supercedar

Bill,

When your car is in park, run the rpm to 3,000 and see if it occurs.

Thomas

Leon Speed

So where exactly are you feeling this vibration? How is the shaking: up-down, side-to-side? Can't make that up from your description.

Bill Ball

It's a general shake in the body of the car. It feels side to side.

Bill Ball

I never feel it in park/neutral at any RPM or accelerating through the gears until I reach upper 70 MPH area.

White Lightnin'

1. Vibration occurs while car is in motion
2. Vibration originates in rear of car
3. Vibration source is in a rotating mass, being felt in all gears at ~70mph


Replace the half shaft/CV assemblies with brand new units; get new rear tires & balanced; get 4-wheel alignment.

I had a pulsating vibration when I bought my car back in '06 around the same speed (car was in stock trim). Replaced half shaft/CV assemblies with new, Bilstein/Eibach upgrade, big brake upgrade, new wheels/tires, new wheel bearings on front, 4-wheel alignment & corner balancing... no more vibration after or since.

Bill Ball

Yeah, but you have no idea which of these items fixed it. I'm going to have to have more evidence that it's the axles. They don't have any play or click noises. I am going to remove and examine them one more time.

blown 87

Bill is doing a repair, not a refresh or a restoration, he can't use the shotgun approach to this.

I applaud you for not wanting to just replace it all.

One of the many reasons I suggested a hi speed on car balancing is that you can listen and feel the car at speed on each wheel.

BTDT on hard to find issues like this.

My guess is that you have a bearing going out, when you replaced the mounts that some bearing is riding some where new or different now that everything is lined up right now.

I really thing you need to spin each wheel at speed with some weight on it, it has helped me before.

That being said, I had a similar issue with my corvette, after replacing all the drive line bearings and wheel bearings at one shot it went away.
But mine was part of a restoration at the time.

dr bob

Bill, can you support the rear carriers while on the lift? That would keep the suspension loaded for some out-of-true or runout testing. I'm pretty sure you have a dial gauge and a magnetic or clamp-on base for it in your collection. Start at the wheels while installed on the car. While the wheel itself may not be the problem, it's certainly worth checking for runout and out-of round both inside and out. Runout you see may be due to something else like bent hub, but those problems usually show up first with a soft brake pedal/extra pedal travel. Then to the CV carriers in and out, and the halfshafts themselves. An improperly assembled CV joint, reversed spider on the inner end of the halfshaft, will do this. Shows up as axial play in the shaft itself. Checkfor 'bent' too, with radial runout at each end. Then disconnect the drive flanges on both sides, and run the car at the critical speed to isolate the problem to either inside or outside the drive flanges. Get someone to do the driving part and let you watch the trans to see if it's moving around at the critical speed.

If it's really mechanical, you'll find it by the isolate-and-eliminate troubleshooting method I'm sure.

supercedar

Bill,

Find a Road Force balancing machine. Today's tires with short sidewall are not as forgiving to imperfections in tires. The high sidewall tires consume these imperfections as the short ones don't. These road force machines will add pressure to the tire when balancing.
I believe the machines are made by Hunter.
Thomas

GregBBRD

Have someone drive the car down the freeway at the worse speed while you drive alongside with a second car. This will allow you to inspect all four of your tires/wheels for any sign of wheel hop. Since the problem is speed related, you might actually be able to see it. We've done this many times on tough to find shakes/vibrations. If it is anyway related to the axles, tires, wheels, rotors, shocks, etc., you should be able to see it.

mark kibort

did someone already suggest putting the car on jack stands and running it at 70mph?

Ive found a lot of problems doing this. also, when you are at 70 80mph, and the vibration hits, put the clutch in and the trans in neutral. also, try different gears.

I dont think wheel bearings would make a vibration like this, but you never know. certainly the up in the air trick, might not work to diagnos them because they wouldnt be loaded
mk

Bill Ball

Hi Dr. Bob:

I have a sliding jack on the lift that can elevate the rear at each side under the low arms. The statement about axial play confuses me. I can move the shafts longitudinally. Is that not right?

OK, I'll bite the bullet and run the car to speed on the lift.

Bill Ball

I've had people driving alongside me and they don't see anything notable.

Bill Ball

OK, at this point you've given me a good collection of ideas. I am going to lift the rear as securely as I can and run the car at speed. I will more carefully inspect the axles, hubs and rotors. I do need to recheck my trans mounts as they seemed temporally related to the problem. I'm not sure what to do regarding the rear wheel bearings as they are not old and sure seem solid. I do need new tires, so I'll try a road force balance this time.

simos

Hi Bill,

I like Mark's idea. When putting the car to jack stands, you may find if the vibration comes from front or rear of the car. This should help you to eliminate
50% of the possible problems.

This was catually the way, I found my vibration issue. I replaced X-over to MSDS headers and installed modified torque converter. The car started to vibrate around 3krpm.
Finally found that headers starts to resonate at that rpm. The solution was to make additional support for headers.. Be carefully of fast spinning rear wheels!!!

-Simo-