Rear End Gear Oil.

86bluecobra · Apr 14, 2007

I was thinking about this last night and thought I would run it by you guys.
What gear oil do you run in your 8.8's?
The reason I ask is last year I swapped to a synthetic castrol gear oil. I used traction modifier aswell. That being said and it may just be a coinsedence but I could no longer do donuts with my car. One side would kick out half way through and do a 1 peel. Now it maybe that the cluches were just worn but since synthetic is slipperyer then regular dino oil I wonder?
What do you guys think? I rebuilt the rear end now new clutchs but I'm about to put oil in it. Should i use synthetic again or go back to dino gear lube?

Daggar · Apr 14, 2007

Yes.. your suspicions are correct. The synthetic oil that you've used has uncovered your aging trac-lok. What's more is that switching out that old oil for new (not necessarily synthetic) could have uncovered as well (depending upon how far gone your traction lock is).

The gear oil that I use is regular ole 90W (non-synthetic). I prefer it to the synthetic for street use for one reason only. It turns brown and is easy to tell when there is water in the differential. Synthetics do a better job (unintentionally) of absorbing/masking when water gets into the diff.

That said... water in the diff is not usually a very big deal in these cars so long as general condition is good and you don't drive through huge puddles etc. For me, it's just a peace of mind thing, I guess.

Final note: Often, synthetics have friction modifier in them already. Check the bottle.

Fett · Apr 14, 2007

What about 75w140 synthetic and friction mod? That is what I put in my rear end (man that sounds bad). But I am going to 31 spline Explorer diff with hardened axles and new clutches in the future, I would like it to hold up as strong as possible. So what should I go for in my daily driver/track car.

Daggar · Apr 14, 2007

You'll likely get as many DIFFERENT responses as you will responses.

My rule of thumb... don't use synthetic fluids on anything that is brand new or rebuilt. Let things "seat" with teh cheap stuff for a while then use what you like. For street/strip vehicles... use the recommended weight. For Race vehicles, I'd likely use a thinner synthetic.

If you choose to use something like Redline or Royal Purple products, use the weight that they recommend for the application.

86bluecobra · Apr 14, 2007

Yep I'm off to go get some new regular old 90 wieght gear oil.

HISSIN50 · Apr 14, 2007

I agree that the extra FM (lowering the coefficient of friction) probably did not hurt. This is why I recommend not adding a small bottle of FM with most synthetics. If the rear chatters it's easy to add the bottle but if there's too much slip, it's hard to remove the extra FM.

I'm one who does run synthetic in the rear - I think it's a good idea for folks living in extreme climates. It will flow WAY faster when cold than conventional gear oil and for me, I like it for the high temps of the desert. I don't run extra (the small Ford FM bottles) of modifier when using a synthetic with FM in it. I use Redline.

Good luck.

Shakerhood · Apr 14, 2007

Fett said:
What about 75w140 synthetic and friction mod? That is what I put in my rear end (man that sounds bad). But I am going to 31 spline Explorer diff with hardened axles and new clutches in the future, I would like it to hold up as strong as possible. So what should I go for in my daily driver/track car.

75W-140 sounds a little bit on the Thick side, the service manual calls for 75W-90, you might want to just go to straight 90 instead of the Multi Viscosity.

86bluecobra · Apr 14, 2007

I always though that Friction Modifier was to help improve the clutch friction. Am I wrong? Would extra FM hurt the rear end?

HISSIN50 · Apr 14, 2007

FM lowers the coefficient of friction. That is, it makes things more slippery. That's why I recommend doing it the way I do (with synthetics, see how they do without the modifier and add it later if the clutches chatter).

And the heavy weight oil noted by Chris should be ok. In later 8.8's, they went with a 140 weight. A note of interest: most, if not all synthetic 140's will flow BETTER at cold temps than a conventional 90 weight. Sounds like a win-win to me. Of course, consult with your favorite fluid manufacturer for confirmation on this (as well as seeing about FM. Many 140's do not come with modifier in them, so adding some on one's own can be a wise idea).

Woodrow · Apr 14, 2007

Put a spool in it and call it a day

86bluecobra · Apr 14, 2007

Woodrow said:
Put a spool in it and call it a day

Kinda a daily driver in the summer. Spool would be a little nasty.

86bluecobra · Apr 14, 2007

HISSIN50 said:
FM lowers the coefficient of friction. That is, it makes things more slippery. That's why I recommend doing it the way I do (with synthetics, see how they do without the modifier and add it later if the clutches chatter).

And the heavy weight oil noted by Chris should be ok. In later 8.8's, they went with a 140 weight. A note of interest: most, if not all synthetic 140's will flow BETTER at cold temps than a conventional 90 weight. Sounds like a win-win to me. Of course, consult with your favorite fluid manufacturer for confirmation on this (as well as seeing about FM. Many 140's do not come with modifier in them, so adding some on one's own can be a wise idea).

Oh oh. I put 2 bottle of FM in the car. oops.

Shakerhood · Apr 14, 2007

HISSIN50 said:
FM lowers the coefficient of friction. That is, it makes things more slippery. That's why I recommend doing it the way I do (with synthetics, see how they do without the modifier and add it later if the clutches chatter).

And the heavy weight oil noted by Chris should be ok. In later 8.8's, they went with a 140 weight. A note of interest: most, if not all synthetic 140's will flow BETTER at cold temps than a conventional 90 weight. Sounds like a win-win to me. Of course, consult with your favorite fluid manufacturer for confirmation on this (as well as seeing about FM. Many 140's do not come with modifier in them, so adding some on one's own can be a wise idea).

My Bad, I never knew that some later model 8.8s came with 140.

BigHairyMonkey · Apr 14, 2007

86bluecobra said:
I was thinking about this last night and thought I would run it by you guys.
What gear oil do you run in your 8.8's?
The reason I ask is last year I swapped to a synthetic castrol gear oil. I used traction modifier aswell. That being said and it may just be a coinsedence but I could no longer do donuts with my car. One side would kick out half way through and do a 1 peel. Now it maybe that the cluches were just worn but since synthetic is slipperyer then regular dino oil I wonder?
What do you guys think? I rebuilt the rear end now new clutchs but I'm about to put oil in it. Should i use synthetic again or go back to dino gear lube?

i cant do donuts either (tear). i fear my t-lok is dying as well. When i get on it in a straight line itll go ass out all the time, if i try to hook a donut i just get one tire fires.

Rear End Gear Oil.

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