FM145 Strength

[Rustbucket350]

How strong is the FM145? It held up fine dumping the clutch with a 4.0 but could it handle roughly 250 hp? I have some ideas brewing for the motor.

 

[Transman304]

Sounds like you have been pretty lucky with that transmission. There is a big difference between use and abuse. Your results may vary, but I would suggest using the M5OD. HP is a consideration but Torque is what will destroy parts. The Mazda transmission seems to handle the torque better than the Mitsubishi. This is just my opinion based on what comes across my bench and the damage that I have seen. Let us know how it works out.

 

[adsm08]

Um, the FM145 doesn't stand up to the 2.9, by all rights you should have destroyed it already.

The FM145 uses ball bearing which are prone to torque induced failure, and 5th gear seems to just explode from time to time.

The M5OD uses roller bearings which spread the force along the length of the roller, instead of concentrating it on the tip of the ball, and I have never heard of the same types of gear failures in the M5OD that the 145 is known for.

 

[Rustbucket350]

Ha it's got 180,000 miles on the trans and once I filled it up with gear oil it's never shifted better. Dumped the clutch and spun the tires through second (twice to test it), then drove it 120 miles in two days. I guess I'll be looking for an M5OD or better once I get my turbo piping laid out because my gut tells me I'm pushing my luck.

 

[Rustbucket350]

So after 300 miles the FM145 is still going strong. Maybe that will change and maybe it wont. I do plan on picking up a used M5OD but I'm surprised this trans is holding up at all and I don't shift like a grandpa. Next discount or all you can carry day I'll be shopping for an M5OD to go with my turbo build but I think it's safe to say the FM145 will hold up to a 4.0.

 

[4x4junkie]

I think failure is more likely to occur with sustained loading (driving up a long grade, or towing a trailer). Heat builds up and/or the ball bearings become starved of lubrication.
Short bouts of abuse don't seem to bother it as much.

I lost the output shaft bearing on my FM146 behind my BII's 2.9L... just so happened to be while towing too. Overfilling the trans fluid by a half-quart or so might help it last a little bit better.

 

[Rustbucket350]

Time to eat my own words. I blew it out. The fact that it leaked bad probably did not help. Only took 3,000 miles but what can I say? I liked the gear ratios in it. Putting a 2wd M5OD in since nobody in the whole state has a 4wd one.

 

[adsm08]

I guess it's time to say "I told you so".

Check out Cobra Transmissions, they often have the parts needed to covert a 2wd M5OD to a 4x4. If that fails PM 1BadExplorer. He isn't as active on here these days, but he always comes up with weird stuff for me.

 

[Rustbucket350]

I'll have to check that out. In the meantime, is there a factory driveshaft that will work for the 2wd version in a Bronco II? I can't seem to find a length dimension for the M5OD anywhere.

 

[adsm08]

The M5OD is the same length as the FM146 and A4LD. Your issue is going to be the 2wd part since all the BII up until the last year had the 4x4 setup, and just a dummy T-case if they were 2wd. Possibly the best bet would be get an Explorer front drive shaft and swap a slip-yoke onto it. Maybe.

 

[Rustbucket350]

Well that is just not the news I wanted to hear. I suppose a custom driveshaft is going to be in the works asap.

 

[Zane]

I know this is an old thread but it's on the first page of google search (fm145,strength,tq ratings) so I thought I'd add some info about the 5th gear issue. a notorius problem with the 5th gear bearing sleeve wearing into the 5th/reverse synchronizer hub. This problem further has cause the failure of the 5th gear on the mainshaft, causing the 5th gear to seize to the 5th/reverse hub and then break.

The problem is inherent, because the mating-surface area of the 5th gear bearing sleeve is too small. Although pressures against the hub are amplified while the transmission is a high operating temperatures, they decrease significantly when the transmission cools to ambient temperature. This continual pattern causes the sleeve to work loose against the 5th/reverse synchronizer hub and then begins to wear into the splined area of the hub.

http://autotransmissionblog.com/ford-ranger-5-speed-fm145-fm146-5th-gear-problem/

There are now fixes for this issue available on the market making the fm145 a good daily driver trans, And with today's cryogenic treating process you can get your trans internals cryo treated adding an additional 20-30% strength over stock. So swapping isnt the only option.

 

[adsm08]

I know this is an old thread but it's on the first page of google search (fm145,strength,tq ratings) so I thought I'd add some info about the 5th gear issue. The bearing against the 5th sincro expands and shifts during towing and high trans heat operation. It than cools and gets stuck against the sincro causing intense friction heat and results in the bearing and sincro welding to 5th gear. Now this is just a summary of the article on the issue which I suggest you read

http://autotransmissionblog.com/ford-ranger-5-speed-fm145-fm146-5th-gear-problem/

There are now fixes for this issue available on the market making the fm145 a good daily driver trans, And with today's cryogenic treating process you can get your trans internals cryo treated adding an additional 20-30% strength over stock. So swapping isnt the only option.

That still doesn't fix the fact that someone was dumb enough to use ball bearings instead of rollers on the input and output shaft bearings.