ATF in manual tranny
 

I've been using automatic transmission fluid in an old car (a '67) with a standard transmission. The manual says it should have far heavier 80W or even 90W oil. After many miles and years (approximately 20000 miles and 8 years), seems like ATF (Dexron III Mercon) works just fine. I was worried ATF could somehow cause extra wear or other problems.

As to the benefits, I unfortunately don't have hard data to tell how much it affected FE. I can say that it made the gears much easier to shift. 2nd gear especially was getting very hard to shift into, taking a lot of force on the gearshift to do it. Started by being hard to shift into 2nd while cold, and had gotten to the point of being hard to shift when warm and nearly impossible when cold. ATF solved that problem.

Since I had the transmission out last weekend, thought I'd take a pic of the gears so you can see for yourself. Didn't see any metal particles in the fluid.

https://www.fuelly.com/attachments/fo...4d0a7c72ba.jpg

Chrysler recommended ATF in their manuals in the 60's.
I learned about the BMW requirements the hard way, mineral oil or you get to replace the synchros.

regards
gary

How about ATF in the differential? Pretty much all FWD automatic and manual transmissions use the same oil to lubricate the gears and the diff. I was thinking about using atf in my RWD bmw differential.

Personally I'd hesitate to put ATF in a rear differential on my vehicles because of the risk of extra wear. Since the power is being rerouted at a 90 degree angle, the ring and pinion gears have a whole different set of sliding stresses on them (the gears slide across each other rather than just meshing).

It probably would increase mpg though.

Careful, if it's an open diff you'll probably be okay but a limited slip rear end would probably die with ATF back there. IMHO if you want a thinner oil back there go with a light synthetic motor oil back there. ATF is more of a friction modifier than a lube.

Yeah theres a lot of issues with the ideas. I have a spare diff in the garage so I might sacrifice this one in the name of science. Its an open diff by the way.

The fact that ATF has friction modifiers is what saves synchros from burning up... a fact a lot of people miss when putting synthetic motor oil in the tranny.. it's lubricant properties are pretty high usually too, due to being made from Group III high VI oils, the ones that are practically synthetic... limited slip diffs with clutches probably suffer from not enough friction modifiers, there are special diff additives that are meant for that.

BTW, my trannies are getting TDH UTF at the moment, TDH universal tractor fluid. Generally, it has higher heat tolerance, better lubricity, better quality base oils and damn good detergent and friction modifier packages (it's designed for wet brakes and clutches) .. and the best bit is, it's half the price of generic ATF. Don't use it in anything that NEEDS ATF+4, Mercon V or Type F, but anything that uses regular ATF will probably like it a lot.

also remember that any oils fluids nowadays are far better than what they had back then...

A popular "band-aid" to worn sycros in a Honda standard trans is to use GM syncromesh ATF fluid.

I've done it already and it did help the syncros work smoother.

I used GM Dexron in a Borg Warner T5 manual for more than 350 000 miles with no problems at all.
I changed it every 60 000 miles along with the diff oil as a matter of routine.

Pete,