Vibration

[Laird Scooby]

Originally Posted by packers1712

So I tried Dave's loosening off the centre bearing fixings trick but unfortunately with no success having said that I only managed to try it once and he did say it may take a couple of goes so I'll try again when I get chance and report back.
I did get the new tyres fitted and that made no difference so it isn't tyre balance related!
I also noticed that my prop appears to be a "cut and shut", I'm guessing its been made using an existing none O/D prop as the car now has an overdrive box but didn't leave the factory with it! All of this suggests to me that the prop will be the cause, Ill keep you all updated!

Doug.

Something else worth trying, i take it you unbolted the prop from the diff when you did the job? Try undoing the 4 bolts on the diff flange and rotationg the propshaft 180 degrees and refitting the bolts. It shouldn't in theory make any difference but many have reported that it does.
You may also find it's worth trying the centre bearing adjustment again after.

That said, if the propshaft is a modified one for the OD box, you may find that needs balancing itself.

[Army]

Oh dear if you are sure the propshaft has been modified I would certainly remove it and get it checked out.

If on a work bench you can support the ends and the centre bearing then you can easily check the static balance. You need free running bearings but essentially you spin the propshaft and note the position where it stops. If it always stops at the same place then it isn't statically balanced and thus the next stage - dynamic balancing - is not going to be achieved.

Before spending a lot of money to get a propshaft checked by someone else measure the length of the modified shaft to make sure it is the correct length (!)

[Laird Scooby]

Found a couple of (allegedly) local propshaft balancing services for you :

https://www.propshaft-services.co.uk/

http://www.omicron.uk.com/workshop/propshaft-balancing/

First is in Feltham near Heathrow, second is in Mulbarton, about 6 miles south of Norwich. There was also one in Wolverhampton but thought that was even further than those two so didn't link to it.

The biggest problem for you will be getting to either place either in a different car with the propshaft in the back or driving the car complete to have it balanced. All depends on how they want the propshaft delivered and when lockdown is eased.

[packers1712]

Agreed, I need to keep going logically, so I'll definitely do the centre bearing loosen, drive and re-tighten again a couple of times.
I didn't remove the prop from the diff when the gearbox was out so that is potentially where the problem lies too!
I'm saying that the prop looks modified however this is the first one I've seen(on an Amazon) and some of the welds just don't look factory quality to me.
I'll get there eventually, its not un-driveable just annoying when slowing down coming up to junctions and round-a-bouts when the the rest of the car drives good for over fifty years old!

Doug.

[Army]

If you are even slightly unsure about the "is it modified" / "is it not" situation =>

Post up a picture

There are more than enough people here who will know what it is meant to look like

####

There is no point in rushing off down an Alice in Wonderland rabbit hole

[Laird Scooby]

Originally Posted by packers1712

Agreed, I need to keep going logically, so I'll definitely do the centre bearing loosen, drive and re-tighten again a couple of times.
I didn't remove the prop from the diff when the gearbox was out so that is potentially where the problem lies too!
I'm saying that the prop looks modified however this is the first one I've seen(on an Amazon) and some of the welds just don't look factory quality to me.
I'll get there eventually, its not un-driveable just annoying when slowing down coming up to junctions and round-a-bouts when the the rest of the car drives good for over fifty years old!

Doug.

Thinking about it logically, was there any vibration before renewing the prop centre bearing? If you didn't remove the prop from the diff, it won't be that so i'd suggest leaving that as it is.

Also does it only happen on the over-run? Or is it just worse on the over-run? Have you checked your engine mounts?

[Burdekin]

Originally Posted by Laird Scooby

Thinking about it logically, was there any vibration before renewing the prop centre bearing? If you didn't remove the prop from the diff, it won't be that so i'd suggest leaving that as it is.

Also does it only happen on the over-run? Or is it just worse on the over-run? Have you checked your engine mounts?

Yep check/replace the engine, gearbox and exhaust mounts/rubbers. If they’ve not been replaced for a while it’s a good idea to just replace them. Check exhaust and gearbox has clearance and not rubbing.

Get someone else to drive the car and sit in different parts of the car and see if you can tell where it is coming from, get them to do the same. My hearing is rubbish but my wife is fantastic at telling where a noise or rattle is coming from.

[packers1712]

I inherited the car with its replaced centre bearing so no idea if the vibration was there prior to that, I drove the car back from Bath to Bedfordshire but can't specifically recall it having a vibration or not, most of the trip was on motorways so very rarely at the speed when the vibration occurs, also the car had virtually no interior in it and loads of spares in boxes ratting around all over the place so I'm not sure I'd have noticed anyway!
As I've mentioned previously the gearbox mount has definitely been replaced recently and the engine mounts also don't look that old either, I'd say I notice the vibration more on over-run as the car seems to spend longer at the offending speed, where as when I'm accelerating it feels like I'm at that speed for less time, I'm not sure how scientific any of that is mind?

Doug.

[Laird Scooby]

Originally Posted by packers1712

I inherited the car with its replaced centre bearing so no idea if the vibration was there prior to that, I drove the car back from Bath to Bedfordshire but can't specifically recall it having a vibration or not, most of the trip was on motorways so very rarely at the speed when the vibration occurs, also the car had virtually no interior in it and loads of spares in boxes ratting around all over the place so I'm not sure I'd have noticed anyway!
As I've mentioned previously the gearbox mount has definitely been replaced recently and the engine mounts also don't look that old either, I'd say I notice the vibration more on over-run as the car seems to spend longer at the offending speed, where as when I'm accelerating it feels like I'm at that speed for less time, I'm not sure how scientific any of that is mind?

Doug.

Hmmmm, lots of clues there already!

The pervious owner has obviously had a problem with vibration and gone down the obvious routes to sorting it, to no avail. Presumably one of the reasons (undisclosed of course) for the sale.

Has the car been lowered or does the back end sit lower than Gothenburg intended it to?

Certainly on the later Volvos (including my 760) which share a very similar drive-train layout, if the rear springs go weak or the back is lowered, it alters the diff pinion centreline from where the propshaft centre line is.

This can cause vibration in the diff nose and this can also be caused by weak bushes on the rear suspension, particularly around the front end of the suspension/diff area.

Could be worth a trip round the four corners of the car with your tape measure to check the trim height (centre of wheel to the wheel arch vertically above and compare it to the specs, usually given in Haynes but i daresay in Green Books too) and look for any other anomalies.

If it has been lowered and there is an adjustable ride height, try setting it back to normal height. If it hasn't been lowered, the springs could be just weak especially if they're the original ones.

[Derek UK]

When you are driving on at a speed where the vibration is worse and it is safe to do so, depress the clutch and see what the results are. Repeat the same test by just knocking the gearbox into neutral. Let us know what your findings are.
I agree that unless it was done at the time the whole shaft, both pieces needs to be balanced. The prop shop will check and replace the U/J's if needed. Have you confirmed that the 2 parts are currently in phase as per the WS manual?