E36 325i Coupe - Driveshaft Resonance

[wrs 120]

Hi,

I've been trying to find the source of a long-term driveshaft resonance problem. Every 30,000k's I need a new set of UJ's as they're stuffed due to the resonance problem.

If the heatshield is removed, the halfshafts disconnected from the diff and then the car run on a hoist you can see the driveshaft going into resonance at specific speeds - can move up to ±5mm in the centre hanger bearing.

Things that have been done to try to fix the problem:

Replace the driveshaft with a new one with new UJ's and new hanger bearing (3 times).

Replace the diff.

Replace the Gearbox.

Replace the Gearbox and Engine mounts.

Replace the diff mounts

Replace the rear subframe mounts.

Replace rear trailing arm bushes.

None of these changes have ever removed the resonance - just changed the frequency a bit or made it better for a short time but it always returns. New rubber mounts only hide most of the problem for a while but it returns within 2000km. It seems none of these changes have fixed the underlying problem causing the resonance and only temporarily masks it at best.

The resonance frequency changes when parts are replaced - eg a new gearbox mount. The frequency goes up due the mount being stiffer but as it softens the frequency drops. Depending on the state of the rubber mounts (new vs been in for a while) the resonance occurs first at about 37km/h when the rubber is new and drops to around 25km/h as it softens. The resonance is also present at higher road speeds at multiples of whatever the first resonant frequency is at the time (eg; 25, 50, 75, 100km/h). At higher speeds the driveshaft moves a lot less but causes vibration instead.

About the only thing not done which will be checked this Wednesday is to check the alignment of the diff and gearbox flanges to make sure they are parallel.

Any ideas???

[Ahmedsinc 414]

I'm not overly clued up in this area but is there a possibility it could be chassis misalignment? Has the car ever been pranged to your knowledge?

Pretty unusual, bad luck!!

[mops 4]

Interesting issue.

Some things to confirm:

New driveshaft was balanced ? On a proper machine that allows balancing two piece driveshafts ? What if the stick the driveshaft only in such machine and spin it ? does it vibrate then ? New UJ's sound suspicious to me. BMW driveshafts mostly have whats known as 'stacked' UJ's which are not replacable. BMW replaced the whole driveshaft. It is actually possible to replace the UJ's, and specialist shops do it but apparently BMW itself does not

Replaced guibo ? Guibo bolts straight ?

Who did the driveshaft work ? Apparently in these driveshafts need to have some give on the spline where it joins. The collar nut is supposed to be tightened to certain torque allowing the spline to extend/contract

Is it an auto or manual ? torque converted rt pressure plate might be off balance causing that issue. Dual or single mass Flywheel ? Dualmass might cause issues if its too worn

Otherwise engine running smoothly ? Im thinking maybe if compression is down on one of the cylinders then the torque is not linear across entire engine cycle causing drivetrain components to eventually 'hammer out' imbalance.

Is the vibration speed dependent or does it change depending on amount of torque applied (full power vs cruise vs coast vs light application of handbrake). Is the vibration dependent on engine RPM (as in same roadspeed, but different gear)

There's also a possibility that this might be the case of driveline misalignment. This is not eay to diagnose, but basically the crankshaft and all related flanges should be directly in line with gearbox and driveshaft and diff. I have seen cases where "geniue OEM" engine mounts were different height than what was on a car.

Another very remote possibility is that if engine was rebuilt in the past the rotating assembly might be out of balance, but this would normally cause other issues, specifically damaging the engine itself.

Cheers.

[wrs 120]

Thanks for the response - will try to answer all the above in the same order:

Yes, driveshaft has been balanced all 5 times it's been done - have seen it being done twice - yes, 2 piece balancing with the hanger bearing already fitted - you can touch the hanger bearing and it's smooth as. 3 different people have had a go at doing the UJ's all with the same result. Is usually balanced at 1000-6000 RPM range but not below 1000 RPM where the problem first starts when in the car. It appears to be possible to replace the UJ's - the Hasting BMW shop has done it a few times using the same machine shop I've used twice and they've never had problems.

No guibo - Jatco Auto (oh yeah) - the trans flange bolts directly to the first UJ flange. Currently running on the original trans after a full rebuild. Has had a temporary second hand trans in it too (while the original trans was being rebuilt) with the same resonance problems.

As above 3 different workshops have had a go at doing these - 2 of them very good one very bad (first one - got a refund).

If you put the trans into neutral and let the car coast down in speed as you pass through the road speed the resonance occurs at it happens. Happens at any torque but a little worse under load. Engine has done 180k with no major change in the resonance since the problem began - seems to be due to other factors, compression ok for the k's. Doesn't appear to be excited by the engine. Is road - speed dependant only and not related to engine speed or the gear you're in.

Driveline missalignment - unknown and will hopefully find this out on Wednesday. If it's been crashed prior to me owning it, it's not on any NZ records. It's an import so who knows what happened outside NZ. Currently has all genuine BMW mounts for the engine, trans, rear subframe, aftermarket trailing arm bushes.

Engine M50B25 - original, no mods - computer rechipped. The problem was there before the rechip though.

Edited June 30, 2014 by wrs

[wrs 120]

Thanks for the help and suggestions in the previous posts.

Based on comments made above I did a little more research into driveshaft vibration problems - specifically looking for info where people had an original BMW driveshaft reconditioned with new UJ's. I found 3 separate instances (one here) where people had issues with driveshaft vibration immediately after new UJ's were fitted - even if done by a good machine shop and properly balanced something was different causing a vibration.

So, I ordered a second hand driveshaft from SD and fitted it today. All vibration is gone. With the previous fix of the rear gearbox mount fixing the shudder and a genuine unmodified BMW driveshaft I finally have no more problems.

So the few warnings you see on various forums about it being very difficult to get a reconditioned BMW driveshaft to be successful appear to be very accurate - I've given it 5 goes at 3 different shops with 3 different types of UJ's and none of them have worked.

The irony of all this is I only reconditioned the first driveshaft because it was way cheaper than buying a brand-new one from BMW spare parts. After 12 years of owning the car the spare part price has dropped significantly and a brand-new driveshaft now only costs about 20% more than a recon...If only I'd checked this before trying another recon a few weeks ago...