The mysterious knock
 

Hi all,

So I have finished my MOT work and the car is all back together and working great - the issue is that with the vibration gone from the steering rack track rod end I now have a knock.

Having checked all the bushes ther is no apparent movement in any that is excessive. All the bushes are visably in good nick and the drop links/anti role bar looks in good shape too. Engine mounts look good also with the only one i'm unsure of being the rear engine mount - but it does look fine and there appears to be no vacume leak.

Any suggestions / ideas on how to track down this knock?

It's coming from the front drivers side btw.

Nigel.

If it’s a bobble like knock, it could be a loose brake pad.
Happened to me!🤔

Get it in the air so the suspension is unloaded and check everything. You can't do it by eye.

When I had a similar noise on my XC90 I traced it to the strut top mount.

It's an easy enough DIY job but it's a heavy car so don't be tempted to use cheap bearing and rubber mount IF it is indeed this. I shopped around and manged to get genuine parts at a very good price.

Quality aftermarket should also be fine but don't buy cheap rubbish as you will end up doing it twice.:regular_smile:

So it appears that the noise is related to accelleratrion and sounds like a dull hammer drill actrion so it suggests to me a ball joint? It cant be the steering rack arm/track rod as they are new.

I have alrteady iunspected the wheel jacked up with no load on iot and there is no movcement - having done the lower arm on a different XC90 I really dont fancy doing another as it wasnt hard but it was a faff.

Any other thoughts?

Double check the rear bush on the lower front wishbone.

I have checked all the suspension components and cannot find a reason for this knock/vibration.

However, I am suspicious of the right engine mount underneath the crankshaft the end of the engine. It looks very deteriorated and is in the region of the vibration.

Just to clarify the sound, it’s a knock/vibration – knock over bumps vibration on acceleration only. In manual gears it does the same as it does in auto. If I hold it in second gear and Accellerate I still get the vibration removing, in my mind, any gearbox related issues.

I’ve ordered a new engine mount regardless as it does look knackered and I will change and see whether this fixes the problem. I’m hopeful this will be the case

Are you sure it isn't the front mount as the rubber bush perishes and then start to knock on acceleration/deceleration etc and its the easiest to change or perhaps the wishbones bolts are loose and need nipping up?

When you rebuilt the suspension did you replace the bolts or reuse?

Stretched bolts can also give unusual knocks etc ... just another to add to the list.

New bolts so its not that.