I'd like to clear up b*****t about gear oil in a M5OD trans.

[90B24wd]

As I am cleaning up a 2.9 M5OD tonight getting it ready for a rebuild, I have noticed that this trans is in very mint condition internally. And why I say this is because while I was cleaning the bearings with solvent, it spins quietly & smooth (even when dry). What I got here is a well broken in trans!!!
I don't remember what the mileage of the truck but, it was an 88 2wd bought 7-8 years ago for parts. (payed $75.00 for it) The outside was caked with grime. This trans is the in best condition compared to the other 4 that I tore apart this week. Some of the others were screwed up rebuilds. The machined & bearing surfaces looks like a mirror. Even the syncros is in mint condition.
I do not know how long the gear oil was in there but thank you to the person who put it in.
The bad part is where the syncros mates to the gears, it is shiny and smooth. This can be corrected with 80 grit sandpaper. The only reason why I think that gear oil should not be used is because where the syncros meshes with the cone part of the gears, it becomes to smooth not letting the syncros to bite the cone for smooth shifting.
I do not have to change any bearings. I'll only change the output shaft & seals.
Gear oil is good for gears & bearings but not for smooth shifting.
I would like to try a trans oil made by Specialty Formlations but don't know where to get it from.
So for those who have gear oil in their M5OD trans it is not all that bad. And it is not because this trans has close tolerances ATF must be used either.

 

[Sasquatch_Ryda]

K...it was DESIGNED to be run with Mercon ATF in it. Nuff said.

 

[Explorin94]

The gear oil that was in it more than likely wasn't 80w90...it was probably a thinner gear oil. Sanded the mating surface for the snycros? WHY?

 

[Captain Ledd]

OR you could just use ATF and change it often (or really just when you're supposed to). No sanding syncro's, no hard shifting, and no crazy wear.

 

[shane96ranger]

I would bet it's more likely it's motor oil than gear oil. This is quite common.

I just had my T5 built and it's had 15W-40 (diesel oil) in it for years, so that's what went right back in it. When I put the oil in, it was starting to make noise and shift rough, and this cleared right up when I changed the oil. My friend owns a trans shop, and he has a builder in there that's been building manual trans' for years. I asked him (without giving my history on it) what fluid he recommended for the T5 and he said 10W-30 or 15W40. Ford says ATF should go in it.

 

[shane96ranger]

I just found this thread:

http://204.14.93.181/forums/showthread.php?t=85049

 

[rkneeshaw]

what good is the trans if the synchro's wear out sooner due to gear oil vs Mercon?

 

[rboyer]

You take your findings from one single mazda trans that ran gear oil through it and post them as if they are gospel. I have seen plenty of these transmissions which ran gear oil for a prolonged amount of time and one thing is certain, they get hot and bake gear oil onto every single non-moving part inside the transmission. That baked gear oil holds any metal which would have made it's way to the magnetic drain plug. That little plastic "pump" in the front of the transmission actually does alot more than you think it does too and when faced with a thicker fluid it's almost useless. I have already drilled out lexan for use as a top cover so that I could see the difference in splash feeding between heated gear oil and transmission fluid and it barely pumps the stuff at 2500rpms. Not to mention the extra cushioning between the bearings causes the transmission to experience a longer slow-down time between shifting. Oh and did you know that certain gear oils are corrosive to yellow metals?

 

[jhammel85]

I don't see the point of not using what it was designed for. If it was designed to use ATF, then use ATF.

 

[7.5L_STX]

in my old 2.3 2wd i ran 80/90 and besides being a little hard to shift when below freezing i never had a problem with it.

but i only put that in there cause i didnt know better, so if it takes ATF and you KNOW this fact then put ATF in....is it that hard to follow directions?

 

[Explorin94]

Man......can we beat a dead horse or what??????????

 

[Bent Bolt]

As I am cleaning up a 2.9 M5OD tonight getting it ready for a rebuild, I have noticed that this trans is in very mint condition internally. And why I say this is because while I was cleaning the bearings with solvent, it spins quietly & smooth (even when dry). What I got here is a well broken in trans!!!
I don't remember what the mileage of the truck but, it was an 88 2wd bought 7-8 years ago for parts. (payed $75.00 for it) The outside was caked with grime. This trans is the in best condition compared to the other 4 that I tore apart this week. Some of the others were screwed up rebuilds. The machined & bearing surfaces looks like a mirror. Even the syncros is in mint condition.
I do not know how long the gear oil was in there but thank you to the person who put it in.
The bad part is where the syncros mates to the gears, it is shiny and smooth. This can be corrected with 80 grit sandpaper. The only reason why I think that gear oil should not be used is because where the syncros meshes with the cone part of the gears, it becomes to smooth not letting the syncros to bite the cone for smooth shifting.
I do not have to change any bearings. I'll only change the output shaft & seals.
Gear oil is good for gears & bearings but not for smooth shifting.
I would like to try a trans oil made by Specialty Formlations but don't know where to get it from.
So for those who have gear oil in their M5OD trans it is not all that bad. And it is not because this trans has close tolerances ATF must be used either.

WOW ! You sure told us !

 

[90B24wd]

Sorry if I got anyone angry. All I'm doing is posting my observations on a trans that someone else has put fluid in other than ATF. ( it's gear oil I can smell it) I'm putting
ATF back in there. What I'm saying is that the gear oil did not mess it up internaly, it only helped the moving metal parts in the trans honed itself for a better fit. I can't wait to put this in trans in my truck cause the other trans in there now is a whiner. I'm working on 4 other trans and did not like what I saw in the others. (they probaby only had ATF in it?)
Alot of these trans whine because ATF failed to properly lubricate the gears & bearings. They say
to put ATF why, only because it will make shifting gears easier!!!

 

[90B24wd]

WOW ! You sure told us !

Thanks Bent Bolt,
I guess your the only one who knows what I'm trying to say.

 

[gribly]

Okay, you take your finding on one tranny you pulled apart, and I'll give you my rebuttal.

I bought my Mazda with 140k miles, at 170k miles it started vibrating HORRIBLE at 15mph. I'm talking enough vibration where I could mix a drink by setting it on the dash, and you can't see out the rearview mirror as if I had subs. After putting it in the air and getting awfully confused when everything checked out, changing wheel bearings, changing brakes, tearing the rearend apart and replacing rear bearings and brakes - my uncle Ricky suggested we check out the fluid. It was gear oil, no question. So, I put in ATF, and 200 miles later - no more vibration. Truck drives like a new one.