518 Cat Transmission

[mills]

My 518 quit moving after pulling a load up to the landing, and now I'm stumped.
Background - My brother was running it, he dropped the logs at the landing, backed up, pushed them up to the saw, started back for another load, went twenty feet, shifted to second, and the skidder quit pulling. Now it won't even try to move in either direction. Although he hasn't ran it a lot he said he never heard or felt anything out of the ordinary. I had ran it an hour before and everything seemed normal.
Doesn't feel like it's trying to shift, like it's  stuck in neutral. Oil levels are good. Winch still works. Pressure gauge on the dash shows in the green. Don't hear any noise when you shift it, or rev the engine up. Output shaft is not turning. Had problems before with the air brake interlock, so took it loose, but it made no difference. Took the cover off the shifter box, and everything seems to be moving as it's supposed to with no evidence of anything coming apart. Verified that it has good oil flow. (Don't ask.  :-\) Oil and filter were changed maybe a hundred hours ago with the expensive Cat oil.

The way it stopped with it already moving has me baffled. It's an 86 model, so I don't think there are any electrical safety interlocks on it. What am I missing???

[bushmechanic]

I'm not that familiar with the Cat skidders but sound to me like you have lost the coupling between the engine and transmission. I would think a FF member kiko would be your best bet to ask about this.

[coxy]

is the shaft turning under the floor board by your feet that comes off the tq converter  there was a guy that had trouble with a shaft in the tranny that had a keyway in it and the drive gear would slide and it would stop moving they would take another skidder and bounce the other and the gear would slide back some times you could run it all day no trouble and other times they said every 10 ft they had trouble  if the winch is working then the tranny is turning in side to make pressure cause the cat winch works off the tranny there is hydro lines that come out the top by the brake caliper and go to the winch   I know on the tj there is a fiber gear that turns the tq converter and when that goes you have no hydro power

[kiko]

Machine serial number?

[mills]

kiko
Serial number: 95U01347
Machine arrangement: 6W4050
Transmission: 1ZC00622
coxy
The winch shaft is turning. Haven't put a load on it, but the winch rotates and freewheels like normal.

Does the brake interlock do anything except mechanically keep the shifter from moving? Process after starting engine is to let the air pressure build, release the e-brake, and then punch the brake pedal. Try to shift before the air pressure builds enough, and the shifter will move, but the transmission will not engage. Makes me think I'm missing something in that area. The diaphram on the brake interlock has had a small leak for years, but the only time I had any trouble was when the compressor went out.

I kind of enjoy figuring out problems ... except when it costs me downtime, and potentially thousands of dollars. >:( :P >:(

[coxy]

when I put the parking brake on you can not move the shifter that is with both  the 81 and 89 

[mills]

Finally back up and running.  8)

After several attempts I was fairly sure it was in the shifting valves which are way past my comfort zone. Called in a "real" heavy equipment mechanic friend of mine. After going through the same basic steps I did he hooked a gauge to the test ports in the shifting valve. Found no pressure on the modulating valve. Took it apart and found a small sliver of steel on the spool. Not sure where it came from. The filter and oil looked clean. Just something else to watch out for now. Amazing that a mighty oak won't hold it back, but a sliver smaller than a pin will shut it down.