Hey guys ive got this new problem with my 88 bronco
in gear at about 20 mph it starts this vibrating if i let off the gas it stops
the vibration continues whenever and at whatever speed im at after 20mph when i step on the gas if it helps ive been idleing rough but sporatically
351w with 4brl carb

 

You might want to take a good look at the driveshaft before doing any more driving above 20 mph!!!!! Look at joints and slipjoint looseness( if too sloppy laying under driveshaft and push up and down- chock wheels when doing this). If AT, leave in park,( no chocks) emerg. brake off, grab a tire and rock- roll truck back and forth to check visually and listen for odd noises

 

What you are describing is typical of a dying double cardon u-joint. Its the front u-joint on the rear driveshaft. If this is the problem, chances are you wont' be able to feel it or see it using Trublu's method. The "centering ball" and spring are what weaken in them and when there is little or no torque applied this condition allows the driveshaft to fall out of alignment with the rest of the driveline components...hence, your vibration. Its not enough slop to see or even feel necessarily but has the same effect as losing a balance weight on the driveshaft.

 

Could be u-joints, but also transmission/engine mounts.

-Matt

 

u joints most likely ...its gotta be driveline..

and its accelerating

 

Thanks guys i think it is a u-joint since there is a clunk when i put it in low and step on the gas and release real quick still have the rough idleing though i think i might need a tuneup (wires,plugs,cap etc)

 

Hey guys it definately is the rear shaft front u-joint good call grey and the rough idle is the carb dumping fuel at the excellerater pump looks like i need a new carb
Thanks for the help

 

Rocking truck back and forth on my drive on lift is how I found the front u-joint bad in my 93- every body has their diff ways of checking things and mine worked for me.