Rear end diff fluid

Braman'sGTO · Jun 27, 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.

Rob · Jun 28, 2005

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.

toddhson · Jun 28, 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.

GTODEALER · Jun 28, 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

GM Kid · Jun 28, 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.

Subdriver · Jun 29, 2005

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

Braman'sGTO · Jun 29, 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?

Xman · Jun 29, 2005

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.

Subdriver · Jun 30, 2005

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

2005Goat · Jul 6, 2005

3 quarts for the Harrop cover.

Braman'sGTO · Jul 6, 2005

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

Braman'sGTO · Jul 7, 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?

GTODEALER · Jul 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

Braman'sGTO · Jul 7, 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.

GTODEALER · Jul 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

2005Goat · Jul 8, 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.

Braman'sGTO · Jul 8, 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.

GTODEALER · Jul 8, 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

goatsandstrats · Jul 8, 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

Braman'sGTO · Jul 8, 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

Rear end diff fluid

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