I have a bad vibration on my 96 caravan. its not always there and seems to show up when it cold outside. it vibrates at about 55 on cold days and 70 or so if at all on warmer days. its a violent shake(the whole van seems to shake), i have to slow down to about 25 and it goes away.

Sounds like wheel bearing

bent tyre or dish rim, check tyres and rims and speed balance would help.

I'd have to check your suspension. You think the tires are ok? Did you try rotating the tires to see if it made any difference?

Most vibrations at speeds from 45mph to 55mph indicate tire balance problems. If there is no vibration outside this range have the tire balance checked. If there is a vibration that starts around 50mph and continues at higher speeds there could be a problem with the CV joint(s).

Hi:
Since your BMW 540 series is a rear wheel drive car, a common cause of that sort of vibration is often the U joints on your drive shaft. The vibration often only shows up and certain speeds.

It isn't a particularly expensive repair, but is something to have checked out!

check the fuse an reley that control the blinkers also check all bulbs make sure they are all good.

Lift the back of your car.With a stable rest and with the two hind wheels hanging, run your car up to the speed where you experienced vibration. have someone take care of the throttle and shifting while you observe the transmission shaft. You may have an imbalanced shaft.

Vibrations while driving like you are describing can come from tires that have defects (internally broken belts) (wheel weights that have fallen off) or a bent rim (perhaps from another driver [not you :-) ] hitting a curb) Are the tires worn? Have they been balanced and rotated regularly? You report no vibration in the steering wheel.
Vibrations during braking can be warped rotors or discs (but this doesn't sound like your problem since these kind are usually felt in the steering wheel during braking).
If and only if you feel like you can do this safely,
you can try getting the car up to 55, placing the car in neutral, then switching the "engine off" but leave the "key on" (be warned the power steering will go out but the vehicle can still be steered though the steering wheel will be much stiffer) if you try this (do it perhaps in a vacant parking lot or on an empty road) and the vibration goes away with the engine off but while the vehicle is still moving, then the vibration is engine or transmission related. If this is the case you might hope for maybe a bad engine mount. Bad engine mounts can be diagnosed with the vehicle stopped as well. However, if the vibration remains with the van moving forward but with the engine off, the vibration is likely a problem with the tires or suspension. Try to provide some more info.
If you don't feel comfortable trying the above suggestion, please take the vehicle in to an ASE certified suspension and steering professional for further diagnosis.

Finally, I had a similar situation happen to me today. I was riding with a friend in their van and the vehicle started vibrating more and more around 55 mph. We stopped and carefully checked the front tires (including the lug nuts for tightness) but
found a tire defect. (it had several broken steel belts that caused a bulge in the tire and thus the vibration) We changed the tire and the vibration was gone. Good luck to you.

seems your problem is within your clutch,defective part,usually a defective release bearing will cause gear shifter and pedal vibration but not as bad as yours,but by pressing on clutch pedal vibration stops,point to clutch!

I had similar problem with my '99 outback. Replaced the front half shafts and seemed much better. A few months later seemed to be comming back so replaced the driver side shaft again and the problem disappeared. I had put in rebuilt shafts and the driver side shaft was not rebuilt correctly.