Drove my recently acquired '85 D100 (76K miles, auto, I-6) around town today looking for some new shocks (it has the originals and they are shot). Anyway, as I was hitting around 50mph (fastest I've had it) the truck developed a bad shake that felt like it was in the rear of the truck. I slowed down and the shake stayed around. It was so bad I really thought I had a flat and pulled over.

Everything looked good so I decided to go on home. It still had the shake all the way home and I never drove it above 35mph.

I looked at everything (springs, wishbones, etc.) and everything looked good. The truck has never been hit so I don't think anything is wrong there. The tires have even wear. Could this be a simple case of a tire weight being thrown or something more sinister? Also, the truck felt like it was pulling to the right when I was braking. Of course I was paranoid at this point and may have been overly "sensitive".

I changed the front shocks tonight and will change the rears tomorrow and then go on a short test run. I don't expect that the shocks will make a difference.

Any ideas on things I should check during my "shakedown cruise"?

Thanks!

 

Take it for another test drive after you change the shocks. If the vibration is still there you could try swapping tires front to rear and see if the problem goes to the front end.

 

Got the shocks replaced and took it on a test drive. Couldn't find a place close by to get the truck above 50 but it seemed okay (and drove much better with the new shocks).

When I first started the truck up this morning it idled fine but when I put it in gear the truck developed a big vibration (almost like I felt yesterday). When I put the truck in park the vibration went away. That only happened for a minute or so. I don't have a tach so I'm not sure if the engine developed a bad miss or if there was something else causing it.

Bill

 

It's probably the transmission shuddering. Put some stop-shudder fluid in it.

 

check the u-joints on the rear drive shaft. I rencently had two issues with that. I was driving along all of a sudden a really bad vibration. I could not drive over 20mph with out it vibrating. I was only a few blocks away from home so I justed idled it home. I then got home and went to park it, put it in reverse and CLUNK! The drive shaft dropped. The loose and wobbly drive shaft caused the first vibration issue. Months later the another insident of the vibration. So I look under the truck and two of the bearings of the rear u-joint are gone.

 

Sounds like a tranny mount to me. Wiggle the tail shaft and watch the mount for excess movement.

 

A friend had vibration under accelleration, turns out his driveshaft slip yoke was shot, the pinion nut was loose, and something else was loose too. A rebuilt driveshaft and tightened nuts fore/aft fixed the problem. Climb underneath and try wiggling stuff back and forth. Use some force - there shouldn't be much movement at all and if there is, check it out.

Also it wouldn't be a bad idea to balance the tires anyway.