Rear differential “popping”
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Mountain Pass
Joined: Apr 2012
Posts: 215
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From: Charlotte, NC
Rear differential “popping”
1995 f250 5.8L auto with C4 limited slip differential. 2wd, 90k miles. I recently changed the rear diff fluid, replacing with 75w90 synthetic that included the friction modifier. Since then, the diff “pops” when turning sharp, suggesting the diff isn’t “slipping”. In fact, the left rear tire locked up but then mysteriously came free when re-opened the diff to examine. I couldn’t see anything mechanically wrong inside- no broken teeth or seemingly worn gears. After simply twisting and turning each tire, the diff freed up and would spin, albeit tires spun in same direction (I thought they would have spun opposite). Anyway, resealed diff and refilled with fluid. Still making the “popping” noise in tight turns. Any ideas or suggestions as to cause? Thanks.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
A wheel locking up suggests something is wrong in the diff or with the brakes, and since you didn't see anything obviously wrong in the diff next step is to pull the drums off for a look.
Logistics Pro
Joined: Aug 2010
Posts: 3,716
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From: Chillicothe
As stated add more friction modifier, and that SHOULD help. But I have had personal experience with a gm limited slip that was never happy with synthetic fluid. Tha specific vehicle wanted old Dino sauce 80w90 and a friction modifier in order for it to not chatter in turns.
Hotshot
Joined: Jul 2020
Posts: 10,501
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From: Near Salt Lake City
I just put a refreshed 12 bolt 4.11 posi in a 68 Camaro
I used conventional 80w90 and 2 tubes of GM modifier
Not real familiar with the GM stuff, I am hoping 2 tubes with my conventional fluid will be okay
I used conventional 80w90 and 2 tubes of GM modifier
Not real familiar with the GM stuff, I am hoping 2 tubes with my conventional fluid will be okay
Hotshot
Joined: Jun 2015
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I recently changed the rear diff fluid, replacing with 75w90 synthetic that included the friction modifier….In fact, the left rear tire locked up but then mysteriously came free when re-opened the diff to examine.
..albeit tires spun in same direction (I thought they would have spun opposite). .
..albeit tires spun in same direction (I thought they would have spun opposite). .
Um.. yeah. Open differentials spin in opposite directions. Limited slip and lockers spin in the same direction.
Hotshot
Joined: Jul 2020
Posts: 10,501
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From: Near Salt Lake City
After adding another tube of friction modifier you take it to a parking lot and do a few figure eights
That will work / exercise the clutch packs, and get the added friction modifier worked into the clutches
Then you can re evaluate
That will work / exercise the clutch packs, and get the added friction modifier worked into the clutches
Then you can re evaluate
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Hotshot
Joined: Jul 2020
Posts: 10,501
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From: Near Salt Lake City
The labels always say you need no additional modifier
Hell, Ford says you only need one tube of theirs (the real stinky stuff) which is flat *** wrong
Hell, Ford says you only need one tube of theirs (the real stinky stuff) which is flat *** wrong
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Hotshot
Joined: Jun 2015
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Geez. That is the smallest I could make it.
Hotshot
Joined: Nov 2017
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From: Northern Ontario
I can remember having to add a couple on GM axles, a couple of times… don’t ask me what axles they were, can’t remember off hand. 12 or 14 bolt, and D36 iirc.
Same issue on a 350 several years ago as well, 10.5. One bottle added freed everything up.
I used some of that gear oil ‘with additive’ in my ‘96, I put in a bottle of it as well. I have no idea what concentration the oil has for the additive.
Same issue on a 350 several years ago as well, 10.5. One bottle added freed everything up.
I used some of that gear oil ‘with additive’ in my ‘96, I put in a bottle of it as well. I have no idea what concentration the oil has for the additive.
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