Subaru STi Syncro/Gear oil Conundrum!
- Thread starter Jconrad
- Start date
- Status
MolaKule
Staff member
gathermewool
Site Donor 2025
Originally Posted By: Jconrad
Hmmm, well now I'm confused. I believe my trans calls for a GL-5 gear oil. So would your GL-4 Redline be sufficient for the 6Mt?
Also, does cSt basically mean how thick/thin the oil is? And does that number correlate with synchro engagement?
MolaKule, is your recommendation made knowing the front LSD and transmission share an oil bath, and that GL-5 is required?
I'd for sure like some smoother shifts, but, like the OP I never grind (nor do I have any issues like he's seemingly having,) and wouldn't want to risk my diff. Know, however, that I don't track my car (though I may some day,) but do drive spiritedly, and do have fun in the snow when it's safe to do so.
Hmmm, well now I'm confused. I believe my trans calls for a GL-5 gear oil. So would your GL-4 Redline be sufficient for the 6Mt?
Also, does cSt basically mean how thick/thin the oil is? And does that number correlate with synchro engagement?
MolaKule, is your recommendation made knowing the front LSD and transmission share an oil bath, and that GL-5 is required?
I'd for sure like some smoother shifts, but, like the OP I never grind (nor do I have any issues like he's seemingly having,) and wouldn't want to risk my diff. Know, however, that I don't track my car (though I may some day,) but do drive spiritedly, and do have fun in the snow when it's safe to do so.
Last edited:
MolaKule
Staff member
Quote:
MolaKule, is your recommendation made knowing the front LSD and transmission share an oil bath, and that GL-5 is required?
Yes, I am fully aware of the common oil bath and his comments:
Quote:
I believe the trans calls for 75W90 but I'm not too concerned about having a quart of Synchromesh 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)
MolaKule, is your recommendation made knowing the front LSD and transmission share an oil bath, and that GL-5 is required?
Yes, I am fully aware of the common oil bath and his comments:
Quote:
I believe the trans calls for 75W90 but I'm not too concerned about having a quart of Synchromesh 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)
Last edited:
MolaKule
Staff member
He has thinned his oil down from about 15.0 cSt to 12 cSt.
But what he has NOT diluted is his Anti-Wear additives since the Pennzoil Synchromesh Brand has a good measure of them to protect the internals.
But what he has NOT diluted is his Anti-Wear additives since the Pennzoil Synchromesh Brand has a good measure of them to protect the internals.
gathermewool
Site Donor 2025
Originally Posted By: MolaKule
He has thinned his oil down from about 15.0 cSt to 12 cSt.
But what he has NOT diluted is his Anti-Wear additives since the Pennzoil Synchromesh Brand has a good measure of them to protect the internals.
That was my main concern, and reason for reiterating the GL-5 spec. Thanks for commenting. Any further information would be great, as well.
He has thinned his oil down from about 15.0 cSt to 12 cSt.
But what he has NOT diluted is his Anti-Wear additives since the Pennzoil Synchromesh Brand has a good measure of them to protect the internals.
That was my main concern, and reason for reiterating the GL-5 spec. Thanks for commenting. Any further information would be great, as well.
Redline says the GL-4 MT-85 is not for use with hypoid gear sets, and since the Subaru trans has a hypoid gear set inside it, my conclusion is that it is not the right lube. Am I mistaken?
In the 5 speed manual in my 2005 Legacy, Subaru recommends a 75W90 oil, but also approves a single weight 85W if temperatures are above -22 degF (does anyone even manufacture a 85W automotive gear oil?). Both have to be GL-5.
In the 5 speed manual in my 2005 Legacy, Subaru recommends a 75W90 oil, but also approves a single weight 85W if temperatures are above -22 degF (does anyone even manufacture a 85W automotive gear oil?). Both have to be GL-5.
MolaKule
Staff member
Quote:
Redline says the GL-4 MT-85 is not for use with hypoid gear sets, and since the Subaru trans has a hypoid gear set inside it, my conclusion is that it is not the right lube. Am I mistaken?
Thanks SubeLGT, that is what I have asking around the various sube threads and until your response, no one seemed to know or no one would answer with a definitive response;
1. what type of drive system is this?
1a) Transaxle, this a transmission and differential in one case and usually has a spider gear differential, and can take take anywhere from a 10 cst GL-4 (5W30) to a 14.5 cSt (75W90) GL-4.
1b) separate transmission and differential with separate units and separate fluids, what type of differential is this? Spider gear or hypoid? If the differential is a hypoid type of design and the fluid should have a GL-5 protection rating.
1c) separate transmission and differential which share same fluids, what type of differential is this? Spider gear or hypoid?
If indeed it is a hypoid differential AND it shares a common oil sump or bath, then yes, the protection rating of the fluid should be a GL-5.
If the spec is for a 75W90 GL-5 gear lube, which is a 15-17 cSt fluid, then it sounds as if the owner will have to put up with cold weather shifting problems. In my view, this a dumb design.
If he currently has half Pennzoil Synchromesh GL-4 and the 75W90 with a GL-5, I don't think it is going to grenade, but he should replace the fluid with a 75W90 with a GL-5 rating.
Redline says the GL-4 MT-85 is not for use with hypoid gear sets, and since the Subaru trans has a hypoid gear set inside it, my conclusion is that it is not the right lube. Am I mistaken?
Thanks SubeLGT, that is what I have asking around the various sube threads and until your response, no one seemed to know or no one would answer with a definitive response;
1. what type of drive system is this?
1a) Transaxle, this a transmission and differential in one case and usually has a spider gear differential, and can take take anywhere from a 10 cst GL-4 (5W30) to a 14.5 cSt (75W90) GL-4.
1b) separate transmission and differential with separate units and separate fluids, what type of differential is this? Spider gear or hypoid? If the differential is a hypoid type of design and the fluid should have a GL-5 protection rating.
1c) separate transmission and differential which share same fluids, what type of differential is this? Spider gear or hypoid?
If indeed it is a hypoid differential AND it shares a common oil sump or bath, then yes, the protection rating of the fluid should be a GL-5.
If the spec is for a 75W90 GL-5 gear lube, which is a 15-17 cSt fluid, then it sounds as if the owner will have to put up with cold weather shifting problems. In my view, this a dumb design.
If he currently has half Pennzoil Synchromesh GL-4 and the 75W90 with a GL-5, I don't think it is going to grenade, but he should replace the fluid with a 75W90 with a GL-5 rating.
Last edited:
I didn't know it was such a complex question! Haha
I just want to add though, this is not a cold weather problem. This is an all the time-everyday-all weather problem. It gets a tiny bit better when car is warmed up (as any trans does) but especially before I added the synchromesh it was really hard to get into first gear within any sort of "reasonable" (aka: push and hold in clutch in for 5 seconds) time.
I still think my synchros work because they were stopping my gears from grinding. And I think the Motul 300 was/is too slippery to operate/spin my probably aging synchros. By adding the synchromesh my oil became more "abrasive" and the synchros started working better.
Again, not perfect, but definitely better. 3Qs Motul-1Q Synchromesh
I just want to add though, this is not a cold weather problem. This is an all the time-everyday-all weather problem. It gets a tiny bit better when car is warmed up (as any trans does) but especially before I added the synchromesh it was really hard to get into first gear within any sort of "reasonable" (aka: push and hold in clutch in for 5 seconds) time.
I still think my synchros work because they were stopping my gears from grinding. And I think the Motul 300 was/is too slippery to operate/spin my probably aging synchros. By adding the synchromesh my oil became more "abrasive" and the synchros started working better.
Again, not perfect, but definitely better. 3Qs Motul-1Q Synchromesh
MolaKule
Staff member
Quote:
I still think my synchros work because they were stopping my gears from grinding. And I think the Motul 300 was/is too slippery to operate/spin my probably aging synchros. By adding the synchromesh my oil became more "abrasive" and the synchros started working better.
I doubt it.
Elf Motul 300 probably has everything but the correct friction modifer in it.
Adding the Pennzoil Synchromesh gave the mix some of the needed and correct friction modifier, and the Pennzoil thinned it down a bit.
You could have helped us out by giving more information.
Like I said, I am surprised Subaru made such a dumb design.
I still think my synchros work because they were stopping my gears from grinding. And I think the Motul 300 was/is too slippery to operate/spin my probably aging synchros. By adding the synchromesh my oil became more "abrasive" and the synchros started working better.
I doubt it.
Elf Motul 300 probably has everything but the correct friction modifer in it.
Adding the Pennzoil Synchromesh gave the mix some of the needed and correct friction modifier, and the Pennzoil thinned it down a bit.
You could have helped us out by giving more information.
Like I said, I am surprised Subaru made such a dumb design.
Last edited:
Here's a link to more info on the OP's 2004 STI 6MT transmission.
http://ken-gilbert.com/wrx/STi_Manual/04...Description.pdf
The link below has a menu on the left hand side for easier navigation if you wan to view a different part of the manual.
http://ken-gilbert.com/wrx/STi_Manual/
I also have access to other service manuals if information is needed on other subaru models.
http://ken-gilbert.com/wrx/STi_Manual/04...Description.pdf
The link below has a menu on the left hand side for easier navigation if you wan to view a different part of the manual.
http://ken-gilbert.com/wrx/STi_Manual/
I also have access to other service manuals if information is needed on other subaru models.
Originally Posted By: MolaKule
Quote:
I still think my synchros work because they were stopping my gears from grinding. And I think the Motul 300 was/is too slippery to operate/spin my probably aging synchros. By adding the synchromesh my oil became more "abrasive" and the synchros started working better.
I doubt it.
Elf Motul 300 probably has everything but the correct friction modifer in it.
Adding the Pennzoil Synchromesh gave the mix some of the needed and correct friction modifier, and the Pennzoil thinned it down a bit.
You could have helped us out by giving more information.
Like I said, I am surprised Subaru made such a dumb design.
I have to disagree with you on that post..
You just said the Motul was likely too slippery and the Pennzoil added a sufficient amount of friction modifier. Which is what I just got done saying. In fact I've already tried it and it worked to some extent...
And what more information do you need? The front differential and the transmission share the same fluid, that's really as far as I know not having taken one apart. By no means would I consider it a "dumb" design either. I'm merely having more difficulty than most with my specific vehicle.
Quote:
I still think my synchros work because they were stopping my gears from grinding. And I think the Motul 300 was/is too slippery to operate/spin my probably aging synchros. By adding the synchromesh my oil became more "abrasive" and the synchros started working better.
I doubt it.
Elf Motul 300 probably has everything but the correct friction modifer in it.
Adding the Pennzoil Synchromesh gave the mix some of the needed and correct friction modifier, and the Pennzoil thinned it down a bit.
You could have helped us out by giving more information.
Like I said, I am surprised Subaru made such a dumb design.
I have to disagree with you on that post..
You just said the Motul was likely too slippery and the Pennzoil added a sufficient amount of friction modifier. Which is what I just got done saying. In fact I've already tried it and it worked to some extent...
And what more information do you need? The front differential and the transmission share the same fluid, that's really as far as I know not having taken one apart. By no means would I consider it a "dumb" design either. I'm merely having more difficulty than most with my specific vehicle.
gathermewool
Site Donor 2025
Molakule? What more information did you need? I could have elaborated if you had any questions, but your recommendation and response to my inquiry made it seem as if you were fully aware of the STi's design and lubrication requirements.
Why do you think the design is dumb? I do believe that having a common sump leads to the common fluid requirement erring on the conservative side (GL-5,) which COULD reduce synchro life/action, but I always thought that was the price to pay for such a robust system.
Also, there are GL-5 lubes out there that are less caustic toward yellow metals, right?
Either way, I've noticed no change in shifter feel with any of the fluids I've used, including Subaru's Go Extra S, Motul Gear 300, and Redline's NS. These transmissions are again know to be robust, but will never be described as buttery smooth.
Why do you think the design is dumb? I do believe that having a common sump leads to the common fluid requirement erring on the conservative side (GL-5,) which COULD reduce synchro life/action, but I always thought that was the price to pay for such a robust system.
Also, there are GL-5 lubes out there that are less caustic toward yellow metals, right?
Either way, I've noticed no change in shifter feel with any of the fluids I've used, including Subaru's Go Extra S, Motul Gear 300, and Redline's NS. These transmissions are again know to be robust, but will never be described as buttery smooth.
I have a 2009 legacy with a 5 speed manual transmission, and my transmission also has a common sump up front. My car now has 130k on it, and most of the time my transmission shifts just fine. When I try to shift too fast however, the transmission will grind. I don't think the the transmission has always acted this way, I feel like I could shift fast without any problems before. I just assumed that synchros were getting a little worn, and that's why I can no longer shift very fast. I'll admit I have to try and shift pretty fast for it to happen, so it's really not a big deal. Now I'm wondering if GL-5 fluids could have accelerated my synchro wear? I've used the following gear oils in the past:
-Factory fill -> Amsoil Severe gear 75w-90 -> Subaru Extra-S 75w-90 -> Amsoil SVG 75w-90 -> Supertech synthetic blend 75w-90, which is what I currently still use.
-Factory fill -> Amsoil Severe gear 75w-90 -> Subaru Extra-S 75w-90 -> Amsoil SVG 75w-90 -> Supertech synthetic blend 75w-90, which is what I currently still use.
It sounds more like your clutch isn't disengaging fully.
Have you tried selecting second, then back across the gate into first ?
Or just part releasing the clutch to reposition the dogs incase they're meeting face to face ?
FWIW Motul Gear 300 is one of the best MTF/transaxle fluids I've tried (in a L/Rover g/box, not a Subbie)
Gearboxes can be idiosyncratic even within the same model, what appears to shift nicely in one can be clunky in another.
Gear 300 is often recommended for Subaru's, as is Neo 75W-90HD and Castrol Syntrax 75W-90, but be careful with Syntrax as Castrol have recently changed the name of a lot of their products, you need the one that's blended for the Jaguar XJ220 transaxle.
All I've listed are dual rated GL4/5's for hypoid gear use. I've used Syntrax for 300,000km in a Nissan Y61 Patrol g/box with great success.
Have you tried selecting second, then back across the gate into first ?
Or just part releasing the clutch to reposition the dogs incase they're meeting face to face ?
FWIW Motul Gear 300 is one of the best MTF/transaxle fluids I've tried (in a L/Rover g/box, not a Subbie)
Gearboxes can be idiosyncratic even within the same model, what appears to shift nicely in one can be clunky in another.
Gear 300 is often recommended for Subaru's, as is Neo 75W-90HD and Castrol Syntrax 75W-90, but be careful with Syntrax as Castrol have recently changed the name of a lot of their products, you need the one that's blended for the Jaguar XJ220 transaxle.
All I've listed are dual rated GL4/5's for hypoid gear use. I've used Syntrax for 300,000km in a Nissan Y61 Patrol g/box with great success.
I took a look at this diagram http://ken-gilbert.com/wrx/STi_Manual/ and noticed there are quite a few bushings, o-rings and grease areas involved with the shifter linkage. We all know that these things deteriorate with age, especially if moisture is present. If you are using the correct MTF, and your clutch is in good shape, consider focussing on this area before rebuilding your transmission.
I'm not familiar with the Subie, but I plan to do this http://www.s2ki.com/s2000/topic/772277-regrease-shifter-diy/ soon on my 2004 S2000. It's starting to get notchy all the time now.
I'm not familiar with the Subie, but I plan to do this http://www.s2ki.com/s2000/topic/772277-regrease-shifter-diy/ soon on my 2004 S2000. It's starting to get notchy all the time now.
gathermewool
Site Donor 2025
Originally Posted By: INDYMAC
I took a look at this diagram http://ken-gilbert.com/wrx/STi_Manual/ and noticed there are quite a few bushings, o-rings and grease areas involved with the shifter linkage. We all know that these things deteriorate with age, especially if moisture is present. If you are using the correct MTF, and your clutch is in good shape, consider focussing on this area before rebuilding your transmission.
I'm not familiar with the Subie, but I plan to do this http://www.s2ki.com/s2000/topic/772277-regrease-shifter-diy/ soon on my 2004 S2000. It's starting to get notchy all the time now.
Good point. Since swapping out all of my shifter bushings for poly, I've noticed that my yearly lubing results in a noticeable lowering in shift effort. Every so often I'll lube up in winter and slightly over-tighten the shift linkage, which will result in very hard shifts when it expands with the heat of summer. When I pull the shift boot off, there's poly dust all over the place!
I took a look at this diagram http://ken-gilbert.com/wrx/STi_Manual/ and noticed there are quite a few bushings, o-rings and grease areas involved with the shifter linkage. We all know that these things deteriorate with age, especially if moisture is present. If you are using the correct MTF, and your clutch is in good shape, consider focussing on this area before rebuilding your transmission.
I'm not familiar with the Subie, but I plan to do this http://www.s2ki.com/s2000/topic/772277-regrease-shifter-diy/ soon on my 2004 S2000. It's starting to get notchy all the time now.
Good point. Since swapping out all of my shifter bushings for poly, I've noticed that my yearly lubing results in a noticeable lowering in shift effort. Every so often I'll lube up in winter and slightly over-tighten the shift linkage, which will result in very hard shifts when it expands with the heat of summer. When I pull the shift boot off, there's poly dust all over the place!
MolaKule
Staff member
Quote:
You just said the Motul was likely too slippery and the Pennzoil added a sufficient amount of friction modifier. Which is what I just got done saying. In fact I've already tried it and it worked to some extent...
No I was disagreeing with you. The Motul has an excellent base oil with a close viscosity and but it does not have the friction modification necessary for manual synchromesh transmissions.
You just said the Motul was likely too slippery and the Pennzoil added a sufficient amount of friction modifier. Which is what I just got done saying. In fact I've already tried it and it worked to some extent...
No I was disagreeing with you. The Motul has an excellent base oil with a close viscosity and but it does not have the friction modification necessary for manual synchromesh transmissions.
Last edited:
MolaKule
Staff member
Quote:
Molakule? What more information did you need? I could have elaborated if you had any questions, but your recommendation and response to my inquiry made it seem as if you were fully aware of the STi's design and lubrication requirements.
Why do you think the design is dumb?
I was basing it on J's response and wrongly assumed he knew what kind of mechanical systems he had there.
When you have a hypoid differential using the same fluid as the transmission, you are forcing the transmission to shift in a fluid that is not optimum. That is, it is difficult to make a fluid to have the GL-5 protection properties for differentials and at the same time provide some measure of friction modification to the transmission.
Not to mention that wear particles from both are being exchanged in the bath.
I do hope the Subie transmissions are robust because with a nutty design such as this, they certainly need to be.
Molakule? What more information did you need? I could have elaborated if you had any questions, but your recommendation and response to my inquiry made it seem as if you were fully aware of the STi's design and lubrication requirements.
Why do you think the design is dumb?
I was basing it on J's response and wrongly assumed he knew what kind of mechanical systems he had there.
When you have a hypoid differential using the same fluid as the transmission, you are forcing the transmission to shift in a fluid that is not optimum. That is, it is difficult to make a fluid to have the GL-5 protection properties for differentials and at the same time provide some measure of friction modification to the transmission.
Not to mention that wear particles from both are being exchanged in the bath.
I do hope the Subie transmissions are robust because with a nutty design such as this, they certainly need to be.
Last edited:
gathermewool
Site Donor 2025
Originally Posted By: MolaKule
Quote:
Molakule? What more information did you need? I could have elaborated if you had any questions, but your recommendation and response to my inquiry made it seem as if you were fully aware of the STi's design and lubrication requirements.
Why do you think the design is dumb?
I was basing it on J's response and wrongly assumed he knew what kind of mechanical systems he had there.
When you have a hypoid differential using the same fluid as the transmission, you are forcing the transmission to shift in a fluid that is not optimum. That is, it is difficult to make a fluid to have the GL-5 protection properties for differentials and at the same time provide some measure of friction modification to the transmission.
Not to mention that wear particles from both are being exchanged in the bath.
I do hope the Subie transmissions are robust because with a nutty design such as this, they certainly need to be.
Thanks for the clarification. Knowing this, what would you recommend?
Quote:
Molakule? What more information did you need? I could have elaborated if you had any questions, but your recommendation and response to my inquiry made it seem as if you were fully aware of the STi's design and lubrication requirements.
Why do you think the design is dumb?
I was basing it on J's response and wrongly assumed he knew what kind of mechanical systems he had there.
When you have a hypoid differential using the same fluid as the transmission, you are forcing the transmission to shift in a fluid that is not optimum. That is, it is difficult to make a fluid to have the GL-5 protection properties for differentials and at the same time provide some measure of friction modification to the transmission.
Not to mention that wear particles from both are being exchanged in the bath.
I do hope the Subie transmissions are robust because with a nutty design such as this, they certainly need to be.
Thanks for the clarification. Knowing this, what would you recommend?
- Status