Discovery 2 - Low Frequency Knock

[boaterboy]

I'd be grateful for any thoughts on the reason for the subject problem.

It occurs only when turning right and mostly on fairly tight turns and at low speed, eg roundabouts.

The noise can be 'felt' in the cabin and it appears to come from the centre to rear of the vehicle.

Thank you for any help given.

 

 

[Blanco]

Turning knocks generally come from the front driveshaft CV's, it might 'feel' like the centre just because it is transmitted back down the drivetrain? Right turns generally demand more from the RHS so that would be the first check.

[boaterboy]

Thank you for your reply, Blanco.

With a worn CV on one side would not the effect/noise be felt on turning in the opposite direction, too?

And, to some degree when going straight ahead?

Finally, (sorry, for yet another question!) can wear in a CV be readily felt by jacking the car up (say)?

 

[Blanco]

Wear tends to be felt at the extremes of turning, where displacement from in-line is most pronounced. Due to the steering geometry the inside wheel always describes a tighter radius than the outside and will therefore 'knock' first.

I guess you could jack the car up, much easier to check on a ramp if you know anyone. Generally knocking while turning doesn't have too many possibilities. Check first the condition of the bellows, if that is toast and the joint has shed its grease then there's your answer.

Also it is quite a heavy job, requiring much force if the disc hasn't been off before or recently. If the disc is toast then beating seven shades out of it is fine, otherwise it can be quite difficult. Get round everything with  a wire brush and plenty of PlusGas beforehand.

[boaterboy]

Thank you so much, Blanco, for your most comprehensive reply. I really appreciated it. 

[boaterboy]

In spite of your advice Blanco I still can't trace the source of the knock.

However (and please don't think this a daft thought!), could it be as simple as the silencer system knocking against the chassis?

My thinking is as follows - 2mm gap between the front box & the nearside of chassis, silencer system mounted on rubber hangers, silencer system fairly weighty, vehicle goes round fairly tight RH bend at low speed, engine vibrates / rocks on mountings, centrifugal force throws silencer system to the nearside - which causes front silencer box to knock on chassis.

The knock is neither there on LH bends nor straight ahead at any reasonable speed - although some trace (very occasionally) whilst moving away at low revs - latter caused by engine movement on mounts? 

I can certainly produce a similar sounding knock by pushing / kicking the silencer box against the chassis. I've tried adjusting / moving the system hangers without success. Maybe the rubber hangers have gone 'soft' resulting in excess movement? I don't know how to keep the silencer box away from the chassis to test my theory - the silencer box will get too hot, I guess, for me to stuff anything between the box & chassis. 

Has anyone experienced the above, please? 

 

 

 

 

[missingsid]

2mm is very close and for me quite easily the cause.

Do you not have any wood or rubber, it should be very easy to prove and would not take a long journey to show up.

TBH given the close proximity I would look at a resolution anyway.

[boaterboy]

Thank you for your thoughts, missingsid.

I could stuff something between the silencer box & the chassis in order to test the theory but I am concerned that the silencer box will get hot and could pose a fire risk?