Vibration from new propshaft

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nick88highline
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Vibration from new propshaft

Post by nick88highline »

So I bought a brand new propshaft from BMW a few months back and installed it. Took a long time researching everything about how to replace them correctly.
Reassembled everything and took for test drive. Noticed a small vibration through the front seat at between 25-30MPH, and then a significant vibration through the seat again at between 55-60MPH, above that everything is ok.
I did everything as I should like pre-loading the centre bearing by 5mm.
I even had the rear wheels balanced, but it made no difference.
I'd also changed the transmission mounts, gearbox output flange and seal. At this point I thought I may have messed up the alignment of the gearbox, but actually you just can't as there is no real adjustment, at least not in the later cars.
I then decided to swap back the old propshaft, which I did, and the vibration went away.
I got the new propshaft checked for balance, and it's ok.
So I'm really puzzled as to what else could cause this. The centre bearing on the new propshaft is not quite as easy to turn as the old one, but can this account for the vibration?
There is a little oil/grease spray from around the edges of all the UJs on the new shaft, but maybe this is normal.
The splined joint on the propshaft (which slides back and forth without a problem or any play) does not have a clamping sleeve like the old one and the splined are protected by a rubber boot.
I can only find one instance of someone having a similar issue, but they do not appear to be active on this site anymore.
Has anyone got any ideas?
I've contacted BMW, but no reply as yet.
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Ralph in Socal
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Re: Vibration from new propshaft

Post by Ralph in Socal »

Center bearing should have free movement without any noises. It's a precision sealed unit. The u-joints should not be leaking out much at this point since they are also staked, sealed units. The lack of vibration with the old DS tells you there's a definite issue with the new one.

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Re: Vibration from new propshaft

Post by conez0 »

Sounds like the 2 halves of the driveshaft might not be balanced with each other. Did you ever separate the two halves? And if so did you mark them and assembly the exact same way? Being off by even one spline may affect the dynamics as the driveshaft spins quite fast.

I assume you are getting vibration only, and not thumping (as you would with a failed center bearing).

Potentially stupid question if its a new driveshaft but does it have the bushing installed where it connects to the transmission output shaft? Theres a small bushing inside the driveshaft that essentially "centers" the driveshaft on the transmission output flange.

New center bearings are sealed bearings so its pretty typical for them to feel somewhat "tight" when rotating by hand. I would only be concerned if its very tight or if theres unevenness in the rotation.
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Re: Vibration from new propshaft

Post by nick88highline »

Thanks both.
conez0 wrote:Sounds like the 2 halves of the driveshaft might not be balanced with each other. Did you ever separate the two halves? And if so did you mark them and assembly the exact same way? Being off by even one spline may affect the dynamics as the driveshaft spins quite fast.

I assume you are getting vibration only, and not thumping (as you would with a failed center bearing).

Potentially stupid question if its a new driveshaft but does it have the bushing installed where it connects to the transmission output shaft? Theres a small bushing inside the driveshaft that essentially "centers" the driveshaft on the transmission output flange.

New center bearings are sealed bearings so its pretty typical for them to feel somewhat "tight" when rotating by hand. I would only be concerned if its very tight or if theres unevenness in the rotation.
The shaft has not been separated into two halves. I marked it the moment I got it and the UJs are in the same plane as per the old one.

Vibration only. The old propshaft is thumping at low speed and that's because the centre bearing rubber is too soft.

The later propshafts do not have a removable centering bushing, it's machined into the shaft itself.

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Nick
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Re: Vibration from new propshaft

Post by wattsmonkey »

Are you using the same guibo?
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Re: Vibration from new propshaft

Post by nick88highline »

wattsmonkey wrote:Are you using the same guibo?
Just to clarify that this is an auto model (from 1988) so no guibo.
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Re: Vibration from new propshaft

Post by wattsmonkey »

Durr!

Sorry Nick
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Re: Vibration from new propshaft

Post by Brucey »

Image

#2 is the autobox propshaft

Thinking about it, is it possible that both the thumping with the old shaft and the vibration with the new one are manifestations of the same fundamental fault?

In order for a simple propshaft not to suffer from 'quarrelling vibrations' , it is essential that the drive flange at one end is exactly parallel with the drive flange at the other end. This means that if the engine is nose-up or nose-down, or the diff is nose-up or nose-down, vibrations are likely.

Now, this isn't a simple propshaft, but I believe the same logic applies. So that is something to check. Ideally use a (digital) inclinometer on the flanges.

The other thing is that if the engine is able to move forwards or backwards or the rear subframe is on the move (e.g. under load through wheel thrust) this will tend to cause the telescoping joint in the propshaft to want to move. If it doesn't move freely enough, it will tend to kick the centre bearing off to one side (because the propshaft is trying to shorten itself), at which point the stiffness of the rubber mounting becomes important.

Any kind of (quite minor) fault in the diff mount or beam mounts can cause the propshaft to start telescoping around under load, and this will have a different effect depending on the delicate interplay of friction in the sliding joint vs stiffness of centre bearing rubber.

Thus symptoms can vary from thumping at low speed to vibration at higher speed, depending on the exact properties of the propshaft.

BTW

1) if everything is OK elsewhere, I don't think the centre bearing rubber can be 'too soft' provided it isn't actually torn. If you benefit from more stiffness there, it might be that this is a sticking plaster fix for some other lurking fault.

2) because the propshaft is in sections, ideally it ought to be checked for balance when it is articulated in the same way as when it is installed and working; a tiny machining error in the UJ yokes can make for a shaft that is perfectly balanced when it is straight, but immediately goes out of balance when the shaft is articulated.

3) as mentioned above, if the input and output flanges are not correctly aligned, 'perfection' will be unattainable.

hth, might be food for thought anyway...?

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Re: Vibration from new propshaft

Post by nick88highline »

Thanks Brucey. There I was thinking this would be easy. :shock:
BMW have promised to give me a new propshaft, so we'll see how that goes.
Engine mounts, gearbox mounts, subframe bushings and diff mount have all been renewed with genuine BMW parts over the last 2 years, but not all at once and I had the thumping before I started changing any of them. The thumping from the old shaft only happens during moderate to hard accelaration from a standstill and goes away (not to return) at around 15MPH. No other vibrations can be felt at any speed with the old shaft. This thumping does not happen with the new shaft. I can easily move the old shaft (near the centre bearing), when installed, by pulling on it, but the new one didn't move much at all. The centre bearing rubber on the new shaft is much harder than the old one.
I will get hold of a digital inclinometer, although it appears that the allowable deflection angles are very small, so I'll need something with a good deal of precision.
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Re: Vibration from new propshaft

Post by LarryM »

I recently purchased a brand new propshaft from BMW for the manual swap I have planned for my E24. This discussion has me concerned, especially considering the poor quality I've been experiencing lately with some BMW replacement parts (see the thread on "heater valves"). I think as a precaution I'll have it spun up and checked for balance before installing it in the car. Don't want any last-minute surprises.
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Re: Vibration from new propshaft

Post by nick88highline »

So I got a new propshaft from BMW and re-installed exactly as before, took out for test drive and still had vibration at 25-30, but no vibration at 55-60MPH.
I took some measurements of working angles discovered that the transmission output shaft points 2.4 degrees downwards and the differential points 2.4 degrees upwards, so they are both parallel which is ok. The working angle of the first UJ at the transmission end is 4.6 degrees, which is probably a little high, but there is nothing you can do to lower that figure very much. The working angle of the "odd" UJ at the differential end is 0.6 degrees which is good as this angle should be a low as possible given that it has no companion UJ. The difference in angles between the front and rear propshaft is 0.4 degrees.
So I focused my attention on the centre bearing. I decided to loosen the mounting nuts and let it return to its original position without any pre-load and then re-torqued the nuts. Took out for a test drive and the vibration has pretty much gone, with only a very minor hint between 25-30MPH. No other noises, thumping or vibration at any speed and all this WITHOUT pre-loading the centre bearing. I've read some strange stories about why the pre-loading is required, with some suggesting it's only required when the car is lifted of its wheels...
Anyway, problem solved for now. The question is how long can the centre bearing last? Given that my old propshaft (which had over 175,000 miles on it) had a centre bearing support that was a soft as jelly, meaning there was no pre-load possible, I suspect it will be ok for quite a while.
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Re: Vibration from new propshaft

Post by SWAUS6 »

Reading this thread with interest, hoping it might help answer why my car has a varying slight to moderate vibration between 65-80 kph. Its been occurring since having the guibo replaced a few years ago, which was causing the typical thumping. The indy repairer assured me it was ok, although I was never convinced; in hindsight and reading the sage advice by you all, it may be that the shaft sections were not realigned when he put them back together.

I'm thinking of taking the car to a reputable service centre here in Western Australia for advice and a fix, although was keen to get a perspective on the possible cause from here first. If the shafts are out of spline position alignment, I gather they will need rebalancing, or is there a possible cause in the shafts angle alignment either side of the centre bearing that might be fixed as Nick describes?

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Re: Vibration from new propshaft

Post by nick88highline »

SWAUS6 wrote:Reading this thread with interest, hoping it might help answer why my car has a varying slight to moderate vibration between 65-80 kph. Its been occurring since having the guibo replaced a few years ago, which was causing the typical thumping. The indy repairer assured me it was ok, although I was never convinced; in hindsight and reading the sage advice by you all, it may be that the shaft sections were not realigned when he put them back together.

I'm thinking of taking the car to a reputable service centre here in Western Australia for advice and a fix, although was keen to get a perspective on the possible cause from here first. If the shafts are out of spline position alignment, I gather they will need rebalancing, or is there a possible cause in the shafts angle alignment either side of the centre bearing that might be fixed as Nick describes?

Thanks

Nathan
If the propshaft sections were not assembled correctly, so that the UJs are not in the same plane, then you will have problems, but this isn't something you can do accidently unless you know nothing about propshaft science. The splines are quite coarse and so it's really obvious when the sections are not assembled correctly. If it has been assembled incorrectly then you'd have to remove it, pull it apart and put back correctly so that the UJs are in the same plane; no amount of balancing will help if they are not.
As I understand it, the guibo has to be correctly aligned as well, although I'm lucky enough to have an automatic which does not have one. :lol:
I'm afraid to say that tracking down vibrations in the driveline is not easy and can take a lot of time and patience.
Good luck
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Re: Vibration from new propshaft

Post by Brucey »

following a failed guibo I would suggest that it is a very good idea to replace the centring bushing; this is very likely to be worn eccentrically during the guibo failure. I suppose it would be possible for the mating parts to be worn too, but I have not seen this.

BTW I have seen quite a few propshafts where the spline joint cannot be assembled 'perfectly' in that the splines do not actually permit this; one spline is out ACW and if you reassemble the joint one tooth CW from there the alignment is out in the CW direction instead, i.e. neither possible orientation is 'perfect' and the original alignment used was some kind of compromise. It is highly unlikely that a perfectly balanced shaft will retain its balance when it is assembled even one tooth out; you need to use the same orientation as before. So if the spline joint is disassembled, in some cases you need to choose which 'wrong setting' to choose when putting it back together again.

In fairness there is no need to dismantle the spline joint when replacing the guibo, but you don't know what folk will do.

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