1985 250SX Transmission Issues

[newby200x]

I recently acquired this machine knowing it needed some work. One issue was the seized forks that I posted earlier...turns out they still have movement, but one of the lowers was completely rubbed through by an oversized tire. The main issue I knew about was that it was stuck in first gear. No up or down movement would change that. We bypassed the neutral safety switch and the thing runs like a top, it just won't go past first gear. I've never experienced this issue before, but after some research, it seems 99% of the time there is just something broke w/in the gear shift mechanism (shift shaft or dowel pins). This would be a quick and easy fix so I pulled the trigger on it. Fast forward a couple weeks and I finally dig into the machine and everything is tip top shape w/ all of the gear shift components. However, I managed to find a broken tooth from a gear at the bottom of the cases. I put it all back together and now it would shift into neutral, but the weird part is it won't shift up into any gears, but it will shift down into "a gear". When I shift it down into a gear it's not first, but it seems like second or possibly even third. Anyone have any good guesses as to what is going on here? Bad shift forks? A broken gear, or several broken gears? I wasn't planning on going completely internal on this thing, but it seems inevitable at this point. I do have a spare transmission, so luckily I won't need to purchase any parts other than a gasket and seal kit.

[Footy]

I would replace any or all broken gears, All shift forks, and any/all shift springs.
Maybe even replace the shift shaft if you have one that you know is good.
Because of how similar the engine is the to TRX300 you may be able to get the shift springs new from honda.

[6speedthumper]

I picked up a 250ES years ago that was stuck in 4th. The shift shaft had broken. The piece that engages the shuft drum split and spread apart. Remove the stator cover to inspect and replace. Hope that helps.

[newby200x]

I thought I'd provide an update to this just in case anyone was curious. I pulled the motor from the machine and began disassembly this past weekend. After pulling the clutch cover I discovered one of the oil pump bolts worked itself loose and made its way around internally. It took a tooth off the clutch basket gear and a tooth off the primary drive gear on the crankshaft. I split the cases and could not see any visible damage to the gears, shift drum, or shift forks, at least to the naked eye. Since I had a complete spare transmission, I went ahead and swapped out all the gears, shift forks and shaft, and the gearshift drum. After replacing all of this, I still could not get it to shift through all the gears. I split the cases and put it back together more times than I care to admit trying to diagnose the problem. Finally, I decided to just go through all of the transmission components again piece by piece and double check everything was correct per the manual. Turns out I had an incorrectly sized washer in between the 3rd and 5th gears which would not allow the gears to engage with each other. Since I didn't take a pic of this prior to disassembly, I'm not sure if this was the root cause of the problem to begin with, or if I accidentally put the wrong washer in while swapping the transmission parts. The dowel pin on shift drum also looked a little wore down and rounded off so I feel like it could have slipping as well. All of the gaskets on this machine were black, so my logic tells me someone has been inside this motor before. With the transmission finally fixed, it's time to complete the rest of the assembly.

[Footy]

Great news!