Deducing a cause and solution for shaking at speed

[Earendil]

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.

If there is no change in vibration when you put the clutch in you have only eliminated the engine and pressure plate. The drive shaft, transmission, and clutch are all still spinning. If you put the car in neutral you can eliminate about half the transmission and clutch, but the drive shaft is still spinning.

A bad drive shaft will shred a center support bearing, and if it does that you might actually feel less vibration in the tunnel instead of more. With the bearing out the drive shaft almost free-wheels in there, and isn't solidly connected. Can you feel the vibration in the shifter?

If the steering wheel really is the harshest point of vibration than it has to be coming from the front end, specifically something in the suspension components or attached to it.

[kung fu jesus]

Interesting!

I haven't felt the shifter, I will try that!

Funny thing, the front has been rebuilt in the last 3k miles:
New control arms (Lemforder)
New hubs
New drop links
New CABs (THR units)
New wheels (hubcentric)
New Tires (twice)
New rotors
New pads
New Steering guibo
New rack (rebuilt unit, new)
New inner and outer tie rods
Balanced (x3), road forced balanced
Rebuilt P/S pump
New upper P/S line
New P/S reservoir
New upper strut mounts

Changed the knuckle assy on the right side last weekend.

In the rear:
New right axle
new rotors
new pads
new upper strut mounts

Changed diffs, new diff bushing.

I feel the shake in the wheel and also the floor at the front including the pedals.

[kung fu jesus]

Alright, borrowing a set of known good wheels and tires just eliminate any doubt of a bad wheel(s). If the symptoms persist, I will pull the trigger on a remanufactured driveshaft, new CSB, guibo and Trans mounts (because I'm in there).

[JEMichaels]

Alright, borrowing a set of known good wheels and tires just eliminate any doubt of a bad wheel(s). If the symptoms persist, I will pull the trigger on a remanufactured driveshaft, new CSB, guibo and Trans mounts (because I'm in there).

Holy. Christ. I click the thread to glean knowledge about my own shake and at my novice stage, the amount of money you've put into this e30 makes me think, yea I can live with the shake. GL finding the problem

[kung fu jesus]

Thanks! I now have a reman driveshaft, guibo, CSB, exhaust gaskets, mounting hardware and trans mounts sitting in my office, but the weather has been too cold to install them. :(

I don't have a garage at my home, just a large open carport. The recent snow didn't help.

Hopefully, I can get at this on Saturday, maybe Sunday.

The expense hasn't been *too* bad, just a little frustrating. Actually, for being relatively new to these cars again, the DIY repairs have not been difficult. I do feel a little foolish for not recognizing the driveshaft as a problem because I had my logic reversed.

The biggest reason for continuing this thread the hope that it might_just help someone in the future. I cannot tell you how many threads on different boards I read with no report as to what the solution was.

[kung fu jesus]

Oh, I also figured out the sound I *thought* was just the fuel pump was actually the CSB. I come from the Miata world and have done extensive work with them. It's pretty common to hear the pump because it is just behind your right shoulder, so when you drive them, you can hear it buzzing a little. I started noticing the buzzing I heard in the e30 was speed dependent, plus the location, and that the fuel pump in this car sits under 5 inches of foam called the back seat.

My mechanical learning of this car has been accelerated to ludicrous speed because of my hunt for the solution. :) I guess when it is solved, I *should* have a pretty reliable, solid-driving car sooner than I anticipated.

[kung fu jesus]

If there is no change in vibration when you put the clutch in you have only eliminated the engine and pressure plate. The drive shaft, transmission, and clutch are all still spinning. If you put the car in neutral you can eliminate about half the transmission and clutch, but the drive shaft is still spinning.

A bad drive shaft will shred a center support bearing, and if it does that you might actually feel less vibration in the tunnel instead of more. With the bearing out the drive shaft almost free-wheels in there, and isn't solidly connected. Can you feel the vibration in the shifter?

If the steering wheel really is the harshest point of vibration than it has to be coming from the front end, specifically something in the suspension components or attached to it.

A reman driveshaft solved the issues!

Thanks!

The first unit wasn't properly balanced, the reman company sent another one quick without fuss. The original DS had notchy u joints in the rear. The giubo and trans mounts were shot. The CSB was getting flaky.

She drives fantastic now! So happy!

[Earendil]

Sweet! Glad to hear!

[kung fu jesus]

Six hours to do the first, removing the exhaust, 3 hours on the second, letting the rear of the exhaust droop. *Just* beat the snowpocalypse part two. :)