if i let off the throttle at highway speeds i get a severe vibration.could this be caused by my worn out trans crossmember bushings?i guess it could be caused by my dead cylinder.

 

Let me assume you're talking about an Aerostar.

You can check the crossmember for worn bushings. The most severely worn bushings will have the inner sleeve hitting the outer sleeve, making metal-on-metal noises when you accelerate or decelerate. They should not cause a vibration.

I would look for some really bad U-joints, or possibly transmission problems.

Vibrations from a dead cylinder usually come from accelerating; you get uneven power generation. You don't usually feel that from letting off the gas when all cylinders go to minimal power generation.

 

Is it a 4WD model? I had the same thing with no noise or vibrations normally but a bad vibration when I lifted off at highway speeds when the front driveshaft bearing went in my transfer case. It can be checked by seeing if there is any play in the front driveshaft.

 

no but i do need to check the u joints.

 

I would also check your hubs/lugs to make sure that none of them are broken.

 

my lug nuts are tight.the ujoints seem not to have any play though i was surprised to see they aren't greasable.its also surprising not to see any rust since so many of you have problems with it.