Limited slip diffy

1941 - 1945, MB, GPW modifications, sugestions, and ideas, official MWO's and unofficial WWII field mods NO EBAY or COMMERCIAL SALES.
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JAB
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Post by JAB » Thu Sep 18, 2003 11:12 am

Sorry about the delay.

Assuming it's a Power-Lok, which I think is the only limited-slip (as opposed to a true locker) available for this aplication, here's the scoop, straight out of the Jeep manual. There are two different tests, both of which are done in the vehicle. I think with a little inginuity you could figure out a way to do it in a vice though. The condensed version will follow, but 1st I need to explain that they are refering to a semi-floating rear axle with a large nut centered on the tapered shaft, which makes for an easy place to attach the torque wrench for this test, as it is the center of the axle shaft. Basically the first test is for the style with the dished plates. The second test is for either, but primarily for the style with the flat plates. The 1st test is to jack up one side, block the opposite & with the tranny in nuetral put a torque wrench on the nut of the raised axle. Discounting break-away torque a good unit should give a reading of 40 lb-ft (5,53 kg-m) or more. Test two involves raising one side with a floor jack (the type with wheels) & adjusting the brakes on the raised wheel until you can barely turn the tire by hand. Slowly & easily try to drive away. If you can, it passes the test. If it flunks either test then it's time for a re-build, which essentially means replacing the worn discs. They come as a set & should be replaced as a set, if you can find any. In the manual it states that none are available for the flat type & that a few variations existed in the other. Also, this is for a model 44 axle, so the torque reading may be off. I have the pamphlet that came with my model 25 Power-Lok, but have not been able to find it yet. If I do, I will update this for you.
-Jeff

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Post by JAB » Sat Sep 20, 2003 9:08 pm

I have the pamphlet that came with my model 25 Power-Lok, but have not been able to find it yet. If I do, I will update this for you.
Found it & here's the update; It's 40 lb-ft for the model 25 too. It's interseting in that they reccomend against the rolling jack test. There's also a picture of an adapter to check the torque on the full floating axle too.

& to add to Bob N.'s post with the Lok-Rite product; I'd consider that a locker, as opposed to a limited slip. The limited slip products typically have clutches that slip when overloaded to prevent breaking parts when too much load & traction are applied. A locker on the other hand either locks both sides together (ARB, spool) or, like the Lok-Rite or Detriot Locker, do not allow either tire to ever rotate slower than the ring gear. (In other words, with the Lok-Rite, when you are stuck one tire will always go at the same speed as the ring gear & the other will either go at the same speed or faster, like during cornering)
-Jeff

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Post by Alasdair Brass » Sun Sep 21, 2003 3:11 pm

Thanks Jeff,
I have tested this diff and it seems to be about 50 ft lbs. I guess it is up to spec. Now, is it worth putting in??? Hmmm, dunno.

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Post by JAB » Mon Sep 22, 2003 12:03 pm

If you use your jeep as a daily driver in rain & snow I'd recomend against it. (Can easily cause spin-outs on these short, light vehicles.) If you use it for parades, displays, & some 4-wheeling & you don't mind all the effort to install it (for what I consider minimal pay-back) I'd go for it. The limited slip units can give marginally better traction in off-road conditions with minimal risk of breaking a shaft.
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Post by Keith Buckley » Mon Sep 22, 2003 1:18 pm

Not sure whether those posting here are being careful to specify Limited slip vs Full lockers.

The lock right is a mechanical locker, and is excellent in mud and rock, but you WILL break your right rear axle shaft eventually. Usually on a hard right hand turn, on hard pavement, at low inflation (if you have oversize tires). You will also have little or no control in wet, ice , or snow. Massive unpredictable oversteer.

The limited slip will not affect your handling under normal driving conditions. It it nice to have off road, and may actually make it less likely to snap an axle by distributing the torque.
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Post by Bob N » Mon Sep 22, 2003 2:51 pm

Keith, I was thinking of getting one of those lockers but based on what you have written I think that I will just stock with regular 4x4 and carry a come-along and some rope.

The two times I have been really stuck, a locker wouldn't have helped. Managed to get myself hung up on 3 three stumps. Didn't see them in the tall weeds. :cry: ...and then the time I drove into a 6 foot hole of water. Luckly I did hang up before it went straight in. But it was hopelessly stuck.
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Re: Limited slip diffy

Post by Mark 1 » Tue Jan 02, 2018 2:51 am

I am after an LSD [ not a locker ]for the rear axle of my Jeep, does anyone know where I can get one ? I know the original ones are like rocking horse poo to find, so a current after market unit is fine. cheers.

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Re: Limited slip diffy

Post by tamnalan » Tue Jan 02, 2018 10:28 am

No help on that, sorry...

You consider putting a lock rite in the front axle? It together with locking front hubs would be a nice combination, or if you don't want the hubs too, then you could remove the little "pill" in the transfer case so that 2WD-low range is possible.
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Re: Limited slip diffy

Post by Marty, SoCal » Sat Jan 13, 2018 6:22 pm

Herm the Overdrive Guy sometimes has model 25 Power-Loks in stock. He also sells the much more common Dana 27 units with special carrier bearings that allow it to fit the Dana 25.

http://hermtheoverdriveguy.com/d232527- ... oss-shafts

Note the carriers in the 25 and 23-2 are the identical parts.
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Re: Limited slip diffy

Post by markos100 » Sun Apr 07, 2019 4:50 pm

Gents, They are GREAT ! Makes the jeep go on sand, two tracks, hills and loose dirt ( with and without H2O ) Preserving forward momentum keeps all wheels pulling better and avoiding having to "Spin your way out of a mess"
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Re: Limited slip diffy

Post by Marty, SoCal » Mon Apr 08, 2019 9:35 am

Having the extra traction of a tight limited slip or Lockright also can help prevent axle shaft breakage in a situation where a wheel is spinning free in the air or mud then suddenly hits solid ground, a huge shock is transmitted into the axle shaft/s.

In the Power Lock diff, you can re-arrange the plate stacking to allow for a little less action when it's used in the steering axle. Herm the overdrive guy usually has rebuild clutch packs available. Instructions on stacking the clutches for more or less bite are usually in the package.
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Re: Limited slip diffy

Post by OldPappy » Wed Apr 10, 2019 4:22 am

A very Interesting read.

For my project, I have a pair of NOS Marine surplus M38A1 axles. I know the rear axle has a limited slip differential, don't know about the front.
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Re: Limited slip diffy

Post by Marty, SoCal » Wed Apr 10, 2019 5:58 am

Here's instructions for the bigger Dana 60& 70 version, assembly is the same, (less torque on the bolts for the case halves of the smaller 25/27 or 44 units). Note the different arrangement of the clutch stacks that you do depending on the amount of traction you want:

http://clubs.hemmings.com/potomacramble ... 5315-3.pdf

Rebuild kits for the Dana 25. 27 and 30 Power-Lok diffs are the same. 44s kits are different, but available, too.
One of many sources for these:
http://www.alldrivelines.com/ypkd30-pc- ... 5-dana-27/

I'm bringing my GPW with a rear Power Lok up to Plymouth on the 17th, if you see me tooling around in it, stop me and we will find a muddy spot to demonstrate it! 8)
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