Differential dampers

[Gina]

Harmonic dampers.

Well they are not in the manual and there is nearly nothing about them on the web.

I was fiddling with steering and checking bushes and saw this large round steel thing fixed to the middle diff.

Turns out its a harmonic damper. The steel cable around it is to prevent total loss should the rubber in the middle completely collapse.

Just how important they are is nowhere to be found save to say if they put them on to dampen some kind of harmonic vibration removing them could result in high frequency oscillation of something or other ( uni joints shaft ??? ) with potential for complete and catastrophic failure .

If any one has experience with these things and in-depth knowledge I would be glad to hear it.
I rather imagine the mass is set to prevent harmonic vibrations as a result of the turning mass of various parts being out of balance in certain situations. Usually speed related ( RPM , MPH . ???)

a picture of mine .

[gazby]

Drove an old '77 Range Rover classic for 12 years and 500,000 Klm, which is pretty much the same chassis as a Discovery 1, it never had a "harmonics damper" fitted to the front axle, it drove perfectly ok, at least as good as our '98 Disco 1, so I cannot see what it's all about, but some engineer somewhere decided it was needed so go figure.
The Rangie also never had front and rear anti roll bars, those I have removed from the Disco and cannot feel the difference to drive, maybe the same applies to that "harmonics damper".
I my working life I have had experience with coal preparation plant structures that needed suspended weights on the structure to change the natural resonant frequency to stop the vibrating screens from destroying the decks of the building structure.
It seems like that would be the theory and an answer to the weight addition to the Disco front axle at the diff centre, cancellation of vibration.

[waltsd]

I never knew anything about them until when driving karajini national park, worst corrugations ever, this big bang occurred and I just happened to see something fly out the back. After finding it in the bush on the side of the road I had no idea what it was!! Some nice guy in his brand new Rangie stopped and told me where it was supposed to be attatched and that it helps stop vibrations in the front, but I should be right to drive without it!

I drove several weeks without it, but when I did put it back on, I and the missus, could tell that their was less front end vibrations. Very Minor though I must admit!

I have read on the net that some people with upgraded suspension do away with it as its gets in the way of some components!! But also that for a daily driver it does make less vibrations on freeway driving. - I must admit I agree - even if minor!

[Tank]

The rubber centre section also doubles as a V8 engine mount, I removed mine on my v8 as it put a nice dent in my extractors, Regards Frank.

[Utemad]

I removed mine but only because I broke an engine mount. I used the harmonic thing as the engine mount as Tank said above.
I fitted a new mount into the harmonic thing because it is a very handy spot to store a spare engine/gearbox mount :)

[LR Girl]

Gina, the dampers you refer to were fitted by dealer service centres in response to customer complaints about harmonic vibrations. Service centres were instructed to fit them only if a customer complained about harmonic vibrations, Land Rover were clearly not concerned about any specific catastrophic failures or they would have been fitted as the subject of a recall. I had one fitted to a '94 Rangie 'soft dash' - on the front axle. It is possible that they were fitted after road test from the factory on later cars, but I am not aware of this ever having been the case. If you search hard enough on the 'web' you should be able to find a copy of the bulletin - it is out there in the public sphere.

Harmonic vibrations can be severe enough to cause some significant catastrophic failures. Back in the 1950s ALCO (American Loco Co) had crankshafts fail on V16 Diesels because of harmonic vibrations caused at synchronous match between the crankshaft and camshafts. Needless to say they were strong crankshafts that were breaking!

[Blknight.aus]

just a vibration dampener for the front end as mentioned....

soon as you fit anything more agressive than the stock road bias tyres that come fitted to the vehicle from factory you'd never know if it was there or not because of the tyre noise.

[DiscoClax]

They were fitted to tune out 2nd order driveline vibrations (from the front driveshaft universal joints). It can be removed without fear of causing damage, it just may change the amount of vibration felt when driving at highway speeds (say 80km/hr plus) with less-agressive tyres. D2s got a double-cardan joint at the transfer case to smooth things out. That was LRs 'proper' fix and allows the use of cranked arms, etc without vibrations :)

[LR Girl]

I have never seen one fitted to a rear axle, but the LR bulletin also listed a part number for the rear as well. Service staff were instructed to selectively fit the dampers and test drive the vehicle to determine to which axle one should be fitted (or to both) to best minimise the harmonic vibration.

[superquag]

My '95 softdash Vogue (shorty, 100") has one on the front axle, towards the RH side.
Dunno if it does any good or not, - but not going to take it off as the smoothness is nothing to rave about when compared to similar age "other" brands...
I run H/T tyres, non-aggressive and 235/70.