# Rear end diff fluid



## Braman'sGTO (Mar 14, 2005)

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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## Rob (Aug 7, 2004)

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.


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## toddhson (Feb 20, 2005)

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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## GTODEALER (Jan 7, 2005)

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! :cheers


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## GM Kid (Mar 21, 2005)

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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## Subdriver (Dec 28, 2004)

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

:cheers 

AMSOIL Ordering Information
AMSOIL Preferred Customer Program


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## Braman'sGTO (Mar 14, 2005)

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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## Xman (Oct 31, 2004)

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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## Subdriver (Dec 28, 2004)

Braman'sGTO said:


> 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. :cheers


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## 2005Goat (Mar 21, 2005)

3 quarts for the Harrop cover.


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## Braman'sGTO (Mar 14, 2005)

thanks, I picked up 4 so I wont be short either way


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## Braman'sGTO (Mar 14, 2005)

OK, the Harrop rear end diff cover was just installed and I used the Amsoil severe 75-140 gear oil, now I have a noticable amount of gear wine from the rear end diff. Is this normal when you have the Harrop rear end diff cover and a higher performance gear oil in it? Do any of you guy's with the same setup have more wine from the rear end diff? Will adding some friction modifier help reduce any of the noise?


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## GTODEALER (Jan 7, 2005)

Braman'sGTO said:


> OK, the Harrop rear end diff cover was just installed and I used the Amsoil severe 75-140 gear oil, now I have a noticable amount of gear wine from the rear end diff. Is this normal when you have the Harrop rear end diff cover and a higher performance gear oil in it? Do any of you guy's with the same setup have more wine from the rear end diff? Will adding some friction modifier help reduce any of the noise?


Post after you've added the modifier, if you still have a noise... then we will address then, but to answer your question... no, noise isn't normal. :cheers


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## Braman'sGTO (Mar 14, 2005)

well I just got my car fixed it was a simple matter of pitting some washers on the ABS sensors they were rubbing on the half shafts. No gear noise or other noises, the new diff cover is the shiznit, there is less rear end body roll and plants the rear much firmer. the rear end of the car no longer feels mushy when accelerating and turning, cant wait to change out the swaybars the hotchkis or slp.


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## GTODEALER (Jan 7, 2005)

Braman'sGTO said:


> well I just got my car fixed it was a simple matter of pitting some washers on the ABS sensors they were rubbing on the half shafts. No gear noise or other noises, the new diff cover is the shiznit, there is less rear end body roll and plants the rear much firmer. the rear end of the car no longer feels mushy when accelerating and turning, cant wait to change out the swaybars the hotchkis or slp.


If you really want a difference, change the rear cradle bushings out with Harrop polyurethane ones, with what you have + a rear sway bar your wheel hop and general feel of the car will be sooooo much better! BTW, I sell the cradle bushings for $159.00 and I have 2 sets in stock! :cheers


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## 2005Goat (Mar 21, 2005)

I installed the Harrop cover and the bushings when I changed my gear ratio. I haven't been to the track with this setup yet but I will let you guys know how well this helps with wheel hop. I'm going to the track tomorrow night if it's not raining here.


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## Braman'sGTO (Mar 14, 2005)

the only way I'll have to worry about wheel hop is if I end up in the grass, im just planning on running it on road courses. what I would like to do is improve my handeling a little more, I want to pull 1g on a skid pad with the stock wheels and tires. Does anyone know what kind of brake upgrades you can do to an 05 and have it work with the stock 17" wheels.


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## GTODEALER (Jan 7, 2005)

2005Goat said:


> I installed the Harrop cover and the bushings when I changed my gear ratio. I haven't been to the track with this setup yet but I will let you guys know how well this helps with wheel hop. I'm going to the track tomorrow night if it's not raining here.


That plus the rear sway bar (SLP) completely stopped one of my customers wheel hop issues!! :cheers


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## goatsandstrats (Jul 2, 2005)

GTODEALER, can you confirm or deny a statement by my local dealer (who is has been pleasant to deal with on a previous pontiac purchase - used Grand Am) concerning my 05 GTO... 

When asked about changing diff fluid out to synthetic, he said around 7.5 k miles but added it had synthetic in it. 

Do the 05's come with synthetic diff fluid.

What is your recommendation of changing it out. 

Side note.. At what mileage would changing out the M6 fluid to synthetic.

And any suggestions for brands of syn fluids in tran and diff.

Just want some advice from another source as local dealer has only sold a half dozen or so of the 05's and not many 04's.

I'm trying to take all of this advice in and make a good decision. 

I'd rather change fluids early than too late.

Thanks


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## Braman'sGTO (Mar 14, 2005)

do you know if the eurethene cradle buchings work with the BMR sub frame connectors? Im not quite sure if I want to get the subframe connectors yet just wondering


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## LYNMUP (Nov 26, 2005)

Does the rear diff use a gasket or an "O" ring? I want to put RP in it but need to know if I need gasket of not! Also, do you have to remove the whole cover to drain it?


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## LYNMUP (Nov 26, 2005)

Just found a link that answered my questions. Normal RTV will do it!


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## Rob (Aug 7, 2004)

You don't have to pull the cover at all. There is a drain and fill plug on the cover.


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