Vibration at 70+

[sakudog]

Friends!

My car has a vibration that starts around 70MPH and stays rather consistent up to whatever past 85MPH +

What I have done thus far:
New GTA wheels / BFG Tires that have been road force balanced
New Suspension (bushings, Aarms, Springs, almost everything)
Re-balanced drive shaft with new Spicer U-joints (spun to 35,000RPM silky smooth)

Car doesn't shudder under braking, handles great, feels silky smooth up to 70 then it shakes.

What should I check next?

Possibilities include:
Transmission Mount
Motor Mount
Wheel Bearing
Axle could be slightly bent?

 

[charlief1]

I doubt the axle shaft being bent or you'd feel it at a lower speed. You could check it just to be sure but I doubt it. What you might try is to put the axle up on jack stands and then get the speed up to 70+ to see what happens. If it's still there then it's in the rear but if not then it's somewhere else.

 

[turbo nasty]

Trans mount, worn pinion bearing, front/rear end components/bushings, shocks,

 

[sakudog]

So the suspension is new, A-arms, bushings, springs, bilsteins so I'm pretty sure I can rule that out.

Charlie: I'll try your test and post what I find.

 

[charlief1]

If you're very careful you can get under the car and touch the axle or tranny to feel the vibration easier but be very careful so you don't get hurt.

 

[sakudog]

Well I put the axle up on jack stands and did a visual inspection, the transmission mount looks a bit old and rotted but it's still in tact.

Started the car and brought it up to speed, right at 65 you start to feel it and at 70 it's very evident.

I used a 1meter plastic tube to poke around touching various things to find vibrations and UNFORTUNATELY for me it sure seems like the torque converter is the culprit. The previous owner had the trans built by Jimmy's in Chicago & a Vigilante 2800 stall converter installed at the same time. At cruise you can hear a slight ticking sound that the previous owner thought was coming from the stall. I guess the stall is just a POS?

The engine & trans feel like they are vibrating because of the stall's vibration, which may explain the RMS leak the car has as well.

Input is welcomed!!!

 

[turbo nasty]

There are items in the TC that can come loose so its possible

 

[sakudog]

Checking the previous owners posts he heard a rattle that he ultimately decided was the TC (and I've heard it as well) maybe one of the bolts backed out again/all the way?

Now IIRC, is it sometimes possible to unbolt and rotate a TC 180 degrees to minimize/reduce vibration? I remember on the T-56 cars I've put clutches in that sometimes the PP was 180 off and a rotation of the PP would resolve things like this...

Car only vibrates like this with the Trans in D.

Input from experts welcomed!

 

[sakudog]

Update:
Did the TC lockup test and I can hear the TC unlocking, = still vibrating at 75
Removed pinion snubber (thought it was close after the car was lowered) = still vibrating at 75
Had maybe 1mm of play in the Passenger Side wheel, after pulling the wheel, tightening the castle nut on the WB and putting the wheel back on that is gone = still vibrating at 75
Took it up to 120 and did the brake engagement test = still vibrating down to 75
Took it up to 120 and put it in neutral and allowed it to coast down to 55 (love Texas Tollways ) = still vibrating down to 75

So I'd love input but it seems like I should be checking:

Trans output bushing / play / (no idea how to check this)
Rear END pinion / Changing rear fluid (hasn't been done since 08 as I can see from previous owner)
Axles

Again tires and alignment is fine and for good measure I ordered new engine mounts & trans mount as they are 25+ years old.

 

[sakudog]

Rear end looked good, no odd wear, the fluid was very milky...now it has Royal Purple.
Pinion gear had zero play/movement etc

I haven't had a chance to drive the car since the change as we had biblical rains here in Austin, TX but today I hope too!

Someone has suggested clocking the DS 180 degrees on the yoke as a potential solution...I'm open to suggestions.

 

[charlief1]

Use 2 hose clamps on the drive shaft and make sure that the screws are in the same location. Run the car lifted up and then move 1 of the clamps slighty each time and see if the vibration gets better or worse.

 

[BGNeXtreem]

This happened to me one time swapping transmissions all it turned out to be is I didn't have the drive shaft seated good straight in the pinion yoke. Unbolted the four bolts and repositioned it took it for a spin and it was good

 

[sakudog]

It was 3 bad BFG Comp2s! These tires are new and had less than 1K miles on them. They have been upgraded for FREE by Michelin (who now owns BFG) to a set of Michelin 245/40/18 & 285/35/18 PS2s that fit my new CCW LM20s perfectly. This process wasn't easy and I owe thanks to my communication degree from the University of Texas in having enough tact to deal with all the French Canadian's at Michelin's support center. Discount Tire was very nice about everything so I owe them thanks as well. I'm rolling on stock rims and drag radials until Mid August when my CCWs show up!