Odd Vibration

Hi Mich,


I had the same problem with my gearbox looking like it was to low and needed lifting, I posted this a few months ago but had no response from any others.

-----------------------------


Currently putting the car all back together after re under sealing and I have come across an interesting problem for want of a better description.

I am running a CR getrag mounted to standard M30 on standard engine mounts,
the gearbox cross member I fabricated myself and the gearbox is mounted as high as possible in the car, with barely a finger spacing between it and the tunnel.

So... I'm bolting the drive shaft back on and realize the rubber donut is cracked, I by a new one locally (after sizing up with what I had turns out to be a E36 joint??? who knows why, but it fits nice), but the problem I am getting to is the center drive shaft bearing and the whole alignment of the driveshaft and the output of the gearbox.

With the gearbox and engine mounted as described above (I believe this is as high as possible to go) and when I bolt up the drive shaft, the center bearing is approx 30-33mm
lower than the mounting tags on the floor of the car, I have to really push the drive shaft up hard to get it into place to be able to bolt the center bearing up, this is then putting a lot of load on the center bearing, the output bearing of the drive shaft and the flex joint.

My conclusion is that either I have the wrong center bearing (is this possible?) or that the CR box is perhaps taller than the standard box and that the out put is in a different place, or that because my car was originally an Auto trans the mounts are different??

Anyway, I have found a nice solution to the problem, I am simply going to space down the center bearing by 30mm with some nice alloy spacer blocks my tool maker friend is making for me, will still have loads of ground clearance, the drive shaft is still well up in the tunnel


Anyone else come across this??


Steve
 
+Pamp

I guess you have checked this but I had an odd vibration with my auto- before conversion to 5 speed. Culprit; Transmission mount, again, I'm sure with all the work you have done this was checked- but if not...
 
Hi Steve,

I've also tried to lower the center bearing. That was no solution for me, still had the same problem. Too bad.

That' s why I'm thinking of ligt up the roof of the tunnel. I prefer not to.....
 
Hi Mich,

You say you lowered the center bearing, but "still had the same problem" do you mean the vibration? or the mis aligned drive shaft?

As for the mis aligned drive shaft, I can only assume that every e9 out there with a 5 speed conversion must have this same problem?
With my lowering of the center bearing I now have the first half of the drive shaft perfectly in line with the gearbox out put, i.e, no twisting at all of the big rubber flex joint.


Guys? your comments and thoughts here please

As for vibration, may be get the drive shaft re checked for balance, I had a shaft shortened and balanced a few years ago on my race car, but first time out it nearly shook me of the road, back to a different balancing guy and hey presto problem found.

With problems like these its just check check check, and replace everything !
 
Thanks for your repsonse. I want to solve this problem finally so that's is ready for use in summer!

Yes, the same problem is vibration at +/- 40/45 km. You feel the driveshaft shaking in tunnel at the point of de center bearing.

The drive shaft is balanced 3 times now. Also tried another drive shaft of aan friend, same problem.

Do you know how much you lowered the center bearing?

Can it have to do with rearwheel bearings or the diff?
 
I had not followed this thread closely and may have missed several things. Since you tried a drive shaft that was known to be good from another vehicle, one wonders whether your drive shaft would have exhibited any vibration in the donor vehicle. If not, then you are (most likely) left with alignment or other installation issues. Something else to consider, all of your trial and error testing may have created a new issue with your rubber coupling. Not saying it has happened, only that it is something to consider. Again, if you have not done so, getting under the car and observing the vibration may be the best diagnostic tool.

This thread raises many of the same issues: http://www.mye28.com/viewtopic.php?t=90752

More on the subject:

DRIVESHAFT VIBRATION: 101 (not for CV axles)
Most people have trouble determining if the vibration in their vehicle is coming from the DRIVESHAFT or not. There are typically two types of vibration most vehicles would have. A fast cycle vibration or a slow cycle vibration, to help understand this lets say we put a bucket of water on the passenger’s floor. If the vibration in the vehicle produces small ripples on the top of the water this would be considered a fast cycle vibration. This type of vibration is usually a drive train vibration, things like the driveshaft, motor or torque converter. If the vibration puts waves on the top of the water or splashes, this type of vibration is a slow cycle vibration and usually is an axle or tire vibration. People have trouble determining where the vibration in their vehicle is coming from. Try the test below if your not sure.


JACK TEST
A simple way to do this is out the vehicle in question up on jack stands (make sure the vehicle is completely secure), block the front tires and run the vehicle up to the speed you have the vibration. Make sure you use the brake to stop the drive train before you put the car in park if it’s an automatic. If the vibration is a fast cycle vibration you may want to have the DRIVESHAFT checked for balance. This may make no sense to you but you may try indexing the shaft 180 degrees (just pull the shaft off the rear yoke and put it on the opposite way). What this does is change the resonant frequency property of the driveline and in many cases it takes the vibration away. If you have a slow cycle vibration take the tires off the car (make sure you put lugs back on the axle to keep the brake in line) and run the vehicle again. If the vibration is gone you now have to find out if it’s the rim or the tire and good tire shop can help you with that. This is a simple test for any vehicle but please if you’re not completely sure of how to put the car on stands safely bring the car to a certified technician to perform the test. If you want further help with understanding this process or want help understanding vibration problems please call or e-mail us. http://www.driveshaftshop.com/driveshafts-101
Click to expand...
Drive line angles: http://www.jeepfan.com/tech/driveline-angles/


Checking drive shaft alignment can be accomplished with a makeshift tool. Here is an example of a bmw tool used to check alignment on an E10/ '02. Naturally, if shims (washers or similar) are necessary to align the center bearing, even as a temporary measure, probably worth a try.

hth
PagesfromPagesfromRepairManualBMW1502-2002.jpg
 
Yes, I asume that the drive shaft I borrowed is oke. It was running well under the donation car.

To make things clear: the vibration I have is only at 40/45km (second gear or in higher rpm in 1st gear) , you hear and feal the drive shaft shake/vibrate. Above (and under) that speed the shake/vibration is gone.

I'm collection idea's to use on test day. For now I will:

- change the guido
- check the alignment of the drive shaft
- check enige mounts, diff mounts
- run the car with wheels of the ground (with and without wheel on)
- change the centre bearing
- lower the center bearing (more than 10mm)
- .....

Any other suggestions are more than welcome!!!!! Thanks for al the ideas so far, keeps me motivated the solve this problem.
 
Last edited:
Hi Mich,


I lowered center bearing by 30mm with some aluminium spacer blocks i had made by an engineer, for me this makes the first half of the drive shaft perfectly in line with the output shaft of the gearbox, with absolutely no twist in the guibo joint.

I haven't road tested this yet, but have no reason to believe that it will cause any problems.


Steve
 
yep, but that what was needed to get the drive shaft coming straight of the gearbox.
The drive shaft is still well up in the tunnel, so ground clearance is not a problem.

I'm still wondering if any others have this problem that you and I have, I cant see how they couldn't, my gear box is up in the tunnel as far as possible with out touching.
 
Also need to check all the U-Joints. A failing u-joint will get stiff and cause this kind of vibration.
DaveG

Mich said:
Yes, I asume that the drive shaft I borrowed is oke. It was running well under the donation car.

To make things clear: the vibration I have is only at 40/45km (second gear or in higher rpm in 1st gear) , you hear and feal the drive shaft shake/vibrate. Above (and under) that speed the shake/vibration is gone.

I'm collection idea's to use on test day. For now I will:

- change the guido
- check the alignment of the drive shaft
- check enige mounts, diff mounts
- run the car with wheels of the ground (with and without wheel on)
- change the centre bearing
- lower the center bearing (more than 10mm)
- .....

Any other suggestions are more than welcome!!!!! Thanks for al the ideas so far, keeps me motivated the solve this problem.
Click to expand...
 
I had that sort of vibration before converting to 5 speed and it was indeed the guibo.

I am sure you already tested this but I am curious of the vibration persists at 40kmh even if you put the car in neutral. If it does persist I think it should exonerate engine mounts and some transmission issues as culprits.



Mich said:
Yes, I asume that the drive shaft I borrowed is oke. It was running well under the donation car.

To make things clear: the vibration I have is only at 40/45km (second gear or in higher rpm in 1st gear) , you hear and feal the drive shaft shake/vibrate. Above (and under) that speed the shake/vibration is gone.

I'm collection idea's to use on test day. For now I will:

- change the guido
- check the alignment of the drive shaft
- check enige mounts, diff mounts
- run the car with wheels of the ground (with and without wheel on)
- change the centre bearing
- lower the center bearing (more than 10mm)
- .....

Any other suggestions are more than welcome!!!!! Thanks for al the ideas so far, keeps me motivated the solve this problem.
Click to expand...
 
Ok, it's been a while but I did sovled the problem. Didn't had the time to try it earlier. I spoke to a guy that prepers BMW's for racing for a few year, he knew the problem from e24's. Most of the time it wat a worn gearbox. I was lucky that I had another one on stock, so I changed it yesterday and toke it for a drive. I runs great now! thanks for al your advise and time.


My cs is almost ready for the summer. Still need to lower the front. I will start an other topic for that.
 
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