[Stan CJ]

I assume my 1979 Jeep would benefit from a limited slip differential in the rear and would ask for opinions on the benefits of installing one. I'm sure it will be fine if I just freshen up what I have, but since I have made the decision to rebuild now would be the time to make changes.

I have been researching the different style of limited slip carriers for my AMC 20 differential. I would like to ask opinions on what limited slip unit would best fit my needs. I will be powered by a 4.3 V-6 and an th350 auto trans through a D20 transfer case. The jeep will be mostly driven on the street and dirt roads. It will be a tribute to my farther in law that my wife will drive mostly.

With that info can I get some opinions on a differential options, would not want the carrier to be too aggressive as to skip the tires on pavement. I would like to have a unit that will not be one that takes constant maintenance. I will also be using the Moser axles. The photos are what I have now. Thanks

 

[emiller35]

I believe most will agree that the Tru-Trac is about as good as it gets for the LSD carriers.


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[80cj]

I think currently, the Detroit Trutrac is the best of the LS units available for the AMC 20. It's effective yet you never know it's there until you need the traction. I've never heard of breakages, no clutch plates to wear out and no need for friction modifier oil additives.

 

[dolsoncj7]

I'll 3rd that. I just recently upgraded my AMC 20 to 3:54 (it's an around town/beach crawler) from the factory 2:73, which you need to replace the carrier. I went with the Trutrac and it was an easy decision.

 

[Stan CJ]

Thank you for the responses, have ordered the Trutrac carrier, Moser axles and Timken bearing kit.

 

[dolsoncj7]

That is probably a pretty common configuration that a bunch of us have used. Precisely what I did, so you'll probably get solid answers as you go about doing it.

I would probably add an additional shim kit, just in case you trash something. I seriously wrecked the factory carrier shims - especially the thick ones. I didn't like making a thick sandwich of new shims, but with the extra set I bought I could come up with any combination of thickness. Adds $30 to everything. I also went with the Ratech's crush sleeve eliminator.

 

[Axhammer]

You will be happy with the Torsen style limited slip you ordered, it will work well for your intended use. Just keep in mind, with that style LSD, when one wheel has zero traction, it will send 100% torque to that wheel. In other words in a situation when one wheel is in the air, or on ice, it will act like an open differential, it will send all torque to the wheel in the air or on ice (with no traction), unlike a clutch style LSD.

The torsen style LSD requires some traction to both wheels for it to work, or in other words to transfer torque to the opposite wheel. If you ever get in a situation where one wheel has zero traction, and your Jeep stops moving due to this, a light application if the brakes will trick the differential into transferring torque to both wheels. A light application on the E-brake will do the same thing, as a light application of your foot brake.

I just thought I would throw that out there, since no one brought up this very distinct characteristic, between a clutch style LSD and a Torsen style LSD. I definitely would not say one is better than the other in all situations, but for your intended use, you made a good choice.

On another note, what gear ratio and tire size are you planning to run? Now is the time to regear the axles if you need to. With a V-6 and an automatic transmission your gearing requirements will be different than if you were running a manual transmission.

I bring this up, because I run an automatic transmission as well. With a warmed up inline six and a TF999 automatic transmission, my CJ-7 actually gets by pretty good with 273’s on 31’s. I believe 331’s would work well in my rig with my current engine on 31’s.

 

[Stan CJ]

Axhammer, did not know the difference between LSD designs and that information will be valuable, when a wheel looses contact with the earth. I can see myself scratching my head and saying "but I have a posi"

Checked the housing and have A stamped on it. Checked gearing and indeed have 3.54 gears and will be running 31 inch tall tires. I considered a differential gearing change, but decided against it.

The gearing on the original 3 speed is comparable to the TH 350 going into the CJ. I'm transplanting a Vortec 4.3 and expect the torque converter to work a little harder so the trans shop is addressing that issue.

When the trans comes back I will mock up the power train and post some photos of the progress.

 

[Axhammer]

354 gears will work good with that V-6 and automatic transmission, it should turn out to be a great street driver for your wife with that setup.

The LSD in the rear will make much more capable off-road as well. If you have the coin put one in the front too, but that’s totally optional, and not needed for your intended use.

The good thing about the Torsen LSD’s is that they act like an open differential until traction is limited, and then they deliver. Also, they don’t have parts that wear, or need periodic maintenance, or the need for friction modifier additive in the gear lube.

 

[jeepdaddy2000]

The torsen style LSD requires some traction to both wheels for it to work, or in other words to transfer torque to the opposite wheel. If you ever get in a situation where one wheel has zero traction, and your Jeep stops moving due to this, a light application if the brakes will trick the differential into transferring torque to both wheels. A light application on the E-brake will do the same thing, as a light application of your foot brake.

I have a Gleason Torsen in the rear of my CJ. When I worked as a mechanic I would do demonstrations by raising one wheel with a floor jack. I would put it in first gear and the tire would spin. When I eased down on the brakes the unit would seamlessly engage and drive across the floor, dragging the jack with it. I wheeled the crap out of it and eventually transplanted it to the rear of my Waggy when I did my gear swap. It finely wore out and then broke.
While the two are slightly different in design they work the same. That being said, be aware the GT unit isn't rebuildable so years of heavy use will eventually wear it out. I assume the same is true for the TT

 

[80cj]

All limited slips require resistance from the wheel without traction in order to energize the clutch mechanism whether it's a gear or friction disc clutch unit. In my experience, the best of the limited slips is the Dana Spicer Power Lok. With four spider gears, it is very robust and the clutch mechanism applies increasing pressure on the clutch packs as more force is put on the unit but it uses clutch packs which will eventually wear out. Very difficult to find an AMC 20 Power Lok.

 

[CSP]

The beauty of the Tru Trac is it requires the least amount of differential resistance to get it to lock. Clutch types require more force. The fact that there aren't clutches to eventually wear out is a big seller too.

 

[John Strenk]

My Astro van had an Eaton LSD and is called the G80 Mlocker - Mechanical Locking Differential, GM Order/RPO Code G80(on trucks and vans). Normally it acts as an open differential, though as long as you are under 20mph and have a wheel speed difference over 100 RPM it then locks up behaving as a locker forcing both wheels to turn at exactly the same speed.

• Wheel speed difference (left to right) in excess of 100 RPM will cause a flyweight mechanism to open and engage a latching bracket.
• Stopped flyweight triggers a self-energizing clutch system until both axles turn at the same speed (full lock). Automatically unlocks.
• Latching bracket swings away from the flyweight mechanism above 20mph preventing lockup.

It was a very cool LSD that didn't need any friction modifiers to operate. Too bad you couldn't get one for a Jeep unless you put in a 10 bolt axle...

 

[80cj]

My Astro van had an Eaton LSD and is called the G80 Mlocker - Mechanical Locking Differential, GM Order/RPO Code G80(on trucks and vans). Normally it acts as an open differential, though as long as you are under 20mph and have a wheel speed difference over 100 RPM it then locks up behaving as a locker forcing both wheels to turn at exactly the same speed.

• Wheel speed difference (left to right) in excess of 100 RPM will cause a flyweight mechanism to open and engage a latching bracket.
• Stopped flyweight triggers a self-energizing clutch system until both axles turn at the same speed (full lock). Automatically unlocks.
• Latching bracket swings away from the flyweight mechanism above 20mph preventing lockup.

It was a very cool LSD that didn't need any friction modifiers to operate. Too bad you couldn't get one for a Jeep unless you put in a 10 bolt axle...

I have one in my 2001 Chevy S10 and it really hasn't worked very well. My friend has one in his 2003 GMC Sierra and has good comments about it. The S10 has the smaller 7 5/8" rearend and maybe that has something to do with it. Don't know how well those act if one wheel gets off the ground and you try to lock it by applying brake since it's a flyweight/cam set up.

 

[jeepdaddy2000]

I can't speak for the newer GM units, but just about all the posi diffs I encountered in the 80's-90's were broken, with shattered clutches, gear teeth stripped on the cam plate, and blurred teeth on the flywheel. I worked in a 4X4 shop which saw the results of oversized tires, poor gearing, and teenaged throttle feet so maybe under more normal circumstances they hold up better but my experience rates them low for durability.