I think it's a great idea. The short lifespan of the donuts would be well worth a smooth ride. I've thought of eliminating the U joints in favor of CV joints.

Since 1992, what has been common to all of your combos?
Spindles?
NO

Wheels?
NO

Driveshaft?
NO

Balancer?
NO

Flywheel?
NO

Driver?
LOST 50 pounds.  Does that matter?

Brakes?
NO

Hubs?
NO

Springs?
NO

Shocks?
NO

Car body?
YEP

Steering assembly?
NO

most changed multiple times, including engine and transmission.  Beginning to think it must just be ME.

I put my car in the air and ran it at 70 and 80 MPH. Found the left rear tire out of round by 1/4 inch. I could only spin the front tires by hand. Putting a stick next to the side wall and next to the tread revealed they were round. BUT I haven't done anything about it yet.

The BMWs all have 2 piece drive shafts, including the short 2002. The front driveshaft mounts to the tranny with  a Guibo disc. The rear of the shaft mounts to the center support with a U joint. The rear of the back driveshaft mounts to the IRS with a CV joint.




carey wintroub



Granted, the bmw driveshaft doesn't move with the rear axle, but I think borrowing technology from the over engineered germans couldn't hurt. They don't go to the effort to use 2 piece driveshaft for nothing.

Last edited by Bearing Bob (9/01/2020 11:57 PM)

MS, Glad to hear you are again thinking about solving that pesky issue.
I believe Steve-G went to CV joints for his vibration.  I would be interested in getting his feedback.

Perhaps for the next Bash, someone could kidnap (just kidding) Gary (from Denver area, not RV6) and drag him to the Bash with his bag of tricks and have all of us with vibration issues get these issues SOLVED.

Seriously, perhaps a trip to a dyno where the car could be observed at 75mph with a few properly placed go-pro cameras could be of benefit.  If you held the car to a speed where the vibe occurs, and recorded and viewed the videos, something might show up.

After that, there has got to be somebody that knows someone that works around a wind tunnel to work on the aerodynamic aspect, should the stationary dyno fail to provide a culprit.

What do I know.... I'm an accountant....

Steve69 wrote:

Have you tried a GoPro Camera under the car where you think the noise is coming from?  Maybe some video at 75mph might help you pin point the noise and where the problems at
 

That's a good idea for someone to try.  I would probably manage to run over the GoPro.

Bearing Bob wrote:

The BMWs all have 2 piece drive shafts, including the short 2002. The front driveshaft mounts to the tranny with  a Guibo disc. The rear of the shaft mounts to the center support with a U joint. The rear of the back driveshaft mounts to the IRS with a CV joint.




carey wintroub



Granted, the bmw driveshaft doesn't move with the rear axle, but I think borrowing technology from the over engineered germans couldn't hurt. They don't go to the effort to use 2 piece driveshaft for nothing.

 
Reminds me of a LoveJoy connector.
Also notice the use of three on each side.

If you look at Rock Auto under BMW’s you might be able to find one close to the length required.

BTW are you using lowering blocks?
Have you tried raising the rear to see if it disappears?

With the rear lowered, could the driveshaft be near straight?

If so, could that cause harmonic vibrations at certain speeds?
U-joints like some angle to them as I recall from the “Magazine days”.

What kind of rear leaf are ya using again?

I have 4-1/2 leaf reverse eye springs and 1/2” blocks.  But, there have been several different combinations of springs, blocks, pinion angles through the years all with same high speed harmonic. Yes, shaft angles are nearly straight.  I figure the lowered stance may be a contributor, but I am not changing the stance!  There has to be a way to cure this.

I have thought of mounting the tranny crossmember on rubber isolators.  It does have stock rubber type transmission mount.

MS wrote:

I have 4-1/2 leaf reverse eye springs and 1/2” blocks.  But, there have been several different combinations of springs, blocks, pinion angles through the years all with same high speed harmonic. Yes, shaft angles are nearly straight.  I figure the lowered stance may be a contributor, but I am not changing the stance!  There has to be a way to cure this.

I have thought of mounting the tranny crossmember on rubber isolators.  It does have stock rubber type transmission mount.

Just for S. and giggles, try those 70’s super extended shackles to get rear back to normalish height to see if vibration disappears....just for troubleshooting purposes only.

And in 1/4 of a day you’ll know if it’s the cause of the vibration.
This way, you’re not messing around with the lowering blocks and axle placement.

I like the stance too.😎

Last edited by Nos681 (9/04/2020 8:11 AM)

Almost all the German cars are IRS where the pinion does not move.  I can’t recall seeing a guibo in anything that had a straight axle.

I know this is repeat info.... Driveshaft angles should be equal and opposite.  If your transmission output shaft it 2 degrees down your pinion should be 2 degrees up.  Have you checked your angles with sandbags in the car to get it to ride height?

It is worth every penny to have your driveshaft balance touched up by a driveshaft shop post u-joint replacement.

It is possible your engine / transmission is not parallel in your car causing an odd side to side driveshaft angle.
It is possible your yoke may not be concentric on your rear end. 

Ever think of getting a go pro camera or something similar to video under-car?

Saw this and for some reason it made me think of this thread.
😀