This is my first post here, I have to say that I love this board, all of my other problems I have figured out through searching, you guys have covered almost everything!

 

My question:

I have a '91 Loyale 4x4 sedan with 150k miles and I think the shifts could be a little smoother. I did some searching and it sounds like Redline 75w90ns is recommended for our older Subies. Should I use this in the Tranny AND the rear diff?

Second question:

On NASIOC 'Scotty's Cocktail' comes highly recommended, but it's all people with newer Subarus. I was going to give it a shot, but I am a little concerned, I would like to keep my syncros as long as I can. For those that do not surf NASIOC the cocktail consists of:

 

1 qt Pennzoil Synchromesh

2 qts Castrol HypoidC 80w90 (Or 75w90)

1 qt Redline Lightweight Shockproof

 

Can I just substitute the 75w90ns for something else to make sure my syncros will not have any excess wear? Thanks so much in advance for your input.

at 150,000 miles it could still be the original fluid or very old. i'd start with just a basic high quality ATF flush first. new fluid could help very much. have you had the car long enough to be sure it doesn't leak at all? install a trans cooler while you're at. if you use the expensive stuff, install new hoses and clamps.

 

i've never used Redline so i'm not positive, but i would be very surprised if you put that in the rear diff. gear oil and transmission fluid are very different. use gear oil in the rear and front diff.

GG

I believe the gentleman has a manual shift tranny

 

Redline is an excellent choice for the the tranny

(transaxle/ front diff) but

the rear diff can use normal gear oil

( unless it's an LSD unit)

I just put a synthetic castrol 80w90 in my impreza gearbox this past friday night. I am really happy with it so far. I got it at autozone and it is in a blue bottle. BTW, the impreza has 141k on it.

I replaced the fluid about 30k miles ago when I got the car, but I just used cheap Coastal stuff. I've had no leaks and it still appears to be in great shape, but I'm probably going to remove the driveshaft to replace the bushings in the shift linkage, so I figured it couldn't hurt to try using better fluid. And yes, if it wasn't clear I have a manual transmission.

You are correct that Redline's 75W90NS is the proper fluid. It IS gear oil, and as such could be used in your rear diff, but the 'proper' fluid is their regular 75W90. Those two fluids are the same basic thing, except that the NS's frictional properties are made to work well with synchronizers. Redline's site and their technical contact (Dave Granquist) are very good resources.

 

If for some reason you decided to not use the Redline 75W90NS in the transmission, I would encourage you to contact SpecialtyFormulations(.com). They are a company that mostly makes specially formulated lubricants for race teams and other specialized applications, but they have over-the-counter transmission and gear lubes as well. The correct one for our Subarus is MTL-R. It is a GL-5 75W90 fluid made specifically for synchronized gearboxes. It is not to be used in the rear diff. I have it in my XT6 5-speed now and it is excellent stuff.

 

I would be very, very wary of the cocktail mentioned on NASIOC from a durability/longevity point of view. It would be great for the synchros, but death on the front differential. I have asked people who use something OTHER THAN a 75W90 GL5 lube how many miles they've ever put on their tranny with the other stuff (like Redline MTL or Pennzoil Synchromesh), and no one has ever answered me. To me this is good reason to think that they've never seen the results on their front differentials of a too-thin fluid which lacks GL5 protection over time.

 

Do as you will, of course, but you are correct that Redline 75W90NS is the fluid for your transmission.