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Synthetic Manual Transmission Oil ?? GL4 vs GL5


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25 replies to this topic

#1 rweddy

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Posted 13 April 2004 - 03:57 PM

Has anyone run Mobil 1 in their manual tranny? What about Redline MTL fluid?



The reason I ask this is in another car I nearly ruined the tranny buy putting mobil one in. It started shifting very notchy and very hard between gears. :banghead:
This was cured by putting in Redline MTL which is GL4 rated instead of GL5 like Modil 1. Then it shifted better then new with the Redline MTL in it. :D


I was told by a petroleum engineer that gl5 is actually too slick for proper synchro engagement, but many manufactures have just changed to recommending gl5 so they will not have to carry two types of gear lube at the dealerships.



But I know that in Subarus the front diff and transmission share the same fluid.

So would I be hurting the front differential by running the Redline in there??

#2 hklaine

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Posted 13 April 2004 - 05:44 PM

I use RedLine 7590NS in my Subi and have had no problems.

From www.redlineoil.com

75W90NS:
"This GL-5-type gear 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."

They also have another product
75W90:
"Our most popular gear oil, this is the preferred product in nearly all car and light truck differentials, both conventional and limited-slip. 75W90 is preferred for most racing applications. It contains friction modifier which is recommended for limited-slip units. 75W90 Gear Oil can be used in many transmissions and transaxles; however, other Red Line lubricants have better frictional properties for rapid synchronization. Exceeds API GL-5."

I don't particularly care for modifiers (friction or viscosity) and being as my car is not a limited slip I decided to go with the 75W90NS. I have been using it for quite some time with no ill effects. Shifting improved dramatically, especially in cold weather.

I double-clutch my car, but have not had any issues with synchros in situations where I have shifted w/o double clutching. BTW the car/tranny has 106k on it.

Just my personal experience. Haven't tried Mobil 1 or other synthetics for that matter.

-Heikki

#3 nickb21

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Posted 13 April 2004 - 09:49 PM

I put Mobil1 75w-90 in my MT5 and rear diff 4 or 5k ago. I haven't noticed a huge difference over the oem oil. And during some cold dips while upstate (-20F) it got really firm. Only complaint with shifting is the 2->3 shift feels a bit "notchy" as you put. Might try redline at some later point.. Or maybe a little dose of friction modifier would help?

Sidenote; I wonder if a syn. gear oil affects the reaction time of the viscous coupling?

--N

#4 hklaine

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Posted 13 April 2004 - 10:53 PM

I was actually going to mention this in my original reply. I feel that in the viscous coupling behavior, reaction became smoother and faster. Again I noticed this improvement primarily in cold weather. From my experience with this, my first AWD car, the action of the viscous coupling seems smoother when the gear fluids are warmer. Perhaps the synthetic helps here by being less prone to change in viscosity with temperature.

As for the shifting becoming more "notchy" I think there is validity to that as well from my experience. I personally prefer the notchy feel. (which can be enhanced further with trans mounts and shifter bushings)

*end rambling

:banana: <--- WHAT is this thing?!

#5 harborseal55

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Posted 14 April 2004 - 12:38 AM

I switched from whatever was in the car when I bought it to Redline 75W90NS in in my 96 Legacy 5spd and it really helped out the shifting. It had 115K when I bought it and often "chunked" into 2nd gear instead of smoothly engaging, and that went away completely after the NS had been in for about 2-3K miles and has shifted great ever since (now has 170K). The 75W90NS is less common (many places that carry Redline oil seem to carry the 75W90 but not carry the 75W90NS) but the NS appears to be what you want to use for the transaxel.

#6 sprintman

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Posted 14 April 2004 - 12:44 AM

GL5 75W90NS for the trans and 75W90 for the diff. Don't mix them up. Exactly as per the Cobb Tuning website. Works really nice. Going to change to GL4 MT-90 soon in my Mazda turbo trans, just need to do an Auto-Rx clean first

#7 rallyruss

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Posted 14 April 2004 - 12:45 AM

I will back up the MTL from red line. Have used it in manny different vehicles all with excelent results.

#8 rweddy

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Posted 14 April 2004 - 07:25 AM

[quote name='hklaine']As for the shifting becoming more "notchy" I think there is validity to that as well from my experience. I personally prefer the notchy feel. (QUOTE]

FYI that notchy feel is not a good thing. This is your grears hitting each other because the lube it too slick for the synchros to do their job.

#9 hklaine

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Posted 14 April 2004 - 08:30 AM

From Cobb:

75W90A GL-5+ grade oil which has a friction modifier and is more suited for a mechanical limited rear end instead of the transmission. If you want friction in the transmission, use the MT-90.
75W90NSAnother GL-5+ oil which offers good lubrication and bearing life. Best for the rear diff but can be used in the transmission.

Some Legacy models, mine for one, does not have a limited rear.

Perhaps notchy wasn't the best word for me to use as the feel I am discussing was increased with the bushing install and I don't think they would cause the gears to hit each other for any reason (?)

I don't mean a gear clash type feeling, or a resistance point when engaging the gear. What I really intended to express was that the engagement seems cleaner and more direct. Less play when shifting, and I found that this became better with the synthetic oil. The trans goes right into gear smooth and effortless in any temperature. Double clutching to reduce synchro involvement doesn't hurt either.

-Heikki

#10 rweddy

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Posted 14 April 2004 - 08:43 AM

From Cobb:

75W90A GL-5+ grade oil which has a friction modifier and is more suited for a mechanical limited rear end instead of the transmission. If you want friction in the transmission, use the MT-90.
75W90NSAnother GL-5+ oil which offers good lubrication and bearing life. Best for the rear diff but can be used in the transmission.

Some Legacy models, mine for one, does not have a limited rear.

Perhaps notchy wasn't the best word for me to use as the feel I am discussing was increased with the bushing install and I don't think they would cause the gears to hit each other for any reason (?)

I don't mean a gear clash type feeling, or a resistance point when engaging the gear. What I really intended to express was that the engagement seems cleaner and more direct. Less play when shifting, and I found that this became better with the synthetic oil. The trans goes right into gear smooth and effortless in any temperature. Double clutching to reduce synchro involvement doesn't hurt either.

-Heikki


Gotcha, thanks for the clarification. Right now I am having issues when down shifting into 3rd gear, goes in fine but semi grinds. I am hoping that changing to synthetic will clear up this issue.


Is there some way to tell if you have lsd??


Thanks!!

#11 frag

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Posted 14 April 2004 - 09:33 AM

About the effect of gear (and front diff) oil on the viscous coupling behavior (manual trans).
There can be none since the viscous coupling unit is a sealed and, in that respect, independent unit from the rest of the tranny.

#12 hklaine

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Posted 14 April 2004 - 05:43 PM

It's generally marked on the diff with a stamp/sticker, at least it was on the older Subi's. For some reason I was under the impression that LSD's weren't even available in the Legacy until 2000. Anyone know?

Frag: Where does the fluid for the the viscous coupling come from? It uses a separate reservoir?

Rweddy: You can always double-clutch the downshift if new fluid doesn't help. I had a '88 GL in which the 3rd gear synchros were shot for about 10k miles before the head gasket went and the car was scrapped.

-Heikki

#13 frag

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Posted 15 April 2004 - 09:35 AM

It's a sealed unit bolted onto the tail of the trans. Not serviceable. The fluid is in there between the plates.
Here's an adress where it is explained (posted by Commuter somewhere else...) http://auto.howstuff...fferential9.htm

#14 Setright

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Posted 16 April 2004 - 01:21 AM

Read this thread again: Someone is mixing up Redline 75W90 and 75W90NS

#15 hklaine

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Posted 16 April 2004 - 07:17 AM

frag: Thanks for the link. I understand the concept of the VC, just didn't know that it was sealed with its own fluid that was never replaced/flushed/serviced. Good to know.

-Heikki

#16 DerFahrer

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Posted 16 April 2004 - 10:28 PM

This topic has been hashed over so much on the old USMB it isn't funny. I don't know if any of those threads made it over to the new board, but I feel differently than most on this topic.

I refuse to use Redline, or any synthetic gear oil, in my Subaru MT's. I switched my Legacy over to Valvoline partial synth GL5 about 2 years ago. It drove peachy for a few months, then I would start grinding 4th a bit. Per someone's suggestion, I tried Redline 75W90NS GL5 in the tranny. Immediately, I was not able to shift into 4th without grinding unless I double-clutched. So I tried someone else's suggestion and mixed Redline MT90 GL4 with Redline 75W90NS GL5. Solved the problem entirely, but I had put GL4 oil in a transmission that asked for GL5.

Upon making the stupid mistake of playing with the axle seals in the tranny when changing axles, I made a huge leak (by huge I mean leaving a quart of gear oil on the driveway overnight :eek: ). So I began pouring whatever oil I could get in there until I had a professional fix it. I drove the fixed car away from the dealer with the previous GL4-GL5 mix, Mobil 1 synth, Redline 85W140, and whatever the dealer put in to compensate for the loss in my tranny! It shifted fine.

Feeling uneasy abour having 50 different types of gear oil in my tranny, I took Legacy777's suggestion, who doesn't even own an MT Subie :) , and put straight Castrol dino 80W90 in the tranny. It shifted more smoothly than any other oil I used before. I put the same oil in the XT when I got it with no problems, and after I did my tranny drop on the Legacy, I bought some el cheapo Coastal 80W90 in a gallon container from Discount for $5, and mixed that in with the rest of the Castrol I had around. That's what's in the Legacy now, and it shifts beautifully.

Therefore, synthetic oil is too slick for Subaru manual transmissions. Its extra-slick properties do not allow enough friction in the synchronizers and the gear speeds are not properly matched. Others on different Subaru boards have tried my methods and reported similar results. I feel my argument is based enough on simple trial-and-error to refute any mathematical claims Redline or anyone else may make.

#17 rweddy

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Posted 17 April 2004 - 11:52 AM

Therefore, synthetic oil is too slick for Subaru manual transmissions. Its extra-slick properties do not allow enough friction in the synchronizers and the gear speeds are not properly matched. Others on different Subaru boards have tried my methods and reported similar results. I feel my argument is based enough on simple trial-and-error to refute any mathematical claims Redline or anyone else may make.


I agree, but this is why they make MT-90 which is a GL4 tranny fluid, which is not too slick for manual transmissions. I am just wondering if this would hurt the front differential running this fluid, since they tranny and diff share fluids??

#18 BitBasher

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Posted 09 November 2006 - 02:05 AM

We've had a 2001 Forester 5spd for a little over a year now. I wasn't pleased with shifting, being notchy and stiff, with a weak 1st gear syncro. With 80K km on it, I thought that it wouldn't hurt to change to synthetic trans oil. I couldn't find a GL4 oil locally, so I went ahead and used in Castrol Syntec GL5 75W/90. Shifting was improved, but the syncro on 1st was no better. After living with it for 30K km, I added a bottle of GM LSD (limited slip differential) friction modifier. Since then I've put 1K on it, and am happy to report a significant improvement.

#19 frag

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Posted 09 November 2006 - 01:40 PM

This topic has been hashed over so much on the old USMB it isn't funny. I don't know if any of those threads made it over to the new board, but I feel differently than most on this topic.

I refuse to use Redline, or any synthetic gear oil, in my Subaru MT's. I switched my Legacy over to Valvoline partial synth GL5 about 2 years ago. It drove peachy for a few months, then I would start grinding 4th a bit. Per someone's suggestion, I tried Redline 75W90NS GL5 in the tranny. Immediately, I was not able to shift into 4th without grinding unless I double-clutched. So I tried someone else's suggestion and mixed Redline MT90 GL4 with Redline 75W90NS GL5. Solved the problem entirely, but I had put GL4 oil in a transmission that asked for GL5.

Upon making the stupid mistake of playing with the axle seals in the tranny when changing axles, I made a huge leak (by huge I mean leaving a quart of gear oil on the driveway overnight :eek: ). So I began pouring whatever oil I could get in there until I had a professional fix it. I drove the fixed car away from the dealer with the previous GL4-GL5 mix, Mobil 1 synth, Redline 85W140, and whatever the dealer put in to compensate for the loss in my tranny! It shifted fine.

Feeling uneasy abour having 50 different types of gear oil in my tranny, I took Legacy777's suggestion, who doesn't even own an MT Subie :) , and put straight Castrol dino 80W90 in the tranny. It shifted more smoothly than any other oil I used before. I put the same oil in the XT when I got it with no problems, and after I did my tranny drop on the Legacy, I bought some el cheapo Coastal 80W90 in a gallon container from Discount for $5, and mixed that in with the rest of the Castrol I had around. That's what's in the Legacy now, and it shifts beautifully.

Therefore, synthetic oil is too slick for Subaru manual transmissions. Its extra-slick properties do not allow enough friction in the synchronizers and the gear speeds are not properly matched. Others on different Subaru boards have tried my methods and reported similar results. I feel my argument is based enough on simple trial-and-error to refute any mathematical claims Redline or anyone else may make.


This is only a sample of one, but i use Mastercraft (Canadian Tire line of products) full synth in my manual transmission and have absolutely no problem shifting. I can even shift down to first while the car is still mooving a few kilometers per hour.

#20 rweddy

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Posted 09 November 2006 - 01:47 PM

This is only a sample of one, but i use Mastercraft (Canadian Tire line of products) full synth in my manual transmission and have absolutely no problem shifting. I can even shift down to first while the car is still mooving a few kilometers per hour.


Read this post.

http://www.ultimates...ead.php?t=41827

#21 Strakes

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Posted 09 November 2006 - 02:51 PM

On the NASIOC, many run "Uncle Scotty's Cocktail":

1qt Redline Lightweight Shockproof
1qt Pennzoil or GM Synchromesh
2qt Castrol Hypoy-C 80w-90

To avoid the "is it going to fry my transmission", many change this every 10-15K miles.

#22 fnlyfnd

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Posted 09 November 2006 - 09:10 PM

what's this "fring of tranny" you speak of??

#23 Strakes

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Posted 09 November 2006 - 11:04 PM

I haven't heard of anyone messing up their transmission with the cocktail. I've been using it and love it. Some are concerned that it isn't up to the owner's manual recommendations of keeping it all one brand of fluid. Plus, I think the GM synchromesh is GL4 and that may get some raised eyebrows. So taking their legitimate concerns into consideration, I like to change my transmission fluid more often to compensate for the lack of 100% GL5 fluid. IIRC, the main difference between GL4 and GL5 is the percentage of certain additives...GL5 having more of them.

#24 DerFahrer

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Posted 09 November 2006 - 11:21 PM

I've learned a lot about this type of stuff since that posting. It appears I had the diff and gear oils mixed up, as the regular Redline 75W90 belongs in the transmission because it has friction modifiers for the synchros, and the Redline 75W90NS belongs in the diff, because it does not have friction modifiers, and they're not needed since there are no synchros in the diff.

That said, I am running the GM Synchromesh and am very happy with the results. I was having a slight resistance engaging 3rd and 4th gear downshifting with the plain cheap dino oil I was using. That went away with the Synchromesh.

And before anyone wonders about its compatibility with Subaru transmissions, my dealer keeps it in stock for use in Subaru transmissions to alleviate this very problem. We feel that confident about it.

#25 rweddy

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Posted 09 November 2006 - 11:37 PM

I've learned a lot about this type of stuff since that posting. It appears I had the diff and gear oils mixed up, as the regular Redline 75W90 belongs in the transmission because it has friction modifiers for the synchros, and the Redline 75W90NS belongs in the diff, because it does not have friction modifiers, and they're not needed since there are no synchros in the diff.

Yep this is correct, I have run 75W90NS in 5 of my 12 subaru's and it has always worked great, here it the chat I had with a redline tech.
>Request Type : Technical Request
>Message : Hello
>
>I am trying to figure out what type fluid I should run in my vehicle
>manual transmissions. I have used your MT-90 in multiple vehicles
>with great success.
>
>My question revolves around running a GL4 transmission fluid in a
>Subaru where the transmission and front differential share the fluid.
>
>The factory recommends using GL5 fluid but I have run GL4 in most
>all my manual box and the difference between running GL5 and GL4 is
>night and day, with the GL4 working sooo much better.
>
>What type of fluid would you recommend I run in a Subaru with shared
>transmission and front differential?
>
>Thank

Richard,

In your Subaru transaxle where the GL-5 gear lube is called for I
would recommend the 75W90NS, I would expect the shiftability to be
close to the MT-90. The NS fluids have no friction modifier so are
not to slippery for the synchros the problem with most GL-5 gear
oils. The 75W90 would be suitable for the rear differential.

Regards, Dave
Red Line Oil




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