Hello folks, I am wondering if I can please call on your collective experiences?

Yesterday morning my P38 (Diesel Auto) suddenly developed a vibration that starts at 20mph and then fades out above 30mph, coming back more subdued at 70mph with a feel very similar to when you drive over the rumble strips on the edges of a motorway.

The vibration at 20-30mph is quite pronounced and is felt through the floor and pedals. It is felt as a general vibration through the steering wheel as opposed to any direct forces being felt through the steering.

There were no preceeding warnings, I haven't hit anything as far as I am aware and I have not noticed any unusual noises (over the clatter of the diesel engine :) ).

I have accelerated hard from standstill to load everything up with no vibration issues or unusual behaviour until I reach the 20-30mph bracket.

I have yet to try locking it in gear and driving through to see if the gearing has any bearing on it.

I have had the front wheels off and rebalanced today with no improvement.
Whilst the wheels were off I checked over the front axle but found nothing amiss.
All four front ball joints were replaced with quality new items last year.
It has had good quality new tyres and brake discs in the past six months.
The nearside wheel bearing assy. was replaced about a month ago.

I have had an initial check of the prop-shafts and cannot feel any play in the U/Js. I will try lubricating them when I get chance, assuming that there are grease nipples (off to check RAVE again straight after this).

Has anyone experienced similar? The internet suggests that it is more common to have vibration issues at higher speeds.

Any help or pointers greatfully recieved.

Regards,

Smiler.

Seems as though your covering most things, the grease nipples are on the uj's on the prop, have a look at engine mounts aswell, a vibration as bad as you describe doesnt sound good

Although it's probably the wrong speed for rears, you might want to get the rear wheels balanced too (or swap them over to test). I had had a similar issue with a car once and went nuts looking at the front end which turned out to be fine.

Out of balance rear wheels usually make their presence felt at around 60mph, they are rotating too slowly to set up any resonance at lower speeds. I'd be looking for a seized UJ or the harmonic balancer has fallen off one of your axles.

Could only see the harmonic balancer on the rear, Will have another look for the front.

Steering damper has been suggested by a Defender owner. I have removed it and although there is resistance to movement I am not sure if it is enough to do its job. It also drives no differently without it fitted.

I shall have a look for the front harmonic balancer first and failing that Isuspect I may need a new damper regardless. Unless of course RAVE givesdetails of how much resitance it should give so that I can test it...

Hmm, can't see anything wrong with the harmonic damper. In fact I can't see the blumin thing at all! Just two empty bolt holes...

Seems that they didn't fit one on the front axle of the diesel as it would foul on the sump, diesels only got them on the rear. Some very early cars didn't get them at all but there was a TSB about fitting one to the rear axle if a customer complained of vibration and they then became standard fit. That just seems to leave the propshaft UJs. You won't be able to feel any slack with them still attached, you'll need to undo at least one end to check them properly.

Oh, ok. Thanks for that. It does seem a rather large lump to randomly fall off without noticing.

I shall have a play over the weekend if it's not too hot out...

Right, I am getting told that the diesel does and doesn't have a front harmonic balance weight fitted in equal measure. Anyone know for definite?

Also, replacing the steering damper has dulled the vibration a bit but not cured it. It has masked the symptom rather than reduced the cause.

Have you perused the Rimmer Brothers 'Death Wobble' vids.. yet Smiler ?

Part 1: https://www.youtube.com/watch?v=wtr2aBu1reI

Interesting video, but not the same symptoms. I don't have any shimmy through the steering wheel. It just vibrates in tune with the rest of the vehicle.

I have had one new thought though, maybe I've broken an anti-oll bar link. Could it possibly be that the now free end of the anti-roll bar is vibrating at a naturual frequency at around 25mph? I'll try to get under there tomorrow.

You really do need to get under it and have a good look. I'm still inclined to think it is a seized propshaft UJ (probably on the rear), anything else isn't going to be rotating fast enough to hit resonance at that low a speed, but you aren't going to find that without taking it off to check properly. You could always try driving it with the rear prop removed and see if the vibration goes away. If you do that make sure you put nuts on to hold the parking brake drum on or that will try and make a bid for freedom. Driving it like that permanently will bugger up the viscous coupling in the transfer case but just driving it for a short time to check won't do any harm.