I have a bad drive train vibration from about 2800 rpm up..Heres what i've done..it's a 440 with t-flight,8 3/4rear..motor is smooth in neutral. I have 2 converters.stock and 3000 stall.no change..stock drive shaft,and 3 + inch shaft custom made and both balanced as I had to have them stortened for my install.I have 2 center sections for the rear, one has 3:91 gear the other 2:76 open for road trips..that was the original 741 chunk that came with the rear housing, the other is a 489 with posi.Vibration with any combo is at 2800,tires balanced a few times plus another set,plus the Hoosiers.I'm out of things to try..feels like drive shaft type of vibration.I have gone from down 2 dg to o dg to up 2 dg on the pinion angle.Any ideas ???PLEASE READ MY LAST POST FOR THE RESULTS ..VIBRATION IS ALMOST GONE,THANKS EVERYONE FOR YOUR HELP.

How is pinion angle ?

Oh, you must have added that bit..

Is the exhaust mounted ridged or with good rubber hangers? Is it hitting anywhere?

tail shaft bushing?

Sorry OZ did edit that in.. with exhaust or just the headers ,,still there

Possibly a bad bushing in tail shaft?

engine mounts arent sagging? The headrs have any contact with the block? even just a little contact will be felt in a unibody car. What car is it?

cracks in the flywheel?

Many things can cause a driveline vibration:

Too much downward pinion angle will cause a vibration on deceleration.

Too much upward pinion angle will cause a vibration on acceleration.

Driveshaft run out

More than 1" slip yoke (internal) stand out

Less than 3/4" slip yoke (internal) stand out

Sloppy fitting slip yoke bushing

Sloppy fitting slip yoke splines

Sloppy fitting U-joint saddles/missing clips

Solid motor mounts

Poly transmission mount

Loose pinion yoke

Engine/bellhousing alignment

Torque converter/vibration damper balance

Exhaust grounding out on body

etc...

Not an exhaust problem..headers don't touch anything..vibration is there with the rest of the exhaust system off,for a 1/4 mile run..and yes it runs faster with the exhaust on.Car is my 1956 Plymouth you have seen here a lot.

DR Diff ...the vibration is there at a constant speed.. not only on accel or decell.just crusing at a steady 3000 rpm or so.

Does it change if you put the car in nuetral at that speed ?

Maybe it's an issue in the engine or trans ? (if it does it at 3000 rpm in any gear lets say)

What angle is your pinion centerline at rest?

What angle is your transmission centerline at rest?

These angles should be a couple degrees within parallel.

DR diff..righr now it is as close to zero as I can get it..Drive shaft when first made for me was a hair too long and was hard to get in, but once past the yolk it still had about a half inch play..I took it back and had it shortened another 3/4 inch..it had the vibration both ways..no change

OZ HEMI.. yes the vibration is there if I put it into neutral at that speed..trans bushing thing may be my next thing to check..Thanks Jeff

Be interesting to get the car on a chassis dyno so you could look under it at speed and see if you can see anything moving, feel for vibration at different points,etc...

Aside from what Cass said about angles...are the u-joints in good shape too ?

Cracked flexplate maybe on a long shot ?

Not moving it is smooth @ 2800 in neutral right? I gotta go w driveshaft related as you originally mentioned. ujoint/shaft/yoke/angles