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Unread 02-05-2014, 06:49 AM   #1
BigClay
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1998 TJ Wrangler 
 
Join Date: Oct 2011
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1990 MJ Questions

So let me start off with I know very little amount MJs and XJs, I have been a ZJ man my whole life.

I am looking at a 1990 MJ over the interwebs, and before I make a trip to go see it, I wanted to get some more info. It has a 4.0 and 35" tires on it, and I am assuming a short arm lift. A 8.8 already swapped in the rear with a detroit, stock front axle (is it a LP or HP 30?) with a lunch box locker and 4.56 diffs front and rear.

So tell me what is good or bad about this year MJ. What t-case does it have? What should I watch out for or expect?

Thanks for any comments.

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Unread 02-05-2014, 08:23 AM   #2
Timeless
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1987 MJ Comanche 
 
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Stock tcase is a 231. Stock front axle is a HP disconnect dana 30. The disconnect sleeve is known for being problematic and many people either manually lcok it into the engaged position or replace the two piece shaft with a one piece.

1990 will have a RENIX fuel management system which depending on ones perspective is better or worse than the 91+ HO's. RENIX is pretty simlpe to diagnose if you do have a problem but it has its own quirks too. Nothing terrible though.

With any old rig, be wary of rust. Considering the PO did some work to it, make sure its not all booty fab. Expect the unexpected.
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Unread 02-05-2014, 08:37 AM   #3
BigClay
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Quote:
Originally Posted by Timeless View Post
Stock tcase is a 231. Stock front axle is a HP disconnect dana 30. The disconnect sleeve is known for being problematic and many people either manually lcok it into the engaged position or replace the two piece shaft with a one piece.

1990 will have a RENIX fuel management system which depending on ones perspective is better or worse than the 91+ HO's. RENIX is pretty simlpe to diagnose if you do have a problem but it has its own quirks too. Nothing terrible though.

With any old rig, be wary of rust. Considering the PO did some work to it, make sure its not all booty fab. Expect the unexpected.
Thanks for the info!

Will a XJ non-disco front 30 bolt right in to a MJ?
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Unread 02-05-2014, 09:19 AM   #4
Timeless
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Yes. TJ, XJ, MJ and ZJ front axles all use the same geometry. XJ and MJ front axles are all HP, TJ's vary (I think) and I know nothing about ZJ's.
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Unread 02-05-2014, 09:24 AM   #5
BigClay
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Thanks, I got the ZJs covered, they are factory LP D30s, no HP, but a XJ HP D30 will swap directly to a ZJ.

Are almost all XJ parts the same as MJ? Meaning if I see an XJ aftermarket part will it usually work on an MJ?
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Unread 02-05-2014, 01:36 PM   #6
Nick05
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front bumper is xj, rear is dodge dakota. the xj is basically the same from the doors forward, the seats do mount different though. these things are prone to rust, and if its standard even more so due to leaky clutches.
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Unread 02-05-2014, 01:45 PM   #7
BigClay
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Quote:
Originally Posted by Nick05 View Post
front bumper is xj, rear is dodge dakota. the xj is basically the same from the doors forward, the seats do mount different though. these things are prone to rust, and if its standard even more so due to leaky clutches.
So XJ leaf springs are not interchangeable with a MJ, instead I need to look for Dakota leaf springs?
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Unread 02-05-2014, 02:10 PM   #8
Nick05
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i am unsure on the leafs, but i would imagine they were the same. i was referring to the bumper itself it you are looking to upgrade. i don't know where all they grabbed parts from to make these things. i think suspension is the same as xj, along with drivetrain(except for shorter shafts), but i am sure someone else will chime in. for renix system, check here http://www.jeepforum.com/forum/f11/c...hread-1819634/ . someone else was talkin about renix fuel management, that might help with some of the crazy things they do
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Unread 02-05-2014, 03:43 PM   #9
Timeless
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Most parts, from the transmission cross member and forward are interchangeable between XJ's and MJ's. There are of course variations depending on XJ year. Nearly everything from there back is different.

Some early dodge dakota rear bumpers will work as far as I know. But not all.

XJ leafs are a different length than comanche leafs. Comanche leaf springs are SUA, XJ's are SOA. Distance between eyes is different too.

Do yourself a favor and do some reading/research on comanche club.
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