Help!...as always..

['95Newbie]

I have an issue with vibration. I thought it was related to my "dead" #4 cylinder, I have since replaced the engine with another (not new/rebuilt), but alas....naw. So here is the deal....when driving at speeds around 72mph. I get a vibration when I let off the gas...I can look at the rear-view mirror and see it shaking. Could this be a drive-shaft issue? Tranny? Any helpful info PLEASE! Again this only happens at these speeds and ONLY when I stop accelerating.

 

[Bad_Vision]

yes to all of the above.
u joints and mounts can cause this. i would have started with u joint. if the mounts are good and the u joints are good you may be looking at a unbalanced flywheel.

 

['95Newbie]

How to fix?

About this flywheel...how do I fix?...dare I ask how much? At speeds below 70mph it seems there is no vibration. I guess as always 69 is the magic answer...LOL

 

[Bad_Vision]

the flywheel would be the last think i would check. the u joints would be the first, then the tranny mount.
u joints are like 8$ then tranny mount is like 15$ the flywheel is 50$
so its not i big $ fix but the flywheel is at least a 2 hour project.

 

['95Newbie]

So far....so good?

So I should have mentioned I replaced all u-joints a couple months ago. It seems as though as long as there is torque on the( driveshaft,tranny) there is no vibration...as soon as I let off...whamo..BTW thanx for your quick and informative response...brudda

 

[Bad_Vision]

crawl under the truck and grab ahold of the tranny and push it back and forth if it moves with little to moderate shaking then the mount should be replaced.

 

[77'911]

I would check the following:
1)drive shaft u-joints, grease them with M1 syn while your there
2)check motor and trans mounts
3)check rear and lateral control arms
These can make the truck feel, twitchy and cause vibrations when on and off power.
regards