Shaking Violently - Don't know what to look for

[bwhite757]

Ok, I've had my M880 going on 4 years now without a single major issue. I've only had to replace the fuel pump, everything else has been working great on it. Until yesterday. I fired it up (after it had been sitting for a few months) to clean up some storm damage on my land, I loaded it up with tree debris and a trailer behind it. I got everything to the dump without issues, but on the way home I was going about 40mph and the truck started shaking violently. Forward to back kind of motion, not side to side. I came to an abrupt stop, and checked for a bad tire, or something else visual. Everything looked fine so I decided to try and drive off. After I got over about 20mph the shaking returned, becoming more and more violent the faster I went. I limped her home, unhooked my trailer, and took it out to see if maybe my trailer was the culprit. Not the case, anything over 20mph and I can barely keep control of her. So I once again brought her home. Jacked her up and pulled the tires off the front, everything appears in good shape and tight. I'm not much of a car mechanic so I don't really know what to look for. The drive shafts appears to be fine, tires are good (new last year), and I'm just pulling my hair out at this point. I always said if something major happened to her I would just get rid of it, I only paid $500, and I've gotten my money's worth out of her. Can you guys help me out as to what to look for? If it's relatively simple and something I can fix, I'll get her back on the road, if not I forsee a For Sale sign on her pretty soon.

Thanks

 

[NDT]

Could you have bumped it into high-lock setting on the transfer case?

 

[bwhite757]

Can't believe it was something so simple. My 6 y/o was riding in the truck with me at the time, and I'm guessing maybe she was playing with the shifter without me noticing. Oh well, the truck is driving fine once again! Good deal, thanks so much!

 

[MWMULES]

When you had the front jacked up did you check wheel bearing play with the wheels on? Just before I lost a front bearing that's how the truck was acting it held together long enough to get off interstate and into parking lot. Napa carries the bearings. The only other time I had something close to that happen were rear wheels got mud packed on the back side and unbalanced the drive train.