I want to know what brand, weight, type, etc of fluid to use in my transmission. It's a M5OD with 200,000 plus miles on it. The current owner has been using a very heavy weight transmission fluid in it, and I want to know what weight or type or brand to utilize in it as soon as I do the drain plug fix so it won't throw it all out. Is there a certain manual fluid....or do manuals still use ATF? I've seen or heard of alot of people using ATF or ATF-modifiers in manuals. Just a question...

 

Mine was a leaker too so I replaced the rubber plugs with steel cup plugs. I have herd you can put some rtv on them after cleaning them off for a quick fix. For fluid I used valvoline durablend ATF but any ATF should work. I would do something soon even if you change the fluid and have to keep toping it off. I saw the insides of a Mazda 5 speed that had used gear oil, the front two gears melted from the heat and many others turned that funky blue tint.

 

I have been running Mobil 1 ATF in my Mazda 5 speed since 70,000 miles. Once put heavier oil in it and it didn't want to shift.

 

So why isn't there Manual-specific fluid?

What do you mean "...a mazda 5-speed that had used gear oil...the front two gears were melted" What are you talking about? Had used the wrong fluid, or too light a fluid?

 

The transmission was an M5od. The transmission was filled with gear lube 80w90. The way the transmission liberates its gears is by splashing oil around and onto a funnel like piece that directs the oil down onto the first two gears in the case. The gear lubes weight, the way it flows, and behaves does not allow it to follow the designed path. The two gears ran with out lube and the heat melted the teeth off. The surrounding gears were heat marked and in need of replacement too. The heat got so bad in there that the plastic funnel was partially melted. ATF transfers heat and flows much better than any of the thicker lubes. I wish I had taken a picture of this mess.

I guess you can say they had used the wrong fluid...one that was way too heavy.
M5OD is designed to use ATF so that’s what I would use.

 

I had a Ranger with the M5OD. I changed the ATF at 30k with Mobil 1, The tranny hated it! Any time I made a long trip or carried a load the shifting would get very stiff, like the synchros were not geting lubed. I changed it out immediately with Havoline Dexron/Mercon and it went right back to it's old self, shifting smoothly under all conditions. I don't know if the mobil lacked the proper friction modifyers or what, but my tranny definately did not like it!

 

Mobil 1 ATF probably reduced friction too much for worn syncros. The way they work is that they need friction to operate. I have used type F (not friction modified) ATF in worn manual transmissions with good results.

Jim

 

Hmmmmm. So maybe I should change out the Mobil 1 before it's too late? They don't make synthetic Type F though, do they? Guess I better consult my owners manual too. I thought Type F was only an issue on slushboxes and power steering units.

 

Tallpaul: I dont think you have anything to worry about.

 

Thanks, It is shifting fine right now. Just for the peace of mind I may look in the manual and ask a couple questions, perhaps of the Mobil tech line. I suspect I am ok and maybe the tranny above had issues before the Mobil 1 was put in and it just happened to get bad while the Mobil 1 was in there.

 

The type F was a bandaid fix for an already worn box. If it shifts fine on M1, leave it in there. If you really want to experiment, Redline makes a confusing array of ester-based synthetic lubes.

Jim

 

I just looked and my truck's manual says to use a Mercon fluid. The Mobil 1 ATF says it is good in all Mercon applications. So I am OK, but being that I am a Valvoline guy, I think next time I will go with Synpower ATF (why I didn't think of that before?). I had one of the most knowledgable folks on the oil guy site (MolaKule) tell me his recommendations for manual trannys that call for ATF: Redline High Temp Dextron III and Redline MTL (preferred). I suppose I should research that one some more before I decide to go Valvoline. Anyway, I have a couple years to think about it. Thanks all.