Subaru STi Syncro/Gear oil Conundrum!

[Jconrad]

Hello all! So I have a bit of an annoyance and hopefully this huge community of oil gurus can shed some light on a problem of mine.

Anyway.. I have a 2004 Subaru STi with 99k miles and for some reason the transmission is just utterly stubborn. More than the acceptable amount.

When I am at a stop (dead stop) I cannot get this thing in first gear quickly (i.e. First in line at green light). I have to push in clutch, wait probably 5 seconds, then it goes into gear. If I just try to put it in gear, I get met with strong resistance (like hitting a wall), but if I wait a few seconds it goes into gear. If I double clutch it just makes problem worse.

Now.. I have never, ever (ever) heard this transmission grind into gear. Not at low RPM, or high RPM, or even downshifting. Clutch is disengaging fully. No weird bearing squeals or abnormal noises.

I am wondering if possibly my oil (All Brand NEW Motul 300) is possibly too thin for my aging syncros. If I try replacing a quart of 300 with that Pennzoil Syncromesh would that be beneficial or horrible? IDK what oil was in it before, but it did same thing...

Do Motul 300 and Syncromesh play well together?? I have no idea? And I spend about 100 dollars for the good oil, so I don't want to ruin it.


Or is there something else wrong with my poor 6Mt? I tried the IWSTi community and apparently stumped them

Thank you all so much! Sorry for long post!

 

[Rand]

it says its extemely slippery probably designed for DIFF and MT's without synchros

but that could just be their marketingspeak.

Quote:
Ester-based and 100% synthetic, GEAR 300 is formulated for gearboxes and rear axles, especially for competition cars - racing circuit, rallies and endurance trails. GEAR 300 is test proven effective to extreme pressure resistance in all types of cars and under all types of uses. GEAR 300 extremely high lubricity reduces friction. It also offers anti-wear, anti-corrosion and anti-foam capabilities.


here is what I would do.

goto walmart buy 4qt's of their generic 75w90 gl-5 gear oil

Drain your MT save fluid
Fill with cheapo walmart fluid.

drive abit.. see if its better.

If it is.. use the Motul in the Rear end, and go shop for something good for the MT.

 

[Jconrad]

Wow! Quick reply!

Oddly enough Motul 300 is one of the most recommended gear oils I could find for the 6Mt, but maybe just not mine specifically.


I could certainly try some cheap dino oil for a little bit. Do you think I'm on the right track by messing with gear oil? I have already thrown too much money into trying to fix this..

If I do swap would you try flushing the trans with anything? Solvents etc.

 

[MolaKule]

Quote:
PAG’s in general have wonderfully stable VI but I’ve nothing to share on the OSP front. Seems Dow can’t give it ( OSP ) away.


Why would you put a differential fluid in a Manual Transmission.

I suspect your clutch may be out of adjustment and or you need a fluid replacement with an application specific manual transmission fluid.

What is the viscosity of the Motul 300 at 100C?

 

[Jconrad]

Originally Posted By: MolaKule
Why would you put a differential fluid in a Manual Transmission.

I suspect your clutch may be out of adjustment and or you need a fluid replacement with an application specific manual transmission fluid.

What is the viscosity of the Motul 300 at 100C?


I changed oil because of its stubbornness. It was either Extra-S or Motul 300 and Motul was more preferred especially in colder weather (Ohio).

I'm 95% sure my clutch is fully disengaged. Once in gear (with clutch pedal always to floor) I can take it out of gear and put it into any gear 100 times without problem.

"Motul 300 is 15.2 at 100C"

And what do you mean "application specific"? Its a performance car and I'm a lead foot on many occasions

I'm mainly wondering if there is an oil that combines nicely with Motul 300 that would help syncro engagement? I don't know a thing about the chemistry behind oils.

 

[Hounds]

JConrad, I am not a Roo guy, but like all officious intermeddlers, I have an opinion.

I'm going to take your word for it that the clutch system (disk, pressure plate, hydraulic fluid) is in working order, and that -- this is important -- the only changed variable is you changed the transmission fluid (gear oil). If that's correct, then IMHO you need to return to whatever fluid was in your Roo before the change or try a different fluid. WRT the latter, my humble recommendation is either the Pennzoil Synchromesh you mentioned or Amsoil's Synthetic Manual Synchromesh Transmission Fluid. (I'm not hawking the Amsoil, btw. I just know from years of experience using the stuff in a grillion Honda Si's that it works exceptionally well.)

However, for the sake of discussion, let's assume tha the stuff you have in there is not the source of your problem. (It is, but we're considering alternatives, right?) The other remote possibility is the clutch (hydraulic) fluid -- which, just like brake fluid (which it is) -- has become contaminated over time (it, too, is hydroscopic), and just like brake fluid, the air in the fluid is compressible, so the clutch either doesn't fully disengage (hard shifting) or is slow to dissengage (hard shifting). If you had difficulty shifting before you changed the gear oil -- be honest now -- then, were I you, I'd start here: change/replace the clutch fluid and bleed the system.

Final point: You really don't want to continue to operate the clutch in the manner you described. If you do so, the first-gear synchomesh, which is now doing all the work of slowing the gears down so you can engage them, will be shot in no time. In other words, what's occurring is THE classic way to ruin the lovely brass rings that allow the gears to engage without clashing.

 

[INDYMAC]

Lots of variables to play with here.

-It could be that you have the wrong transmission fluid in there. Try a MTF like Amsoil without mixing.

-Check your clutch master cylinder to make sure it's not leaking. Change your clutch fluid and bleed all the air out (may take longer than you think without vacuum).

-Regrease your shifter. This may surprise you on how well the shifts feel afterward.

 

[Bottom_Feeder]

Originally Posted By: Jconrad
It was either Extra-S or Motul 300 and Motul was more preferred especially in colder weather (Ohio).

You chose... poorly.

Dump what you have in there and fill it with Extra-S. No flushes, no mixing, no solvents. Just get all the Motul out and use Extra-S.

 

[Jconrad]

@Hounds:
I just want to add that I just replaced my Master/Slave/braided clutch line/DOT-5 oil a week ago and it is fully bleed (3 times

). The clutch is disengaging.

And This happened before I changed oil. I tried changing for the sole purpose of fixing problem. But idk what the original owner had in transmission before me.

I will look into your amsoil tho!

@INDYMAC:
I may just try a normal dino oil to see how that helps, quite possibly Amsoil.

Like I said to Hounds, hydraulic system is brand new and fully bled. 3X

And I could grease up my linkages and such, but my problem wouldn't be fixed by waiting 5 seconds to shift I don't think.

@Bottom_Feeder:
Thanks.. haha

I just don't know if I'm willing to drop 100 dollars on experimental oil just yet. If I try cheapo oil and it works I'll just have to spend the money, but my little money pit has me gun shy!





And again, thank you everyone for your comments!

 

[Bottom_Feeder]

I really wouldn't call using Subaru's own Extra-S 'experimenting'. Actually, using anything else BUT Extra-S would be experimenting. It would be money well spent in my opinion. I'm not saying it'll fix your problem, but it is an excellent fluid designed to cover what the transmission needs AND what the front diff needs, which is usually two different things as far as what is offered in the aftermarket.

Basically, if you still have the shifting problem after using Extra-S, then you'll pretty much know the problem is not with finding the correct fluid. It'll be a mechanical issue.

I have a 2001 non-turbo 2.5 RS. I can tell you as far as easily-available non-synthetic gear lube goes, Valvoline High Performance (white bottle) gear oil is the closet thing on paper to being what the Subaru transaxle needs but it got real notchy and a bit grindy after only a few thousand miles. Never again. Subaru OEM lube for me for now on.

 

[Jconrad]

Haha yeah I agree with you on the experimenting!

But my original goal was to buy a ~7 dollar quart of some mystery fluid with better synchro-meshing capabilities to try in my Motul. But I didn't want to ruin the properties of my current oil either..

Either way if the Motul doesn't work for me I guess I won't care if it gets trashed.


I guess my main question is: If I mix Pennzoil Synchromesh or Amsoil's Synthetic Manual Synchromesh with my Motul 300, would that cause any problems and would that possibly fix a slow synchro problem?

If so, which fluid and how much? (1 quart, 2 quarts etc)



If mixing a fluid does help, I'll probably buy the genuine Subaru stuff and try that. If not.. well idk?

 

[Mykl]

I had an '04 STi. I believe Subaru recommends new fluid in that gearbox every 40k miles, and the house fluid is more than sufficient. Remember, with that particular unit there's a LOT going on between the six gears and two limited slip differentials. I stuck to Subaru's specified maintenance schedule using their fluid and after 5000+ RPM drop-clutch launches and banging the shifter around during many autocrosses and track days (in addition to my aggressive street driving), the gearbox felt as good as new when I sold the car.

No matter what you put in it you aren't going to change the fact that the gearbox in that car is on the "burly" side. It's a stiff box that you have to be a little rougher with than most, but it's one of the stronger transmissions you'll find in any car, so beating on it isn't such a problem as long as you take care of it.

I would go back to Extra-S and freshen up the clutch hydraulics. If that doesn't fix it maybe the first gear syncro is shot.

 

[gathermewool]

The tranny and front gear-type LSD (front) call, which share the same bath, call for GL-5 gear oil, so Motul Gear 300 is perfect. When I compared these, it had the best on-paper specs than any of the others I put in the same category (e.g., Amsoil, RL, M1.)

STI gear boxes are known to be crunchy and clunky, though usually pretty stout. I tried to "cure" some of my crunchiness by switching from Extra S to Motul Gear 300 to Redline NS (no friction modifiers, for better synchro operation according to some,) without really any perceived difference at all. There are always some days that are better than others, and the first one of those I had after each gear oil change resulted in my thinking I'd finally found the perfect oil. The next day, or the day after that, it was back to be just as *normally* crunchy. (NOTE: these swaps were after ~30k on each oil, so there was plenty of time to evaluate any difference, over both hot and cold conditions.)

HOWEVER, if your synchros are on their way out, then a less-slippery oil may be in order. Something like Redline NS may help, but nothing will fix a failing synchro, IMO.

I would NOT use an MTL that is not GL-5 rated, as required.

 

[Jconrad]

Okay, well to update everyone, I gave in and decided to try Pennzoil Synchromesh. I bought one quart of it and drained one quart of the Motul. I did notice the Motul seemed almost less viscous than the Synchromesh which I wasn't expecting.

Anyway, It seems to have helped as per my maiden voyage. I can hear the synchros spin more pronounced than I could before and the shifting seems less notchy. Again I have yet to do a long term test (clearly!) but first impressions are good.

It has me wondering if I should now try to mix more pennzoil just to see if it gets even better, or try Extra-S (which scares me because if it is too slippery again I would have wasted 100 dollars)..

Still no grinding either! Haha

Again, thanks everyone for your posts!

 

[gathermewool]

I'm not sure about OH, but it's warming up here. All of my shifting issues usually arise as the temps fall below 40F, and magically disappear around this time, though my synchos may not be in as bad of shape as yours, being four years newer.

Also, Subaru requires GL-5 gear oil for a reason, though I doubt 1/5 being MTL would really harm anything. In all honesty, I'm not sure using five quarts of MTL would really harm a DD, and may be better for synchro engagement and logevity. FWIW, I believe Motul is both GL-4/5 rated, as evidenced by the not-as-nasty-as-the-competitors' smell, IIRC.

 

[Mykl]

Crunchy gears in cold weather is normal for that box. Mine was always grumpy on a morning when it had to sit outside in freezing weather. After it warmed up it felt good again though.

 

[SubLGT]

Originally Posted By: Jconrad
Okay, well to update everyone, I gave in and decided to try Pennzoil Synchromesh. I bought one quart of it and drained one quart of the Motul. ........


The Motul:Redline Lightweight Shockproof cocktail at 1:3 ratio also gets good reviews from Subaru owners. But if your STI trans is one of those with an oil pump, it is not recommended as I recall reading.

 

[MolaKule]

Quote:
And what do you mean "application specific"? Its a performance car and I'm a lead foot on many occasions


What we mean when we say "Application Specific" is a transmission oil developed and formulated for Manual Transmissions only in contrast to differential fluids, which have entirely different viscosity and additive package.

If your vehicle really does require a 75W90 (what does your owners manual state?), the something like this should help with the shifting.

http://www.redlineoil.com/product.aspx?pid=140&pcid=7

 

[Jconrad]

Well this is not a temperature specific problem. First was always difficult to get into gear. Whether is was 80F out or 10F out. Whether I drove for one minute or 2 hours.

It seems so me that Motul was/is just too slippery for my synchros and that by adding some synchromesh it helped them work.

I believe the trans calls for 75W90 but I'm not too concerned about having a quart of syncromesh in there. One day I may switch all over to extra-s or Redline, but for now it seems much better as a daily driver. (much more live-able, not perfect tho)

Shockproof kinda scares me due to the pump because it seems like a sticky goo, but I've also heard an argument about how they completely removed said pump in later 6MTs.

For now I think I'll save my money and drive it like it is, see if she changes any throughout time. But I've put probably 50 miles on it so far and the transmission seems way less notchy and more fluid to shift.

 

[MolaKule]

Originally Posted By: Jconrad
Well this is not a temperature specific problem. First was always difficult to get into gear. Whether is was 80F out or 10F out. Whether I drove for one minute or 2 hours.

It seems so me that Motul was/is just too slippery for my synchros and that by adding some synchromesh it helped them work.

I believe the trans calls for 75W90 but I'm not too concerned about having a quart of syncromesh in there. One day I may switch all over to extra-s or Redline, but for now it seems much better as a daily driver. (much more live-able, not perfect tho)

Shockproof kinda scares me due to the pump because it seems like a sticky goo, but I've also heard an argument about how they completely removed said pump in later 6MTs.

For now I think I'll save my money and drive it like it is, see if she changes any throughout time. But I've put probably 50 miles on it so far and the transmission seems way less notchy and more fluid to shift.


I think you may have seen a response from me before I corrected it:

This is the link which I gave after correction:

http://www.redlineoil.com/product.aspx?pid=140&pcid=7

I am basing this reommendation on your comments about adding Pennzoil Synchromesh, which is a 9.3 cSt fluid.

The average viscosity of the fluid you have in there now is 11.9 cSt.

The Redline MT-85 is 12.0 cSt.

Again, it is your vehicle and good luck with your choice.