FM145 trans fluid

[Slammin Sam]

After checking the tech area and searching the trans forum, the most recent post to answer my question is from 07. So I'll take a shot at it now. I have an 89 B2 with 142,000 miles and the fm145 trans. I purchased from the original owner in late Oct, 13. I have every receipt since new! It received a new clutch about 15,000 miles ago. Now that the temps are going down, the tranny is real hard to shift the first few miles until it warms up. I fear the bottom line is a rebuild, but I'm hoping a fluid change will postpone the inevitable. I need suggestions for a fluid (maybe new synthetic?) that might ease the shifting.

 

[4x4junkie]

Might just be that the oil in it is too thick.

Mitsubishi trans uses 80w gear oil (I used 75W-90 no problem when I had the FM146 in mine, coldest temps I saw with it was around 5°F)

 

[adsm08]

I have always used 80-90 to good effect. On bad advice I once used ATF in an FM transmission to catastrophic results.

If you have an 89 it is more likely that you have an FM146. They are mostly identical but the 146 is about 2" longer and a straight shifter.

 

[greaseandmetal]

Exactly what brand/product do you use adsm08? I'm using Motorcraft full synthetic manual transmission fluid for WSD-M2C200-C and its hard to shift. I probably need a synchro job done too.

 

[Slammin Sam]

At the peril of renewing a year old thread, I thought I should post a follow-up. After much research, I decided to use Amsoil Synthetic Manual Transmission and Transaxle Gear Lube. Its rated SAE 75W-90 API GL-4. The GL-4 is the important part. Unlike GL-5 rated lube, it will NOT attack your brass syncros. So far its only been down to 10 degrees above zero, but initial shifts have been much better, not perfect but better. I'm satisfied I've done everything I can to help the old FM-146. If you're changing your tranny fluid, stay away from GL-5 rated lubes. Find the GL-4s. At $16.00 a quart Amsoil isn't cheap, but I heartily recommend it.

 

[cavedweller]

When I change the lube in my FM146,I use a GL-4 rated lube.....When I tried a GL-4/5 lube I ran into what it sounds like is happening to you,GL-/5 will KILL your sychros ...These trannies VERY are particular ,HA,HA,HA...Hard to find a staright GL-4 in the local stores nowadays around here....Ordered 3 quarts of RedLine,from Red Line Synthetic Oil Corp...Phone # 707-745-3214,was VERY surprised at the difference ,no more 3-4Th gear down shift clashing,..My synchros seem to be in a Quitely blishful state....