i am wanting to change the front diff/trans fluid in my 97 OBS and the rear diff fluid. its a 5-speed and i am wondering what weight and brand to use front and rear?? any suggestions would be appreciated

I believe GL-5 spec 75w90 is what you'll want.

 

Do not reccomend Mobil1 for the FRONT diff, the chemistry doesn't play well with the syncros in the manual trans. It is fine for the rear though.

Standard GL-5 Gear oil. 80w 90 is your basic gear oil, and will be the cheapest in parts stores. 75w 90 is typically a synthetic mix or will contain higher amounts of detergents and additives. It works just as well, as long as it says it meets the GL-5 spec.

Then there is 75w 140 which is a full synthetic mix that provides the best low temperature flow rate with the best high temperature protection. 75w 140 is also $$. Unless you really want to spend a bunch of extra $$, or you plan to race the car, you can just stick with the plain jain 80w90.

 

When changing the rear diff fluid, remove the FILL plug BEFORE you drain the fluid. That way you aren't stuck with no fluid in the diff if the fill plug can't be removed.

Standard GL-5 Gear oil. 80w 90 is your basic gear oil, and will be the cheapest in parts stores. 75w 90 is typically a synthetic mix or will contain higher amounts of detergents and additives. It works just as well, as long as it says it meets the GL-5 spec.

Then there is 75w 140 which is a full synthetic mix that provides the best low temperature flow rate with the best high temperature protection. 75w 140 is also $$. Unless you really want to spend a bunch of extra $$, or you plan to race the car, you can just stick with the plain jain 80w90.

 

When changing the rear diff fluid, remove the FILL plug BEFORE you drain the fluid. That way you aren't stuck with no fluid in the diff if the fill plug can't be removed.

 

Little quips of knowledge like this, never cease to make me grin when I think back on situations where I wish someone has told me beforehand. Good looking out.

I used Valvoline synpower TDL 75w90 and works really well for both rear and front drivetrain.

thanks everyone!! it really is great to have people around with this info when its needed. so i guess i will go with the 80-90 as long as it meets the GL-5 spec in the front and rear. thanks again to everyone for all the info. by the way, how much fluid should the front and rear hold?

I used the supertech semi-synthetic from walmart. I think it was 75w-90. I think 2 quarts took care of the front and rear, but mines an auto.

I see it was already mentioned...many years back when people were saying that Mobil1 synthetic gear oil ate up the syncros in their soob's manual trans. I guess it had a lot of sulfur in it, and it was a little too much for the yellow metal syncros to handle.

The manual transmission and front diff share fluid and hold just shy of 1 US gallon IIRC. The rear diff holds roughly 1 qt.

 

Little quips of knowledge like this, never cease to make me grin when I think back on situations where I wish someone has told me beforehand. Good looking out.

It's one of the things I love about this forum.

I have seen that posted many times by other members. I kinda think stuff like that should go into a tips 'n tricks thread somewhere.

If your diffs' fluids have never been changed before, expect to have to get on the drain/fill plugs with a 2' breaker bar to get em loose.