Limited slip diffy

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Alasdair Brass
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Limited slip diffy

Post by Alasdair Brass » Thu Aug 21, 2003 9:51 pm

Hi guys,
I have been given a limited slip diff for a jeep. Has anyone fitted one to the rear axle? Any improvement off road? I'd be interested to hear.

Thanks in advance.
Al
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Post by Frank » Thu Aug 21, 2003 11:46 pm

Hi Al.
I think that Anders in Sweden (If I remember correct it was him you did the Boat ride with) did that on his jeep a few year back.
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Post by Glen » Fri Aug 22, 2003 3:59 am

Major difference for the good. It is very possible to have "2 wheel drive" while in 4wd, one front wheel spinning, one rear wheel spinning and jeep going nowhere. The posi in the rear helps prevent this. I have seen 2 jeeps, one with, one without, make a slow climb on a hill. The non-posi did not make it up. The posi did without breaking a sweat.

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Post by kevin c » Sun Aug 24, 2003 2:50 pm

A friend broke the front axle of his unmodified CJ3B, so when I decided to install a limited slip I got conservative and put it in the rear of my stock M38A1. It tends to plow in deep mud as the front end quits steering before the back end is done pushing but if I get stuck I can usually put it in reverse and get out easily. You'll know the differance right off. I bought one of the gear drive models, not sure who makes them today. Lockers are more hard core but a bit more dangerous on vehicles that tend to tip over. Another in the front axle would be pretty wild, but awfully tough on drive components.

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Post by Alasdair Brass » Mon Aug 25, 2003 2:44 pm

Thanks for the response guys, I will have to decide whether I should try it, just for fun.

Regards
Al
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Post by JAB » Mon Aug 25, 2003 7:05 pm

Are you sure it will fit your aplication? I've used & installed many over the years & I'm not aware of any that fit the MB/GPW Spicer 25 or 23-2. I know that some were made many many years ago but these are no longer available, nor are the parts that are needed to rebuild them. Are they being made again?

BTW, my experience with them over all has been this: A true "locker" works great but can easily cause a lot of broken parts because traction becomes the limiting factor. If you have 100% traction (no differentiation) it's easy to exceed the design perameters of the components & something will break (usually an axle shaft), especially with the torque multiplication of low range. With the limited slip however, in my experience, after a short "break-in" period it "slips" so easily as to not be worth the bother of installing it, until it wears out & really sticks & slips unpredictably. However; there are a HUGE amount of variables involved here. Without writing a novel, if you leave the tires & engine alone & don't get too crazy with the go pedal you'll probably either be very happy with it or never notice the difference. Every vehicle I've owned with the exception of my MB & GPW's has had a limited slip or a true locker (locking differential). With the exception of my '72 Grand Pri, '96 Grand Cherokee & '01 Ram 3/4 ton PU (which use limited slips) I installed the "traction enhancing" differential myself (many jeeps of various sizes & several brands of true lockers & limited-slips). About the only time I notice that its there is when it starts to wear out & gives me a case of what the manual calls "slip-stick condition". This is when they get dangerous on icy roads because they actually "work" better & can cause you to unexpectedly fishtail on a turn if you're not in 4WD. It's one of those things you swear at or swear by! In my trail-rig I have the ARB air-locker which is great because I can turn it off while on the road.

If you actually do have one that'l fit your aplication you'll need a "friction enhancer" to add to the gear oil. I've found that the Ford version works best & is also the least expensive. Also, the Amsoil gear oil that I use claims that you do not need that additive & I would agree with that.
-Jeff

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Post by Alasdair Brass » Mon Aug 25, 2003 9:50 pm

Hi Jeff,
Thanks for your comments. The diff came out of an MB and is a modified Spicer one ex a Aussie Ford Falcon. I was told there was one from a DitchWitch that fits without modification too.

The guy that had it fitted told me his MB went much better of road but was not so good with one in the front as well, no steering in slippery conditions. He took the one I have out of the front and left the rear one in. I'll thunk about it!

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Al
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Post by Bob N » Tue Aug 26, 2003 2:23 am

The device you mention it appears is in fact still in production (or back in production) as the LOCK-RIGHT PERFORMANCE LOCKERS. Not sure who all sells these but it is available from www.vintagejeepparts.com The on line catalog lists -

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FRONT 1945-64 CJ'S DANA-25 & 1964-71 CJ DANA-27 2115 319.95

If it fits the DANA 25 it should fit the 23-2 ?
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Post by JAB » Tue Aug 26, 2003 12:49 pm

If it fits the DANA 25 it should fit the 23-2 ?
I always thought they were the same but never "proved" it. If anybody knows for sure I'd like to know. Don't have the time right now to disassemble two side by side just to compare. :?
-Jeff

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Post by Sean Bathrick » Thu Sep 11, 2003 2:20 pm

I sure hope they are interchangeable. I just got the ring and pinion for a Dana 25 to replace the missing one in my 23-2. I was told that only the axle shafts were different, obviously. BTW, I was going to comment on this post anyway. My M38A1 is a USMC model and supposedly, they had different things than the run of the mill A1's. Undercoating was one, which is a major pain in the !@#%& to get off when you are trying to go to bare metal to fix a dent, or just for a nice finish on the frame. The other was a Dana Powr-Loc front end, Dana 25, still used in the M38A1 if memory serves. I was looking for parts a while back and saw Dana was still making the Powr-Loc for the 25. I think you'll be happy with the results off road. Any sort of limited slip, posi trac, or whatever is always helpful and something nobody knows is there except you.
Sean

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Post by Alasdair Brass » Tue Sep 16, 2003 2:10 pm

Hi Guys,
I've had a good look at this Spicer diff, does anyone know the test procedure? It is a plate type, 3 x lugged plates per side. and spider shafts are ramped. Everything looks to be in good condition but I figure there must be a test.

Best regards
Al
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Post by Sean Bathrick » Tue Sep 16, 2003 3:41 pm

Hi Al
I never really got too involved in rebuilding axles and being in the middle of my 23-2 rear axle right now I know why. But what you are looking to test is your breakaway pressure. The breakaway pressure is basically the amount of torque required to make the plates and disks slip. In other words it's the torque that is built up in your differential when the tires are trying to go different distances (one spinning and one not). What you do to check the actual torque is, jack it up, put a torque wrench on one axle shaft and keep the other from rotating, usually a friend holding it tight. You then apply torque using the wrench. The axle won't move until a certain pressure is reached. When this happens the axle will start to rotate. If I remember right, if the breakaway pressure too high you won't get any differential action at all between the 2 wheels and end up with basically a welded diff. And this situation isn't recommended for our little full floating axles as you know. The pressure should be around 50 to 60 ft/lbs, again, memory, but each manufacturer should have specs on their own product, and whether it is a street or off-road application. I wasn't with my friend when he tested his out with the wrench and all. I just heard all about how much of a pain it was to set. The extent of my testing was jacking it up, locking one wheel and turning the other, just to see that it was working, which it's not. I am needing to rebuild the limited slip in my M38A1 and have nightmares over all the shimming that may need to be done to adjust the breakaway. I am postive that a shop that specializes in gearing could test it all out for you. I hope I answered your question.
Sean

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Post by JAB » Tue Sep 16, 2003 4:32 pm

Although I don't have the specififcs, that test sounds about right, from memory anyway. I'll try to look it up later when I get home. However, your comment about shiming to obtain the break-away specs does not ring a bell with me. Although I have a very low opinion of limited-slip type differentials (I prefer true "lockers" that actually "do" something, unfortunately including breaking parts) I have re-built several Spicer brand power-loks & trac-locks over the years. In all cases it was a matter of replacing worn "clutch" discs & Bellvue springs. All of the shims that I encountered were soley to position the ring & pinion to obtain the proper operating relationships, they had no relationship what-so-ever to the breakaway torque.

BTW, your M38A1 uses an older version of the extremely popular Dana 44 & a variety of limited slips & lockers are available for it. The catch is that you probabaly have a 10 spline unit & most of the available traction enhancing devices require the use of 19 or 30 spline axles. Sometimes you can swap side gears though.
-Jeff

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Post by Alasdair Brass » Tue Sep 16, 2003 7:56 pm

Thanks for answering men. This diff does offer some resistance when one side is held and the other rotated. I feel that it is likely to be on spec but I will measure it. My big problem is that I am not sure at all what it came from. I am told that this type was never fitted to a Ford Falcon so what I was previously told is not correct.

After studying the design, I can see that my previous understanding of how they work is wrong. With one wheel off the ground, one of these diffs is of no more use than a regular diff. It needs some driving resistance to force the clutches into gear so both wheels need to be on the ground and driving to some extent. It is amazing, asking around, that few people who have worked in the car industry for years have any real knowledge of the workings!

Thanks again,
Al
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Post by JAB » Tue Sep 16, 2003 8:02 pm

With one wheel off the ground, one of these diffs is of no more use than a regular diff. It needs some driving resistance to force the clutches into gear so both wheels need to be on the ground and driving to some extent.
Correct. In fact, lightly applying the brakes when in a jam can occaisionally get it to "work" enough to get you unstuck.
-Jeff

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