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Old 07-02-2013, 10:08 PM   #1
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LSD/POSI question

I have a limited slip 8.8. It pretty much always turns both tires no matter what. The other day I got stuck and only one rear tire was turning. My front is locked and was turning great. The rear however I could clearly see that one was trying to move and would spin here and there, but overall would not turn as much as expected. My understanding has always been that with a Posi or Limited slip the ratio is something like 60/40. So the tire that spins may get 60% of the power rotation, but that the other 40% would go to the tire with traction and turn it no matter what. This rear has been awesome, but I have beat the living crap out of it. Not sure if I need to replaced the little disks in there, or if I am just noticing this for the first time since it happened to stop spinning on the driver side. Some help would be great. I would also add that I have a Riddler diff cover so it does take a little more fluid than stock. Only about 1/2-3/4qt more, so I figured 1 bottle of limited slip additive would still be enough.

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Parts already gathered for assembly: 2001 Ford 302, 1990 Mustang GT 5.0 ECU and wiring, NP435, NP205, Pair of axles from 04' F350 SuperDuty (Sterling 10.5 Posi rear, Dana 60HP Front-Both Disk Brakes 3.73 Gears), 37" H1 Tires, 9" lift TJ Coils for 2 link conversion in front, Stage 2 Clutch Kit, 3 Row Aluminum Radiator, Chevy Astro Steering box (4" front Stretch), XJ Rear Leaf Springs (6" Rear Stretch), and lots more.
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Old 07-02-2013, 10:24 PM   #2
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I just got my 8.8 and tore it down to look inside. Just from what I remember from looking at it and from what I've read about LSDs I think it might be time to rebuild it like your thinking.

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Old 07-02-2013, 10:35 PM   #3
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The kit from frpp is ok. It will bring it back to moderate for mud/snow wheeling.

I would skip the additiclve on the next go around. It actually makes the clutches slip more. It isnt to male more traction, rather to help prevent the discs from chattering under locking and unlocking (which rarely happens ). Back in my mustang days switching the steels/plates around and running the ford performace packs without additive made for a nice tight lsd.
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Old 07-02-2013, 10:41 PM   #4
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Quote:
Originally Posted by Norcal_Chris View Post
The kit from frpp is ok. It will bring it back to moderate for mud/snow wheeling.

I would skip the additiclve on the next go around. It actually makes the clutches slip more. It isnt to male more traction, rather to help prevent the discs from chattering under locking and unlocking (which rarely happens ). Back in my mustang days switching the steels/plates around and running the ford performace packs without additive made for a nice tight lsd.
That is what I will do then unless someone has a better suggestion. I would put in a locker, but I live in the city and kill tires too fast already rotating them through my front with a Spartan in it. It seems I have to rotate every 1000 miles to keep them even. I couldn't imagine how fast I would go through them if I put a locker in the rear. It just sucks I cant afford to drop $1200 in my rear right now to buy a selectable and have a pro install it.

Or I guess I should say for the small gain there are things way higher on the list.
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Complete rebuild axle/engine/everything swap in progress:
Parts already gathered for assembly: 2001 Ford 302, 1990 Mustang GT 5.0 ECU and wiring, NP435, NP205, Pair of axles from 04' F350 SuperDuty (Sterling 10.5 Posi rear, Dana 60HP Front-Both Disk Brakes 3.73 Gears), 37" H1 Tires, 9" lift TJ Coils for 2 link conversion in front, Stage 2 Clutch Kit, 3 Row Aluminum Radiator, Chevy Astro Steering box (4" front Stretch), XJ Rear Leaf Springs (6" Rear Stretch), and lots more.
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Old 07-02-2013, 11:04 PM   #5
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Quote:
Originally Posted by OverkillYJ View Post
That is what I will do then unless someone has a better suggestion. I would put in a locker, but I live in the city and kill tires too fast already rotating them through my front with a Spartan in it. It seems I have to rotate every 1000 miles to keep them even. I couldn't imagine how fast I would go through them if I put a locker in the rear. It just sucks I cant afford to drop $1200 in my rear right now to buy a selectable and have a pro install it.

Or I guess I should say for the small gain there are things way higher on the list.
I just re-read what I wrote now that I am home at the computer.


When I had the 8.8 in for the few months I used it it worked pretty well. I definatly noticed that there was a LSD in the back. Sure on rocks with a tire in the air it would spin, but coupled with the spartan in the front it worked great. All i did for mine was pull it all apart and look at the clutches. My diff was from a 99 explorer with low miles and you could tell because the clutches looked great. I just slapped it all back together with some plain gear oil and drove it. No chatter or issues.

If you wanted to get into the switching clutch/disc orientation and such, there is a good youtube video showing the best reccomended stack of plates to run.
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