Deducing a cause and solution for shaking at speed

[kung fu jesus]

I am revisiting the shaking in my e30. I am trying to deduce where to head next with locating, diagnosing and solving the issue.

65-80 mph shake in the steering wheel, I can feel the shaking in the seat, too. When I put my hand on the driveshaft tunnel between the front and rear seats, I feel no vibrations at all.

I switched out my wheels and tires with another set and encountered the same symptoms. Both sets of wheels and tires are freshly balanced. One set had had two different sets of new tires installed with a *little* help moving from 205/45-16 Continentals to 205/50-16 Michelin Pilot A/S 3s. The other set of wheels are 15" basketweaves with worn Bridgestone Star Specs (205/50-15).

In the past 5000 miles, the car's front end is rebuilt; new control arms, FCABs, swaybar links, rotors, hubs, inner/outer tie rods, steering rack, steering guibo, upper shock mounts and alignment. The car is on Billy sports and H&R Sport springs, maybe 50k miles on them.

In the rear, new shock mounts and spring pads.

The shaking doesn't always starts the same and the intensity varies. Sometimes on long interstate curves, the shaking diminishes or reduces. Sometime it does the same at varying speeds. It is a bit perplexing.

I have considered a driveline shake, but because I don't feel the tunnel vibrate, I am less suspicious of the driveshaft or half shafts causing this. Pushing in the clutch at those speeds to freewheel seems to have no effect on it.

Right now, I am now considering the RCABs and rear subframe mounts. I suspect I am getting an oscillation in the chassis through worn mounts and bushings.

I am welcome to suggestions, reasoned causes, personal experiences and solutions for this issue.

Thanks for the time and consideration!

[vpilarrt]

Did you have the front end aligned after the rebuild?

[kung fu jesus]

Yes, twice.

[vpilarrt]

I would suspect the driveshaft support.

[kung fu jesus]

Wouldn't I feel it with my hand on the rear tranny tunnel?

[cabriodster87]

Check brake rotor runout and excessive dragging from caliper piston/pin and make sure inner tie rods are good and tight..True story

EDIT: Static or Dynamic balance on wheels?

[kung fu jesus]

New rotors up front didn't change the symptoms. I inspected the calipers for bonding, cleaned and relubed the pins. The old pads showed no signs of uneven wear, either. All wheels and tires were balanced dynamically.

[I8UR911]

Center support bearing or driveshaft. Be 100% certain that there is no issue with the calipers as well.

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[kung fu jesus]

Thanks for the input! Had some experienced e30 owners look over the car. Their advice after getting the car in the air and riding in it was diff bushing, diff itself (unusual pinion lash), right side halfshaft (odd shudder while cornering and accelerating).

[jlevie]

If you feel the vibration in the steering wheel it is coming from the front suspension. Out of balance, out of round, tires or a bent wheel are the obvious suspects. Worn shocks will will magnify slight tire problems and at 50k your shocks are probably rather worn.

If your 16" wheels aren't hubcentric and a good fit on the centering rings it may be impossible to balance the wheels off the car.

[kung fu jesus]

Much appreciated! The shocks aren't off the list of possible suspects.

The wheels are hubcentric as are the 15" OE basketweaves.

[jlevie]

Have you put them on a tire machine and checked for out of round and balance?

[kung fu jesus]

Yes, three times now. One set of questionable, new Continental DWS were replaced with new Michelin Pilot Sport A/S 3s

[Earendil]

I'd double check the drive shaft. A vibration that came and went only happened to me once, and it was because the U-Joint in the drive shaft was worn-to-shit. What happened was that the U-Joint could shift and become out of line, causing a very high frequency shake that was felt throughout the entire car. But it could also shift back into place, usually by putting the car in reverse, and then the vibration would go away or diminish greatly until the next hard shift and it would pop out of place again. You do not want to know what kind of wear is required in a U-Joint to cause shifting like that, and if you have that much wear you should check it out ASAP.

Here is what mine was like. I was probably a bad shift away from snapping it by the time I figured it out. http://www.youtube.com/watch?v=6AgKzL_G7Zo

[kung fu jesus]

Thanks for the input!

I swapped out the differentials and checked the play of the driveshaft while the diff was out. I could rotate the assembly maybe an eighth of an inch in either direction total. Have replaced the right axle, front right hub, front right spindle, both rear rotors, and the diff mount since I last posted.

The only question I have about the driveshaft being the cause is the shake doesn't dissipate when I push in the clutch at speed and free wheel. I also don't feel the vibration in the rear floor over where the center support bearing is.

When I removed the FR shock to change out the spindle, it was in great shape, no leaks.

Essentially the only items left that I haven't replaced are the left rear axle, the rear hubs (that do not roar or wobble), and the driveshaft assembly.

Right now, I am contemplating replacing the rear hub flanges and bearings.