Machine has the shakes

[reaperman]

Hi all, this is my first post and like many first posts on a forum, unfortunately its because troubles sent me here. With that I'll get started. Yesterday I was wrapping up a afternoon of cutting wood and on my final tree is when my machine all of a sudden started to shake pretty bad. I wasn't doing anything at the time it occured, only backing up on some rough ground. The noise associated with the shake is almost like something was caught somewhere and rubbing against perhaps the fan. I shut the machine down and was looking for what sounded like a stick hitting against something in the engine compartment. I pretty much ruled that out since it would be hard for a stick to get inside. And then I was looking at the motor mounts to see if one had came loose and cause everything to shake. After seeing nothing, I figured I better limp my machine back home before it was stranded in the frozen river bottom. The machine seemed to drive back home fine (at very low rpms) and the hydraulics appear to be working normally. The shake seems to be centered behind the seat near the fan. Raising the cab and inspecting what I could see showed my nothing. After tossing the dilemma around in bed last night, my gut instinct is telling me that maybe the u-joint is going or has gone out. I dont know if that would cause the machine to shake this bad or not. I havent checked that out this morning. I know to actually see the u-joint is almost impossible without pulling the engine, which I wont do, yet. The other possibility is maybe the hydro pump? But the hydraulics seem to work fine, despite the handles moving back and forth with the rythem of shaking of the machine. I need some input, has anyone had a machine act this way?? I want to get this fixed asap, I love my machine and rely on it for countless tasks around home. And with winter here, although no snow yet, I use it to keep my 1/4 mile long driveway open. And for cutting firewood, its as valuable to me as a chainsaw. I just dont understand how anyone can cut firewood without a babcat.

 

[OldMachinist]

What model Bobcat is it?

 

[reaperman]

What model Bobcat is it?

Oh sorry, I forgot to mention the machine is a 642 with 3185 hrs.

 

[OldMachinist]

Oh sorry, I forgot to mention the machine is a 642 with 3185 hrs.

I'd say the U-joint is the first place to check.

 

[wings5j]

I'd say the U-joint is the first place to check.

I don't have a guess as to the problem but wanted to add, that you should be able to put your hand on the u-joint if you can stretch your arm back in there far enough.
By using a flashlight and inspection mirror you can actually get a look at the u-joint. This is the technique I use for getting the zerk fittings in the best spot for greasing.
John