[West Coast GTO]

Last year replaced the driveshaft after installing a used short TH400 tailshaft and paid a mechanic to remove old long tailshaft for the shorter unit. I still have a vibration ( although not as bad). Also, changed out the rear differential fluids and refilled with proper lube and additive( posi 10 bolt).
Just raised the car onto jack stands and noted this:
1. Small side to side movement at rear driveshaft yoke at u-joint( pressed side, not bolted side.
2. Definite side to side and up and down movement at rear trans yoke to driveshaft junction. Enough that I can slightly see the rear yoke seal move. I don't own a gauge that would allow me to test movement.
3. I can grab the rear tire and move the wheel forward/ backward approximately 3/8" to 1/2" before gear engages. I don't know if this is correct tolerance or very sloppy.
Any suggestions would help.

[tom s]

was your new drive shaft balanced?Have you checked if the balance weights are still in place?I threw one a couple years ago and had to have mine redone.Tom

[West Coast GTO]

Tom,
Yep, the business that built the driveshaft also epoxy coated it after balancing, then spun it again. Everything still in place.

Originally Posted by tom s

was your new drive shaft balanced?Have you checked if the balance weights are still in place?I threw one a couple years ago and had to have mine redone.Tom

[HWYSTR455]

Sounds like you've found at least some of the issues. U-joints should have zero side to side movement. Replace both joints.

Make sure at the diff yoke the joint caps are properly located between the 'nubs'.

If the slip yoke moves up and down in the trans, the trans rear bushing needs to be replaced. If you do replace the bushing, I suggest replacing the slip yoke too.

Moving the wheel/tire, as in spinning it in either direction, and feeling slop, will not cause a vibration, unless the carrier or wheel bearings are bad.

Grab a rear tire/wheel, top and bottom, and push/pull back and forth. If there's slop, it needs wheel bearings.

Grab the diff yoke and wiggle it. If it wiggles, pinion bearing or preload needs attention/replacement.

When working with a trans swap, or an old, original driveshaft, it's way more practical to have a new shaft made. IMO, never shorten or mod an OE shaft. Or any for that matter, just easier, and more effective to make a new one.

When going through a diff, always replace the yoke there too, and IMO, even if totally overkill, always use 1350s. If you do that on all your cars, not only do you never need to upgrade if you increase power, but there's never a question of what type of joint you need. And you can keep a pair in stock to cover all your rides.

First and foremost, driving down the road, at the speed or when you feel vibration, if you put it in neutral and coast, does it still vibrate? If yes, it is a source from behind the transmission.

.

[West Coast GTO]

I posted this in the " Street" section:
"How much pinion gear slop( movement noted by twisting pinion yoke with driveshaft removed) is considered normal on a posi 10 bolt rear end? I can twist the pinion yoke approximately 1/2" total before engaging the ring gear. I can also get the same amount of movement by grabbing the wheels and rotating back and forth.
I admit I know almost next to nothing about differentials and am trying to chase down a driveline vibration. Car is raided on floor jacks with wheels free to spin. "

Also, I am taking the car to a local differential specialist; he believes that the crush sleeve was never crushed, the pinion nut was just snugged down and then the backlash was set.

[HWYSTR455]

Yeah, not sure how not crushing the sleeve would cause a vibration, not an optimal wear pattern maybe, not a vibration. Unless it's loose, if you can wiggle the pinion yoke, then yeah maybe.

Is the diff guy also a driveline/driveshaft shop?

If nothing else, another set of eyes should help. If the locators on the pinion yoke are boogered, this would be a good time to replace it.

.