Vibration on Highway at 60+

[ynst]

Thank you all for your great responses!

Yesterday we ended up swapping the driveshaft from my father’s 71 RR. Back on the highway and the vibration was still there, but did seem to improve it some. It vibrated from 63-68 MPH but seemed to get better at 70 and above. If at 70 and putting into neutral and letting it coast to 65, it doesn’t vibrate. However if I raise the RPMs in neutral in that speed range, it does vibrate.

I’ve ordered the rear bearing and will give that a shot next. I’ve also seen some folks with the tail shaft weight dampener installed. Do you think it’s worth throwing one of those on as well?

Thanks again and will let you guys know how it goes!

"However if I raise the RPMs in neutral in that speed range, it does vibrate."

It ain't the drive-line. It's the engine that's causing the vibration.

Time to balance the engine rotating assembly.

My engine balancers (3 of the 4 I've used have passed away) all say the same thing. There's a trick to getting rid of that persistent engine vibration around 3000 rpm but nobody pays attention to it.
My late friend Goodwin Hannaford up in Maine got rid of that vibration in my GTX a couple of years after I got it back on the road. The vibration had been there for years but, back then, I didn't think anything of it, especially since I was drag racing it every summer and the lift bars were always banging the rubber snubbers on the front spring hanger all the time.

"Plymouth is out to run you over this year" instead of win you over this year like the commercial said.

By the way, those are the same wheels and hubcaps that are currently, still,on the car.

That's me blowing the doors off my kid brother's SS 396 '67 Camaro at Lebanon Valley Dragway

The car was off the road and in indoor storage for about 40 years before I got around to putting it back on the road.

I noticed the vibration right away having been driving newer, smoother-running cars for years.
It never bothered me back when the car was new but after all of those years driving "comfortable" cars I really noticed it after I got done repainting it and putting it on the road.

Since there was a bit of rust on the cylinder walls from being stored all those years and the rust had pitted a couple of cylinder walls I decided, after putting two or three thousand miles on it after the repaint, I'd have Goodwin go through the engine for me at 113,000 miles back in 2017 and the vibration went away. The only minor vibration I'm sensing is tire balance, now.

 

[oldkimmer]

I read through that. I could try replacing the tailshaft bearing and the rear end seal he mentioned. I believe my angles are correct but will triple check!

What are the angles? Check and report back. Kim

 

[Moparfiend]

Any updates @RyanB89 ?

 

[RyanB89]

Sorry for the delay in getting back to you all, the snow and cold weather really puts a damper on trying to work on these old cars.

Update: Replaced the rear bearing...no improvement. The reason for me narrowing it down to the tranny is with the driveshaft removed and on the lift, bring it up to highway RPMs and the vibration is felt right under the console/shifter. Most notably in gear, seems to improve a little bit in Park but still feel it.

Double checked the harmonic balancer, it's an internally balanced one. No weights on the TQ. Flex plate appears fine, no cracks.

Could it be the TQ going bad? I hate to keep throwing money at different ideas, but I'm stumped.

Cheapest route might be finding a used 727 and swapping it in just to test it. Or should I buy a new TQ and flex plate and try those with the existing trans? I'd hate to go spend $1,000 on a fully rebuilt tranny and find out that's not the issue.

Thanks again for everyone's ideas and thoughts.

 

[khryslerkid]

How much of the slip yoke is sticking out of the tailshaft with all fours on the ground?

 

[RemCharger]

I'm curious if it has a cast crank in it.

 

[dvw]

Could definately be the converter. Far more likely than internal transmission parts.
Doug

 

[RyanB89]

Hey guys, wanted to update you all on my progress. After months and months and hundreds of dollars thrown at this car, I finally got the vibration to stop.

Ended up pulling the tranny, installing a full rebuild kit from Cope, replaced the torque converter/flexplate and knock on wood, the vibration is gone! Not sure which of the components was the actual fix, but I do know the trans had some some pretty worn components.

Next up is new 15” wheels and bigger tires, then getting the car an alignment.

Should be good to go! Thanks for everyone’s input and ideas, you guys are invaluable!