Drumming/vibrations

[Mike Stevens]

And before you ask, yes, I have searched the archives!

My Stag has just started exhibiting a vibration at around 25-30 MPH and, to a lesser extent, again at about 50-60 MPH - obviously harmonically related! I'm pretty sure it's road speed related as it does it in any gear at the same road speeds and with the clutch dipped and revs at tickover.

I've checked the prop and drive shaft UJs for looseness and stiffness (by unbolting one end of each and checking for "full and free movement").

The frequency of the vibration would appear to be about the same as the prop rotation (from calculation).

What are your thoughts? As it's suddenly appeared I thought about prop balance or maybe quill shaft bearing. I didn't notice any excess play in the latter when I had the prop unbolted that end, but I wasn't particularly looking for it.

I did find one thread in the archive that did describe what I've found, but sadly there wasn't any resolution!

I'd really appreciate Russ's opinion on this. Maybe I'll PM him!

TIA.

Cheers,
Mike.

[Lingen]

Mike. I would check that the flanges on the gearbox output shaft, and diff input shaft are both done up tight, but as this vibration has happened suddenly, they probably aren't the problem. Perhaps a balance weight has come off the propshaft. You might be able to confirm this by a tell-tale mark, or you may need to get the balance checked to confirm the problem.
In the worst scenario, if someone has jacked the rear of the car up under the diff nose extension, it may be that it has started to break off around the welded flange to which the diff is bolted, in which case, don't drive it any further until it has been seen to. I have had one fail on the road, and it is pretty scary!
Mike.

[Mike Stevens]

Hi Mike,

Thanks for your thoughts - much the same as mine. I think prop balance is the first thing to check.

Having had big saloons since 1974 I've come across the diff nose piece problem before so I've noe got them all with welded straps. However, I shall check it out again when I'm next underneath over the weekend!

Cheers,
Mike.

[wilf]

If it is a two-piece propshaft (bonded together with rubber bits) the bonding could have failed. Cure is a new, solid, propshaft.

[Mike Stevens]

Good point Wilf. I'll check it out over the weekend.

Thanks.

Cheers,
Mike.

[Westfaling]

Have you checked that the front and rear propshaft UJs are aligned?
Nick

[Dave M]

I had similar issues, replaced the prop (not with CV jointed one they are crap in my opinion ) and replaced the gearbox mountings, best the cars ever been, I actually enjoy driving it now. If you want details of the prop supplier please let me know, cost me £95 for a brand new manual prop complete with Ujs.

[Mike Stevens]

Thanks guys, all good stuff. Sadly it's been far too wet here today to do anything, but I suspect the next job is to remove the prop and check the gearbox mountings. They've only been on there for 2 years since the major rebuild in 2012, but with the quality of some of the modern parts - well who knows!

Cheers,
Mike.