Rear end diff fluid - Pontiac GTO Forum
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post #1 of 23 (permalink) Old 06-27-2005, 04:32 PM Thread Starter
 
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Hey guy's what is the type of rear end diff fluid that I sould use on the GTO and how much friction modifier do I put in? In getting the Harrop diff cover and I want to have all the stuff I need ahead of time. I would like to put in higher performance fluid but I still want it to meet GM spec. Any help you guys can give would be great.
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post #2 of 23 (permalink) Old 06-28-2005, 04:46 PM
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I just put in Royal Purple 85/140. No friction modifier. Don't know how much you'll need with the new cover. Stock took a little less than 2 quarts.

Rob
04 IBM M6 GTO
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post #3 of 23 (permalink) Old 06-28-2005, 05:23 PM
 
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I use the Royal Purple 75W140 with no modifier, at first I made the mistake of using Valvoline 75W140 synthetic, next day rear got very noisy in turns, even though it said no modifier was needed.
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post #4 of 23 (permalink) Old 06-28-2005, 05:44 PM
 
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Yell at subdriver, he's an Amsoil dealer and that stuff rocks!!!! I personally have Royal Purple, but now that I heard about the Amsoil I'm ordering it on the next change!
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post #5 of 23 (permalink) Old 06-28-2005, 06:31 PM
 
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When I was trying to sell my '01 Corvette, the diff was making a whine that scared away one potential buyer. I posted a question on Corvette Forum and a member told me to put some limited slip additive in the differential. The GM part number is 1052358. I went to a local dealer, got the little four-ounce bottle from the parts department and squeezed some into the filler hole on the diff. No more whine.

I squeezed in the whole four ounces, but about half of that ran back out again. My vast math skills leave me to believe, therefore, that two ounces should've been about right.
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post #6 of 23 (permalink) Old 06-28-2005, 07:07 PM
 
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The actual GTO diff fluid spec is:
"Use GM Part no. 89021809 Axle lubricant 75W-140.
Plus 1oz of friction modifier 7098 GM Part no.89021958"

The stock GTO diff takes just under two quarts.

The AMSOIL Severe Gear Extreme Pressure Synthetic 75w140 meets both specs and does not need the extra limited slip modifier.

I use the Severe Gear 75w90 in my diff without the friction modifier and my diff does not chatter. That said, if your diff does chatter, as mentioned above, adding a bottle (or half bottle) of the friction modifier should quiet it.

AMSOIL does have a limited slip friction modifier:
AMSOIL Slip-Lock Differential Additive

If you plan on doing this yourself, I also find this handy:
AMSOIL Hand Pump



AMSOIL Ordering Information
AMSOIL Preferred Customer Program
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post #7 of 23 (permalink) Old 06-28-2005, 09:21 PM Thread Starter
 
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Well I tried to order a few quarts of the AMSOIL 75-140 and the damn web site would not allow me to create an account to order. Does anyone know were else I can get some from?
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post #8 of 23 (permalink) Old 06-28-2005, 10:42 PM
 
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I got my Royal Purple 85W-140 at my local NAPA dealer. Picked it up when I needed it. No modifier to add and rear end is quiet as a mouse.
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post #9 of 23 (permalink) Old 06-29-2005, 09:00 PM
 
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Quote:
Originally Posted by Braman'sGTO
Well I tried to order a few quarts of the AMSOIL 75-140 and the damn web site would not allow me to create an account to order. Does anyone know were else I can get some from?
Dropped you a PM. I can set you up with a preferred customer account.
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post #10 of 23 (permalink) Old 07-06-2005, 05:22 PM
 
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3 quarts for the Harrop cover.
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