Manual transmission oil

[Yoni_d]

Hi Guys

I want to change my transmission oil and I am a bit confused about the oil type I should.
My car is 1980 4.7 manual with LSD. In the manual I think it is recommended to use Dextron 3 oil type...however, I saw here that a full synthetic oil is recommended 75W90
What do you think I should use?

Thanks for your help.

[harborman]

Originally Posted by Yoni_d

Hi Guys

I want to change my transmission oil and I am a bit confused about the oil type I should.
My car is 1980 4.7 manual with LSD. In the manual I think it is recommended to use Dextron 3 oil type...however, I saw here that a full synthetic oil is recommended 75W90
What do you think I should use?

Thanks for your help.

Dexron might be for the Automatic trans, not manual as I just put it in my auto.

75w90 is different and I would say for the manual trans but you better make sure before you do anything. Auto trans fluid is red in color.

[JhwShark]

Originally Posted by Yoni_d

Hi Guys

I want to change my transmission oil and I am a bit confused about the oil type I should.
My car is 1980 4.7 manual with LSD. In the manual I think it is recommended to use Dextron 3 oil type...however, I saw here that a full synthetic oil is recommended 75W90
What do you think I should use?

Thanks for your help.

Not Dex for manual, and I would avoid synth gear oil in an old case unless it has complete new gaskets. The synth will not swell the old gaskets as munch as classic gear oil so leaks can happen...

[SeanR]

Buy some 75w90 gear oil. I've been real happy with Redline and get it from Roger at 928sRus

[JK McDonald]

Hey Yoni, There will be a variety of lubricants available for your 5 speed and limited slip differential, just select a high quality brand. Here in the states many 928 owners use Castrol, Redline or Royal Purple 75w-90 Gear Oil with an additive (often a Phosphorus derivative) for limited slip. By the way, the multi-grade oils are designated with the 1st number (75w) as the viscosity and the 2nd number (90) as the equivalent oil thickness.
This simply means that the multi-grade oil is preferred because it is formulated chemically to be a thinner oil but protects as a thicker oil.

Some 928 owners have tried a synthetic or synthetic blend engine, transmission or differential oil because they are considered to provide a little better protection. But most have found that the synthetics tend to get past the seals rather quickly if used in an older car while being considerably more expensive.

I think Mobil 1 Synthetic 75W-90 for differentials sells for about $10/Qt in the U.S.

Good Luck, Michael

[Yoni_d]

Thanks! So from what you are saying (sorry for the question, I just want to be sure), I should go for the 75W-90 oil? will it be ok with the seals?

[Maleficio]

Yes, use synthetic simply for the improved performance (very slick and quiet). If you develop small leaks, go back to non-synthetic gear oil.

I like to dope my gear oil with Tufoil oil additive. Works great, and feels like you've taken 500 pounds out of the trunk.

Tufoil Engine Oil Treatment

[Yoni_d]

Thanks a lot!

[Pete R]

I use redline(but many will be adequate). I live in New England and had hard shifting issues with regular fluid when it got cold out. The synthetic fixed it due to not getting a thick and slippery when cold. I have no seal issues.

[AaronCross]

Originally Posted by Maleficio

I like to dope my gear oil with Tufoil oil additive. Works great, and feels like you've taken 500 pounds out of the trunk.

There a certain ratio you use to do this? Or is there a recommended tranny use with this stuff? thanks

[Maleficio]

Originally Posted by AaronCross

There a certain ratio you use to do this? Or is there a recommended tranny use with this stuff? thanks

I like to put in 8 ounces of Tufoil. I don't follow a ratio or formula, just dump an 8 ounce bottle into the gearbox then fill it up with syn gear oil.

I do the same for the diff and transfer case on my 4WD. If it's got gear oil in it, I pour in Tufoil. It's almost absurd how well it works.

[rjm65]

I've only used 75W90, but interestingly the manual for my 79 does say it's ok to use Dextron if multi-grade hypoid oil is not available. Can't imagine how they can be compatible seeing as the viscosity is so different. Anyone ever try Dextron in a manual trans?