75W-80 vs ATF

[widman]

Some of the new transmissions are coming out with a requirement of GL-3 75W-80. That puts viscosity in the range of an ATF, a little less EP protection, and no real real requirement for synchronizer work.
Why not use a decent ATF? Friction coefficient of ATF would seem to work better on synchronizers, viscosity is right.

Anyone got the inside story?

 

[Pablo]

Quote:

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Some of the new transmissions are coming out with a requirement of GL-3 75W-80. That puts viscosity in the range of an ATF, a little less EP protection, and no real real requirement for synchronizer work.
Why not use a decent ATF? Friction coefficient of ATF would seem to work better on synchronizers, viscosity is right.

Anyone got the inside story?

---

GL-3 is an obsolete Gear lubricant specification. Who is specifying this?

http://www.lubrizol.com/products/automotive-gear-oil/J306.asp

75W-80, on the low end is close to an ATF, but not the same on the upper end of the spec. 7-11 cSt. I would use a good synthetic gear oil in the correct viscosity range, it will give you both the low temp properties and necessary gear AW/EP protection.

 

[gtx510]

How about using Redline MTL, D4 ATF, or Hi-Temp ATF? Or Amsoil MTF?
http://www.redlineoil.com/pdf/6.pdf
http://www.amsoil.com/StoreFront/mtf.aspx

Or getting ghetto, using a 5W30 syn that doesn't have moly additives, and shortening the OCI?

 

[widman]

That is what I've always told people, but last night I received an email from the Mitsubishi/Chrysler people asking me to supply it for their new transmissions. I'll go visit them Monday to read the books and see where this is coming from, but wanted to check out the waters.
In general I'd be tempted to put a good ATF or a Synthetic engine oil in it before looking for a reduced additive gear oil. But they have to follow the factory recommendations, and look to me to do that for them.

 

[aquariuscsm]

I also have always wondered why Mustang and Camaro/TA manual transmissions require ATF (and outlive the life of the car) as a fill,while Nissan,Mits,and Toyota require GL4 gear oils. Are the internals of the transmissions made up of different types of metals? Or are the bearings and so forth in the Japanese transmissions different and need the thicker gear oils for cushioning and protection?

 

[mechtech2]

Those transmissions don't really require ATF - it is not the best fluid - they are OK to use it.
One fluid for auto transmissions, manual transmissions, and power steering systems keeps things simple in the shop.
ATF is not the best, but is decent.

 

[aquariuscsm]

Is it maybe the bulk fluids trend? A one fluid fits all? I was afraid Nissan filled my new transmission with a GL5 differential oil. When I asked them what they use,all they know is it`s a bulk oil that`s in a huge drum that they put in everything. Funny thing is,that when I drained my transmission and filled it with the Nissan MTF,the shifting grinds went away.

 

[Whitewolf]

The short answer is that it depends to a great extent on the synchronizer design and the materials used in the synchronizers. Some may be able to work with ATF, some perhaps not so well.
It's all about the friction. Ideally what you want is a high enough dynamic mu (measure of friction) to synchronize the two components, but a lower static mu in order to allow the cone to break away to allow the detent to occur so that the locker ring can slot into place to complete the engagement. Since the friction is dependent on the material and the fluid, the fluid choice is important. Most manufacturers carry out their validation testing on a specific fluid and since that testing is both long and expensive they do not have the resource to validate multiple products so they often recommend the specific fluid that has been tested.
Drivers that shift slowly and don't rev hard would be hard pressed to tell the difference between fluids but someone that uses high revs and shifts quickly will.

 

[gtx510]

Quote:

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I also have always wondered why Mustang and Camaro/TA manual transmissions require ATF (and outlive the life of the car) as a fill,while Nissan,Mits,and Toyota require GL4 gear oils. Are the internals of the transmissions made up of different types of metals? Or are the bearings and so forth in the Japanese transmissions different and need the thicker gear oils for cushioning and protection?

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I've wondered myself and thought it was the bearings clearainces or type so I did some googling.

http://rickwrench.com/FalconClutch.html

http://www.fordmuscle.com/archives/2005/12/T5Rebuild/index.php
"Ford began using the Borg-Warner designed T5 in small passenger cars in the early 80's. However these early non-World class (NWC) models weren't suited to handle the power of modified V8 engines, and it wasn't until the availability of the World-Class (WC) T5 gearboxes designed for the new fuel injected 5.0L Mustangs that the popularity of the transmission took off. Compared to NWC T5's the WC's benefit from needle bearings under the gears and tapered roller countershaft bearings for reduced friction. This change also allows the later to run considerable less viscous ATF fluid rather than heavy gear oil."

But it's the net and there's always someone who disargees. 75W90 is probably right for a Datsun T5 but not a WC T5.
http://www.datsunzgarage.com/borg/index.htm



I always thought synchros needed less additives so that they wouldn't slip and thus could match speeds quickly, but they needed so for wear protection. And the gears/bearings need additives too.

 

[Whitewolf]

The right additives. That's the point and what is right for one material combination may not be right for another material combination. You are correct though in that you also have to consider all of the other areas such as bearings etc.
It's complicated and I was just trying to point out one of the main problems.

 

[widman]

AH, needle bearings. Another good reason for the thinner fluids. But would still like more comments on the difference between GL3 (no real valid spec) 75W-80 (that falls into the same range as ATF) and an ATF that works very well in Ford/mazda transmissions.
If both have the same viscosity and ATF has good low speed frictional characteristics (and works well with many synchronizers), any opinions on why not spec something known as opposed to GL-3?
Don't bother just suggesting brands. That is not the question.

 

[Whimsey]

I don't have a difinitive answer but maybe the manufactures spec what is more readily available in that locale. Outside of the US automatic transmissions are not that popular. So if a manual transmission is spec'd for ATF in the US maybe in another locale they spec a closely related fluid that is more common there.

Just a guess :???:.

Whimsey

 

[unDummy]

Good guess, but the real reason is to keep you going to the dealer for parts and service where they throw in incorrect bulk oil with unknown specs

Concerning OE recommendations, its all in the design of the unit. Trying to compare 'like' transmissions isn't safe, since parts suppliers can change to make the unit within a given budget.

Also, I haven't seen all those long life manuals using ATF. This is the reason why gear oils and various OE manual lubes exist.

 

[Whitewolf]

Theose fluids exist because Oil Companies work with(or on!) transmission manufacturers to validate on a given fluid. From then on it is a very expensive problem to validate an alternate fluid so any OEM that purchases that particular transmission is basically stuck.