Time to change the tranny fluid and rear diff

Hey i'm at 20,000 miles and i think it's time to change the tranny and rear diff fluids. I purchased the car used w/ 15,000 miles so i figure changing the fluids early might be a safe guard to hard driving by the previous owner.

Any who what i'm wondering is i've heard so many differing opinions on what to use in the tranny. Right now i'm planning on mobil 1 75W90 in both the tranny and rear diff. Some people say use dino oil some say synthetic. Some say synthetic is ok but mobil 1 is too thin. Can anyone see a reason to not use mobil 1? I've used it for years on my parents cars my Mustang and now on my Subaru and i like it. I think it's a good high quality oil. What do you guys think? I've heard synthetics will give you issues with the syncros cuz it's too slippery. Any thoughts on this? Thanks guys.

 

i would use 90w of any kind in the rear and 75w in the front, depends on what you like, 90w in the tranny would have harder shifts, but wouldnt hurt much, maybe gas mileage. someone else chime in, i dont have an sti

 

Redline makes some really nice synthetic gear oil, and you can get it with different friction additives. Here's a link to a nice tech article on gear oil.

http://www.cobbtuning.com/tech/gearoil/index.html

 

synchromesh?????

 

AMSOIL 75w all the way. Just did changed tranny/diff in my 03 WRX and it shifts a lot smoother than before.

 

Amsoil is synthetic right? I've heard that some poepl have like synthetic at first but later on it's caused grinding problems any one hear this or have any thoughts on it?

 

Any one at all?

 

I've read lots of posts both good and bad about using synthetic fluid for the MT. I rarely heard anything bad about standard dino oil in the MT. Seeing that it's cheaper and there seem to be less bad things said about it, I just went with Valvoline 75-90w for my MT.

I put in Mobil 1 75-90w in my rear diff, though.

 

put in mag 1 oil in your tranny....stop my grindding.....happy.....sopposly these are ment for lsd but oh well.....works great...

 

i use redline no slip. I was having the usual 02-03 grinds...put redline in and all the gears are good except for of course 1st.

 

I'll be doing a 30K sercive on my fiance's 04 WRX wagon soon.

I'll order some Redline 75w90 to replace trans/frt & rear diff fluids, let me know if you want some too. I'll check on the price Tuesday, the 6th.

 

I'm not sure if this was a coincidence or not, but about a month after running Redline 75w90NS in my tranny, I had to replace both 1st and 2nd gear synchros. The car was bone stock at the time with 12k miles, and had no signs of grinding before switching fluid.

 

ive used gm syncromesh for the last 25,000 miles and it totally took care of every grind i had, and hasnt ground since!

 

+111111111

 

About three weeks ago I put in Amsoil Severe Gear into my 02 WRX Wagon. It seems to shift better to me. The main reason I wanted to go sythetic was to improve cold weather shifting. Tho old lube, I am guessing, was dino oil. The old stuff seemed to work ok, but was very unpleasent in the winter until the car warmed up.

 

Who sells GM syncromesh other than then dealer? Do you just add this into the new fluid? Or is this a fluid by itself?

 

autozone is the only place that carries them other than the dealers.

wall of tvs: let me know how much they cost, i wanna try some in the rear diff.