60 mph shimmy

I went through the same kind of vibration chasing. Had my harmonic balancer rebuilt, had the tires balanced a couple of times, measured/changed the pinion angle, had my driveshaft rebuilt/balanced, all with no change. Someone here suggested I change the trans mount, but it looked fine and my trans guy said there was nothing wrong with it. What the hell, it was cheap ($25-30), easy (about an hour), and non-hipo specific (easy to get).

It worked and the car was transformed! Smooth as silk all the way through the rpm range/speeds. The mount I took off looked great, no cracks in the rubber or metal.

Try this, note the rpms where the vibration occurs (not the speed), once you've found that rpm, try it in differant gears at the same rpm. It may be subtle, but I'll bet its there. These engines seem to have a harmonic at certain rpms (probabley differant on every engine due to differing balancing) that just might be enough vibrate an old trans mount.

Let us know what you find,

Mario

I don't have a rally pac, so I can't measure the RPMs.... My brother spent neary $20K chasing a vibration in his corvette with no luck. Rebuilt motor, balanced motor, new exhaust, 3 driveshafts, U joints gallore....I'll have to ask him about a tranny mount.

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These engines seem to have a harmonic at certain rpms (probabley differant on every engine due to differing balancing) that just might be enough vibrate an old trans mount.

Let us know what you find,

Mario

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You're very correct Mario. I remember when you had your problem and we were communicating about it.

MOST V-8 engines will have their worst chance of a vibration at peak torque. That is where the 4th order Torsional Vibration is the greatest. This is the vibration that a crankshaft damper was designed to dampen out. Many times there can be a 2nd mode of torsionals, where the vibration returns higher up the RPM range and where the damper wasn't designed to function. This won't occur on otherwise stock engines, usually built up ones. If held there very long (circle track racing) things usually break, like the crankshaft. FoMoCo's spec for crankshaft torsionals is .25º Peak to Peak Double Amplitude. Which means from front to back the crank can twist a qtr. degree max either side of zero. This is why some of the places that rebuild dampers worry me. If it's a trailer queen or a car that only turns 3000 RPM occasionally, no biggie. But if you are going to go road racing with a geniune K engine and had the damper rebuilt I would shelve it for a Fluid Damper, etc. Crank Damper are engineered with certain inertia and rubber durometer to cancel the frequency that is generated by the torsionals.

Anyhow, enough of that....Mario nailed the trans mount thing. I just did my clutch and didn't let the mount fall "natural" onto the cross member before tightening it. Now I have a terrible vibration at 3500 RPM at ANY SPEED. I know its the trans mount because I can float the vibration out and cruise normal, an imbalance would not go away like that. Once I get back on the gas and back off it returns until I play with the throttle again. Today I am going to get under the Kar, loosen the mount, rev the motor a little and retighten it.

I know it's the mount because I had a helper not let the jack back down to the cross member before he tightened the bolts. More or less he pulled the mount to the cross member about an 1/8". Heck, he may have even tore the mount and I'll end up replacing it.

That would be me Mario that suggested the trans mount! <img src=images/icon_smile_big.gif border=0 align=middle>

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That would be me Mario that suggested the trans mount! <img src=images/icon_smile_big.gif border=0 align=middle>

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GOOD JOB! I know it wasn't me at the time.

I've had a vibration in mine since forever. thought it could be ring and pinion related but I am going to check the trans mount. question is, if there was nothing wrong with the ones replaced above in this thread, was it just mis-aligned?

You da man, Gasman!!!!<img src=images/icon_smile_big.gif border=0 align=middle>

You guys most likely have alot more mechanical ability than I do but I had the same problem on my 65 A code. I narrowed it down to the rear by jacking up off of the pumpkin and letting it idle, both rear wheels wobbled. I changed both axles and still had the wobble. After banging my head a bit I cleaned the paint off of both brake drums where they meet the wheel and the vibration went away!!! Check this before you spend alot of money, apparently 40+ years of painting the drums it can build up enough to cause a problem.. just my 2 cents, good luck.

UPDATE:

I had my car road force balanced yesterday. They spent almost 2 hours on my car and here's the best case they came up with:

1. Suspension looks good

2. 3 out of my 4 wheels failed the test and should be replaced. 1 of those wheels is a "NEW" styled steel wheel.

3. 3 out of my 4 tires failed the test and should be replaced. Too bad the good tire isn't mounted on the good wheel (:

They told me it would be pointless to attempt an alignment and that match mounting them would still yeild a failed result according to the road force computer.

I think I'm just going to live with this minor inconvenience. Most people wouldn't even notice it. I'll look at replacing tires and wheels together in the future. Not sure where to find true SS wheels, though ):

Troy

Thanks for that update.

I am willing to bet there are 1000's of Mustang owners around the globe dealing with the same thing after buying China's finest repop Steel Wheels.

I have 3 66 and a 67 rim. I plan to make the 67 a spare and use my new repop 66 for the car. But this worries me. If they can't road force it to work I'll have to go back to the wider 67 rim.

I do not want to put a car on the market that is not right nor not enjoyable to drive. I just got back from a 80 mile ride and other than melting from the heat, it rides smmmoooottth and soft. But I am sure the American Racing wheels and Firestone radials help.

Thanks again for your steady updates.