Greeting folks, Some time ago I was throwing out questions about 642 drive chain size. I was wondering if I needed to replace the chains.....What was happening was then turning the machine, loading out of a stock pile or bank I would hear a hard bang noise which I thought was a drive chain jumping on a sprocket...After opening the machine up I removes the chains and took them to one of our local chain and bearing dealers...I was informed by then that the chains looked nearly new and that it would be a total waste of money to buy new ones...The sprockets look to be in very good condition....I purchases some half links thinking I could tighten the chains up.....I could not shorten them up at all....Soooo , it all went back together still not knowing what was causing the banging noise....Running the machine now with the , what seems like the metal to metal loud bang noise happening more frequently both while truning and digging we see the right front wheel skipping when the bang noise occurs... My question is , are there axle splines that engage with the drive sprockets? If so if this is the source of the banging when turning and digging what is the process for pulling this part of the machine apart? ? ? Also what kind of special " bobcat tools" are needed for the tear down ? Thirdly, does anyone have bearing and seal info and numbers for the 642......Thanks in advance for your help... Have fun, buckshot
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flyerdan
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I think that if you were producing enough torque to make a splined sprocket slip, it would be a one and done, more like a shear. It's possible that the bang could be something loading up and releasing, like if one of the tires is a different size. Like one new one, or a new set on one end. The different diameters, however slight, will create an imbalance in forces.
You might check out the manual thread for tools and part numbers, don't recall seeing anything for the 642 but it might be there.
You might check out the manual thread for tools and part numbers, don't recall seeing anything for the 642 but it might be there.
flyerdan, Thanks for your input...Yes that's what it sounds like but the tires are all the same size and have been on the machine for a long time....The chains are tight and the sprocket chain teeth are in good shape.This bang noise was present when I bought the machine but has been occurring much more often now. I took the machine to bobcat for a fifteen minute free test drive and when the service manager was operating it during a few turns it began to bang and I was able to see the right front wheel skip a beat in rotation....The right rear wheel was driving as it should and the left side operates properly...That is why I am trying to see if anyone out there in loader land has ever experienced something like this .....Rather then re inventing the wheel I hope to gain some knowledge from others first about the tear down process......All the bobcat service man would tell me was leave it and they would make the repair at $90. some dollars an hour plus parts....I had to inform him that I had to do the tear down my self because being retired I don't get overtime any more.......... Have fun, buckshot
Well, I got the sprocket off and the axle out.....the splines and bearings are in great shape...Nothing slipping there...I'll put a new axle seal in and get it back together.....I am now still searching for what is causing this bang noise.....Does anyone know what the measurement for the amount of slack in the chains should be? I am at a loss on what is causing this banging noise when loading or in forward motion...
flyerdan
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A bearing would have been my next guess, but one bad enough to do that would be quite evident on examination.
Not sure what the chain slack should be, but they will function normally when they're loose enough to slap around on stuff.
If it's only on the one side, and nothing loose inside could come into contact with the front sprocket, check the back for free movement as well. The front wheel jerking could be from transmitted shock from the back and it shows there as it's generally got less weight on it.
Failing finding anything there, I'd put it back together, then get all the wheels up, bucket down in front and a floor jack in back (or forklift if you're lucky) and see if it exhibits the same symptoms ubloaded.
One thing I just thought of while it's apart: count the number of teeth on the sprockets. It's unlikely, but one might have been replaced with an aftermaket that has a different number. That would, of course, act like a different size tire. There has to be a reason it's doing this, it's just a matter of finding it.
