Diff and trans oil for 240SX

Time to start prepping the car for the season and I'm going to change out the diff and trans fluids. So what kind of fluids are you guys using? I was reading through some of the stuff on Redline's website and all it did was confuse me. Here's what appear to be the choices from Redline (it doesn't have to be redline, they just seem to be the most well known):

Trans: MT-90, lightweight shockproof (but says not recommended for syncro boxes)
Diff: 75W90, lightweight or heavyweight shock proof

Jim (its66) says he ran lightweight shockproof in the trans and heavyweight shockproof in the diff and I've heard of other people using the MT-90 and 75W90.

I'm more interested in protecting the trans and diff from destruction than in transferring every last .01 hp to the ground if that makes a difference in choice.

Thanks.

David

FWIW, I've been using MTL in the tranny and Lightweight Shockproof in the diff (helical diff), and haven't had any problems with either. After checking the Red Line website though, I looks like the MT-90 may be a better choice for the transmission (according to their recommendations - it is slightly heavier). I did have a previous gearbox start jumping out of 4th gear, while using MTL, but considering the mileage it had on it (almost 200K) I can hardly blame it on the gear oil.

In my 300zx I run just plain old 75-90/80-90 synthetic gear oil. The only diff problems I've ever had were a welded one that broke the welds & got binding on itself & eventually flash boiled out all the oil (that diff still stinks).

In the transmission I've either used the same synthetic 75-90, or synthetic ATF. The ATF idea came from a guy w/ a Sentra, they ran it in the Sentra w/ success, so we started running it in our Miata, then I put it in my 300zx and it helped to keep from beating the syncros on 2-3 upshifts.

The miata has 3 or 4 12 hour races on the box w/ that oil and no problems.

Shockproof is not recommended in trannys..MT90 or MTL should work fine.

We run shockroof lite in rears

Mobil 1 in both.

I've run MT-90 in the trans for a while - no issues, and smooth shifting.

The diff - I ran 75w90ns, but it would overheat the fluid. After some recommendations (from this list), I added BG MGC to the 75w90 and haven't had an issue since. And the car's run several 12-13 hour enduros this way.

I've recently tried the heavy shockproof, and it seems to also keep the temps in check, but I have yet to enduro the car with this lube setup.

Joe, what weights M1 are you running in the diff and trans???

joe

Trans: 75/90
Diff: 75/140

Mobil 1. No rear gear problems ever.

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Mobil 1. No rear gear problems ever. [/b]

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+1. I use the 75/90 Mobil1 in both tranny and diff.

Do you guys have to add any limited slip additive to the Mobil 1?

I have a Nismo competition diff. My understanding is that these diffs tend to run pretty hot. I of course didn't know this to start and have put many sessions on the car without changing the diff fluid. It still seems to work ok, though, so hopefully it isn't damaged.

David

I don't because I have a Torsen. No need on a gear-driven LSD.

David, the additive is there to help INCREASE the friction levels with the clutch plates and make them work. It is my understanding that without the additive, you don't have any real heat issues you just don't get as much lock up as intended (guys with real knowledge on this, K-man, Joe H., Steve E., can correct me if I am wrong).

Redline makes 75w90 rear gear oil in two flavors -- one with the additive and one without. I have used that since 2004 on a Quaife rear end (Torsen) and have had no issues. I haven't personally used the flavor with the additive but I suspect it would be good, and I also suspect that you don't really have any damage to the clutch plates but again I might be wrong.

Good luck with it.

My take on the additive is that it's for street-driven cars so the clutch plates don't bind on tight corners.
The M1s as listed are cheaper than Redline and are readily available; typically cheapest at Wal Mart or Autozone.
I would think that trans and diff fluid, like engine oil, should be changed regularly during a season.

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David, the additive is there to help INCREASE the friction levels with the clutch plates and make them work. It is my understanding that without the additive, you don't have any real heat issues you just don't get as much lock up as intended (guys with real knowledge on this, K-man, Joe H., Steve E., can correct me if I am wrong).

Redline makes 75w90 rear gear oil in two flavors -- one with the additive and one without. I have used that since 2004 on a Quaife rear end (Torsen) and have had no issues. I haven't personally used the flavor with the additive but I suspect it would be good, and I also suspect that you don't really have any damage to the clutch plates but again I might be wrong.

Good luck with it.
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You need to reverse that Jeff. The additive is to modify the friction coefficient and keep the plates in the clutch type diff from chattering. Usually not needed in race diffs unless you run lots of preload. Quaife could care less but it does have surfaces that bind under load and the additive will reduce it.

No additive to the mobil1

I made a jig to check the breakaway pressure on the diff while it's in the car. Once it falls below my minimum setting I take it out and re-clutch it or shim it. I switched to mobil 1 because it does not leave my shop smelling like a dead cat for several days after a race. I still sell Redline products and in most applications I have found them to be very good stuff. In my application Mobil 1 fits the program best.