Seat of the pants vibration over 60mph

[skyman]

My 61 runs smooth as silk until I hit 60mph. As soon as I go over a vibration begins and gets worse the faster I go. It is not rpm related nor clutch related. I have balanced the drive shaft and all four wheels. I have a set of Coker repro radials. I am beginning to think that is where the problem is. Has anyone experienced a similar problem with these tires?

 

[Rowdy1]

Did You.........

Try putting it on a lift and running it or something similar to do a visual? No clunking of any sort? You say you had the tires balanced, was it a high speed balance or static? That would make the difference if it wasn't a high speed. Let me know what you find, I'm sure you will.

 

[JohnZ]

Chances are it's tire-related; I have similar symptoms on my '67 with Coker redline radials. They took a LOT of weight to balance them, and I finally had them run on a Hunter 9700 machine, which indicated that their radial runout and loaded radial force variation was excessive, in spite of being in perfect balance (Chevrolet used to call this "smooth-road shake"); re-orienting them on the rims wouldn't cure it. Not saying this is necessarily typical, as I also had a set of Coker wide-white radials on my '57, and they were just fine. Use the locator at www.gsp9700.com to find a shop near you that has a Hunter GSP-9700 machine and see what the machine tells you.

I'm going to have Diamondback make me up a set of their redline radials - they use brand-new Bridgestone/Firestone radial casings which will hopefully be round and have in-spec loaded radial force variation.

 

[Toy4Hal]

You say "seat of the pants" vibration and not steering. That generally takes the issue away for the wheels and puts it into the driveline. Not always I'm sure, and you have replies from some knoweldgeable people.

I have been chasing vibrations in my 62 since i got her. I had some of both: Steering vibrations and "seat of the pants". it has taken much time but I'm almost clear of all vibrations..

Steering vibration was ultimately solved with the wheels. Not on balancing (of course that helps) but finding one wheel that was warped. Once i replaced that wheel, and did a rebalance of that wheel/tire, steering vibrations are gone.

Now to the "seat of the pants". I also got my draveshaft balanced. They found it out of balance at the axle end. They balanced it and, it helped some. But not all. I then saw some scoring on the yoke after the balancing was done. So, I replaced the yoke. Still some vibration. I took the driveshaft back to check the balance again. Well, sure enough, it was out of balance at the front! Now that the rebalance was done, I am "almost" vibrate free! A little vibration comes in at 65, and leaves at 70. Had her up to 90 this weekend and so smooth it was scary!!!! The remaining vibration is tolerable, but I now think I can get rid of the last of it by replacing the tail shaft bushing (where the wear on the yoke was ocurring).

I apoligise for being so long winded. But it has been a chase, and not a fun one.

Hope this helps!

Hal

 

[JohnZ]

Driveline vibration on a C1 is much more difficult to cure than on a C2, as the U-joints on a C1 are running on the extreme ragged edge of their design operating angle limitations when everything is set up perfectly. Many times, C1 driveline vibration can be cured by shimming the trans crossmember down from the frame "X"-member using washers as shims. Most C1's had them from the factory, but they've disappeared after 40+ years of transmission outs/ins. There were several dealer TSB letters over the years advising them to shim that crossmember down to cure driveline vibration, and to take careful note of the factory shim count when R&R-ing transmissions. My '57 had no shims when I got it, had an aggravating vibration after I restored it, and shimming it down 1/4" cured it instantly.

 

[Rowdy1]

VERY Interesting John

Thanks, in the few times I've had the current and old trans in & out, I've replaced the bushing mount and wondered about shims. Again you have given some great tips from your experience

 

[Viet Nam Vett]

Thanks, in the few times I've had the current and old trans in & out, I've replaced the bushing mount and wondered about shims. Again you have given some great tips from your experience

John Z............The Man..!!!