gearbox oil

FWIW, I ran some clarifying questions by David Granquist of Red Line, and he agreed I could share his responses here verbatim. This was very helpful for me to fully understand the views shared in this thread:

“The MTL, MT-85 and MT-90 all contain the same coefficient of friction, the same antiwear just different viscosities. The MTL was the first product made so continues to carry the name.” [Note, MTL is 75W80 weight.]

“The primary difference between the MT-90 and the 75W90NS is the GL rating.” [Note, MTL/MT-85/MT-90 are GL-4, and 75W90NS/75W90 are GL-5.]

“A GL-4 suitable for low offset final drives as well as straight and helical cut transmission gears, a GL-5 covers those as well as high offset hypoid final drive differential gears.” “The Ferrari transaxle doesn’t contain a high offset hypoid ring and pinion so a GL-5 isn’t technically required.”

“In the 308 transaxle the 75W90NS would be recommended as a GL-5 gear oil was originally specified.” [Note, ’85 owner’s manual lists Agip Rotra MP 80W90.]

“The 75W90 compared to the 75W90NS contains friction modifiers, slippery additives, both are GL-5 gear oils suitable for hypoid gears.”

“Friction Modifier can be added to any of the fluids as necessary, being aware that over about 2% will start to adversely affect shiftability. Typically the Ferrari limited slip units don’t chatter so additional friction modifier isn’t necessary.”

“The Ferrari transaxles can be stiff shifting when cold, the MTL being a lower viscosity can help but is a different fluid than called for.”

“The MTL is a lower viscosity than called for, the MT-90 a similar viscosity but a GL-4 gear oil, could be used and would perform well but a little different fluid than originally specified.”

 

I am not going to take any more phone calls on this subject. If you are a client, I am happy to discuss this. If you are not, everything I have to say is here. Read up and make your own decision. I am not sitting by the phone to help you make decisions, put on the big boy pants and make your own.

 

He is wrong. Ferrari specified GL4. There is substantial documentation to prove it. The first car Ferrari specified GL5 was the 512 TR.

 

Alex, I would ignore the Redline rep's advice, as it is contradictory. He got it correct that there are no hypoid gears in a 308 transaxle, and even goes on to say that a GL5 is "not technically" required. That part is great... but then he claims a GL5 is originally specified, so that would be recommended.

I don't necessarily believe that a GL5 rating was specified, and further many other cars' experience has shown that GL5s are terrible with synchronizers in transmissions. Bottom line, not Ferrari exclusive nor do Ferraris get any magical exemptions, GL5s are great for hypoid differentials, terrible for transmissions. GL4s are for transmissions.

I tried the Redline 75W90/75W90NS cocktail when I first got my 308 QV 4 years ago, based on advice from this forum. 2 years ago, I switched it to Redline MTL based on Brian's recommendation (note, there's no confusion about which MTL - there is only one MTL. The others are either MT90 or MTL-85 - those are different products. Neither are necessarily bad, but not necessarily better) The shifting with straight MTL was improved over the 75W90/NS mix.

Tinterow, I have to suggest that you were the one picking a fight. Brian said "Redline MTL" - how is that unclear? That IS a specific product and grade specification, all by itself. Go buy it and give it a try!

 

My owner's manual states Agip Rotra MP 85W-90 and this is what I use since twenty years without any issues. Except, that the modern version is 80W-90.
The data sheet says it's GL5.

In former days, when differentials made trouble or noises we mixed banana peel or sawdust into the oil. No more noise.
O.k., not on Ferraris

Best
Martin

 

Here is the best explanation on GL4 and 5 I have ever come across, directed to classic cars (and Corvairs specifically) but looks very relevant to our V8 cars. Looks to me like the Redline MTL or MT90 would be the best bet relative to our transaxle design, and a GL4 gear oil more generally with a modern additive package will be fine.
View attachment Transaxle_oil.pdf

 

It is now. Back in the 70's when we started using it, it was GL4.

 

You mentioned 'all kinds of trouble with GL5' above.
What kinds of trouble are these?
I only have experiences with my own single 308. I drive around with Rotra GL5 since 40.000mls and notice no issues. Whatever there was in my gearbox, when I purchased the car. It suffered the 'tight corner judder'. And severe judder when accelerating hard while turning left or right. After using Rotra it was completely cured a never came back.
No noises, no second gear issue. O.k., the latter was never present. Not even on the coldest climate conditions. I assume, that my gearbox already had that little design modification (that famous relief hole)

Best Regards
Martin

 

There is far more information out there in the public domain than I can ever tell you.

Just for a place to start. API and the US military describe GL5 and MT1 oil as differential oil. They describe GL4 as transmission oil. Some go so far as to say GL5/MT1 is not for syncromesh applications but only for heavy duty high stress gear lubrication. And some also go on to say the additives to give the low friction properties that GL5 / MT1 has as being contrary to the needs of the syncros and possibly damaging to yellow metal syncros. You have iron syncros, it won't damage your transmission. I have rebuilt many later Ferrari transmissions with brass syncros and the damage exactly matched what GL5 additives are supposed to do to brass syncros.

It s also clear when reading about the development of GL5 lubricants they were addressing issues not applicable to our cars. They were trying to lubricate high stress gear designs, they were trying to develop an oil that reduced friction for fuel mileage and longer mileage change cycles.


No one says it cannot work and in many cases work well but it is pretty clear that was not what it was designed for and can cause problems.
Just because you smoke cigarettes doesn't mean you'll die of cancer.

As far as your impression of your transmissions function, how do you know what it can be like if using the product it was designed for?

 

Brian,

I have no idea, but cannot imagine, what could be better. Smooth shifting, no noises, no corner judder. Only thing I know, that there was some oil in my transmission, when I purchased the car, which was somehow not right, caused juddering and Rotra cured it.

I have also often heard about the theory with the yellow metal and GL5.
Therefore I went the hazardous way and filled my much older Alfa gearbox with Rotra GL5.
This gearbox has much weaker bronze synchros and because a rebuild is cheap and I plan to perform it in a few years I tried this oil. I want to know, how the components look after long term use of the 'wrong' gearbox oil.
But still no issues after 10 years.
I have to admit, that I believe, sometimes things are overrated when it comes to fluids.

Best
Martin

 

What old Alfa has brass syncros? Every one I ever worked on was iron.

As far as being over rated, it was the early destruction of many transmissions that caused me to research this. The data I discovered fit what I had already experienced.

 

GTV 2000 '71 and Giulia Sprint GT '67.
Is this wrong? I never looked inside one yet, but this is, what an old Alfa workshop told me.
Were these fake news?

Early destruction? Would you mind sharing details? I really appreciate your experience collected over decades.
And would prefer such first hand experience against often questionable web search results.
I still think, 80% is BS.

Best
Martin

 

Brian has a cardboard box of mostly 360 synchronizers that were ruined by GL5. Glad mine has really big synchro rings, and two (plus a couple of dog clutches for 1st and 2nd) for each gear.

 

Fake news dude. Both of those things have iron syncros. I have rebuilt many.

They are Porsche style syncros. I'd be using GL4.

 

Interesting. If a single series of a specific part stands proud that way regarding damage, and is such sensitive regarding oil spec I would state 'faulty design'.

Best
Martin

 

Another way to look at is look at other manufacturers and see what they recommend as a lubricant. Near as I can tell the other Graziano users are using GL4.

Lots of transmission are sensitive to oil. Don't live in a cave. Few manual transmissions call for GL5 and many warn specifically against it.

Martin, you are not stupid man but are living in a bubble. I have spent a great deal of time educating myself on the subject. GL5 in not the new and improved GL4. It is an entirely different product designed for a specific reason. It is not like changing from synthetic oil to dinosaur oil in the motor. Both are designed to be motor oil in gasoline engines. The same cannot be said of GL4 and GL5.

 

Hi Brian, Can I ask, since you mentioned it, Are you referring to the Porsche 915 tranny? Sounds like that would be a GL4 candidate as well...

Thanks,

Franny

 

I have no idea what that is. All the Pwagen people I know use GL4.

 

Great. Thanks!

f

 

Have you ever read the book? What does Porsche say?



I guess people just don't get it. Educate yourself and figure it out. Don't just do what some ******* on the internet says.

I guess that is too much to ask of people who cant even be bothered to look in the owners manual.

What a waste of ****ing time.

 

Easy there buddy... Just trying to get the OPINION of someone in the field. Yes I do read the manual, but it is a 30 year old car and products change. It is always best to get a bit more info than the owners manual for a classic car. I wouldn't use the tires speced for the 356. This is similar.

Sorry to bother you... I won't ask you for help again.

Franny

 

"If a single series of a specific part stands proud that way regarding damage, and is such sensitive regarding oil spec I would state 'faulty design'."

Many components are "sensitive" to using the proper lubricant for the component design. For example, many brake systems SPECIFICALLY state not to use Dot 5. Others DO specify Dot 5. It's simply a matter of using the correct fluid for the system. It's not a faulty design of the component to require this or that lubricant. it's just based on component design.

 

The 915 tranny was a gearbox, introduced with the '72 2.4 911 until 1989 with some design evolutions. 915/xy
LOL. Similar discussions on the german P-Wagen forums. As far as I understood, the Porsche classic center in Zuffenhausen states, that "GL4 is sufficient, but GL5 doesn't harm anything".
Service documents switched from GL4 to GL5 during the production cycle of the 915 tranny but noone can say definitely, at which evolution step they switched exactly.
Since there was no relevant design change it may be simply based on the fact, that the 911 with the 915 tranny got significantly more powerful between 1972 and 1989 and therefore applied much more load onto the transmission.
While the 308 lost torque during its production period. (328 excluded)

Best
Martin

 

Maybe that's widely accepted with italian Diva-Cars. But my customers in the heavy machinery business would kill me for designing parts which die because of slightly wrong oil specifications.
DOT 5 brake fluids are a whole different thing. 5.1 and 5 are so completely different. This designations were probably invented by writing desk failures.
Currently I work on a DFMEA ( Design Failure Mode and Effect Analysis) for an US machine builder and it's exactly these things which cause 'red' results.


Best
Martin

 

Martin, if you are interested I could point you to multiple long discussions of the Mazda manual transmissions used in several of their RWD vehicles, including Miatas, that degrade in function significantly if they're filled with GL5, then gradually improve back to normal if you change them back to GL4. That's not a faulty design, that's a specific lubrication requirement that is fit for purpose. Using GL5 is using the incorrect fluid. Interestingly, lots of people try this experiment, because Mazda lists "GL4 or GL5" for the transmission - a mistake on their part, well proven by thousands of Miata owners who've followed that mistake. Perhaps back in the 1980s GL5 fluids weren't known to cause problems with synchronizer function? Or perhaps the GL5 spec evolved and changed to be less compatible with synchronizer function?

Technically, you could run 75W90 GL5 in your engine, it's the same viscosity as 10W30 engine oil... well, you could run it for a while, anyway, before problems cropped up because of the completely different additive packages. Is that faulty design, because an oil of a different specification was used? (No!) That's faulty maintenance, using a different lubricant than specified.