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Komatsu PC40-3 final drive periodic lock-up becomes siezure

Komatsu PC40-3 final drive periodic lock-up becomes siezure

Komatsu PC40-3 final drive periodic lock-up becomes siezure

Howdy folks, I bought a somewhat shabby little PC40-3 a few weeks ago. I was told that one track occasionally locked when going forward but was fine running backwards. Got it home and after checking all fluids and giving it a good grease took it up an old overgrown farm track, clearing the overgrowth and squaring up the eroded track shape. The tracks worked fine until I turned the undercarriage 180 so I could use the blade without shoving a dirt pile into scrub I hadn't cleared yet - that was when the left track started locking up. I checked externals and found the front idler bearing has a lot of play but all the rollers seem fine and I can't see anything catching. Decided to change the final drive gearbox oil (Hy-Dash) and found fine metallic particles and flakes suspended in it. Flushed some new oil through the box then filled it fresh and tried it again - no improvement, in fact it continued to get rapidly worse. I tried to get back to level ground to take a look but it locked and refused to move with direction reversal as before. Lifted the track off the ground but the sprocket isn't even trying to move the chain. When looking for movement I noticed a grouser shake off dirt and heard a faint grating noise that sounded a little like a valve squealing but I fear is a spinning sun gear. Looks like I'll be fixing it right where it is. I have been told the gearbox cover can be levered off. I took an oil bung out and found a bolt that fitted then used a crowbar under the bolt head to lever the cover off but it feels solid and I don't want to break anything. I could drill through the bolt and braze a tyre valve to it then use a hand pump to pressurise the gearbox - can someone tell me if the cover has any retainer, I can't see one. Any advice on how to proceed would be greatly appreciated.

RE: Komatsu PC40-3 final drive periodic lock-up becomes siezure

I don't recommend pressuring the case - if it is stuck it could explosively come off and hurt someone. You can move the machine by lifting the bad track off of the ground with the shovel, then rotate while moving the good track. It is slow but works. (I even saw it done with an old mechanical drive undercarriage once when a chain came off in the mud)

There are a lot of little parts in the final drive. I suggest taking the whole drive/motor out and disassembling it on a clean work bench. Some pictures and/or manufacturer/model info would help tremendously.


PS - I'm not sure what country you are in, but I ran across this supplier of final drives in the USA.

RE: Komatsu PC40-3 final drive periodic lock-up becomes siezure

Your final drive failed. The cover has a ring of bolts that hold it on. Remove these and knock/pry the cover off. You will probably find thing totaled out. It may be hard to find a used one as these tend to have catastrophic failures. It should be a cycloidal drive. http://www.darali.com/page17.html

Ed Danzer

RE: Komatsu PC40-3 final drive periodic lock-up becomes siezure

Thanks Icestationzebra and Eddanzer, I would only try to pop this cover off with air if I was sure there was no snap ring or other retainer holding it on and would drape some heavy fabric over it as a catcher.  I don't intend to disassemble much where it is, just want to inspect and diagnose before deciding what to do next as a whole new drive might cost more than the machine is worth. It is a Komatsu PC40-3 S/N 6868 made in 1985 - 86. The finals are Hy-Dash by Teijin Seiki and if my uploaded pics work you should be able to see the groove where the cover locates - the only bolts are those holding the sprocket on and the one I put in the bung hole, that's where the oil came from, it didn't leak prior. I'm just hoping you might recognise the drive and say "oh it's one of those - do this". Whatever the case, thanks for replying in the first place - cheers. I'm in New Zealand by the way.

Self Deployed - New Zealand

RE: Komatsu PC40-3 final drive periodic lock-up becomes siezure

It looks like there is a round lock ring holding the cover on. Try pushing in to compress an o-ring to gain access to the lock ring.

Ed Danzer

RE: Komatsu PC40-3 final drive periodic lock-up becomes siezure

Pull the motor and walk the machine into a better area to work and test it on. Use the implement to pull yourself up with the other track operational.That way you can test it and repair whats needed.BTW do yourself a favour and take it off the machine, if the final drive has failed you could be in for some machining or replacement of the unit.Rebuilds are easy enough but you may find an exchange service cheaper in the long run compared to machine downtime against service availability $$$$$.    

RE: Komatsu PC40-3 final drive periodic lock-up becomes siezure

Thanks Ed, you're right. The local agent tells me there is a wire ring that is extremely difficult to get out. He suggested I use the bucket with a piece of pipe as a strut to compress the cover but the idea of trying to get the ring out with a pipe loaded against the cover is too risky for my liking - I'm too old to play those games anymore so I made up a crush with long bolts through from the other side of the sprocket pulling an angle iron strongback against a couple of spacers to depress the cover. I just had it all in place when the rain started and it's still too wet and cold to get back to it - we're heading into winter here.
Thanks to you too Newmanite. The machine is several hundred metres along a dirt track with solid undergrowth all around so getting it on level ground is as good as I can do without spending ages walking it out. I never planned to do more than investigate the fault where it is - too dirty and awkward to reassemble something like a gearbox. Luckily the machine only works for us so downtime isn't a problem. Will let you know how it goes.

Self Deployed - New Zealand

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