Vibration help - Propshaft Balancing? - all ideas welcome

[MooZ]

I've recently been having some vibration problems with my e30 propshaft.

I think it all started when I put the rear gearbox mount plate on the wrong way round (thinking that it was symmetrical) which caused some damage to my centre mount bearing (the inner metal casing was cracked, so the propshaft could spin off centre) which then caused damage to the front rubber guibo.

So I replaced both of these and set the gearbox mount plate the right way round. I also replaced the rubber mounts which got squashed and stretched due to the plate being on the wrong way.

This fixed the violent vibrations and I thought everything was fixed, however I can now feel a vibration around 40-55mph (worst around 50mph). This vibration occurs whether I am in gear or out of gear, which initially made me think it could be a wheel bearing, which I checked and were fine.

I am aware that propshafts need to be balanced, however when I split it to fix the centre mount bearing, I noticed two white dots lined up and tried to line them back up as good as I could, which I thought was good enough and would be close enough not to cause any noticeable vibration.

I have been up under the car since and the entire propshaft looks fine and can't be moved or wobbled (at least by hand) so feels pretty solid.

So I am wondering whether I didn't line the shaft back up exactly as it was, I may have been a spline or two out, but it was pretty close. Before taking it all apart again and trying another line up I just wondered if anyone has had this experience before. Would a spline or two out of line cause this type of vibration? Even with fresh mounts all over (CMB, Guibo and gearbox mounts)?

Thanks in advance MooZ

[threelander]

did you replace the donut (guibo) that fixes between teh gear box and the prop mate

[MooZ]

Yes, I bought a brand new guibo/dohnut about 2-3 weeks ago.

However what I forgot to mention, was when I removed the old one, one of the bolts was loose and had rattled itself around til I could break it with my hands, so I found a matching bolt with a similar sized shank on it to replace it with, however the shank was maybe half a millimetre smaller in diameter than the original, but I tightened it up and it's held itself fine.

I didn't know where I'd get replacement bolts.

[Billwill]

Get new bolts for the Guibo, having one different one will throw the weight out.
Possibly whoever marked your propshaft with the white dots may not have done it correctly.
The front and rear universal joints should be on the same plane, ie. if you place the assembly flat on the floor you should see that the front and rear universals line up.
Reading the Haynes manual, I see that they state that when tightening up the centre bearing mounting...first move the bearing 4 to 6mm forward to pre-load the bearing and then tighten the mounting bolts...I have never done that but it sounds like good advice.

[Brianmoooore]

Arrows on the guibo lined up correctly?
Spigot bearing in the middle of the guibo OK?

[MooZ]

Thanks for the replies, do you think the odd bolt would cause that much disturbance to the balancing? I didn't notice any arrows on the Guibo, but I did put it on the same way round as the one I removed. What do are the arrows for?

[Brianmoooore]

Arrows are on the outer edge of the guibo, and must point towards the flange they are bolted to. It's likely to have a short life if it's fitted incorrectly.

[threelander]

also the bolts must be put in correctly ie 3 arrows will point to the gear box and three towards the rear of the car so you must put the bolt in the way the arrow is pointing if you dt my drift lol.you will finish up with three bolts facing one way ane the other three facing the oppossite way.if you put them all in facing one way it wil just trash the guibo in no time