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Unread 11-14-2006, 03:31 PM   #1
DUTTONCPA
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Rear Differential Overheats

I have a 94 Grand with over 200K miles. Had a whinning noise in rear end which everyone agrees was rear end bearings. Due to the high mileage, I had the entire rear end rebuilt, all new gears, bearings, & seals. Less than 100 miles later it got so hot it blew the plug from the rear end and actually caught fire. Obviously the shop took it back and said the vent was plugged. For a 2nd time they put in all new bearings, seals, and ring & pinion. It is still gettting very hot after a short drive and we are afraid to drive too far. I thought it was possibly set up too tight but the mechanic says it was set up at the loose end of the allowable specifications. He used synthetic lube and all new parts.... He is a very trustworthy and certified mechanic that really knows what he is doing, but this seems to be going on too long. Does anyone have any other ideas why this is getting so hot? Any assistance would be appreciated. (I have posted this on 2 different forums in an attempt to get all of the advice I can get!)

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Unread 11-14-2006, 03:47 PM   #2
ajmorell
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Some more information might help such as what axle it is, is it limited-slip, etc. The more you can tell us the more we can help.
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Unread 11-14-2006, 03:58 PM   #3
aj173pa
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He isn't doing something right if it gets hot enough to actually catch fire. I rebuilt my own and I didn't have any of those problems. In fact it went well.

I believe I would go have another shop look at it.
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Unread 11-14-2006, 04:05 PM   #4
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When I had mine rebuilded it wasn't assembled well, it was giving some sounds, but I can't imagine oil getting so hot to burn... It is really weird. Are there any signs of abnormal wear-out of any components? Ring gear, bearings?
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Unread 11-14-2006, 04:10 PM   #5
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It is getting too hot because of friction. I might believe that the vent was plugged the first time, however that plug is in pretty tight. I think I would see it push oil out a wheel seal long before it would pop out the plug. IMHO it sounds like the pinion gear has been set too deep into the crown gear. Despite your trust in this mechanic, I would want to have him remove the cover in your presence just to see how much "silver wear" you have collected. Differentials may get a little warmer than normal initially after rebuilding, but should revert back to normal operating temperature within a few hundred miles. Even after a normal rebuild it is a good idea to change the fluid, just to get rid of any metal worn off during initial run in.
You definitely have something wrong going on there.
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Unread 11-14-2006, 04:10 PM   #6
DUTTONCPA
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It is a stock Grand Cherokee with Dana 35 rear end.

In addition, I put new tires on the rear at the same time as the rebuild. The front were 3/4 worn. Thus there was a difference of about 3/4 tread depth between the front & rear tires. We have routinely changed front tires one year and back the next year for 10 years on this vehicle without a problem, but we are wondering if this mismatch could be part of the problem?
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Unread 11-14-2006, 04:28 PM   #7
mendelmax
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no, difference in tires can't cause diff overheating. If you would have different tires left to right, and drive at really high speed, then maybe something could get hot a bit, but not as much as you said...
Is it LSD or not?
BTW- what t-case do you have?
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Unread 11-14-2006, 04:36 PM   #8
micifus
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Did he do it free of charge the 2nd time. A pluged vent would not cause a diff to over heat. The vent provides little if any cooling.
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Unread 11-14-2006, 04:40 PM   #9
mendelmax
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Quote:
Originally Posted by micifus
Did he do it free of charge the 2nd time. A pluged vent would not cause a diff to over heat. The vent provides little if any cooling.
I would rather agree with "any".
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Unread 01-11-2014, 02:48 AM   #10
Skydivecarl
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Grand Cherokee rear differential overheating.

I have exactly the same problem. Prior to a recent road trip I decided to check the diff' oil level, it was low so I topped it up (EP80/90). After some 30 miles of motorway driving I noticed a smell (burning diff' oil) and the diff' itself had become quite noisy. Upon inspection the diff' had forced oil out of the front seal and onto the exhaust (thus the smell) and was smoking. I left the motorway, let it cool for an hour and topped up the oil returning home on normal roads at a much lower speed. The next day upon inspection found the diff' breather to be completely blocked, cleared this and again topped up the oil, the car was fine around town and assumed I'd rectified the problem. A week later on the same motorway at exactly the same place, exactly the same problem, but worse, more noise from the diff especially when changing direction, I decided not to drive the car any further and returned on the back of a recovery truck. The morning after (when completely cooled) it was fine again. I opened up the differential, completely changed the oil, there was no obvious signs of damage or wear, no excess of metal filings in the oil or anything that would cause alarm, this time I added the specified Jeep 'Additive' to the oil (a friend who is a Jeep agent insists this is critical). Since then it drives fine around town, I'm a bit cautious to drive any distance though. I am told that the lack of 'Additive' (friction reducer) could have been the cause but a bearing issue could also be to blame. Any suggestions anyone..?
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Unread 01-11-2014, 08:03 AM   #11
Technohead
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Its normal for diffs to get too hot to touch.
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Unread 01-11-2014, 10:01 AM   #12
JFM626
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The Jeep additive is a friction modifier, and in essence allows the differential not to chatter when turning, not having much in your oil would also cause your chattering. This could cause the oil to overheat.
Usually a bearing failure would be preceded by a rumbling noise and the presence of metal in your oil.
Use an infra red temperature gun to moniter the temperature. I believe anywhere up to about 180f is Ok. I have seen that in my Jeep after towing my boat.
Someone else might kick in with other figures though.
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Unread 01-11-2014, 04:21 PM   #13
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The oil itself can get warm enough to vaporize water (which then escapes through the vent.)
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Unread 01-13-2014, 07:20 AM   #14
Skydivecarl
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Duttoncpa, how did you sort this problem..? I'm quite confident that if my car was driven for any distance constant running (motorway) exactly the same would happen again, at the moment it's fine around town but that's as far as goes until this problem has been rectified. Any ideas anyone (the problem was described in detail my previous post)..?
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Unread 01-13-2014, 10:22 AM   #15
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my 2 cent.....a lot of mechanics aren't familiar with crush sleeves and wring the pinion nut on with an impact without checking the pinion preload. they just think "oh , its a little tight but that's normal. It will loosen up after some miles". I've also seen people try to reuse a crush sleeve which is a no no. Technically you should use a new crush sleeve when swapping a new pinion seal but folks rarely do.
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