Car vibrates above 43 to 45 mph

[Tom - ATL]

Maybe some of you have heard or have experienced this......

Driving at normal conditions up to around 42 mph my car runs smooth, however above that speed it will vibrate quite badly. Some days it will run smooth up as high as 48 to 50. If you push it on up, say 55 to 60 it seems to smooth out again. The whole car vibrates, the body, the seats, the steering wheel, etc. The wheels and tires have been high speed balanced.

What do you think? What should I look at next?

Need your help. Tom - ATL

 

[Tom Wesenberg]

Check the clearance on the main bearings, especialy the center main. If it needs new babbit I'd install a counterweighted crank at the same time.

 

[Patrick L.]

It could be almost anything.. These engines have an inherent vibration at certain engine speeds,, some shake more than others.. Tires can still shake even though they have been balanced,, the tires could have a problem such as a shifted belt.. I happen to have 2 tires with broken or shifted belts which causes a shake between 30-35 and the engine shakes between 40-45.. It helps me know how fast I'm going without looking..

 

[steve s]

I would have the wheel balance checked again. Modern tires cans sort of move in and out of balance due to tread separation; don't know whether Model A tires do that or not. Also, imbalance issues can shift around as multiple wheel imbalances move in and out of phase with each other.

Make sure that your wheels are snugly mounted to the drums; just because the nuts are tight, doesn't mean the wheels are.

Steve

 

[Brian T]

Hello Tom,
So is there some kind of history on when this became a problem, its always best to trace back to when it started, I would go with Steve`s idea regarding tire balance or wheels.

 

[newshirt]

Get the car up to 50 mph and press the clutch petal in. Does it still vibrate in the 43 - 45 mph range as the car is slowing down?

 

[Tom - ATL]

Sorry I did not get right back ..... The Mains were checked about 3 to 4,000 miles ago. They looked good so we just tightened them up to .001 to .0015, the rear was set at .001.

I'm not sure how tires could cause the vibration as you usually can tell if a tire is out of balance. But I will have them checked again (the tires are not that old).

I have not tried depressing the clutch at speed, but i will tomorrow.

I can not EVER remember it not vibrating, mainly at 43 or above.

I just remembered, we rotated the flywheel 180 degrees, did not help. We rebuilt the U-joint, no help.

Any other ideas? Tom

 

[James Rogers]

Was the inside of the flywheel clean? I find that most have a little oil residue that collects dirt and causes an imbalance. Remember, the engine mostly stops in the same place and if the residue settles to that point it can unbalance it.

 

[Tom - ATL]

James; Yes we wiped the inside just to be sure. Tom

 

[Tom Wesenberg]

Was the crankshaft flywheel flange checked for runout? I understand some crankshaft grinders don't center the crank on the flywheel flange, thus the rear main and flywheel flange won't be concentric. A little runout with a 62 pound flywheel could make a pretty good shake.

 

[Tom - ATL]

Mr. Tom; I have no way of knowing that information as she was running when I bought her. She does seem to be one that was PUT together if you know what I mean. She runs very good except for the vibration. Tom

 

[Tom Wesenberg]

If you rev the engine in neutral with the car standing still, does it still vibrate at about 2,000 RPM?

 

[roundvalley]

Start with easy inexpensive things. Check toe in and tire pressure!

 

[columbiA]

Vibrations around 45 mph are common with a stock "A".The lack of counterweights & small brg journals contribute to the problem.Prudent drivers would keep their speed just below the vibration period to prolong engine life.As the brgs wore the vibrations only got worse until the brgs were hammered out.With the smooth roads of today,many drivers push their car much faster than was common back in the day.I can cruise at 60 in my "A"s,but that is in overdrive with rpm the same as 43 in high gear.

 

[BILL WILLIAMSON]

Not suggesting you do this, just my experience: When I got my '30 coupe, it had all the inheritent vibrations of a Model A, anything over 45 MPH, sounded like I was tearin' up my motor, this vibrated, and that vibrated, you know what I mean! Long story short, a flexible exhaust hanger, Float A Motor mounts in the rear & front (Much like '32 front mounts) and MAN!! it was like a different car, I could then hear what the engine really sounded like, beautiful!! Even at 60 to 65 it was like----HUMMMMMN-Bill W. (And this was a really well built counterbalanced engine, and yes, it would run 80 MPH (which is up to the zero on the speedo) with 3.78 gears and NO overdrive!)