Diff gear oil viscosity

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If you have no leaks run a 75W-140 syn lube if you desire thicker. The 85W-140s are much thicker than the 75W-140 when cool.
 
Is this a Ford? Regardless of the manual I believe all Ford diffs have been back spaced to 75-140 synthetic across the board. Any of the major brands will give you good service.
 
Not sure down there. Was for me in NE. Made the truck sluggish, MPG went down by 2. Clunky in and out of gear. And counter to what i thought, it would drip at the drive shaft seal. Couldn't breath as well though the vent? no idea really. All of this went away going back to 75w90
 
Originally Posted By: SOHCman
Is this a Ford? Regardless of the manual I believe all Ford diffs have been back spaced to 75-140 synthetic across the board. Any of the major brands will give you good service.


1991 Chevy Caprice .
 
Originally Posted By: LeakySeals
Not sure down there. Was for me in NE. Made the truck sluggish, MPG went down by 2. Clunky in and out of gear. And counter to what i thought, it would drip at the drive shaft seal. Couldn't breath as well though the vent? no idea really. All of this went away going back to 75w90


Did it do that both winter and summer ? What is the winter temps in NE ?
 
I had 85w140 in my '85 GMC's 14-bolt full-floating rear end for about 30K, and when I drained it out last year I wasn't particularly impressed - dark film on everything and what looked like scuffing on the gear teeth. Put in Amsoil 75w110 and the difference was surprising. I think it's safe to say Amsoil severe gear 75w90 is so much better than what came in your car that it's the last thing that'll cause wear in the axle.
 
Originally Posted By: WyrTwister
Originally Posted By: LeakySeals
Not sure down there. Was for me in NE. Made the truck sluggish, MPG went down by 2. Clunky in and out of gear. And counter to what i thought, it would drip at the drive shaft seal. Couldn't breath as well though the vent? no idea really. All of this went away going back to 75w90


Did it do that both winter and summer ? What is the winter temps in NE ?

I noticed a drop in MPG over the summer. Some mild clunking but not enough to take action. Winter I just didn't like the way the drive train felt. Summer is 75-100f avg 80s. Winter is -10F to 30F. Avg 20s.
 
Sounds like you may be about 10F colder than we are . And we may be about 10F warmer than you are .
 
AVERAGE summer , it is not unusual to hit 100F a fair number of times . 110F a few times .

AVERAGE winter , 20F quite a bit , 10F a fair number of times . 0F a few times and not many times a winter , below 0F . Around -10F or a little lower , is about the coldest I remember .

If not average , all bets are off .
 
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