[mmahan]

I recently began getting grinds/dificulty when downshifting to 4th. Rev matching makes no difference, and it seems to happenonly when the tranny is "hot" (read: race track, or hard pulls in mountiains). Never happens when car is cold or warm.

HOWEVER, If I push the clutch, pull out of 5th, rev match and push into 3rd (no clutch lift!!!), then shift to 4th, all is well!! No grinds. All other up/down shifts are smooth as they ever were. Makes me think that my Synchros are not happy.


More history: I have ran Redline 75w90NS in my Tranny and 75W90 in my rear diff for over two years with daily driving and many track days with ZERO issues to date. I recently caught another post in which folks were discussing Tranny Fluid Types. In that discussion, I read that folks had experienced "grinding issues" with Redline that went away after switching fluid. I'm wondering if these are the type of issue being referred to, or if they were across all gears? Does it matter? Does it make sense that the fluid would cause issues with only downshifts from 5th to 4th?

I plan to swap fluid, just in case (thinking of going back to Subaru Dino to see), but I'm just wondering if folks think this may be more fluid related than syncro related.

Thanx in advance!

[MaSTi04]

I have an 04 as well, and it's definatly much harder to get into get while running redline. I have had the stock fluid, a local vendor fluid, and now redline. the redline by far is the worse I've run so far. I plan on swapping out VERY SOON. Don't know about others, but this is just my opinion.

[xNICKx]

I have a 04 with 91+k miles on it and Ive had that issue for about 6k miles now. The reason is that the US made subaru make the 5th and 6th gear taller than the close-ratio 1-4 to increase mpg. So this means the 4th gear synchro has to work harder and wear more. There isnt anything you can do such as fluids are concerned to fix this, the only was is to replace the synchro, if you replace it with a stock US synchro it will happen eventually again down the road, you can use the JDM gear synchros and fix the problem all together. My mechanic did it to his STI and he says its like a completely different car.

[mmahan]

xNICKx: did your mechanic use the JDM Syncros, or the gears (5th and 6th), or all of the above?

[Dr. Gonzo]

Originally Posted by mmahan

More history: I have ran Redline 75w90NS in my Tranny

Is that a synthetic or does the "NS" mean non-synthetic? If it is synthetic that may be part of your problem. Synchros like friction and synthetic is much more slippery than dino oil so the synchros can't do their job as well.
COBB's site has a good tech article on this subject.

[mmahan]

Still synthetic:

http://www.redlineoil.com/products_g...5&categoryID=6

From the above site: "This GL-5-type geal oil doesn't contain the friction modifiers for limited-slip hypoid differentials. This makes the transmission synchronizers come to equal speeds more quickly, allowing faster shifting and much easier low-temperature shifting. Can also be used in racing limited-slip differentials where weak spring design causes too much wheel spin. "

This is the one that RLO has told us is OK to use, but now I am finding many other folk with my issue that are saying "use Subie dino oil". There's another thread here on the subject as well.

At this point I'll be starting another thread called "who has re-built their tranny?" in which I hope to hear from folk re what parts they used as replacements (JDM 5th, 6th, synchros, etc)

Thanx again.

[mmahan]

Well... to wrap this thread up for the many that have viewed... it would appear that I am yet anpther case to add to the "Sooby Dino Fluid for Tranny (valvolene 75/90 or 80/90) fixed my problem" list:

I swapped out the Red Line 75/90NS with valvolene, then went to the track for a full day of pounding on her. Ran her for 8 sessions at 20 minutes each with about 40 minutes down time between each session. No grinds anymore and all seems well (YAY!).

I am still expecting to re-build tranny at some point, but I am happy to report that switching back to OEM recomendations seems to have fixed the problem for now. Not the most scientific of methods to be sure, but two weeks ago under the same conditions (with the Red Line) I was having problems that were consistant (read: every single downshift from 5th to 4th made noise once tranny was hot). Now, she is smooth again.

[Insane06STi]

Thats good to hear.

[STiCanyonCarver]

Amen to that.

I ran Redline 75W90NS for two weeks and couldn't stand it. It seemed to make shifting into all gears worse, except maybe for first gear. A complete waste of $50, IMHO. Stick to dino oil in your STi trannys.

Needless to say, my 4th gear synchro still failed at 35k miles. Dealer replaced it under warranty. MY04 and 05 STi's have a real problem with premature failure of synchros. I *heard* that starting in late 2005 Subaru changed to hardened 4th-5th-6th synchros on all USDM cars. Not sure if it's true but hopefully that's what they replaced mine with.

[EricK]

Long story short use "dino 75w90" with 1 quart GM Syncromesh.After using that my trans no longer grinds in 5th.

[SkeetHole]

Can anyone elaborate more of the JDM synchros, 5th, and 6th gear swaps? Is there a change in gear ratio for the JDM 5/6 gears, or are they just a harder gear, same ratio? and if anyone here has done this rebuild, how about some feedback. I dont think my synchros are bad, but maybe 1 time a week while downshifting into 4th, it doesnt grind, but might just slip a few teeth. I dont know what oil is in my tranny though. i bought the car used, but I'm going to drain and refill this week with what i know to be the proper fluid, thanks to this forum Thanks.

[Pitcherman]

There is on difference in the SYNCROS on the JDM tranny and the USDM.....there IS a difference in the 04-05 to 06 Syncros on the USDM. On the 06 the 5th and 6th sycros are heavier duty (carbon) and can take the higher gears. I just had my 2nd 4th and 5th gear sycros replaced under waranty and was told that Subaru is putting the new sycros in all the warranty covered rebuilds.

[smittyjasiii]

this has also happened to me, i just recently got an 04' STi and it has a slight grind in 4th at high rev matches.........hopefully its under warranty!!!!!

[Mykl]

Originally Posted by smittyjasiii

this has also happened to me, i just recently got an 04' STi and it has a slight grind in 4th at high rev matches.........hopefully its under warranty!!!!!

The fluid is probably just worn out. IIRC Subaru calls for a gearbox fluid change every 30k miles.

[0bluesti4]

Originally Posted by Pitcherman

There is on difference in the SYNCROS on the JDM tranny and the USDM.....there IS a difference in the 04-05 to 06 Syncros on the USDM. On the 06 the 5th and 6th sycros are heavier duty (carbon) and can take the higher gears. I just had my 2nd 4th and 5th gear sycros replaced under waranty and was told that Subaru is putting the new sycros in all the warranty covered rebuilds.

lucky you...i told my dealer about the syncro grind and they told me that i just need to shift slower to let the synchros do their work...and that was while the car was under full warranty...now that its out of warranty i wonder if they would replaced that if i complained enough...i was told that after the rebuild the tranny is never the same which sounds like a bunch of bs...