Grind in FM 146 after rebuild


tacorocketswiss

15+ Year Member

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I’ve got a Mitsubishi FM 146 5 speed tranny that was just recently rebuilt. All the components are new. Installed the tranny the first time and third gear wasn’t smooth. Would have a bite going into third and would grind down shifting back to third. Took the tranny out and replaced the third gear synchro. Put everything back together. Same story, not as bad, but still has a bite going into third and now into fourth, and can not get it to down shift into third without grinding unless I perfectly rev match. At that point I’m not even using the synchro. Everything is new, synchros and gears, and I am at a loss. Any pointers, advice, or places to start would be helpful at this time? Thanks.
 
Sounds like the gear might be worn to much at the cone shaped section for the synchro block ring. There is a minimum gap you should have between the teeth on the synchro and the teeth on the gear where the synchro slider contacts the gear, I don't know the specs right off the top of my head, but if the block ring is almost up against the teeth on the gear it's pretty safe to say the gear is to far worn. If there's not enough of a gap there that means the block ring is not able to mesh the slider to the gear the way it's designed to & you will get grinding.
 
ALL the components are new? I very much doubt that.

Unless this was a $2000+ transmission (and the rebuilder owns a time machine), there are SOME used parts in there. Probably most of the hardened parts, as well as nonmoving parts such as the case.
 
I just had my m5od rebuilt and my third seems to grind when i down gear when the trans is cold
 
You can try using some Red Line MTL ( Manual Transmission Lubricant ), it sometimes makes manual transmissions that grind, or hard to shift work better.
 
MAKG said:
ALL the components are new? I very much doubt that.

Unless this was a $2000+ transmission (and the rebuilder owns a time machine), there are SOME used parts in there. Probably most of the hardened parts, as well as nonmoving parts such as the case.
Click to expand...

You've got me on a technicality. You're absolutely right. ALL the components are not new. I reused the housing, bolts, and a few other odds and ends here and there. Let me rephrase that. All wear parts were replaced. third gear and third gear synchro are also new. I can get it to grind warm or cold. Very sporadic, and I couldn't establish a consistent pattern. Someone threw out an idea of a shimmed bearing I missed. Would this be leading me in the right direction? It's been running royal purple 80-90wt. I could use Redline, but at that point I figured I was splitting hairs between Mobil 1, Redline, Lucas, and Royal Purple, etc. I know there are some out there that will disagree, but it's a rebuilt tranny. I hope I dont have a life of grinding third to look forward too.
 
Seriously, I've seen the Red Line MTL fluid make a few difference in a few transmission personally. It is thinner than 80-90wt oil, might help with the lubrication somehow. I'd definitely give it a shot, if your skeptical save your Royal Purple fluid when you drain it so you can put it back in your transmission if you feel the Red Line don't make a difference. If you get the Red Line fluid be sure it's the MTL fluid, not any of their other gear oils, it's got additives in it to help with making the manual transmissions shift smother.
 
Just to be sure -- you live VERY close to the Redline shop. It's in Benicia. You don't work for them, do you? Full disclosure requires this.

Redline makes a nice product, but frankly, it doesn't matter. This thing was designed to work with conventional GL-4 gear oil, and it will work with ANY GL-4 gear oil with the proper viscosity index.

3rd gear alone was replaced? Are you sure it's the correct part? Was it indeed new, or "good?"
 
LOL! No, I don't work for Red Line, I didn't even realize that they were in Benicia. I worked in the transmission industry for just over 12 years & have seen there MTL fluid help with many grinding issues in manual transmissions, especially Hondas. I now own my own business now not working transmissions, I don't hardly touch them any more because it's to much like work.
 
I think it's more than just a fluid issue. Got a grind in third and fourth. Gettin really tired of pulling it and out now. Gears are new, synchros are new. Gap between the teeth of the synchro and teeth of the gear are all within spec. Here's a new one for you guys. Eats the pocket bearing between te input and output within 500 miles. Gettin tired of staring at it and about ready to just eat the cost of a new reman. Any other ideas?
 
If your eating up the pocket bearing between the input & output shafts you'll never get rid of the grinding. What's happening is the pocket bearings are binding the shafts together, the output shaft is trying to turn the input shaft, that will turn the countershaft & that will turn the gears on the output shaft causing it to grind when you shift. Sounds like you need to get a good input & output shaft, rebuild it again or find another transmission.
 
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