# 1966 GTO 4 Speed and turbFluid recommendations.



## Muranator66GTOCNVT (Oct 20, 2021)

newbie here. Love them GTO’s
So I’m changing the oil in the rear Differential’s with Torco RGO 85w-140 with type F Modifier in both of my 66’s 
Drive train a little noisy. In the Manual GTO
I’m just wondering what everyone else recommends for fluid type to run in the four-speed manual.
Also fluid recommendations for the turbo 400 in the auto 66 GTO 

I tried searching the forum and didn’t find anything that has been posted recently Thank you for your help


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## armyadarkness (Dec 7, 2020)

I use Dex 3 in the TH400. You dont state what manual you have, but if it's a Muncie, then 80/90 gear oil


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## Muranator66GTOCNVT (Oct 20, 2021)

armyadarkness said:


> I use Dex 3 in the TH400. You dont state what manual you have, but if it's a Muncie, then 80/90 gear oil


It’s the Muncie M-20 wide ratio.
should I put the additive in there, same as the rear differential?
I’m changing rear diff with Torco 80w-140 with type F additive. Should I use the same weight oil in Muncie m20 or stick with 80-90 weight?


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## PontiacJim (Dec 29, 2012)

Muranator66GTOCNVT said:


> It’s the Muncie M-20 wide ratio.
> should I put the additive in there, same as the rear differential?
> I’m changing rear diff with Torco 80w-140 with type F additive. Should I use the same weight oil in Muncie m20 or stick with 80-90 weight?


Make sure you don't use synthetic gear oil - I see Torco has both and looks like you have sourced the correct one. Use conventional gear oil. Synthetic can be thinner and these old cars want the heavier conventional gear oil as it also acts as a "cushion" between the gears.

IF the rear end has a posi traction unit, you need to add an additive for the limited slip/posi. If not a posi, no additive needed. Not all GTO's had limited slip and many seem to think limited slip/posi was a standard option on the GTO. The Type F says it is for the posi/limited slip rear ends so it should work for limited slip.

Just 80W-90 for the Muncie which you can get at most auto parts stores.


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## Muranator66GTOCNVT (Oct 20, 2021)

PontiacJim said:


> Make sure you don't use synthetic gear oil - I see Torco has both and looks like you have sourced the correct one. Use conventional gear oil. Synthetic can be thinner and these old cars want the heavier conventional gear oil as it also acts as a "cushion" between the gears.
> 
> IF the rear end has a posi traction unit, you need to add an additive for the limited slip/posi. If not a posi, no additive needed. Not all GTO's had limited slip and many seem to think limited slip/posi was a standard option on the GTO. The Type F says it is for the posi/limited slip rear ends so it should work for limited slip.
> 
> Just 80W-90 for the Muncie which you can get at most auto parts stores.


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## Muranator66GTOCNVT (Oct 20, 2021)

Thank You Jim!


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## GTOTIGR (May 3, 2020)

Hi,

I run Driven GL-4 conventional 80W/90 in my GTO’s with good results.








Driven GO 80W-90 Conventional GL-4 Gear Oil


Driven GO 80W-90 Conventional GL-4 Gear Oil



drivenracingoil.com


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## Muranator66GTOCNVT (Oct 20, 2021)

GTOTIGR said:


> Hi,
> 
> I run Driven GL-4 conventional 80W/90 in my GTO’s with good results.
> 
> ...





GTOTIGR said:


> Hi,
> 
> I run Driven GL-4 conventional 80W/90 in my GTO’s with good results.
> 
> ...


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## Muranator66GTOCNVT (Oct 20, 2021)

Thank You. 
Will Order some Torco conventional 80 -90w with anti friction additive


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## coyote595 (Dec 4, 2019)

A newbie with two 66 GTOs is one lucky newbie! Congratulations!


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## geeteeohguy (Feb 2, 2008)

What Pontiac Jim said. Do NOT use Limited Slip lube, Synthetic lube, or any friction modifiers in your transmission. Friction modifiers and synthetic lubes will cause the syncro and blocker rings in the trans to slip and cause gear clash and wear. Good old fashioned 75/85/90 gear oil. (Straight 90 wt went out of production about 20 years ago)
For the TH400, the Dexron/Mercon V is what is currently available. Have not seen the original fill Dexron, Dexron II or Dexron III in decades.


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## Muranator66GTOCNVT (Oct 20, 2021)

geeteeohguy said:


> What Pontiac Jim said. Do NOT use Limited Slip lube, Synthetic lube, or any friction modifiers in your transmission. Friction modifiers and synthetic lubes will cause the syncro and blocker rings in the trans to slip and cause gear clash and wear. Good old fashioned 75/85/90 gear oil. (Straight 90 wt went out of production about 20 years ago)
> For the TH400, the Dexron/Mercon V is what is currently available. Have not seen the original fill Dexron, Dexron II or Dexron III in decades.


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## Muranator66GTOCNVT (Oct 20, 2021)

Thank You for your help


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