Driveshaft Alignment

[smalcol]

Hi all,
I know in the E30 you lower the subframe with spacers for better driveshaft alignment, or is it for tunnel clearance as well? Were there problems with the first swaps because of alignment, what happened?(I'm assuming early failures of the center bearing.)

In my E3 project, I've needed to raise the position of the motor to provide clearance for exhaust and other stuff. I'm slightly concerned with the alignment, but the E3 driveshaft design may help with that. On the E3 driveshaft, the u-joint is before the center bearing, how is the E30 driveshaft configured?

[jalopi]

There's a u-joint before and after the csb on e30 driveshafts. Take a look at the u-joints when the driveshaft is installed... the diff and driveshaft flange should be *almost* perpendicular to each other. same with the driveshaft flange and yoke/guibo to the transmission. you want some angle (5-7* or so) but no more and definitely not zero.

[iansane]

Almost parallel?

[smalcol]

Thanks!

The E30 driveshaft design must be the same as the E3 then, great. The E39 shaft has the u-joint behind the CSB, making alignment of the guibo and CSB critical. I originally wanted to use the E39 shaft, with the rear u-joint of the E3, but the diameter is too big in the little tunnel.

[smalcol]

Just out of curiosity, why "no angle"?

[jalopi]

Almost parallel?

Correct. I got confused and meant to say perpendicular to the u-joint. But yeah, in the situation I gave the two flanges should be almost parallel to each other.

Just out of curiosity, why "no angle"?

With no angle (or far too little) you're not putting any real loads on the ujoints. This is an issue because the little needle bearings won't be forced to rotate, which keeps them from being lubricated. This can cause early ujoint failure.

[smalcol]

Thanks! Makes sense

[The Dark Side of Will]

The driveline alignment stresses the GUIBO, not the U-joints. If your trans output shaft isn't pointed straight at your CSB, then the guibo at the back of the transmission will be running at a constant angle and experience a reduced service life.

That being said, I have NEVER seen numbers or measurements on the internet showing that the driveline alignment actually is bad without spacers.

My swap in progress is into an AWD car, so my numbers wouldn't necessarily apply to a RWD car.

[Northern]

I'm going on 2 years of having my m20 shimmed up somewhere between 1/2" and 1", no noticeable difference in the never-replaced guibo or CSB.

I think people are quick to exaggerate the effects of changing driveline alignment.

[jalopi]

The driveline alignment stresses the GUIBO, not the U-joints.

http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

I think people are quick to exaggerate the effects of changing driveline alignment.

For your case? Yeah, lack of u-joint failure is pretty normal. Talk to guys with lifted jeeps/whatever and it's a completely different story though

[The Dark Side of Will]

http://www.hotrodhotline.com/md/html..._harmonics.php

That's not a BMW driveshaft.

I know how a u-joint works. I know how driveline alignment works in double u-joint shafts. That's NOT what a BMW has.

There isn't a U-joint at the back of a BMW manual transmission. There's a guibo.

If the axis of the driveline doesn't point to the center of the CSB, then there's a non-zero angle across the guibo. Since the guibo accommodates misalignment by flexing, the guibo will see a reduced service life if it has a static misalignment, because it has to flex all the time.

[jalopi]

Pretty much the same concept, minus the zero degree part. I'm gonna go out on a limb and say that 1-5* is going to be negligible.

[The Dark Side of Will]

Pretty much the same concept, minus the zero degree part. I'm gonna go out on a limb and say that 1-5* is going to be negligible.

Have any actual data to support that? The guibo sees over 2500 revolutions per mile (depending on gear ratio). 10,000 miles is 25 MILLION revolutions. I would be annoyed if I had to replace a guibo at 10K miles.

Has anyone actually MEASURED the driveshaft alignment, or is everyone who's concerned about it just going by what they've read on the internet?

[smalcol]

I'm going on 2 years of having my m20 shimmed up somewhere between 1/2" and 1", no noticeable difference in the never-replaced guibo or CSB.

I think people are quick to exaggerate the effects of changing driveline alignment.

Thanks, so to be clear, you've raised the position of your M20 by 1", with no problems, is your trans position the same?

Back to the original question, the need for subframe spacers was because of guibo failures?

[The Dark Side of Will]

I'm going on 2 years of having my m20 shimmed up somewhere between 1/2" and 1", no noticeable difference in the never-replaced guibo or CSB.

I think people are quick to exaggerate the effects of changing driveline alignment.

Oops... sorry, I didn't see this post until now.

Do you have subframe spacers between your crossmember and body or is the engine spaced up from the subframe?

This is a good data point.