1995 GC vibration

[SnoopyCollector]

Looking for suggestions as to the following probelm:

While driving and tach rhits 1250 to 1500 rpm (35 to 55 mph), the entire truck shakes violently. Feels as if its coming from the back of the truck and is similar to out-of-balance wheels. Recently, two days ago, has the wheels rotated and balanced, thinking that was the problem, but no luck - still vibrates at the above range. Have also checked the driveline and u-joints, all appear OK. Checked transmission fluid level (as this is what started some of the probelms, i.e. - lurching du to low fluid), fluid now OK.

Also, if I gas it to get past the rpm range, it stops than sometimes returns when it decreases to the range, and if I slow down below the range, it also stops. -- Doesn't do it each and every time either. Engine at normal operating temp.

Any one have any ideas.

Thanks in advance

[porscheguy9999]

Well I wouldnt trust myself on this, but perhaps your rear axle is bent ever so slightly. So that when accelerating, the camber of the wheels makes the whole structure shutter. Ideally, you want to have 0 degree camber (as in the tire is at a 90 degree angle to the road, perpandicular in other words). But if the end of the axle is bent from some strong force, the camber could change to be negative (the bottom of the tire is pertruding outwards, caused by excess weight for example). Or it could have positive camber (as in the top of the wheel is pertruding outwards, caused by hitting a curb alot somehow. I cant come up with a good example). So that could be the problem. But I cant explain it happening only sometimes. But I'm sure it could turn out to be somthing very simple. Or very difficult. I dont know...

http://www.compgoparts.com/Technical...heelCamber.asp

Wheel camber thingy-mabob. Enjoy.

[FhPt]

I'm wondering if it could have anything to do with the transmission. I'm assuming you have an automatic transmission. Maybe 33-55 MPH is normally the range for a specific gear. When you put the gas down to accelerate through it, can you tell if it down shifts to a lower gear before the vibration goes away? Like wise, when you let off the gas to slow down, maybe this disengages the gear and causes the vibration to go away. If the vehical is vibrating and you throw it into Neutral, I'd have to assume the vibration goes away also, even if you are coasting between 33 and 55 MPH still. Can you tell if it shifts into over drive once you pass through 55 MPH and this is when the vibration stops?

[fredjacksonsan]

That's my thought. The first test I'd do would be in each gear, see if the vibration occurs with the vehicle in "1" at the stated rpm, then in "2", and also with o/d locked out. If it does, it's in the engine/torque converter.

If it doesn't, it might be the lockup in the torque converter shuddering. I've had a vehicle that did that, and if your transmission fluid needs replacing or is the wrong type, it could cause the problem. How lmany miles on the vehicle, and how many has it been since the transmission pan was dropped?


-edit- I also wouldn't rule out Ujoints.

[wheels4]

I dont know how you checked your ujoints but if you didnt pull the driveshaft this is the only way to be sure.I`ve seen to many people not pull the driveshaft and think they were good. Good luck.

[SnoopyCollector]

Thanks for all the replies and suggestions.

AFter reviewing them and having a mechanic friend take it out for a test drive, he determined that the shuddering was due to low fluid level, (I was not aware until now that Chrysler auto-trans are checked in neutral), torque converter lock-up (as suggested) and a major 'miss' of the engine.

After adding additional fluid, the problem got only slightly better.

Doing another tune-up, new plugs and plug wires, besides the engine running hella much better, the shuddering problem is completly gone.

Thanks again to all that responded.