Vibration on Highway at 60+

[RyanB89]

Hey guys, I’ve been through all the similar threads and can’t seem to figure this issue out. Thought a new personalized one might be my best bet.

69 Coronet R/T 440/727. 8 3/4 Rear with 3.55 Sure Grip. Have a bad vibration at 60+ on the highway. Can also simulate the vibration somewhat with the car on the lift and bringing it up to speed.

Had driveshaft balanced and new ujoints installed everything seems tight. While I had the driveshaft out, installed new bushing, rear seal and trans mount. Driveline angles all checkout on the Tremec app.

Vibration appears to come from the transmission. Particularly the tail shaft area. Inspected the flex plate, can’t see any cracks. Tried different wheels/tires and same issue.

What am I missing? Drives great on the backroads, but highway speed vibrates like crazy. Feel it particularly in the center console area, steering wheel is smooth. Rear view mirror shakes like crazy, can’t tell what kind of cars are behind me.

Thanks in advance!

 

[Aron Gleason]

Transmission mount bad???

 

[jimbosride]

Give this a read ??

Thread '727 Vibration GONE'

Jan 15, 2009

Well, the verdict seems to be IN on the 727 vibrations that were driving me NUTS on this particular build.

It's a swapped out 360/727 combo which was shaking the car apart, and destroying tailshaft bushings.

We had a new driveshaft built and balanced first.........installed it, but the vibration persisted.....very little change.

Next, we had a local shop check and change the tailshaft bushing and bearing...it sounded like marbles rattling around in there it was so bad....they chose to leave the bearing (WHY, I will never know....they didn't "feel" it needed changing).... After...

• Pastortom1
• Replies: 11
• Forum: Engine, Trans & Driveline

 

[sam dupont]

Transmission mount bad???

could a guy snug the mount with a ratchet strap around the crossmember and see if the vibration changes?

 

[Lefty71]

Worn slip yoke?

Scroll down theres used whole driveshafts for 200.....maybe try a whole different unit just to see if you are headed in the right direction?

 

[khryslerkid]

How much slip yoke is showing with the car sitting on all fours?

 

[Thunderdan]

could a guy snug the mount with a ratchet strap around the crossmember and see if the vibration changes?

Or 2 crisscrossed big hose clamps?

 

[sam dupont]

long shot, but you could listen to the tail shaft with a stethoscope. The diff too. harmonics can travel through things