Vibration at 60 and up

[moes]

hey guys, a friend found an untouched 69 1/2 A 12 Super Bee with Butterscotch Yellow paint and automatic transmission in a warehouse that has sat for 30 some years. He changed all the fluids and went over the car. Did a tune up and put new tires on it. We just went for a drive, and it has a vibration from the transmission tail shaft area when speeds hit 60 and up. The car only has 45,230 miles on it. We checked the driveshaft, no movement, so the u joints and tail shaft bushing should be ok. I am thinking because it only happened when he was on the gas, he has to lower the axle pinion angle with shims. Any ideas?

 

[Jerry Hall]

Pinion angle, driveshaft balance, transmission mount, U joints, all possible symptoms.

 

[HawkRod]

I agree with @Jerry Hall but I would also check easy, basic stuff first. I'd still check the tires and balance - yes, I KNOW they were just put on, but mistakes happen. One or both of the rear tires may have been balanced incorrectly. Best test is to get a known set of smooth running wheels and tires you can put on the rear and test again. If you can't, I'd still swap the front and rear wheels.

 

[moes]

the tires are Goodyear custom wide tread Redlines and balanced on a road Force Elite balancing machine. Total cost of tires and balancing was $2825 Canadian. He had them check the rims for run out before the tires were installed and had no problems. So I don't think they are the problem.

​

​

​

 

[HawkRod]

the tires are Goodyear custom wide tread Redlines and balanced on a road Force Elite balancing machine. Total cost of tires and balancing was $2825 Canadian. He had them check the rims for run out before the tires were installed and had no problems. So I don't think they are the problem.

​

​

​

I agree it's unlikely. But it is possible, and ask me how many times I have gone on a wild goose chase because I assumed something. And by the way, many Coker (and other limited specialty tires) have been known to be problematic.

I still suggest you do the swap to check it out. It's quick and relatively easy, and can let you make sure they are not the problem.

 

[moes]

we did swap them around and it made no difference

 

[pnora]

Pull the drive shaft and work the joints . I would do that first before shimming anything.

 

[HawkRod]

"Untouched" conveys that this is a very original car. Assuming it is, shimming the rear would only be needed if mismatched stuff was put together and put on the car. Seems unlikely.

Next maybe check to see if there are any witness marks for a missing "washer" that was welded to the driveshaft to balance it. Check the shaft carefully including the joints. Then maybe move to the transmission output shaft.

 

[moes]

the car seems to be sitting lower in the rear than it should be, so that's why I figure the pinion angle has changed in the rear. We did check the drive shaft for movement and there was none. So that is why we eliminated the u joints and transmission tail shaft bushing being the problem. He is getting a tool for checking pinion angles from a friend of his, and we will check the pinion angles with the car on the level garage floor before doing anything.

 

[pnora]

the car seems to be sitting lower in the rear than it should be, so that's why I figure the pinion angle has changed in the rear. We did check the drive shaft for movement and there was none. So that is why we eliminated the u joints and transmission tail shaft bushing being the problem. He is getting a tool for checking pinion angles from a friend of his, and we will check the pinion angles with the car on the level garage floor before doing anything.

Did you pull the shaft and check the joints for not being seized. You cant tell by looking you have to pull the shaft. Pinion angle change is not common even with sagging springs. Seeing the car has sat for 30 plus years the joints very well could be seized and binding.

 

[moes]

when we pull the driveshaft to check the angles, we will check the u joint too. If the joints were seized, you would think you would have the vibration all the time. I think the sagging springs have changed the rear pinion angle up, and it needs some shims to lower it.

 

[pnora]

when we pull the driveshaft to check the angles, we will check the u joint too. If the joints were seized, you would think you would have the vibration all the time. I think the sagging springs have changed the rear pinion angle up, and it needs some shims to lower it.

My opinion is this. Your theory on the sagging springs is causing the vibration. If this was true every car with sagging springs would vibrate. Take 5 minutes to PROPERLY check the shafts joints.

 

[Canadian1968]

the car seems to be sitting lower in the rear than it should be, so that's why I figure the pinion angle has changed in the rear. We did check the drive shaft for movement and there was none. So that is why we eliminated the u joints and transmission tail shaft bushing being the problem. He is getting a tool for checking pinion angles from a friend of his, and we will check the pinion angles with the car on the level garage floor before doing anything.

I just went threw something very similar like this with my 68 Charger. My springs were sagging badly ( 25.25 " to top of wheel arch ) I opted for a set of caltrac mono leafs . The new springs brought the car all the way up to 27.25". My Thinking was the same as yours that the lower ride height was throwing off some of the drive line angles. But after the swap, the vibration was still there, so the ride height made absolutely zero change. I threw a new set of U joints in , just to eliminate that as well. Wheels , brakes, everything checked or changed.

In my case the problem was loose bellhousing to engine bolts !! The one directly under my starter was backed out about 1/4" There were two other bolts that I was able to get about 1 full turn on. The vibration was only at 60 and over just like yours, but very faint , sort of felt it threw the seat . Everything tight..... smooth as silk 100+

 

[sam dupont]

vibration on or off throttle, or both?

 

[70ChargerRT]

Download the Tremec App and check the pinion angle. Lowered my car in the back 1” and now it’s a got a vibration at 70 plus. I’m pretty for sure it’s pinion angle. I just ain’t had time to check it.

 

[moes]

just on the throttle, like I said in post 1. Vibration goes away when he was not on the throttle. That's why I think the pinion has shifted up, and will need to be lowered to bring everything back in line

 

[Fran Blacker]

Beating a dead horse, there must be some play in trans tail bushing. .007 I bet wood rattle some. Had a bad rattle, pulled the bushing .013 clearance.

 

[Don Frelier]

Could be a bent axle as well

 

[sam dupont]

On the throttle is the front u-joint.

 

[RemCharger]

Posts # 7, 10, 12, and 19 is exactly where I'd start.