AW/FM in maual trannies?

[LM]

I'm wondering about AW/FM additives in engine oil, wrt manuf that recommend either engine oil or gear oil, for their manual transmissions or transaxles

I drive an older Saab 900, with the 5spd transmission mounted beneath a longitudinal 4 cyl 16V n/a engine. Transmission recommendations are SAE 10w30 SF/CC, SF/CD, SG - interestingly either gas or diesel - or alternative EP 75 GL 4 or 5.

I don't understand how the lubrication needs of an engine, vs a transmission w/IIRC roller bearings, tapered roller bearings, needle roller bearings, brass? (certain friction dependant?) synchros & shift forks?, gears (not sure if helical or straight-cut), etc., could be similar?

As can be seen from the dated SAE recommendations above - back to AW/FM additives, now - the oils that have anecdotally been the most successful in the classic 900 gearbox have been those w/o moly, but perhaps those that contain ZDDP, and/or possibly boron. And I wonder if running a current gen dino like Penzoil - w/~180 ppm moly - is less than optimum, and possibly deleterious (was moly a common additive back during SF or SG ratings?)? Perhaps the temps & pressure never get high enuf for the moly to fully react - where ZDDP would - OR the moly plates the synchros in deleterious manner?

It seems Redline MTL/MT-90 doesn't contain moly, from a company that uses it heavily in engine oil - so infers it's not an appropriate AW/FM application?

This is a link - not scientific or conclusive - but interesting to me, nonethless, that's got me thinking (orig from Townsend Imports - a Saab specialist in the North Carolina, USA)

Sorry, Links to other forums are not allowed.

One of Townsend's chief mech's was using Amsoil in the gearbox of his own 900, while using M1 10w30 in his engine

It doesn't appear Amsoil Series 2000 Racing is made in a 10w30 grade, as was curious as to the heavier visc use in this specific application, i.e., maybe I should research a premium syn 10w30 engine oil w/o moly, but w/ZDDP and/or boron

I'm currently using Redline MTL (vast improvement in shifting smoothness w/use in my 85 VW GTI, but no notable improvement in my 91 Saab). Honda MTF - a semi-syn I believe - seems to be growing in c900 transmission popularity (many reports of smoother shifting, as compared to all commonly used)

[ April 21, 2003, 03:27 PM: Message edited by: BOBISTHEOILGUY ]

 

[MolaKule]

The best manual transmission lubes are Redlines MT-90 and MTL.

They contain both FM's (polyol esters) and the proper anti-wear additives, such as the phosphate esters.

 

[LM]

Thanks, MolaKule. Have read many of your AW/FM posts in the archive. And I realize lubrication is the overall product composition, not just the AW/FM adds. Thought I'd maybe observed a trend wrt no moly.

I'm just as much or more concerned w/bearing wear (may have mis-inferred shifting smoothness priority, previously)

Excerpts from the link, wrt hundreds of rebuilt transmissions, using service records, albeit variable driver habits, avg failure/mileage figures:

"Factory recommended 10w30 mineral oil ( dino juice) 150000 miles

Common GL 4-5 Gear Lubes 90000 miles

Synthetic Gear Lube (75W) 110000 miles

Mobil 1 Synthetic Engine Oil (10w30) (15w50) 200000+ miles ( very few failures during the years it was used in the shop, Not enough to establish a mileage and then we stopped using it in favor of Amsoil)"

They had only one box on MTL, which failed - virtually all bearings, but gears were pristine - but make clear that the sample size was insignificant, and that other reasons could have definately been the cause. Some Saab 900 MTL users are @ +150K miles

I found the figures interesting, as well as the use of syn engine oils in the gearbox

 

[LM]

I left out the Amsoil

"Amsoil Series 2000 Racing Oil 20w50 225000+ miles ...No true failure rate established because the cars with it haven't failed and this is the average mileage they have on them now."

 

[MolaKule]

While Gear Lubes and engine oils may share the same viscosities or viscosity ranges, the difference is in the additive package. For Gear Lubes you need nitrogen, sulfur, phosphorus, and boron additives in much higher treat rates than with engine oils.

Unless the gearbox manufacturer recommends 20W50 engine oil or whathaveyou in your gearboxes, stick with the gear lubes specially formulated for the application.

In your case, it seems to be a transaxle, I would recommend MT-90.

[ April 21, 2003, 07:45 PM: Message edited by: MolaKule ]