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So I am ready to change my Tranny oil (15,000) and my Rear Diff. and have been doing a lot of research via the internet and Nasioc/Clubwrx.

Coming across some debating I noticed on member noted that using Redline MT-90 would be bad because it was GL-4 and the subaru transmission requires GL-5.

While searching some more i came across Redline's home page and they had an interesting article about GL-4 and GL-5

Most manufacturers of manual transmissions and transaxles recommend an 80W or 90W GL-4 lubricant. GL-5 gears oils which are required in hypoid differentials are not used in most synchromesh transmissions because the chemicals used to provide the extreme pressure protection can be corrosive to synchronizers, which are commonly made of brass or bronze. Typically, the use of a GL-5 lubricant in a synchromesh transmission will shorten the synchronizer life by one half. The extreme pressure requirements of spur gears and helical gears found in transmissions are not nearly as great as found in rear-wheel drive differentials. A GL-4 lubricant provides adequate protection for most manual transmissions, unless a unique design consideration requires the extra protection of a GL-5.
Now with that being said, does that mean that switching to MT-90 will help me out. I know that using the MT-90 formula would be better for my syncro's and worse for my bearings, but in reality I would rather protect those damn syncros, and get some improved shifting for my aggressive driving style.

Also, any suggestions for the Rear Diff, and is Redline good stuff?
 

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You could always run a mix of MT-90 and another GL-5 fluid as a compromise. Right now, I'm running 60% fresh OEM dino and 40% MT-90. Works great! Notchiness is gone, I can shift a bit faster w/o grinds, and the trans feels nice in the cold.
 

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I'm interested in this also. I was just about to order a gallon of Neo tranny fluid. It was a toss up between Redline and Neo but I was going to go with Neo since it's GL-5 rated. Now I'm even more confused by which way to go.
 

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Neo has worked well for a lot of people. In my case, however, the NEO HD felt great for about 1,000 miles, and then I started getting some slight grinds. When I went back to OEM fluid, the problem was eliminated.

It seems that synthetics are hit or miss on our cars. This probably all comes down to build tolerances in individual transmissions, as well as the condition of your syncros.
 

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stealth_rex said:
Neo has worked well for a lot of people. In my case, however, the NEO HD felt great for about 1,000 miles, and then I started getting some slight grinds. When I went back to OEM fluid, the problem was eliminated.

It seems that synthetics are hit or miss on our cars. This probably all comes down to build tolerances in individual transmissions, as well as the condition of your syncros.
At what mileage did you change it?

How about everybody else that has used Neo or any synthetic? I'm at 30k and a tranny fluid change is part of the service. Just trying to figure out if I should use OEM or synthetic.
 

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Real interesting what they said on redlines site good find DarkStar!

Here is my experience

I had some serious grinding at 10k miles. My only mod was Turbo back exhaust. I took the car into a lube stop or whatever and they said the tranny fluid was low. I knew enough to not let them top it off with whatever crap they had so i went to the suby dealer and they filled it up with the right gl5 oil. I had no problems to speak of up till 28k or 30k and it started to grind a little here and there.

Thats when i changed my oil to MT-90 and i'm another person that likes mt-90 i know its not gl5 i just read the tech article on www.cobbtuning.com and picked mt-90 because of what they said.

But i have 33k on now and mt90 has been GREAT perfect shifts much smoother never grinds.
 

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consider:

how many folks have WORN OUT their transmissions? as in, too much wear?

how many folks have worn out their syncros?

how many folks have grenaded their trannies, stripped gears, etc.

make your decisions as to weighing lubrication vs. syncros accordingly. as cobb states, it's always a tradeoff.

ken
 

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Since GL-5 is specified, I don't think GL-5 is going to hurt anything! What they're talking about is putting GL-5 in a tranny spec'd for GL-4.

That being said, I run Redline Shockproof.
 
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