Tranny Fluid vs. gear oil

[gravelcrawler]

Hi all,
The manual says to fill the 4-speed manual transaxle in this car (1988 Festiva, the object of this thread) with MERCON atf. The fluid we drained from the exact same model tranny (the broke one we took out) was hypoid gear oil.

I've always thought that hypoid gears such as ring and pinion gears had to have gear oil. Transmissions don't have ring and pinions and therefore take atf. Transaxles, on the other hand, have the differential inside, and would have a ring and pinion, and should get gear oil. This is where my knowledge ends. I've never rebuilt a front wheel drive car's transaxle. So, is there some different type of planetary gear drive system in a Festiva such that it doesn't require gear oil (no ring and pinion gears)? Why do these cars get atf in the transaxle?

Thanks y'all,
Michael

[GenevaDirt]

welcome to the site...I moved your post to it's own question in the forum so it will get more attention. I do not know the answer but I am sure someone here will enlighten you soon.

[SIBladerunner]

I had gear oil in my 5spd till i changed it to high mileage semi synthetic atf. no performance differences that i can tell, but the whine I had down shifting into first went away when I switched. I think that the transmission responds better to lighter weight oil.

[jglutz]

Good Question and comments.
Gear oils are typically used where splash distribution is used and with a single housing design. The input bearings, gear mesh, and output bearings are on the same axis.
ATF finds it way into manual tranny's with the integration of the differential (transaxles). The thinner viscosity provides ease of distribution with out difficulties of a thicker stickier oil.
Plus ATF is pretty good stuff.

[lastplace]

hypoid gear oil is only needed for a hypoid gear which is used in a rear differential and it is not a good choice for use with helical cut gears found in a fwd transaxle. so stick with the atf if you want the best performance and longevity out of your transmission

[Oren09]

Specifications state Mercon.
Are the gears picky about Mercon? Or can I use ATF+4?
I ask because I have a few quarts of ATF+4 sitting on the shelf.

[FestYboy]

really, for a manual trans, ATF is ATF.... use what you got!

[timmay89]

I've used gear oil in my G5mr tranny, but in the winter it was too much and I had to change back to ATF. Overall I have had great results with ATF.

[blkfordsedan]

I think someone once posted that Mazda actually called for a light gear oil in the 121. Not sure if thats true or not. My Festy had like 32K miles when I bought it. I changed the transaxle fluid at about 60K miles and it had gear oil in it. It was thicker than ATF and had a bluish-green tint to it. Someone very well could have changed it before I bought it, but with only 32K miles that would seem unlikely. It wouldn't be the first time Ford recommended a fluid other than the factory fill. It would be great to find a factory maintenance manual for a 121.

[kartracer46]

I think someone once posted that Mazda actually called for a light gear oil in the 121. Not sure if thats true or not. My Festy had like 32K miles when I bought it. I changed the transaxle fluid at about 60K miles and it had gear oil in it. It was thicker than ATF and had a bluish-green tint to it. Someone very well could have changed it before I bought it, but with only 32K miles that would seem unlikely. It wouldn't be the first time Ford recommended a fluid other than the factory fill. It would be great to find a factory maintenance manual for a 121.

the majority of the ones I have drained have had that exact same oil you speak of with the bluish green tint. It's like a very light weight gear oil. I have never seen it sold in any parts stores yet. I am guessing that is why they recommend ATF. That particular lubricant may never have been sold in the states. I am guessing I am actually looking at the original gear oil that came in the car from when it was new. Maybe? It was just a thought I had one day.

[Zanzer]

^^ Possibly GL-4?

Hypoid gear oil (GL-5) has a high level of EP additives which are bad for yellow metals such as syncros in manual transmissions.

I've used both ATF and 30W motor oil in my transmission without any issues. Although lately I've been thinking of switching them over to Syncromesh because it's been great in the T-45 in the Mustang.

[Larry Hampton]

I've got a drip, leaves a fist sized spot. Don't know where you fill it at.

The only other transaxle I've had was the auto in the Shadow. My toploader 4-speed in my Mustang uses gear oil. They started using atf in the T-5s I believe.

[iceracerdude]

^^ Possibly GL-4?

Hypoid gear oil (GL-5) has a high level of EP additives which are bad for yellow metals such as syncros in manual transmission.

This is absolutely correct, that additive is sulfer and it will shorten the life of your syncros by as much as 50%! You need to also remember that the people commenting here are from all over the USA and the world. So some of the recommendations you're getting for gear lube being "good for them" may be coming from warmer climates than you may be in! That also make me wonder how some of these guys are actually breaking their shift gates, I've gotta believe it's not just from extreme man handling.
I'd advise the use of the recommended ATF, I personally use Mobil 1 synthetic atf, and it shifts great in the winter here. On my Nissan SE-R's I use Redline gear lubes.

[Pgh5spd]

Light gear oil came out of my '88LX years ago, but I've been running ATF ever since. You fill the transmission to the top, so there's no splash involved.

[blkfordsedan]

I am planning on using either Synchromesh or Redline MTL when I change mine next time. Right now I'm using Valvoline Max Life ATF since I couldn't find Mobil1 ATF anywhere local.