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  #1  
Old 06-13-2008, 01:20 PM
rrunnertexas rrunnertexas is offline
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Question 8 3/4 axle lube viscosity

I am about to change the rear end in my 8 3/4" rear axle on my Road Runner. I am also going to change the axle lube to synthetic, although I have had good luck with petrolium lubes.

I have been using 80W90 petrolium based lube for years. When looking at the synthetics available I see that there are several viscosities, 75W-140 and 80W90 to name a few.

Without getting into brand names, etc, what is the advantage or disadvantage of using say 75W-140 vs 80W-90? Is it a big deal in this type of application?

I use a 3.55:1 ratio with a "742" clutch type limited slip. Primary use is long freeway trips and the usual street driving.

Thanks!
David
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Old 06-13-2008, 03:17 PM
crisser crisser is offline
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Iv`e used the 140 wt. before. It`s too heavy, especially in the winter. Also might want to check on the posi manufacturer on what type of oil they want on their clutches. I know Eaton wants you to use dino oil on the older clutch packs.
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Old 06-13-2008, 04:05 PM
peg leg peg leg is offline
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Default Viscosity

I'd go synthetic, for sure, but not 75/140, unless you race.
Two advantages to synthetics. Superior lubrication ,and no need for special lube aditives.
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Old 06-14-2008, 05:00 AM
cudabob496 cudabob496 is offline
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I use 70-90W synthetic in my 8 3/4 496 Cuda
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Old 06-15-2008, 10:32 PM
rrunnertexas rrunnertexas is offline
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O.K., so something in the range of 75W90 would be a better weight for the 8 3/4" in my application/use.

Synthetic lube does not require any friction modifier for the sure grip? Why not? I thought they all needed that stuff.

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Old 06-15-2008, 11:04 PM
namvet67a1f namvet67a1f is offline
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Ever since I ran out of the Mopar skunk-oil ... I have used the Mobil 1 syn.

It HAS that "posi" additive IN it.
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Old 06-16-2008, 10:18 PM
dave5711 dave5711 is offline
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At the dealer i work at we use 75/140 synthetic, AND the additive.

If going with sythetic, there's no reason not to use 75/140 over the 80 90.

It's thinner cold, and thicker hot. better cold lube, and better hot protection.

I've recently put the 75/140 in my own car.
No additive, but I run a spool, not a sg.
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