Driveline vibration!

[TheRKCoronet]

1967 dodge coronet 318, 727, 3.31 gear 741 case

Last time I took the car out I started getting a vibration around 45 mph and progressively got worse past that. Had to park it since I’m not really sure what it could be. Here’s what’s been done so far:
New u-joints
New driveshaft
Tires balanced
New axle bearings
Rebuilt Center section
Engine is rebuilt with fully balanced rotating assembly

I’m just not sure what else it could be? There’s 2 things I was going to try and it was getting a new yoke for the trans since it is reused off the original shaft; or getting the shaft re-balanced. Just wondering if I’m missing something.

 

[pnora]

Does it vibrate when on or off the gas?

 

[#41]

Help us help you by giving a better description of the vibration. In addition to on/off gas, does it vibrate coasting in neutral? Does it vibrate if you rev it up in Park? Seem to be front or rear? etc.

Until then, add Tires? Wheels? Lug Nuts? Driveshaft angle?

 

[Don Frelier]

Did you reuse the straps for the rear yoke?
I've had them stretch and the caps move around in the differential.

Maybe a bent axle?

 

[493 Mike]

As stated above, check drive line angles. Those can be influenced by bad motor and transmission mounts.
Mike

 

[bearman]

Auto or stick trans? Plus all the above.

 

[4vnut]

I had the same vibration at one time and tried all the steps that you took to try and fix the vibration. I finally asked Rick Ehrenberg and he went through all the suggestions mentioned and finally said he thought all signs point to the engine. Engine is a 30 over rebuilt supposedly balanced 440 I had built for the car.
I removed the engine, took the crank, rods, pistons, balancer and the flex plate to a local well known engine builder and he said it was the worst balance job he had ever seen in a 440. Anyway, I reassembled the engine and it runs smooth as a sewing machine now. Oh happy days are here again!

 

[Fran Blacker]

While your looking at front yoke wiggle it. If it moves more than .005 maybe the problem, moves .010 junk.

 

[Big Bad Dad]

What Fran Blacker said above.
The tailshaft bushing in the rear of the transmission can wear out and cause vibration. And it can lead to a failure. I speak from experience.

 

[TheRKCoronet]

Thanks for all the advice and I’ll try and answer them here:

Automatic trans (727)

It happens when I’m on or off the gas.
It’s least likely to be the engine because when I broke it in it ran as smooth as a sewing machine.
As far as the axles, I’m worried that may be the issue but I will obviously have to check and make sure
There is a LOT of pinion slop now that I’ve checked I think my gear mesh is way out of wack
I have brand new straps for the u-joints as well. All my lug nuts are tightened to 100ftlbs. I was thinking maybe a belt in the tire is bad since the tires are from 2013. Trying to move the trans yoke just moves the bushing. It’s a stock unit from O’Reilly.

Hope that helped a little more

 

[AR67GTX]

100 ft lbs is a bit heavy for lug nuts. I think stock FSM is about 65. Not sure what you mean - “Trying to move the trans yoke just moves the bushing.” The bushing is a press fit inside the tail housing, it can’t move. Do you mean the yoke is moving in the bushing? If so, you need a new bushing and/or yoke, or both.

 

[TheRKCoronet]

100 ft lbs is a bit heavy for lug nuts. I think stock FSM is about 65. Not sure what you mean - “Trying to move the trans yoke just moves the bushing.” The bushing is a press fit inside the tail housing, it can’t move. Do you mean the yoke is moving in the bushing? If so, you need a new bushing and/or yoke, or both.

Sorry, moves the crossmember to transmission bushing. The rubber one on the bottom of the transmissison

 

[Big Bad Dad]

Sorry, moves the crossmember to transmission bushing. The rubber one on the bottom of the transmissison

How much movement does the trans mount have? Is it broken?

 

[TheRKCoronet]

How much movement does the trans mount have? Is it broken?

It’s not broken but it is pretty soft for a brand new bushing.

 

[AR67GTX]

Your diff backlash may be too great from wear but I doubt that would ever create a vibration. Based on your description I would be suspicious of a bad tire or tire needing rebalancing. On the mount I think Big Bad Dads question is one that needs asking. I would think if you really shove on the transmission tail that you might see a slight movement but the mount bushing should be pretty stiff - shouldn’t be a lot.

 

[Don Frelier]

I would definitely try different tires.

 

[TheRKCoronet]

Thank you everybody for your help but I found the problem! Driveshaft! I put the car up on stands and put it in drive. The driveshaft is bent. I don’t know how it happened; too thin wall of a tube? Maybe but I’ll be getting a new one that’s thicker wall tubing just to be on the safe side. Before that I did check the axles and they are straight along with setting my axle end play (replaced the little tab that goes on to hold the end play adjustment too). Rebuilt the drums and will be ordering a new shaft tonight!

 

[Fran Blacker]

I'd watch rear trans bushing depending on how many miles you put on with the vibration.

 

[TheRKCoronet]

I'd watch rear trans bushing depending on how many miles you put on with the vibration.

After it started I only put about 3 miles on it, just to get it home

 

[Bill Tucker]

After it started I only put about 3 miles on it, just to get it home

I had same vibration issues and tried everything mentioned above......then, aha!...I coated the slip yoke splines and the outside of the slip yoke with tranny fluid. Once reassembled, vibration is gone!!