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Mitsubishi FM 146 lubricant?


Texican65

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Hi guys! I've got the 5-speed mitsubishi in my '89, had some issues with it over the last 5 years. A few months after I bought the truck in 2011, i had to have the input bearing replaced, and a new 5th gear. I've always run conventional oil, 90w in all my manual trannys, so thats what I used in this truck again. Well, 65,000 miles and 5 years later, and my input bearing has gone bad again. Chattering in neutral, 1st, 2nd, 3rd, and 5th. I decided to just run it anyways, but over a period of a few months it got louder and louder.....had to take her back to the shop.
I took her to a different, reputable transmission shop that's been around for 40+ years, and the owner is so nice and easy to work with, good reviews, tons of business. Anyhow, i picked the truck up to-day and all went well until I asked him what kind of fluid he put in it. I was more interested in the brand of gear oil he used. Well...he says, ATF. ATF I said! Thats not right. He says, "I questioned it too, but that's what it calls for in my computer." And he showed me, it said mitsubishi manual-ATF. I couldn't recall exactly what my Haynes manual said so i went with it. Lo and behold when I go home, 80-90W...right in the manual. Online, some guys say....ATF is fine. Some say, nope ATF is not ok. What should I do here fellas? I just spent $1200 and I need this tranny to hold up another 100,000. Go with the ATF.....or drain it and fill with gear oil? Take it back and have him cover the cost...or just do it myself? I've got a 1 year/12,000 warranty on the work.
And....it seems like it still chatters in neutral a little bit...not much...but I can notice it...until I push the clutch in. Is a little chatter to be expected?

Thanks so much,

Dow
 


adsm08

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My spec sheet says 80-90 as well. I have heard rumors of, but never seen myself, a TSB that revised it to ATF due to shifting issues at temp.

If it was me, I would put 80-90 in it, not tell the shop, because if his system calls for ATF that it what he will warranty it with. After that I would not worry about trying to make an FM trans last another 100K miles. I would drive it until it breaks again and then stop throwing money down the hole and find an M5OD for it. Much better transmission.
 

Texican65

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Thanks adsm08! Guess that's what I'll do. Drain that ATF and swap it for gear oil. I've always used conventional, would a synthetic be better...maybe Amzoil or royal purple....red line? Any thoughts?

Will the M5oD mount to my engine or frame...without modification?

Thanks,

Dow
 

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I have never bothered to use anything fancy. The one time I refilled my FM146 I had a few quarts of Motorcraft gear oil sitting around, left over from a warranty axle seal, so I used that.

The correct M5OD will go right in place of the 146. I had to trim the floor a bit, that was it. I did change my T-case out at the same time so I didnt have to worry about linkages, but if you have an e-shift unit it won't matter.

If you have a manual shift t-case you will need the correct boots.
 

Texican65

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Ok thanks a lot. We'll see how far this tranny goes. How come they're such a piece of crap?
 

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I ran 80W-90 Valvoline synthetic gear lube in my 89 Ranger with the Mitsubishi trans for almost 200K miles with no problems. It is still running with over 250K miles with no trans problems and I am pretty sure the current owner has not changed the gear lube.
 

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The 145 had issues with a weak 5th gear, I don't think that carried over to the 146 though.

The FM series transmissions had issues with the bearings though. They used ball bearings, not roller bearings so it puts almost all the stress of the engine torque on the tip of the ball, rather than spreading it out over the length of a roller. It is particularly hard on the input bearing.
 

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I think mine had the FM146. I tried to tow in 5th gear on a stretch of flat Interstate for 30 minutes and came close to ruining the transmission due to over heating it. The 146 may have been an improvement over the 145 but it still had a weak 5th gear. I had not heard of the ball bearing use in the Mitsubishi transmission but that could explain some of its issues.

I liked the Mitsubishi transmission shifting characteristics over the Mazda transmission but I like the durability of the Mazda better. I didn't have mechanical problems with my Mitsubishi transmission but have heard many horror stories about them.
 

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×2, ball bearings are junk.

I originally had the FM146 in my BII... On mine it was the rear output shaft bearing that went south. Out came the 146, in went a M5OD from a '90 2.9L 4x4. No issues since.

And correct about the lube, the Mitsubishi takes gear oil.
The M5OD is the one that requires ATF (Mercon), so that's probably where the confusion keeps coming from.
 

Texican65

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Nice. Thanks! I had the shop do a new bearing kit, and I drained the ATF they installed and went with Red Line MT-90. Noticed a huge difference immediately, smooth shifting...and very quiet. Hopefully this wasn't all in vain...we'll see....fingers crossed.

Dow
 

Bakersrule

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This is a very old thread.. but i am in a similar situation. Fm146 was bad in the lifted 89. Swapped it out. Was noisy in neutral 1st,3rd, and 5th. Kept kicking out of first too. Used one is better. Replaced oil with 80 90. Starting to get some gear chatter and worried it might be the oil. Original engine did not have a pilot bearing in the crank shaft. But this one does. Is this just an fm146 issue?
 

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This is a very old thread.. but i am in a similar situation. Fm146 was bad in the lifted 89. Swapped it out. Was noisy in neutral 1st,3rd, and 5th. Kept kicking out of first too. Used one is better. Replaced oil with 80 90. Starting to get some gear chatter and worried it might be the oil. Original engine did not have a pilot bearing in the crank shaft. But this one does. Is this just an fm146 issue?
Some suggestions:

You should look at the gear lube bottle that you used. If it says GL-5 on it, it is not the right fluid for your transmission. GL-5 will damage the synchros. GL-4 will not but it's very hard to find. Either way, I personally think that 80w-90 is way too thick for these transmissions. Straight 90w GL-4 (which is the most common type I've seen) is even worse. I use Valvoline Synchromesh MTF in mine...I like it. Shifts very nice in cold weather.

Where are you hearing noise? Neutral, stopped, while driving, clutch in/out, certain gears?

As far as the pilot bearing goes, do you have one in there now? Trucks with 2.9 and 4.0 engines have the pilot bearing in the flywheel. You MUST have that bearing in place, the trans will have a very short life without it.

Last...when you put the replacement trans in, did you check the input shaft for slop? Side to side movement, in/out. A tiny bit is OK, any more than that is not a good sign. These transmissions are well known for input shaft bearing failure and that is the first sign of it.
 

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I think mine had the FM146. I tried to tow in 5th gear on a stretch of flat Interstate for 30 minutes and came close to ruining the transmission due to over heating it. The 146 may have been an improvement over the 145 but it still had a weak 5th gear. I had not heard of the ball bearing use in the Mitsubishi transmission but that could explain some of its issues.

I liked the Mitsubishi transmission shifting characteristics over the Mazda transmission but I like the durability of the Mazda better. I didn't have mechanical problems with my Mitsubishi transmission but have heard many horror stories about them.
Never ToW in OD
 

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Some suggestions:

You should look at the gear lube bottle that you used. If it says GL-5 on it, it is not the right fluid for your transmission. GL-5 will damage the synchros. GL-4 will not but it's very hard to find. Either way, I personally think that 80w-90 is way too thick for these transmissions. Straight 90w GL-4 (which is the most common type I've seen) is even worse. I use Valvoline Synchromesh MTF in mine...I like it. Shifts very nice in cold weather.

Where are you hearing noise? Neutral, stopped, while driving, clutch in/out, certain gears?

As far as the pilot bearing goes, do you have one in there now? Trucks with 2.9 and 4.0 engines have the pilot bearing in the flywheel. You MUST have that bearing in place, the trans will have a very short life without it.

Last...when you put the replacement trans in, did you check the input shaft for slop? Side to side movement, in/out. A tiny bit is OK, any more than that is not a good sign. These transmissions are well known for input shaft bearing failure and that is the first sign of it.
I did check input shaft. Very little play. New engine has the pilot bearing. Will have to check if its the gl 5. If thats what i got i will swap it out for the valvoline synchomesh. Thanks for the tips. The old tranny was the one with noises in neutral 1 3 and 5. This one is quieter but starting to hear somenoise in neutral while stopped. Thanks again!
 

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I did check input shaft. Very little play. New engine has the pilot bearing. Will have to check if its the gl 5. If thats what i got i will swap it out for the valvoline synchomesh. Thanks for the tips. The old tranny was the one with noises in neutral 1 3 and 5. This one is quieter but starting to hear somenoise in neutral while stopped. Thanks again!
I would not be too concerned about it. Some noise in neutral, especially if you have the clutch engaged, is normal.

Fortunately in your case an M5OD from a newer truck is a super easy swap if your FM-146 ever fails... the M5OD is the same length so there are just minor changes to be made to other things during the swap.
 

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