Prop shaft vibration

[Merc450]

i have a 1983 240gl. Only got it about a year ago.. And really impressed.

Ive had a very bad shuddering or vibration that started recently, under low load and at low speed. I did some investigation and expected I had problems with U Joints or bearing on the prop.

Turned out to be a very simple problem....if I ever find the mechanic that worked on the car before I will have some stern advice.

After spending my weekend building ramps to raise the car to remove the prop to take it to a drive shaft shop for reconditioning, I discovered LOOSE BOLTS on the gearbox end of the prop. 1 bolt could be turned by hand and 2 more were not fully tightened. I suspect they are not volvo bolts as bolt and nut are different sizes.

Tightened up and now running like a dream again. Will replace bolts with a new set.

I was delighted I had sorted it .. But angry at the wxxker that worked in the car before I got it..

[classicswede]

At least it was something simple to solve

[D19VDM]

Bolt head and nut being a different size is a Volvo thing. There are a good few of them on a 240 and I suppose it's handy if you only have one set of spanners or one socket set

[Merc450]

I suspect its wrong bolt as bolt n nut on differential end are one size n should be the same... If parts sites are correct as they only offer one type of bolt kit.

Diff end is 14mm bolt n nut
Gear box end is 12mm bolt head and 13mm nut ?

[Clifford Pope]

I think from an engineering point of view having a larger nut than bolt size is probably good practice. It takes less effort to hold a bolt still than it does to tighten the nut.
Also space is restricted on the yoke size of the flange, so commonly the bolt points outwards, eg towards the differential. having jiggled a smaller bolt into position, a larger nut can then be used where there is more space.

[Stephen Edwin]

Is there any reason to suspect the nuts and bolts as being less than a normal proper standard specification for nuts and bolts generally? Are the parts sites offering genuine Volvo parts? You could end up removing proper original nuts and bolts, to isntall hopefully equally adequate third party nuts and bolts.

I would tighten up all the nuts and bolts and check them occasionally. If time gives cause for further concern, or if you have become worried and want additional peace of mind, then I would check the Volvo dealer's price for replacement nuts and bolts.

I suspec guess &c. that the usual cause of loose nuts and bolts is inadequate tightening ... or excess vibration ... which I suppose can perhaps most often be a chicken and egg situation. Tighten them up and check them ocasionally.

[honestjoe]

Hi The prop shaft itself is also balanced..I wonder if it was not marked when removed first time around when reinstalled?...hj.

[Derek UK]

These bolts can be considered as "special" for the task. Having a smaller head allows a slim ring spanner to be used on them. A full size head will only allow an open end spanner to fit and that cannot be fully pushed onto the bolt head. This is why you'll often find the bolt heads are rounded off. The proper bolts also have plain shafts to match the two flanges which holds them in place much better than a bolt with full threads. If they are rounded off they are difficult to remove. Getting a couple of new sets will make replacement MUCH easier.