FM-146 weaknesses

[disciplerocks]

I kept my original FM tranny when doing my 4.0 swap and I must say I am diggin the low gearing and the added torque together. Now I know the Fms are supposed to be weaker, but I have yet to hear from anyone that has ran one behind a 4.0. Is there anyone? What are your experiences good or bad? Where are the weak points?

I need to make this one last until I can source a M5OD, although I may replace it with another FM if it goes out because they are much easier to find, and like I said, I love the gearing.

 

[rednine4]

no experience behind a 4.0... I did run mine for a few years behind a 2.9L absolutely punishing it, and it still held up fine. I think it had 140k on it when I sold the truck and it still worked.

Conversely, I have wasted 2 other FM146s in my other BII hardly beating on them. I guess it depends on luck of the draw...

Things I always did on my one that lasted were keep the fluid up to par. I used a blend of gear oil and ATF (not saying that's the correct fluid because it's not) but it worked well for me. I also avoided using 5th gear because of the design of the trans, it will eat bearings if 5th is used alot. So 4th gear everywhere and it may last you a good while.

 

[disciplerocks]

I finally have enough power to actually use 5th gear, and I can't use it? lol.

 

[BONES]

I'm running the fm146 behind my 4.oL with full width sas and 38" tsl's spools front and rear. I busted a couple rear u-joints under heavy load and actually broke the back of the 1350 apart and the trans is still going strong.

 

[gwaii]

the only thing i broke on the 146(behind a 2.9)was the input gear.twice i managed to shear the teeth off it.that was with severe abuse,though.

 

[disciplerocks]

Good info, thanks guys. Keep it coming. I'm still waiting for the proof the FM wont hold up to a 4.0.

 

[Snoranger]

Good info, thanks guys. Keep it coming. I'm still waiting for the proof the FM wont hold up to a 4.0.

Give it to me for a week or 2. I F'ed up 11 of them behind stock 2.9ls over the years.

I broke a shift fork on 3 of them. (jammed up and broke through the side of the case on one).*
I ripped the teeth off gears. (1st ,and 2nd) 4 of them.
Stripped the teeth off the input shaft on 1.
Ripped the shifter out of 1 of them.*
Snapped 2 output shafts.


* these were my fault. But in my defense, I also managed to bust a B&M Ripper in half on my Mustang.

 

[BeaterMan]

i think it could be the luck of the draw. Ive herd of many of these crappin out prematurely, and others who have beat the livin crap out of them without issue. i have the fm145 in my truck and it has surrvived alot of power shifting, hard roll starts, and 2 transfer case failures, one case failure that wouldnt let the truck drive for more than ten feet then lock up slam the truck- I just rev'd it to the moon and dumped the clutch and the whole tcase when boom and the trans is still going strong. that being said i did have to rebuild mine right when i bought the truck cuz the po had sumerged the truck and filled the trans with h2o then continued to drive it wiping out the bearings.

in my buddys 88, hes got 245k on origional 146 trans with the last fluid change around 130k and still going strong- who knows what, if any, the fluid looks like. and his has gone through 4 clutches in the last 3 years.

 

[4x4junkie]

I had the rear output shaft ball bearing crap out on mine at around 150K miles (spalled inner race which made a clicking/chattering noise in 5th gear). Odd, because I've always heard it's the input shaft bearings that usually let go first on them. This was with a 2.9L ahead of it.

I actually drove it that way for quite awhile though, even using 5th. The noise stayed the same for a good 10K miles before it finally began to get worse and I then yanked it for a M5OD.

 

[disciplerocks]

in my buddys 88, hes got 245k on origional 146 trans with the last fluid change around 130k and still going strong- who knows what, if any, the fluid looks like. and his has gone through 4 clutches in the last 3 years.

Mine has 180k on her and I don't know if the fluid has ever been changed. Its on my list, but she is still holding good.