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Discussion Starter #1 (Edited by Moderator)
I did an 8.8” swap in my swap build, cleaned the inside of the differential and carrier unit. Filled it back up with synthetic gear oil and fiction modifier. With the rear wheels on the ground I can turn the driveshaft through the transmission but the wheels won’t turn. I can heard something in the differential, which I’m thinking is the LSD clutches slipping. I’m thinking of rebuilding the LSD with new clutches and trying to load them a little tighter so they will have more bit. Any advise would be great, unless the factory LSD aren’t worth a ****. Or maybe upgrade to a Yukon dura-grip lsd or an Auburn??
 

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Discussion Starter #3
My father and I have setup and rebuild several differential’s. I did the front/rear diff’s in my super duty, regearing and rebuilding the LSD in it. 50k miles ago with no issues or problems to speak of
 

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Unless something is assembled wrong one of the axles should turn when you turn the driveshaft. The LSD just applies force to the other axle.
The Ford 8.8 LSD's are pretty reliable.
You state that you and your father have rebuilt differentials previously. Has he taken a look at it?
 

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Gears and Differentials
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When you turn the drive shaft at least one of the wheels should turn. If not then something in the rear end is broke. The clutches have nothing to do with that. The Traction Lock in the 8.8 is a good differential and clutches are not too difficult to replace. I stack them different and add another friction disc when I build them. Don't use an Auburn. They suck.
 

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Discussion Starter #6
When the truck is up on the lift the wheels spin fine but fiction on them they don’t. I haven’t opened the differential back up to look yet, to see what might be the wrong.
 

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The rear end will still drive the truck if the factory LSD wears out. So one should always turn when the driveshaft is rotated. You might have to hold one still to see that happen.
 

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Discussion Starter #8
I’m heading out now to pull the differential cover off to see what’s going on. I will let you know what I find. Thanks oldeerslayer you have always been helpful to me on these forums
 

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Gears and Differentials
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Yes, at least one wheel should be turning when you turn the drive shaft. If they turn in opposite directions or only one turns then the clutches are worn out. The 8.8 clutches wear out quick when people don't keep the air pressure equal in the tires or if they run different size tires on the back. There are several different types of clutches for the 8.8. Some have long ears and some have short. Check yours before ordering. If you have the long ones I have a set on the shelf that's been there for a long time.
 

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Discussion Starter #11
I replaced the clutches with Carbon Fiber ones, according to the specs I found .635 was the worn out limit and mine measured .623. I still don’t understand how one wheel will drive if the clutches are shot. The power has to go through the clutches to engage the wheel or axles. Everything else seems to be fine, backlash checked good. The ring and pinion gear look good and the depth checked good. So hopefully my problem will be fixed.
 

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Power does not go through the clutches to drive the truck. Power goes through the gears inside the differential to the axles. The clutches cause friction between the axle gears and the differential case to try to prevent the axle gears from turning independent from the case, which would allow one tire to spin without the other. The only difference between a limited slip differential and a standard differential is the clutches. If you removed the clutches from a limited slip differential the truck would still drive like it had a standard differential.
 
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Old Fart
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Don't leave us hanging, what did you find?

Usually, if you turn the driveshaft and neither wheel turns you have a stripped gear. Back when I had a 69 Bronco with a 9-inch limited-slip I found that they had smaller spider gears to make room for the clutches and after stripping them twice during hard launches I switched to a Detroit locker. I'm not saying the 8.8 is the same but it's a possibility.

I'm not a fan of Limited slips because of reliability when you drive as aggressively as I do so for off-road and drag racing I use Detroit lockers and for road racing, front diffs, and mostly street use I use a Tru-Trac and have never had to perform any maintenance other than lube changes.
 

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Gears and Differentials
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The 8.8 doesn't have that split gear like the 9 inch. The 9 inch Traction Lock is a piece of junk.
 

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Old Fart
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The 8.8 doesn't have that split gear like the 9 inch. The 9 inch Traction Lock is a piece of junk.
I would hope they changed from that crappy design. My little stock 302 broke that POS twice within 4 months so I would imagine a 427 would tear one up at idle. 🤣
 

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Nope. It's still the same design in the 9 inch. The side cover is steel now instead of cast iron, but the internal parts are the same.
 

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Discussion Starter #17
I tore it down and replaced the LSD clutches with carbon fiber ones. I checked the gears and backlash, everything looked good. I reassembled everything and refilled it with oil/friction modifier. I have checked to see if my problem is fixed yet cause I have the truck apart for paint. Once I verify the problem is fixed I will let you all know.
 

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Most clutch plate type LSD's like conventional oils. Synthetics can be too slippery and more so when you add friction modifier. Most good grade GL-5 lubes are formulated for LSD's.
 
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