Thinnest gear oil made for manual transmission????

[grndslm]

Hello,

I'm in search of the thinnest gear oil made for a manual transmission.

Long story, short is that I just bought a '94 Nissan Hardbody with 208k miles. It doesn't appear to be kept up as well as I'd like, but I got it for just a tad more than scrap value, and it DOES run. Very impressive really, but I'd like to fix the occasional transmission whine that goes away when I push in the clutch.

Apparently, this whine is an input shaft bearing... and I'm wondering if I used the thinnest gear oil in existence, maybe it would re-lubricate the bearings??

0w-90? 15w-90? 0w-80? 15w-80?

Prolly doesn't make a difference if it's synthetic or not...

But just for reference, the stock transmission calls for 80w-90 w/ GL-4 (maybe 75w-90).

Definitely looking for something much thinner than 75w-90, tho. What are my options??

 

[Shannow]

By input shaft bearing, and when on the clutch, do you actually mean throwout bearing ?

If so, no oil will fix it.

Mobil 424 is the GL-4 fluid chosen by Oz drifters with Nissan boxes.

 

[grndslm]

Originally Posted By: Shannow
By input shaft bearing, and when on the clutch, do you actually mean throwout bearing ?

If so, no oil will fix it.

Mobil 424 is the GL-4 fluid chosen by Oz drifters with Nissan boxes.

I bought the car, thinking it was the throwout bearing.

But from what I've been reading, it appears to be an "input shaft bearing" that is internal to the transmission. Essentially... when I push the clutch in, no more whine. Therefore, it's probly not the throwout bearing.

Sooo.... I'm thinking that the lightest oil possible will get me to where I want to be.

Perhaps I could just fill 'er up with some 5w-30 or 5w-40, let the engine idle for an hour and then maybe drive around the block??? Then switch back to a 75w-90??

 

[Shannow]

Nah, you need to understand that engine oil viscosity and gear oil viscosity are different colours on the same animal...

a 40 engine and 90 gear are about the same, so there's no 15W-90.

http://www.bobistheoilguy.com/putting-the-simple-back-into-viscosity/

The Mobil 424 is a 75W-80 I think, which would be a 10W-30 in engine oil rates (which it isn't), which makes the BMW SAE 30 requirement in some of their older gearboxes seem not so "funny" after all.

 

[KD0AXS]

Amsoil calls their Synchromesh a 5W-30.

http://www.amsoil.com/shop/by-product/tr...on-fluid-5w-30/

 

[grndslm]

Originally Posted By: Shannow
Nah, you need to understand that engine oil viscosity and gear oil viscosity are different colours on the same animal...

a 40 engine and 90 gear are about the same, so there's no 15W-90.

http://www.bobistheoilguy.com/putting-the-simple-back-into-viscosity/

The Mobil 424 is a 75W-80 I think, which would be a 10W-30 in engine oil rates (which it isn't), which makes the BMW SAE 30 requirement in some of their older gearboxes seem not so "funny" after all.

Something seems wrong with that chart.

Gear oil is thicker than motor oil. My eyes tell me this.

And it appears that your eyes tell you a 10w-30 cannot be compared to a 75w-80, even tho the chart says they're "the same animal".

Definitely something fishy with the equivalents, but I'm willing to admit that the differences are not as great as the numbers used to compare them initially led me to believe.

Originally Posted By: KD0AXS
Amsoil calls their Synchromesh a 5W-30.

http://www.amsoil.com/shop/by-product/tr...on-fluid-5w-30/

Thanks for the recommendation!!

I just might try that out. Might prevent me from doing a double flush, like I was originally planning to do.

But this whole motor oil equals gear oil chart is throwing a wrench in my understanding.

 

[229]

Synchronizers are not compatible with some of the ingredients in engine oil.

 

[Gotch]

Nothing will "cure" a bad imput shaft bearing noise. Maybe "thicker" oil would reduce it, thinner would just make it louder.

I had a bad one on a 98 Civic that I did myself. When I pulled the trans apart I found that the imput shaft bearing was installed backwards at the factory, causing the failure. New bearing (didn't touch anything else) fresh fluid and good to go for another 300k. $100 bucks in parts and a Saturday.

That being said, your symptoms point more towards the throwout bearing...

 

[hounddog]

Factory fill use to be straight 75weight on Nissan manuals. Used a Kendall gear oil. 80w90 was too thick for cold mornings. First or second time shifted cold it would be hard to get in the next gear and might grind some. 75weight eliminated this. If clutch in it goes away its internal in the trans. For a experienced Nissan tech and if parts in stock its a half day,one day job including replacing clutch parts as needed. I handled Datsun/Nissan 15 years. Most all the techs in the shop 12 plus ALL did manual trans repair. It was a daily occurrence in busy times.

 

[JHZR2]

Something like Redline D4 which is a GL-4 add pack equivalent ATF suitable for use in MTs is the thinnest.

There are a few write-ups on BITOG about the various classes of MTFs.

I doubt it will fix the whine though...

 

[SLCraig]

I would just use a new spec'd fluid... Amsoil MTG gets my vote. I used it in my Nissan 6 speed trans and it was fantastic.

 

[scurvy]

Some data from TDIClub as manual transmission fluids have been discussed there ad nauseum. I expect some of these may have varied since the viscosities were checked, so take these as a relative comparison based upon historical data only:

Viscosity Comparison @ 100ºC (in cSt)
17.5 = Royal Purple Max Gear 75W90
16.7 = Motul MOTYLGEAR 75W90
15.6 = Redline MT-90 75W90
15.2 = Motul Gear 300 75W90
15.0 = Elf Tranself Synthese FE 75W90
13.8 = Amsoil MTG 75W90
10.6 = Redline MTL 70W80
9.1 = Pennzoil (GM) Syncromesh
7.5 = Red Line D4
6.3 = VW G052 (part numbers G052726A2 / G05272601)

I couldn't find viscosity listed for the 'latest & greatest' VW OEM manual gearbox fluids (G070726A2) but IIRC it is thinner yet than the G052 fluid. I've had it in my Golf's transmission for the last 100k km and it's been excellent in everything from deep cold to blistering heat but probably time to change it now.

 

[dparm]

Honda's MTF is typically 70w80, IIRC.

BTW, I have never trusted that crazy-low viscosity figure for the VW fluids. It's Castrol TAF-X, and the spec sheet on that does not show the 6 value...

 

[scurvy]

Originally Posted By: dparm
BTW, I have never trusted that crazy-low viscosity figure for the VW fluids. It's Castrol TAF-X, and the spec sheet on that does not show the 6 value...


It can't be, unless you're talking about the original G050 gear oil (although that one is 15.6 cSt @ 100ºC).

Castrol TAF-X lists 14.4 cSt @ 100ºC on its spec sheet.

sunrg on TDIClub bought the G052 fluid and drove it to a Cat lab and had it tested right in front of him.

Maybe I can borrow an Ostwald viscometer from work and test the G070 when I go to change it...

 

[badtlc]

Redline MTL 70w-80. That is the thinnest "manual transmission fluid" I have seen.

 

[aquariuscsm]

You could always try RP Synchromax,which has the viscosity of ATF,BUT,you don`t want it so thin that you ruin the tranny`s internal bearings and gears. Nissan trannies are designed for 75W90 GL4 gear oil. Drain and refill with the best manual tranny gear oil on the planet,Amsoil MTG. You`ll notice an immediate difference.

 

[grndslm]

Hmm....

Well, it looks like I spoke too soon!!! Drove the truck for its fourth trip, on some back roads today. And it is quite obvious to me now that it's just the throw out bearing. So that's great news, IMO.

Made another noise, which I can only assume came from the pressure plate. And there was an issue where I was grinding in first gear a couple times, which I believe was the reason the previous owner sold the truck. Dunno if that's from a leaky slave cylinder or what....

But anyway, this thread was extremely eye opening to me for a number of reasons.

Since I'll be dropping the transmission, that will make filling it up with fresh oil just that much easier. From that viscosity comparison, I think the Amsoil MTG 75w-90 is right up my alley.

Thanks a lot, guys!!

 

[mechtech2]

You are going the wrong way!
The last thing you want is thinner lube!
Is this a real post?

 

[440Magnum]

Originally Posted By: grndslm

Something seems wrong with that chart.

Gear oil is thicker than motor oil. My eyes tell me this.



Your eyes are a lousy viscosity measurement tool. The chart is right.

When GL3 gear oil became unobtanium, Jeep issued a service bulletin for the AX-15 5-speed manual box used in 96-99 XJ Cherokees, suggesting the use of synthetic 10w40 engine oil to protect the synchros in that gearbox. 10w40 was chosen because the viscosity is essentially identical to the 90-wt GL3 gear oil originally recommended.

 

[grndslm]

OK.... Drove the truck one more time today, same distance.... and now the throwout bearing is making ZERO noise, and the input bearing is definitely noticeable when idling next to a building, or wall. So the hunt continues --

Originally Posted By: mechtech2
You are going the wrong way!
The last thing you want is thinner lube!
Is this a real post?

Yes it is.

I am ignorant of many things, but I am no longer ignorant about my transmission bearings needing more oil. My theory would be that the thinnest gear oil would hopefully re-lube the trans bearings. Thicker gear oil is great for GEARS... but I'm in search of bearing oil now.

The idea is NOT for me to run this gear oil any more than at a long idle and then around the block, which is maybe 1/5th of a mile. THEN I'd be changing to a different gear oil, which looks like it might be the Amsoil MTG.

Soo.... the real issue for me is...

Would the Amsoil Synchromesh 5w-30 possibly do a better job at re-lubricating dry transmission bearings than the Amsoil MTG??

[Remember, the 5w-30 is only TEMPORARY and will almost immediately be replaced with the MTG]

EDIT: I also realize that GL-4 is required for the synchros, but as this oil will only be in the transmission temporarily, I'm thinking it won't be a major issue. Maybe anything else will just disintegrate the synchros within an hours time, tho. I dunno. Remember, I'm ignorant.