any ideas dealer said it normal to knock
dealers had it in 4 times

sounds like anti roll bar bush or bottom arm

Cay you say BUSHINGS.... 

Its worth reading the thread:

http://www.rrsport.co.uk/forum/topic15691.html.

If the knocking is when the vehicle is going over a bumpy road with no steering inputs then the info on this will help. If its when you steer left to right quickly then its normal (inherent in the design of the DR system (the price you pay for massive wheel articulations and massive g cornering capability combined) - a small price in my opinion).

Dont let them change the DR roll bar bushes unless they are comlpetely knackered. theres enough evidence on the forums now to suggest that bush changes give a temporary improvement only not a fix because they transmit the noise not create it, if they change the bushes it means they havent found the real issue! Probably lower arm ball joints are to blame but the mass absorber fitment may well solve the problem on its own.

So they need to follow TSB LTB00214v1 to fit the masses, if it still knocks they need to follow TSB LTB00204v4 to diagnose which component has free play.

And take it to a good dealer, some of them couldnt find a knock in a knocking shop  Trust me, i'm an Engineer!

Micrometer wrote:

then its normal (inherent in the design of the DR system

Hi Leo,

I can help out here, i have many years experience in vehicle NVH.

So, the knock which is inherent in the system is the one where you turn the wheel left to right quickly, sometimes referred to as a "water hammer" sound. This is caused by the hydraulic directional valves openning with high pressure one side of it and lower pressure the other. Basicially these two different pressure heads slap against each other as their trying to make their mind up which direction to flow, this is why its inherent in the design, the architecture of system means these pressure heads cannot be equalised before the valve is openned.

Right then, because this is a laws of nature thing the knock happens on all vehicles whether they are new, old or inbetween. the reason why on some vehicles it is loud and sometimes it can not be heard or from new its good and then gets worse with age is all to do with noise transmission.

Every vehicle that comes out the factory has different noise transmission paths for all noise generators due to tolerances and environmental effects. Take the RRS body - it sits on elastomeric mounts, the position of which will be different car to car due to dimensional tolerancing. The mounting position affects the "pre-load" on the mounts which effects the mount stiffness, this will effect the noise transmission path. Elastomeric components change stiffness with age also which again changes the noise transmission over time, temperature also changes the noise transmission - generally cold market cars suffer badly from noises. And really confusingly - the noise transmission path can change direction completely if a certain element changes stiffness for any of the above reasons.

In terms of this particular knock, the problem with isolating it from the driver is that the DR system is connected by stiff elements to multiple points on the chassis frame due to the pipework, this means that when the valve block creates the knock the noise is transmitted at high energy levels all over the chassis frame making it incredibly difficult to absorb.

The "other knock" is also noise transmission related deduced from the fact that LR are fitting a mass to the body mount area which will make the mounting on the chassis resonate at a different frequency. And Charlie, you would be correct about the DR bushes, they change stiffness over time, new bushes will provide a certain NTF (noise transmission function) which will change as the bush beds in and so it will always only give a temporary benefit. Trust me, i'm an Engineer!

Hi trade it in and buy a RR Sport S , no knocking as it does not have the silly ARC or Dymanic Response system that an HSE has ...