Vibration

[20louie06]

So I've been driving my 72 around after it sat for 10 years and I hear/feel this vibration coming from the rear floor area at speed. A bit of background on the car, the tires and wheels are new that were in storage for about a year before I put them on the car. I had the car aligned and she drives pretty straight with no vibrations on the steering wheel. The suspension is new as well. The only thing that I think might cause it is the wheels not being centered. The bore on the wheel is bigger than the hub. I went to buy rings for them but the guy at the tire shop insisted that wouldn't cause it and said I should get the drive shaft checked. I supposed it could be that but I'm going to order the rings just for peace of mind. What do you guys think? I apologize if this has been covered. I didn't find anything.

 

[Don C]

If it is a tire/wheel balance problem it will depend on if they were hub centric or lug centric balanced for the rings to help.

Vibrations can be very time consuming to track down.

Now that you have a few miles on them I would have the tires hub centric re-balanced when you put the rings on.

 

[Jeff73Mach1]

If you have the right lug nuts, they should center the wheels on the studs even if the centering ring isn't installed.

Vibrations can be hard to diagnose but a few things will help you narrow it down.

Does the vibration change under load? If you can put the car in neutral and the vibration stops you can generally eliminate wheels and tires from the equation.

Is it speed sensitive? Does it go away over a certain speed?

I would start by inspecting the U joints, look for signs of driveshaft damage and check that the differential fluid is up to the proper level. Also inspect your shock absorbers for signs of leakage or other failure. While you are under the car you might also want to check the mounting bolts for the transmission cross member, inspect the transmission mount itself and take a moment to move up front and inspect the motor mounts. If either the motor mounts or the transmission mount have been changed, the remaining mount should be of the same material.

There is much more-too much to explain and certainly more than I know, by a great deal, but this shoud get you started without much or any cash outlay and should not take long to go through

 

[Don C]

Sitting for 10 years is a little concern, as rust can form on the ring and pinion gears, leading to uneven wear patterns, but should only be noticeable under load. Use Jeff's method to determine if that may be a possible cause.

 

[20louie06]

Thanks for the starting points guys I'll check that stuff out. The lugs are 60* acorn style which seemingly centered the wheel fairly well. I was just thinking it might be off by a fraction of an inch.

The vibration happens going over 40 mph whether it's under load or not. It's fairly constant but it almost feels like it skips a rotations if that makes any sense.

 

[rocket366]

First I would check the u-joints and the lube level in the rear end.

I would then check the axle bearings as they are sealed type and do not use the rear end lube.

Paul

 

[jpaz]

I had a vibration problem when I got at about 50mph. It was constant between 50-60, then it would get better. Felt like a rotational kind of problem, like drive shaft or something going on with flexplate. After checking everything & coming up empty, it ended up being the trans mount. It was old and the rubber was all kinda crumbling apart so I had metal on metal causing the vibration. So I put a new one on and no more vibration at all. As a matter of fact, it's smoother than ever. I think the trans mount was bad for a long time.

Anyway, that's what happened with mine, hope you can track yours down.

 

[MeZapU]

Take the rear wheels and put them on the front and see if the vibe moves with the tires.

 

[20louie06]

Take the rear wheels and put them on the front and see if the vibe moves with the tires.

This might be a little hard since they're staggered but maybe I can try a different set of wheels.

Sent from my iPhone using Tapatalk

 

[vozaday]

I had a harmonic type vibration that got worse when letting off the throttle at speed but almost went away when I punched it. It ended up being the driveshaft, got a new yoke, u joints and the shaft straightened. Problem solved.

I did also get the tire balance checked and changed out the transmission mount as a start, didn't solve it but it is a rather inexpensive point to start at.

The tires I run have a bigger bore than the hubs, the lugs all keep it centre so that shouldn't be it unless they are loose.

 

[Don C]

Most places use hub centric balancing because it's easier to just spin the cone on to secure the wheel to the balancer than use a lug adapter. So, it's possible the rings will help. If they do the wheel(s) didn't have good quality control during manufacture and the hub and lugs are not concentric.

 

[20louie06]

Well thought I would update you guys. I top off the diff fluid. I was able to put in about 5 oz in there. I checked some of the things you guys suggested and the tranny mount could be replaced. It definitely has seen better days. I also realized something. When I drive it at a cruising speed of around 50 mph and I mash the gas I can hear what suppose it's the tranny shifting under the added torque. Changing the motor mounts would be a good idea too since I get a bit of wheel hop if I try to launch from a stop. Ever since I tuned the engine I started noticing more issues. The engine has never been so peppy which has made noticing issues easier.