GL5 MT1 in an Older Transmission

[redwolf4k]

Hello,

This may be one of the most clouded topics in regards to gear oil. In 2017, is a GL5 MT1 rated gear oil acceptable in a thirty year old brass synchro manual transmission?

GL5 gear oil is cheap nearly everywhere, GL4 gear oil is mainly from specialty brands and expensive.

I wanted to ask the pros here: GL5 MT1 = yellow metal safe?

 

[Kamele0N]

https://bobistheoilguy.com/forums/ubbthr...ear#Post4539638

 

[zeng]

Originally Posted By: redwolf4k
I wanted to ask the pros here: GL5 MT1 = yellow metal safe?


Yes, a GL5 without MT1 = yellow metal safe. Period.
A GL5 with MT1 = more safe, if one must differentiates.

 

[Kamele0N]

You are wrong.... GL5 solo is never yellow metal safe!

GL4+.... GL4/5...or GL5/MT-1 tends to be yellow metak safe...

Althouhg some yenks are saying that it is not so...in 21.st century

 

[zeng]

Originally Posted By: Kamele0N
You are wrong.... GL5 solo is never yellow metal safe!

What a bold and hilarious claim!
Ever read about deactivated/buffered sulfur additives in modern day,that is , current GL5 gear oil formulations ??

 

[redwolf4k]

Thank you for the link, did not realize this is currently being discussed.

Seems to be two camps here, which is why I came here in the first place. If only GL4 gear oil was cheap like GL5, and not becoming exclusive to specialty brands that want $20 a quart. I do not want to support such a price point for GEAR LUBE.

 

[Kamele0N]

Originally Posted By: zeng

Ever read about deactivated/buffered sulfur additives in modern day,that is , current GL5 gear oil formulations ??


Yes but that "buffered sulphur" is in yellow metal safe formulations...

And labeled as... GL4+... GL4/5...or GL5/MT-1

And NEVER under GL5....solo/alone

 

[kschachn]

Doesn't the GL-5 specification in and of itself have yellow metal protectants? My ECHO owner's manual says either is acceptable and it has brass synchronizers. I've used Mobil 1 gear oil for a long time and according to the container it is GL-5 only.

 

[Kamele0N]

Mobil1 shc 75w90 is GL5/MT-1

https://www.mobil.com/english-gb/commercial-vehicle-lube/pds/glxxmobilube-1-shc-75w90

 

[MolaKule]

Originally Posted By: redwolf4k
Hello,

This may be one of the most clouded topics in regards to gear oil. In 2017, is a GL5 MT1 rated gear oil acceptable in a thirty year old brass synchro manual transmission?

GL5 gear oil is cheap nearly everywhere, GL4 gear oil is mainly from specialty brands and expensive.

I wanted to ask the pros here: GL5 MT1 = yellow metal safe?


You're missing a key point here as explained in the linked posts.

Sure GL-5 differential lubes are relatively cheap but they don't have the proper Anti-wear additive mix, nor do they have the friction modifiers that make for smooth synchro operation.

And GL-5 differential lubes have a higher viscosity than specially formulated (dedicated) MTF's, which may make shifting more of a chore in cold temps.

If your transmission requires a 75W90, then Amsoil MTG or Redline MT-90 would work a heckuvalot better in your transmission.

 

[kschachn]

Originally Posted By: Kamele0N
Mobil1 shc 75w90 is GL5/MT-1
https://www.mobil.com/english-gb/commercial-vehicle-lube/pds/glxxmobilube-1-shc-75w90

That's not it, this is it:

https://www.mobil.com/english-us/passenger-vehicle-lube/pds/glxxmobil-1-syn-gear-lube-ls-75w90

 

[zeng]

Originally Posted By: Kamele0N
Originally Posted By: zeng

Ever read about deactivated/buffered sulfur additives in modern day,that is , current GL5 gear oil formulations ??


Yes but that "buffered sulphur" is in yellow metal safe formulations...

And labeled as... GL4+... GL4/5...or GL5/MT-1

And NEVER under GL5....solo/alone


Still insists GL5 corrodes yellow metal synchronizers ?
Listen to Paul's video in post #1 here from 11.25 -15.20

Edit:spelling

 

[Kamele0N]

OK...it seems that you are correct...

 

[redwolf4k]

Originally Posted By: MolaKule
Originally Posted By: redwolf4k
Hello,

This may be one of the most clouded topics in regards to gear oil. In 2017, is a GL5 MT1 rated gear oil acceptable in a thirty year old brass synchro manual transmission?

GL5 gear oil is cheap nearly everywhere, GL4 gear oil is mainly from specialty brands and expensive.

I wanted to ask the pros here: GL5 MT1 = yellow metal safe?


You're missing a key point here as explained in the linked posts.

Sure GL-5 differential lubes are relatively cheap but they don't have the proper Anti-wear additive mix, nor do they have the friction modifiers that make for smooth synchro operation.

And GL-5 differential lubes have a higher viscosity than specially formulated (dedicated) MTF's, which may make shifting more of a chore in cold temps.

If your transmission requires a 75W90, then Amsoil MTG or Redline MT-90 would work a heckuvalot better in your transmission.


This is a good point.

What I gather from everything here is both GL4 and GL5 is safe for use, but GL4 is the fluid I should use in regards to its functionality with a manual gear box. I will do as follows: Put cheap GL5 gear oil in my Diffs and transfer case, but I will order up some Redline MT90 for the transmission, as it is something I have to feel all day long while driving. I really hate spending upwards of $20 a quart for either of these. But I guess it is only once in a while.

Thank you for all the clarification!