cyclical vibration

[pass1over]

put on a new set of new rear tires a few months ago and noticed a cyclical vibration from around 45-55mph from the rear of the car. Took it back and had them rebalance the rears, he showed me a video of my car on the balance machine and it has a little bit of a bend to it. You can see a little run out on the wheel as it spins. I do not remember having this vibration before the new rear tires were mounted.

What I've noticed though is, if I create the cyclical driving condition, then push the clutch in, the vibration goes away. Could this be something other than a slightly bent wheel?

 

[Mojo88]

I've been chasing these types of vibrations for many years. Sometimes they are easy to fix, other times not so easy. Now that I'm getting old (and 'maybe' a little wiser), I try to use the Occam's Razor principle in all these situations. In other words, the simplest and most obvious solution is usually the right one.

So, if you "do not remember having this vibration before the new rear tires were mounted", then I would certainly focus in on that area as the trouble spot.

And then you seem to confirm it by saying, "You can see a little run-out on the wheel as it spins". Damn, if you can actually see run-out on a video, then I would be focused like a laser on that. Maybe the wheel didn't get mounted properly, there could be an obstruction (washer perhaps) or maybe a little rust or crud (on top of, or below the rotor) stopping the wheel from being perfectly true to the hub. I would first want to get the rotor spinning perfectly true (measured with dial caliper), then make sure all surfaces are spotless, and mount the wheel, and check again with dial caliper.... making sure the wheel itself is running true.

Of course, it could just be a defective tire............

Hope this helps.

 

[pass1over]

wheel/tire was mounted on the balancing machine in the video.

I haven't checked it out bolted on to my hubs. I'll have to get a dial indicator to perform this as it's a tool I don't have. I just find it odd that the vibration goes away when the car isn't under power.

 

[Mojo88]

Try actually shutting the engine off at the vibration cycle. Obviously, be careful doing this. Maybe it's engine related?

The big clue for me was when you said; "do not remember having this vibration before the new rear tires were mounted". So I am focused in on the tires. IF this clue is accurate, then I would still focus on the wheels/tires.

But if you honestly can't remember, then you gotta start looking around at things like u-joints and driveshaft.

 

[86GT351]

We go through this alot. If there is a bent rim possibility, dismount the tire and check the balance. It will show off if it is bent.

 

[pass1over]

Try actually shutting the engine off at the vibration cycle. Obviously, be careful doing this. Maybe it's engine related?

The big clue for me was when you said; "do not remember having this vibration before the new rear tires were mounted". So I am focused in on the tires. IF this clue is accurate, then I would still focus on the wheels/tires.

But if you honestly can't remember, then you gotta start looking around at things like u-joints and driveshaft.

that's where I focused first because i didn't remember it before and found the runout on his tire machine. I haven't gone further than that. My '66 is taking up the lift currently, waiting on my modified drop spindles to get back, then I can get it up in the air and check it out.

RPM doesn't matter, it's speed based.

 

[JC SSP]

Do you have another set of rims and tires you can put on and see if the vibration is present? Even putting on two spares….

 

[pass1over]

I don't. Well, I don't think I do. I bought the exact same set of wheels for my '66, but in 18s. I can see if they'll mount up to my '12 (it has 20's) and give it a quick test drive.

 

[JC SSP]

I have to ask… rims are hub or lug centric? Are you using hub-rings to center the rims?

 

[pass1over]

Forgestar CF5 20x9 and 10x10.5 (about 10 years old), I believe they are lug centric. I used the rings that came with the wheels