The Bounce

A

ampico-kid

Senior Member
I've got another problem with my 30 Town Sedan that I purchased last July. I had a new Burtz engine, flywheel, cam, and head installed and just got the car back several weeks ago. I've been sorting through problems not related to the engine, one of which is a bounce. It had this issue before the engine was replaced, so I know it's not engine or flywheel related. When the car hits a speed of approx. 15mph to about 25mph the car bounces up and down causing the passengers to bounce up and down with it. Once beyond 25mph it smooths out and seems to be fine. Thinking that it might be related to the tires or rims, I swapped all four tires/rims from my 30 Coupe to the Sedan, and got the same results. If I'm coasting and step on the clutch, still the same bounce, so I'm guessing it must be something in the drive train between the transmission and the rear end of the car. But what? What should I be looking for? What can I do to attempt to localize the problem? Point me in the right direction please.
 
Synchro909 said:
Sounds like the renowned death wobble to me. IMO, you'll have to go through the front end and steering to rectify it. The causes are many and most likely, you have a number of them acting in concert to cause your problem.
https://www.fordbarn.com/forum/showthread.php?t=305455&highlight=death+wobble&showall=1
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I think I know what you're referring to. In that scenario the wheels would shimmy back and forth left to right and the car body responds by shaking or wobbling back and forth. You can also feel it in the steering wheel. I had that issue with my Coupe. That's not what's happening here. The steering feels completely normal, and the car doesn't shimmy at all left to right, it's more of a very mild up and down motion that almost feels like someone is pushing up and down lightly on the front bumper. I don't think the passengers would be much aware of it except that you're lightly bouncing up and down on the coil spring seats.
 
Find a local knowledgeable Model "A" club member or two and have them check your car. There are a few things that can cause your bounce problem,
 
I would look at the springs,maybe something is cracked. Can you seen any evidence of frame repairs? If one side was repaired it could be stiffer than the other. Not that I've ever heard of this maybe your hubs/bearings are out of round? Can you jack up all 4 wheels and rotate the wheels see how they run out on the car.
 
Thanks guys. At least now I've got some things to check out. Will get back to you when I'm able to do some investigation.
 
Harpkatt said:
I would look at the springs,maybe something is cracked. Can you seen any evidence of frame repairs? If one side was repaired it could be stiffer than the other. Not that I've ever heard of this maybe your hubs/bearings are out of round? Can you jack up all 4 wheels and rotate the wheels see how they run out on the car.
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I can jack up all four wheels at the same time, but what am I looking for? Am I looking to see if one of the wheels doesn't spin in a perfect circle? In other words it "wobbles" up and down?
 
I’ll add check the front radius rod to bell housing connection and the rear radius rods connection at the front of driveshaft tube. Bothe of the connections have castle nuts and bolts that might be loose, remove the cotter pins and tighten the nuts, don’t forget to replace the cotter pins!
One more thought, do you have float a motor mounts ? I installed FAM’s last year and noticed a difference until I adjusted the center bolts on the mounts
 
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Possibly a frozen shock, not allowing the suspension to flex? If jacked up, you could spin the wheels and see if you see an up and down motion. If you do, then try to isolate to the wheel (given you already changed them, not likely), the hub or axle.
 
Big hammer said:
I’ll add check the front radius rod to bell housing connection and the rear radius rods connection at the front of driveshaft tube. Bothe of the connections have castle nuts and bolts that might be loose, remove the cotter pins and tighten the nuts, don’t forget to replace the cotter pins!
One more thought, do you have float a motor mounts ? I installed FAM’s last year and noticed a difference until I adjusted the center bolts on the mounts
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No Float a Motor Mounts. Radius rods to bell housing are tight and secure. Rear radius rods also tight.
 
A good shock will dampen on the down stroke. A good shock should have full travel up and down. A good shock will resist as the needle valve is adjusted. Do not put a big wrench on the needle valve , you will seriously damage it. If it will not adjust with very little effort, do not force it. To test the shock in place, bolted to the frame, take off the shock arm clamping bolt, pull the shock arm off the shock shaft, and use a crescent wrench to turn the shaft. Better yet ask a knowledgable club member to help you.
The OEM shock was referred to as an instrument for good reason.
Check fluid level in each shock.
 
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