Intermittent knocking while driving

[WorkInProgress]

Good morning all, 

I have a problem I’m hoping someone may have encountered before. I realise it’s difficult to diagnose online so I’ll try to include as much info as possible. My bus is a 75 bay. 

Recently I have noticed a knocking sound whilst driving. It is not constant and sometimes it can go 2 or 3 days without making a sound. It appears to be coming from the rear (or rear half). 
*The knocking occurs in all gears.
*It appears to be consistent with speed ie low speed, the knocking is slower, faster speed the knocking is *faster.
*The knocking can be quite loud, then when the clutch is pushed in it stops. Clutch out and it starts again.
*It doesn’t occur when coasting in neutral.
*It happens driving in a straight line or around a bend.
*The sound can be evident one minute and then it will just stop.
*Rear shocks have just been replaced.

That’s about all I can think of. I thought maybe CV joints as both wheel side boots have splits which I’ll replace, but I have no idea what could be causing the noise. 

If any of you learned people have any ideas I’d be extremely grateful. 

Regards 
ASH

[Grantus]

You’ve already solved it - CV joints!  

[WorkInProgress]

You’ve already solved it - CV joints!  

Champion!

Thanks Grantus, I was hoping someone would say that!

ASH

[Mordred]

I agree.  If you have split boots I would be pulling all of the CV's and check each joint for damaged balls or pitting in any of the spider or outer races and replacing all the boots unless they are very flexible.  If you need to replace any (likely) get Lobro CV's, not cheap copies and Lobro boots.  As the boots are tight fit I wouldn't be too concerned about putting clips on the small ends as you will see grease coming out if they aren't tight enough.  If you leave them unclipped it will give them a bit of movement which may stop them splitting.  Replace the bolts is recommended too.  If you don't have the proper 12 point bolts the hex head versions are ok as long as they are high tensile and get the proper anti vibration washers, not standard spring washers. Do them up with a torque wrench to the correct spec in steps.

One of those messy jobs you don't want to cut corners on, as it is a pain when you have to do it all over again too soon.

Adrian

[Andy.]

Simple things to diagnose worn CV's (which can cause a knocking noise)

Jack the van up and give the wheel a spin. If badly worn, you will here/feel the knocking when turning.
While jacked up (use a fixed stand in addition to jack for safety), grab the axle. It should be free to push left/right (towards/away from the wheel) freely and smoothly.
If you hold the wheel, there should be no movement turning the axle (forwards/back). Checking this on the gear box side is a bit harder as even if it's in gear, the output shaft is not fixed. You can hold the outer of the CV and try for movement (rotating)

While hte wheel is in the air, grab the top and bottom of hte wheel and try to rock the wheel (push the top towards the van, the bottom away) and alternate to feel for movement in the bearings. Also spin the wheel, it should turn soothly with no vibration.

This will not always pick up issues. While driving, the best way to check CV's is in a corner when there is more articulation in the axle. Go around a corner fast enough for the van to lean a bit (doesn't need to be excessive) and accelerate lightly. You need to try this turn left and right. The inside wheel/CV's will knock if you have wear (pitting) in your CV's.

If it's wheel bearings, it's more a vibration rather than knocking and it will be the on the outside wheel.

So it's good to have a helper who can listen closer to the wheel you are testing.

[WorkInProgress]

Great advice, thanks guys. Much appreciated.

ASH