Manual transmission/axle fluid
 

I have searched and read many posts about correct or "best" fluid for manual transmission and axle and
not sure I understand.

currently, transmission shifts great and the feel is wonderful; its just time to change the fluid

I have on the shelf plenty of Redline 75W-90 and have used that in many cars with great results, but I
keep reading about Redline 75W-90NS non slip formula.

most of what I have read suggests using the NS in older pre 1985 boxes.

is the non slip fluid for my 90GT 5 speed with PSD, or should I stick with the standard stuff

FWIW: I live in florida and its hot year round!?

No friction modifier is specified for the fluid in PSD equipped boxes. Use a good synthetic 90W or 75-90W standard fluid, not an "LS" fluid.

Mike

Make sure you use a "GL-5" fluid, not a "GL-4".

Still not sure about type of fluid to use: Motorsports sells a trans change kit that includes Redline 75W-90,
but on the Redline website here is the description for that oil:

1. Contains additional friction modifiers for suitability with clutch-type limited slip differentials - for most LSDs, no additional friction modifiers are required
3. This product is not designed for use in most manual transmissions or transaxles in passenger vehicles, since the extreme slipperiness may cause synchronizer mesh issues that lead to shifting problems

that seems to suggest this is not for 928 5 speeds with PSD?

Mobil 1 75W-90 Synthetic Gear Lube. It is labeled "LS" gear but works very well with both mechanical limited-slips as well as PSDs. Much better than Redline in my experience, especially when cold.

FWIW: just spoke with technical support at Redline who said DO NOT USE their 75W-90 gear oil in 928 transaxle.
the correct recommended oil is 75W-90NS which means non slip. here is specs from their website:

1. Designed for transmissions and transaxles - helps to slow synchros for easier shifting across a broad temperature range
2. Popular in Ferrari, Porsche and Subaru transaxles
3. Contains extreme pressure additives like our 75W90 GL-5 oil, but lacks friction modifiers to balance slipperiness
4. Improved copper corrosion protection to prolong synchro life

my car takes 5 quarts.

Excellent, glad that's solved.

Going to have to order me some.. Need to do that myself.

I'm with Jim on this. I've found that M1 LS also reduces leaks. I was running Red Line and had a front seal leak. Based on a recommendation from Greg Brown (see post #7 of the thread below), I switched.

https://rennlist.com/forums/928-foru...ce-or-not.html

My leak has been reduced to a seep and no longer shows up on the garage floor. Further, the tranny shifts fine and PSD works as advertised.

[QUOTEI was running Red Line and had a front seal leak][/QUOTE]

George, which Redline product were you using?

75W90 NS

Transmission Seal Leak with Redline NS
 

Interesting about seal leak. When I took delivery of my 89GT three years ago, it can fresh with new fluids including Redline 75W-90 NS. It too has developed a leak leaving spots on the garage floor and grimy transmission case. I have been thinking about giving it a shot of ATP AT-205 Re-Seal. Anybody tried this?

One caveat to that is that some threads have noted the Redline 75W-90 NS can cause a bit of chatter in cars with the clutch type LSD. For 928 owners with LSD some have found it better to blend the Redline 75W-90 NS with 75W-90 LS.

Having said that, although I currently run Redline in my 84 I do get some occasional drips at the front seal which I had resealed a couple years ago when I had the transmission apart. So I do plan to follow some of the other examples here and give the M1 75W-90 a try.

... and LS is generally available. Got mine at Advance Auto down the street.

Does the fluid recommendation change if you don't have a LSD? My 5 speed 84 has an open diff...