Seems to do it under throttle.Goes away when coasting.

 

my initial thought is ujoints...

 

Oh and welcome to the forum! Many good folks here to help with all the stuff that goes wrong with these rigs.

 

Welcome to FTE, yes its time to get under there and get dirty. Have the drive line "un-loaded" when checking the u joints and slip spline.

Loaded is when you put it in park or shut it off in gear and it rolls that little bit, and binds the drive line, no way to ck for play then.

So in neutral (e brake or chock the wheels) and ck the lower u joint cap or play and ck the two U shaped straps for being tight, and ck for ring and pinion for excessive play. And your R&P bearing.

The ck the d/s slip yoke and then the upper u joint and straps.

Bad joints "chatter" to me, you could of cracked u joint cap and lost a piece. When was the last time you got under there with a grease gun? The slip yoke likes grease.

U-joints are an easy replacement.

Also ck the out put end of the xfer case for play.

 

[quote=77&79F250;14179128]
Bad joints "chatter" to me, you could of cracked u joint cap and lost a piece. quote]

When my ujoint was about to break, it "clanked" every time I put the truck in gear.

 

[QUOTE=Dave145;14179301]x2 on the clank

 

I had a vibration at 20-25mph. And a metal sound like a soda can hitting the fan. I got underneath and pulled, pushed, kicked, and cursed the Ujoints, it didnt budge.
I bought em anyway, believing everyone here....and they were correct. I had powdery needle bearings in a few cups.

If you can, get the greaseable ones with the zerk fitting, so you can hit em with grease now and again.

 

Sounds like a bad U joint .A frozen up u joint may not clank or bang but will cause your driveline to vibrate like hell .so check all your u joints for freedom of movement should be nice and free no binding

 

I had a vibration in my 77, one of the u joint locating tabs broke off The yolk and the one cap started walking out. Vibration would come and go as torque would hold it in and out of alignment

 

Worst comes to worst you may have to remove the drive shaft to really check those u-joints. A frozen one is a bit harder to detect since is tight and not moving much and that may be the best way to check them by removing the shaft and turning them by hand. I also recommend the ones with the grease fittings on them so you can grease them now and again at every oil change . I do that with mine.

 

I should have Mentioned the only real way to check u joints is to pull one end of driveshaft or completely pull driveshaft to check if u joints are binding

 

I get a vibration when accelerating in second gear and yesterday i get the same vibration at 55 and over.

My drive-line is new and balanced from the same shop that has done my work for decades. I had the shaft rebuilt by them thinking it was joints or the carrier bearing but the vibration persist.

I feel it could be coming from my C6?? I know nothing of ford transmissions. Do they ever cut loose and start to vibrate before some failure?

chris