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Unread 01-07-2016, 01:21 AM   #1
Rwrangler
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What type of Differential do I have

I know I have a 4x4 part-time (Command-Trac NP231, rear permanent, front engaged manually in off-road conditions, shift-on-the-fly) 4 wheel drive system, but what is the technical name of the type rear end, posi, limited slip, locking differential?
1991 Jeep Wrangler, 4.0 engine, 5 speed.

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Unread 01-07-2016, 05:37 AM   #2
Mike Romain
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Normally an open differential. If you jack up the rear and spin one tire and the other tire spins the opposite direction, it is an open diff. If the other tire spins the same way, you have a traction device. Now as to what kind? Factory didn't put lockers in so it could be a limited slip if both spin the same way. Or some previous owner could have put anything in it and you might have to open it to see.
A locker normally bucks and chirps the tires in tight turns, but they all don't.
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Unread 01-07-2016, 09:24 AM   #3
cyoos
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Your profile says you have OEM limited slip. If that's correct it's called a Trac-Lok.

Here's a JF thread discussing them.

http://www.jeepforum.com/forum/f12/y...c-lok-1232472/

And here's a random link to it's friction clutch rebuild kit.

http://www.4wd.com/Jeep-Drivetrain-J...n=D%2fS707165X
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Unread 01-07-2016, 01:32 PM   #4
Rwrangler
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I didn't fully explain. It is OEM. No modification, all stock from the factory. I've had the YJ sense new. So it must be a Trac-Loc. Is there a estimate mileage for replacing parts, discs in the Trac-Loc?
cyoos, thanks for the URLs. Thanks to all for the information.
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Unread 01-07-2016, 02:05 PM   #5
cyoos
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Quote:
Originally Posted by Rwrangler View Post
Is there a estimate mileage for replacing parts, discs in the Trac-Loc?
Mileage varies and it depends on your driving habits, but estimates range from around 50,00 up.

If you jack up the rear end and the tires spin opposite directions when you spin one, then it's the clutch packs are worn out and definitely need to be replaced.

If they both turn the same direction then at least thinking about it. One way to test it further is to leave one tire setting on the ground and check the breakaway torque of the dif. I'll try to find some figures, they should be in the FSM. But...

It can be done with either a beam or breakaway torque wrench, and most accurately with an adapter plate (home made for us, of course) that bolts on in place of the wheel and keeps the torque wrench centered to the axle.

I've heard minimum of 20 lbs breakaway torque for a used 8.8 Traction Lok, but I'll check the FSM and see what it lists for the D35.
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Unread 01-07-2016, 03:37 PM   #6
cyoos
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OK, the FSM doesn't have a test procedure nor does the Spicer manual...only the rebuild procedure. But since the Spicer Trac-Lok and Ford Traction Lock are both clutch type LSD's the Ford test procedure should work well for the Spicer also.
t-lock-test.jpg  
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Unread 01-07-2016, 04:04 PM   #7
mike134
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Quote:
Originally Posted by Rwrangler View Post
I didn't fully explain. It is OEM. No modification, all stock from the factory. I've had the YJ sense new. So it must be a Trac-Loc. Is there a estimate mileage for replacing parts, discs in the Trac-Loc?
cyoos, thanks for the URLs. Thanks to all for the information.
Factory LSD was pretty rare on the YJ, but exists.

From what I understand, they were common in Canada. Are you in the frozen north?
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Unread 01-07-2016, 05:04 PM   #8
Rwrangler
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When I bought this YJ I got all the options. I do know if you put the jeep on stands, start the engine, put the transmission in first gear and let idle, it's real hard to stop either rear wheel. About every 8-10 months I change ALL my fluids. When I change the rear diff oil, I'm required to add a additive. I was told by Jeep that the additive was needed to cause more slippage for cornering?
I'm trying to solve a very intermittent violate vibration I get only in first and reverse gear. It seems to happen more in the summer or when the Jeep goes on a long trip.
It seems to have a mind of it's own. Some days the YJ runs like new, other days I could trade it in. Any how. Mine is a 5spd manual (see vehicle info below). Some times when I start out in 1st gear I get a shudder, as if the clutch is bad. And if you use reverse gear it's also real bad. But when your moving and get past the initial clutch engagement everything is real smooth? This has been going on and off for the last 8 years. I first thought it was the clutch. I noticed a oil leak on the bottom of the bell housing and had it check, the shop said it was a rear main seal. So I thought the clutch had a little oil on it. So I had the shop pull my clutch. Clutch disc was perfect, no oil at all and the t-brg wasn't leaking.. But sense the clutch assembly was out I had them replace with all new parts, clean the flywheel, replace the pilot brg, clutch disc, pressure plate and t-brg. No change at all. Everything looks good underneath, U-joints are all good, no slop in trans/transfer/diffs. I also changed out the motor and transmission mounts. Could it be a problem with the rear limited slip diff? I do service the rear diff every year and add the little tube of additive. It seems to be coming from the rear?
THANKS:
cyoos,
mike134
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Unread 01-07-2016, 05:50 PM   #9
cyoos
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I don't know if a bad pilot bearing would cause the problem you're describing, but did the mechanic change it when he changed the clutch? Here's a quick check that might help diagnose the bearing:

http://www.jeepforum.com/forum/f12/pilot-bearing-33711/

I thought it could also be the shifter linkages in the transmission might need adjusting, but 1st and reverse are on separate rods. However, in the transmission there is a "1st/Reverse Hub". The reverse gear is immediately in front of the hub and the 1st gear is immediately behind it, so that could be the culprit.
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Unread 01-07-2016, 06:54 PM   #10
cyoos
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Let me try to get MeanMax in on this. If it is a tranny issue, he will be able to help far more than I can.
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Unread 01-07-2016, 07:17 PM   #11
cyoos
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Here's a short thread, sounds like the same issue you're having, with trusted advice from Jerry Bransford. Check for broken motor mounts.

http://www.jeepforum.com/forum/f9/ax...everse-820925/
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Unread 01-07-2016, 07:36 PM   #12
Drednot
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Quote:
Originally Posted by Rwrangler View Post
So I thought the clutch had a little oil on it. So I had the shop pull my clutch. Clutch disc was perfect, no oil at all and the t-brg wasn't leaking.. But sense the clutch assembly was out I had them replace with all new parts, clean the flywheel, replace the pilot brg, clutch disc, pressure plate and t-brg. No change at all. Everything looks good underneath, U-joints are all good, no slop in trans/transfer/diffs. I also changed out the motor and transmission mounts. Could it be a problem with the rear limited slip diff? I do service the rear diff every year and add the little tube of additive. It seems to be coming from the rear?
It seems like you've hit a lot of the main issues.

The only things I want to ask about...."cleaned the flywheel" and "U-joints are all good"

Cleaned like wiped down, or resurfaced on a flywheel resurfacing machine?

And the u-joints. Are they original? They look good, or they have been recently replaced?

The limited slip most likely wont cause any vibes or shuddering if you are going in a straight line forward or backward. Now, if it only shudders while taking off in first or reverse while turning at the same time, that could be a place to look.
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Unread 01-07-2016, 09:04 PM   #13
Rwrangler
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All the "U" joints have been replace. All motor & trans mounts replace. The flywheel was resurface twice (really unneeded, but did because everything was already out). I had two extra clutch assembles replaced already trying to find this vibration. Clutch, pressure plate, through out bearing, pilot bearing & flywheel resurface. NONE were needed.
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Unread 01-07-2016, 11:03 PM   #14
Drednot
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Ok, sounds good.
How bout the circumstances? Turning only? Straight only? or both?
On slow/gentle clutch release? Quick launch?
Is it a slipping/grabbing feeling, or a jerking/jolting backlash? Noisy? Metallic sounding?
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Unread 01-07-2016, 11:54 PM   #15
Rwrangler
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It does it both turning & straight. And doesn't matter, if I release gentle (which I normally do) or with a Quick launch. The problem I have I never know when this will show up. Every time I'm ready to try and recall the situation, it won't act up? I'm always paranoid every time I release the clutch. It's only on the initial release. If I'm on a slight decline it won't vibrate, as long as there is no resistance it works fine. Other times you can't make it vibrate, you can try to slip or pop the clutch. And when I state vibrate, I mean the rear end shutters so bad it scares me. If I immediately put the clutch in after it starts to vibrates, before complete release and one pump to release it again, it won't vibrate because of the small amount the Jeep is moving. And yet I've tried to make it vibrate or shutter on a steep incline, from a (dead stop which is the only time it will vibrate, going forward or reverse)
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