Thank's Cadima, i've did all you said, but when you said to put the gear in one half cover to check the gear mesh, it's barely impossible to have a good idea of the gear mesh. With just one half cover,the top shaft and diff gear swing side to side and it's not sit at their precise place.

So i've measuring the space between the hole of the top shaft and idler gear to compare with the stock plastic case, and find that in the FLM case, the hole is 0.006" (0.1524mm) closer than in the plastic one. I think it's not a big difference, but maybe with an slightly out of round top shaft, it can be enough to make the gear bind togheter.

Don't know if it's normal, if FLM have make it closer to make a closer gear mesh, but it's closer.
AND, yes, i've found an out of round in my top shaft gear, when i put the top shaft in a cordless drill (the top shaft is remove from the tranny here) i can see the gear wobeling pretty much than it's suppose to be.

But,what i can't understand, is if i put the plastic idler in the FLM case, all spin freely, it's with the aluminium idler that the thing go wrong.

...........:032: