Grinding at running temp with 75w/90...Subaru

[izdizef]

Just did a gear oil change. Valvoline 75w/90 which is just what the manual recommends. This was to try and cure some crunchy gear shifts. Smooth shifts until the car has warmed up then the synchros start acting up again. Figure I need a thicker oil.
Any recommendations from those gear oil gurus out there? I was looking into the Duolec 1605 which is rated at SAE 110 I believe.
This is for my '97 5mt Subaru Legacy. I live in SoCal but I need something that is driveable for the occasional overnight in the mountains.

 

[SuperDave456]

I'm not a Subie guy, but the Amsoil website recommends 75w90 to 75w110.

I'd agree that if the 75w90 isn't working to try something else.
Also, do you know what was in there before? Was it Factory Fill?

 

[izdizef]

I picked up the car with 75k. Just did the change at 86k. Oil wasn't look too dark looking so it probably wasn't a factory fill. Most likely some 75/90 from the dealer, though.

 

[Jeffs2006EvoIX]

If this Subie Synchros are starting to go out, the thicker oil may hide the problem for a little longer. Sounds to me the Synchros are just wearing out period.

It does this in ALL gears? or just certain ones?

Jeff

 

[izdizef]

The Synchros are undoubtedly wearing out/worn. 2nd is the most touchy gear. 4th is starting to act up on downshifts.. although Double clutching and rev matching on the downshifts gives me drama free gear engagement most of the time.

 

[Billbert]

You might want to try Redline MT-90 or Amsoils manual trans fluid. They both use a friction modifier to help the synchros engage. Made my RAV4 shift like butter.

 

[oggb]

Did you use synthetic fluid? If so, dump the synthetic fluid and try some plain old dino juice. Cheapest [censored] you can find.

Also, the Subaru OEM "Subaru Extra-S" supposedly helps a lot with synchronizer issues - but it's pricey. Well, honestly, it isn't much more expensive than regular dino 75w-90. It's been working OK in my Subie for a while now.

 

[izdizef]

conventional Valvoline is what I am using now. The car runs fine at 90 weight then thins out and starts grinding at the 75 range. Im going to SAE 110 unless someone can give me a reason against doing so.

 

[aquariuscsm]

I`ve read on some Subie forums where they had good luck with Shockproof to cure gear crunch. Then the DSM guys cure it with Pennzoil Synchromesh.

 

[SubLGT]

Do a search in the transmission forum at nasioc.com and you will find various cocktails for the synchro issues.

 

[aquariuscsm]

Does your tranny spec GL4 or 5? The Valvoline is a GL5. Maybe that`s why it`s crunching gears? Try a dedicated manual transmission GL4 75W90 fluid (Redline MT90,Amsoil MTG,ect.),instead of a rear differential gear oil like the Valvoline,and see what happens.

 

[SOHCman]

Originally Posted By: aquariuscsm
Does your tranny spec GL4 or 5? The Valvoline is a GL5. Maybe that`s why it`s crunching gears? Try a dedicated manual transmission GL4 75W90 fluid (Redline MT90,Amsoil MTG,ect.),instead of a rear differential gear oil like the Valvoline,and see what happens.


+1

Try GL4 redline MT90, it makes syncros happy. GL5 has additives that make it too slick for syncros to work properly.

 

[izdizef]

interesting. guess i didnt put enough thought into GL5/GL4. Ive read up on the uncle scotties mixtures and others but i dont like the idea of mixing brands and some people have reported failures with these methods.

wouldnt a thicker oil give me better syncro action? i dont want to keep buying oils. ive heard good things about the LE 1605 which is an SAE 110. the Redline MT90 looks alright but I am just hesitant, it still being a 75w/90 and all.

 

[izdizef]

i should also note that my second gear is beyond a typical 'gear crunch' as i sometimes have trouble engaging at all. in all honesty the gearbox is probably beyond repair but I still want to find something to 'bandaid' the problem for the time being.

 

[mechtech2]

Your results are opposite of what is expected from using a thick gear oil in a tranny.
The synchros have to fight the thick oil to cut through more when cold.

I would use Amsoil or Redline manual trans oil, in the proper viscosity.

but since you say the trans is worn out, thicker oil is best for wear. Maybe just leave it alone.

 

[izdizef]

Originally Posted By: mechtech2
Your results are opposite of what is expected from using a thick gear oil in a tranny.
The synchros have to fight the thick oil to cut through more when cold.

I would use Amsoil or Redline manual trans oil, in the proper viscosity.

but since you say the trans is worn out, thicker oil is best for wear. Maybe just leave it alone.

Im a bit confused by this. Are you saying that a thicker oil will not help with syncro engagement? How could you explain then that the oil works fine until it is warm/thin?

 

[aquariuscsm]

Your tranny shifting fine when cold probably has something to do with the internals of the tranny,and not the fluid. Overly thick fluid will definitely mess up the sychro`s ability to work. You`ll see what I mean if you try a thicker than spec fluid. If anything,people go thinner to help a worn tranny (using Pennzoil Synchromesh,Redline MTL,RP Synchromax,etc where 75W90 GL4`s are spec`d).