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Uncle Buck
09-30-2019, 05:29 PM
The 66 has a mild pulsing vibration when cruising. Pulsing is faster on deceleration than cruising.

Pattern varies with speed not RPM

U joints?

Pinion bearing?
Old Fart
09-30-2019, 05:34 PM
I'm thinking u-joints.
bbriann
09-30-2019, 07:16 PM
I'm thinking u-joints.
Agreed , likely U joints
1BAD92LX
09-30-2019, 07:59 PM
Pinion angle could be out with the suspension and ride height changes.
Uncle Buck
09-30-2019, 08:35 PM
It was doing it before the suspension work and before the new wheels, tires and brakes so fair to rule them out.

Oddly, the u joints look pretty new. I suppose they may not be installed well or have failed prematurely.

Cheap enough to just replace them both and see if it's gone I guess.
Old Fart
09-30-2019, 09:30 PM
You'll see when you take driveshaft off, it will be apparent if they are bad. At least it was with the many that I replaced.
Ponyryd
09-30-2019, 10:01 PM
Probably u-joints, could also be trans mount, or pinion bearing/gear mesh issue. Bet to look at the trans mount, if good, remove the driveshaft and feel the joints, they should flop side to side very easily, if they’re tight you can usually adjust them with a hammer hit in the right spot. While the shaft is out grab the pinion and feed for play up and down, if no play give it a spin and it should be smooth.
Uncle Buck
10-03-2019, 09:58 PM
^^ bingo on the trans mount

I crawled under it tonight and gave everything a once over. Ujoints look new and have no obvious play and I can't get any movement at the pinion. The trans mount however looks done. I can move the trans far too much and can see some separate on the rubber from the mount.

It's not a problem. It's a project!
Uncle Buck
10-06-2019, 11:03 AM
Trans mount is on its way but some further recon has me thinking it might be the tailshaft bushing on the trans extension housing. I get a surprising amount of play when I wiggle the driveshaft at the slip yoke.

Has anyone pulled an extension housing with the trans in place to do a seal or bushing?

I'm starting to lean towards a trip to TDS Transmission in Newmarket. They'll know if the play is excessive, can double check the u joints and will have a special tool to pull the bushing without removing the housing if it needs one.