# Rear end



## TxSoldier6.0 (Nov 4, 2008)

I'm hearing different stories about the right fluid for the rear end in my 05 goat Ive heard royal purple is the only product that comes ready to go and that anything else I buy id have to add friction resistor or something like that any advice ?


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## GTO JUDGE (May 14, 2005)

TxSoldier6.0 said:


> I'm hearing different stories about the right fluid for the rear end in my 05 goat Ive heard royal purple is the only product that comes ready to go and that anything else I buy id have to add friction resistor or something like that any advice ?


Some have said RP comes with it in. The manual clearly states to use a specific friction modifier for this rear. There are FM's out there but this rear end is GM modifier specific.


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## TxSoldier6.0 (Nov 4, 2008)

Can I get it at advanced or do I have to go to a dealer ? Do you know what exactly it's called lol sorry for all the newbie ?'s I just don't want my rear end failing cuz I put the wrong stuff in it


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## GTO JUDGE (May 14, 2005)

TxSoldier6.0 said:


> Can I get it at advanced or do I have to go to a dealer ? Do you know what exactly it's called lol sorry for all the newbie ?'s I just don't want my rear end failing cuz I put the wrong stuff in it


SAE 75W-140 GL-5 Synthetic Gear
Oil (GM Part No. 89021809). With a
complete drain and refill add 1 oz.
(25 ml) of Limited-Slip Differential
Friction Modifier 7098
(GM Part No. 89021958).

Advanced Auto won't have it. A GM dealer should.


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## svede1212 (Nov 1, 2005)

It's called type F friction modifier. An uninformed counter person will tell you that's a Ford modifier and try to sell you the GM type. He would be wrong. It's type F. According to the rear end manufacturer they recommend that dino oil is used and not synth like RP is. Torco 85-140 RGO, 2oz modifier or 4 oz if you have the Harrop cover is the best stuff.


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## GM4life (Mar 18, 2007)

TxSoldier6.0 said:


> I'm hearing different stories about the right fluid for the rear end in my 05 goat Ive heard royal purple is the only product that comes ready to go and that anything else I buy id have to add friction resistor or something like that any advice ?


Royal Purple is a hit and miss in these touchy rear ends. GM stuff(JUDGE listed) or Torco is your best bet.


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## TxSoldier6.0 (Nov 4, 2008)

GTO JUDGE said:


> SAE 75W-140 GL-5 Synthetic Gear
> Oil (GM Part No. 89021809). With a
> complete drain and refill add 1 oz.
> (25 ml) of Limited-Slip Differential
> ...


I looked this up on the GM website it says this part number has been superseded


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## TxSoldier6.0 (Nov 4, 2008)

GTO JUDGE said:


> SAE 75W-140 GL-5 Synthetic Gear
> Oil (GM Part No. 89021809). With a
> complete drain and refill add 1 oz.
> (25 ml) of Limited-Slip Differential
> ...


Ok just left the dealership, turns out the oil and friction modifier have been discontinued they've come out with an all is one bottle this new GM part # is 88862624 

This new bottle says on the front contains limited slip friction modifier but its not 75w-140 it is now 75w-90 is this because they already added the FM the lady behind the counter is "certain" this is the new product but to be completely honest I trust strangers with GTOs more than these people lol


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## GTO JUDGE (May 14, 2005)

TxSoldier6.0 said:


> Ok just left the dealership, turns out the oil and friction modifier have been discontinued they've come out with an all is one bottle this new GM part # is 88862624
> 
> This new bottle says on the front contains limited slip friction modifier but its not 75w-140 it is now 75w-90 is this because they already added the FM the lady behind the counter is "certain" this is the new product but to be completely honest I trust strangers with GTOs more than these people lol


What did the Service manager say about it?

I googled up the response you got and from what I am reading is what the woman told you is correct.


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## TxSoldier6.0 (Nov 4, 2008)

Ok sounds good I believe she was the service manager lol FYI it's about $22.50 a quart but I figure it's well worth it rather than a whole new rear end. How often do y'all usually change your diff fluid I'm used to old 4x4 s where ya don't change it till it leaks lol


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## shadyhaven (Sep 19, 2010)

well i must be lucky because i just bought the old 75-140 and the fm right from the dealer. the fm says right on back of bottle, developed for gto. they can search the nearest dealer that has it in stock.


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## TxSoldier6.0 (Nov 4, 2008)

I mean the old stuff is still out there and there gunna sell it until it runs our but if u look your part numbers up on the GM website it even says there discontinued.


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## shadyhaven (Sep 19, 2010)

really? that wouldnt be why i said i got lucky would it? or why i would tell others how to find the old stuff? the 70-90 IS NOT a direct replacement for the gto. it IS the replacement for the corvette. the old stuff is the correct fluid for our diff. the new stuff doesnt have the correct fm and is too thin. from what i have read, torco is the next best thing. if you research the new fluid in gto rear ends you will find alot of negative experiences after 10k miles. i am on my 4th gto and have changed alot of fluids and talked to alot of gm techs.


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## TxSoldier6.0 (Nov 4, 2008)

So pretty much theres no "right" fluid anymore ?


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## shadyhaven (Sep 19, 2010)

the old stuff is it. torco is the only one that i havent heard of any problems. they also have a type f fm, which is the correct stuff. this is what i will be switching to when my gm stuff is gone. amsoil wont even recommend their own products and will tell you to call the dealer. go figure. just call a dealer and have them search for the nearest stocking dealer and buy a bunch!


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## TxSoldier6.0 (Nov 4, 2008)

So if I can't find the old stuff just get torco and f fm where can I find those


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## 87GN06GTO07IRL (Aug 10, 2009)

TxSoldier6.0 said:


> Ok just left the dealership, turns out the oil and friction modifier have been discontinued they've come out with an all is one bottle this new GM part # is 88862624
> 
> This new bottle says on the front contains limited slip friction modifier but its not 75w-140 it is now 75w-90


This is the correct fluid. People complained of rear end noise so they switched to a thinner fluid to stop that. It protects better cold and is the same when hot. A thick 140 fluid is not needed.


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## TxSoldier6.0 (Nov 4, 2008)

Ok thanks for all yalls help I think I am gunna go with the new stuff I be sure to keep an eye on it and give some feedback


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## YellO5LS2 (Jan 9, 2011)

87GN06GTO07IRL said:


> This is the correct fluid. People complained of rear end noise so they switched to a thinner fluid to stop that. It protects better cold and is the same when hot. A thick 140 fluid is not needed.


I thought the first digits were the cold-flow numbers. I could be wrong, but I'm pretty sure the 75w-140 and the 75w-90 have the same flow at cold temps and different ones once hot. Not trying the sound like a know it all - like I said, I could be wrong:lol:

I'm a walking spokesperson for AMSOIL cause my dad sells it and I can honestly say that they make the BEST lubricants money can buy. Mobil 1 is baiscally elephant pee in my opinion and the stuff GM suggests is a nice way of ONLY getting 150,000 problem-free miles out of your engine, trans, etc. I'd rather put 1,000,000 miles on the car, personally. The differences from AMSOIL are obvious from the second you start your engine.

I changed out the diff with AMSOIL 75w-140 and added their friction modifier because GM discontinued theirs. I wasn't going to put a non-recommended viscosity in the rear-end even though the dealer changed the part number. My differential was already quiet even with the stock gear oil, but since I changed the fluid it's even better - smoother - it's like there's no resistance at all anymore.


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## d50h (May 31, 2009)

order directly from torco


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## IcemanGTO (Mar 2, 2011)

YellO5LS2 said:


> I thought the first digits were the cold-flow numbers. I could be wrong, but I'm pretty sure the 75w-140 and the 75w-90 have the same flow at cold temps and different ones once hot. Not trying the sound like a know it all - like I said, I could be wrong:lol:
> 
> I'm a walking spokesperson for AMSOIL cause my dad sells it and I can honestly say that they make the BEST lubricants money can buy. Mobil 1 is baiscally elephant pee in my opinion and the stuff GM suggests is a nice way of ONLY getting 150,000 problem-free miles out of your engine, trans, etc. I'd rather put 1,000,000 miles on the car, personally. The differences from AMSOIL are obvious from the second you start your engine.
> 
> I changed out the diff with AMSOIL 75w-140 and added their friction modifier because GM discontinued theirs. I wasn't going to put a non-recommended viscosity in the rear-end even though the dealer changed the part number. My differential was already quiet even with the stock gear oil, but since I changed the fluid it's even better - smoother - it's like there's no resistance at all anymore.


75W90 gear oil and a bottle of friction modifier is what is required.
The flow rates when cold are different between the 75W90 and
75W140 gear oils because the 75W140 is thicker and takes longer 
to flow.That is why GM dealerships switched to using 75W90 gear oil 
to quiet down the rearends.
I honestly do not belive in the Amsoil hype and I think their products 
are overpriced and are not readily available.
In all the independent tests that I have read Mobil 1 synthetic gear oil came out on top everytime.Mobil 1 synthetic is a excellent quality synthetic oil 
and it is all I would use in a LSX engine.
Mobil 1 synthetic oils are endorsed and highly recommended by GM engineering.They would not recommend Mobil 1 synthetic if it didn't 
work well in GM vehicles.


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## YellO5LS2 (Jan 9, 2011)

I have no complaints about the fluid in my differential. It really didn't feel a *whole lot different *with the ams, but lie it said, slightly smoother. I didn't seem to need the firction modifier either but added it anyway cause it can't hurt. This "hype" you speak of is there for a reason; people like the products. In my opinion it made a difference in the engine and trans. Just an opinion though. Use what you like using, it's not like it can hurt. I may end up changing to the new "recommended" spec if people have good luck with it and the 75-140 isn't necessary, but at the moment it seems just fine.


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## firebird (Feb 6, 2011)

YellO5LS2 said:


> I thought the first digits were the cold-flow numbers. I could be wrong, but I'm pretty sure the 75w-140 and the 75w-90 have the same flow at cold temps and different ones once hot. Not trying the sound like a know it all - like I said, I could be wrong:lol:
> 
> I'm a walking spokesperson for AMSOIL cause my dad sells it and I can honestly say that they make the BEST lubricants money can buy. Mobil 1 is baiscally elephant pee in my opinion and the stuff GM suggests is a nice way of ONLY getting 150,000 problem-free miles out of your engine, trans, etc. I'd rather put 1,000,000 miles on the car, personally. The differences from AMSOIL are obvious from the second you start your engine.
> 
> I changed out the diff with AMSOIL 75w-140 and added their friction modifier because GM discontinued theirs. I wasn't going to put a non-recommended viscosity in the rear-end even though the dealer changed the part number. My differential was already quiet even with the stock gear oil, but since I changed the fluid it's even better - smoother - it's like there's no resistance at all anymore.


hey, aren't you the dude that posted a thread earlier about amsoil being the best oil... i had a feeling you were related to them :lol:

you guys are on every forum singing the same song lol.


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## YellO5LS2 (Jan 9, 2011)

Yes i am and everyone has a hissy fit because I was pushing my opinion on them and offending everyone. I'm toning it down for this thread as you can see. I never had any intention of selling the stuff or coming off as a snob but I am speaking from experience with different fluids. Amsoil is just what I like to use.

I too would like to know though why the viscosity changed. I called three different parts departments at former pontiac dealerships and they didn't have an negative reason for changing. No rear-end troubles with the 140 viscosity, only thing they could really say was that the 90 spec may yield better fuel economy, but under severe load (like how we drive our GTOs) the 140 could be better. I think it's safe to use either viscosity fluid.


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