2012, 06:33 AM   #12
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Quote:
Originally Posted by Muddeprived View Post
I went to where my jeep was and took it apart real quick. I found that I have the 2.75" hat rotors which are the later 2000 and up rotors BUT my hub center (that sticks out) measures 3/4" out. Isn't the 3/4" hub for the taller rotor? I thought I saw a picture of the two hubs and the difference was 3/4" and 1 1/8" or something like that.

If I'm right, the shop that did the work on this jeep (before i owned it) put the wrong rotors on. I am noticing some weird wear on the rotors. The outside of the rotor is worn evenly and smooth while the inside only is worn in the middle about an inch and the rest of it is untouched. Rotors and pads look pretty new.

So am I correct that I have pre-99 hubs but post-99 rotors?
The two pilot dimensions are 7/16" and 3/4" with the shorter one being the early unitbearing.
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Unread 09-03-2012, 07:04 AM   #13
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The two pilot dimensions are 7/16" and 3/4" with the shorter one being the early unitbearing.
So the measurements of this pix are wrong?

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Unread 09-03-2012, 07:31 AM   #14
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So the measurements of this pix are wrong?

Even though that is my picture, I didn't think to measure that part when I took it, it was merely taken to show the most important difference which is the height from the 3 bolt flange to the 5 bolt WMS flange.

When I re-wrote all the instructions for the Vanco kits, I did carefully measure the pilot height and referencing those shows them to be what I said above. There is a link to them on the Vanco site, page 4 of the 15" kit instructions.

I used a pair of known TJ unitbearings to take the measurements.
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Unread 09-03-2012, 08:09 AM   #15
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So now it seems I do have the right hub/rotor combination but still gotta figure out the strange brake wear on the inside of the rotors. Hmm.....
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