Vibrations

[savvy59]

I am asking this question for a friend and hope someone can weigh in with possible solutions.

The car: 1971 Plymouth Satelite, built 360, 904 transmission, 8 1/4 stock housing with new Sure Grip Posi unit, with 3:55 gears.
Rear was assembled by experienced Mopar technician.

The rear makes no noises, but the car has noticable vibration that comes on at 65 mph and goes away at about 80-85 mph. The vibration is felt in the seats and floor but not in the steering wheel.

The car has new universal joints that were balanced along with the drive shaft. Rear wheels and tires were balanced off the car.

THE ONLY ITEMS NOT REPLACED WERE THE REAR WHEEL BEARINGS - CAN THIS BE CAUSING THE VIBRATION?

No vibrations were felt in this car until the posi and taller gears were installed. Can anyone take a guess as to what can be wrong with this set-up?

Thanks for helping me out with this Question.

Curt

[big m]

Curt, if the wheels were balanced off the car, it could be a brake drum that is way out of balance, or foreign matter rolling around inside the tire.

The speed you have noted that the vibration comes in at is typically a rotating assembly out of balance, driveline problems usually have the most noticeable vibrations at 35 MPH or so.

I would try to find a shop that has an on the car wheel balancer, these are the best way to balance the entire assembly. I have never had a rear axle or differential assembly make a vibration, unless it is also making a large amount of noise. ---John

[savvy59]

John,

Great advice - I will pass it along.

They are feeling the same way that the rear end changes should not be causing this vibration.

Thanks,

Curt

[BHWINC]

are they running the correct torque converter and harmonic balancer?
I have seen these items mixed and matched on a few cars in the past. At certain speeds some shook hard enough to turn a pint of milk into froth while being held in the passengers lap.

[big m]

To either confirm or remove the possibility of the vibration cause that Brad mentions, if you rev the engine in neutral, about 2500 RPM, and there is a heavy vibration, the converter or balancer is likely at fault. If there is no vibration, these items are not the culprits. ---John

[BHWINC]

Yep John,
They are going to need to pin point if it is a moving or standing still issue.
if it only does it while moving, do as John suggested and start by checking the rear tire balance, bent rim, bad tire. bad brake drum ,then move on to the axles, bearings and axle tubes drive shaft angles ect....
Is been a long time since I worked on this stuff every day but the 360 with a 904 stood out. From memory I was thinking that 360's all came with 727's? The 904 trans was likley used from a 318, if they used the 318 converter it is not balanced for the 360.
Keep us posted..

[savvy59]

Bad and John,

My friend is away all weekend but gave me this additional information:

"Could you tell them that the engine and 904 trans were in the car and no vibrations occurred at anytime speed, the problem came about after the rear, tires and wheel change, basically with the exception of the rear axles, brake drums, and axle bearings everything from the tailshaft back is new. everything from the tailshaft forward was in the car with no problems. I appreciate all your help, I'm glad we are getting responses."

Thanks for your help, it appears he has his work cut out for him now to try these remedies. I will get back to you both when I have the answers.

Thanks for all your help even though I am somewhat off topic with a 1971 model - but at least its still a Plymouth Question!

Curt

[Fins59]

A few years ago I had a vibration in my '59 like you describe. Started at about 55 mph. Turned out to be the 4 bolts just behind torque converter holding trany to engine. I had replaced trany several months prior to that and used the old lock washers which enabled bolts to loosen. I hunted for vibration a long time and finally discovered it when car would not shift into reverse & was leaking trany fluid. I jacked her up and discovered 3 bolts were loose and one was actually gone. Lined the splines back up and used new lock washers and a little loctite and tranys been fine ever since and no vibration. Those old lock washers were flat, had no locking capability. I still got those old lock washers hanging on the garage wall in a plastic bag as a reminder to not reuse old lock washers.

[savvy59]

Brad, John and Fins,

Just an update on this problem. Everyone was on the right track here (except the owner).

After spending more money on rebuilding the rear again, and making a new driveshaft - it was determined to be the 360/904, balanced /not-balanced issue.
So a new balanced flex plate was ordered for the 360 and the only wieght tab on the 904 converter was ground off.

The owner now admits that the car had vibrations sitting still - now that he can tell the car has no vibration sitting still after the repairs.

Thanks again for all the help.

Curt