Rear knocking

[oldnotbroken]

Hi all,

Been reading this forum for quite a while but being lucky enough to not have had any serious issues with my old x5, I've never had cause to post a question. Being new to the forum, not quite sure if I'm posting in the correct place, and I've already searched the topics for my issue but without success. So here goes, I hope someone can help.

I have a 2007 x5 3.0 diesel, which we use to tow our touring van. On the way back from our last short holiday, it developed an intermittent speed related knocking which could be heard from the rear of the car. There was no specific trigger, sometimes it happened when pulling off, other times it happened on overrun.  Once in a while it would just start while at a constant speed, sometimes I could stop it by lifting off the accelerator, sometimes by speeding up. It did seem to happen more at lower revs when pulling away or uphill, but not always. I spent most if the journey convinced it was coming from the caravan, but having now left the van back in storage the knock is still present although not so frequent so it seems to have been made worse with the extra weight of the van hanging off the back.

It's definitely speed related and its frequency increases in time with wheel rotation. There's no gentle build up, it comes on and stays at the same loudness regardless of how fast it is although it may be a little louder on left hand bends when more weight sits on the drivers side rear wheel.

There's no other grinding or rumbling, and the knock is a very clean metallic sound, like hitting a tin can with a stick.

I'm not thinking suspension as it isn't brought on by road bumps or potholes, so my suspicion is leaning towards the wheel bearing/ rear axle area but, in truth, I have no clue.

If anyone can throw some light on the most likely cause, at least it will give me a starting point.

Thanks in advance for any help or suggestions.

[Greydog]

Morning Paul

Welcome to the Forum

I would check the rear brake back plate I have seen this twice now both time s on E70's of the 2007/8 period

To change it is a heap of work (hub dismantled) as the back plate is sandwiched between the brake shoe support plate and the Suspension hub 

I have cheated and once the disc is off remove the bolts holding the brake back plate and shoe support so it is all loose. Then I managed to change one by cutting it in half to get it off the new one I cut out the section where the Calliper sits then sliding it into place. The Brake shoe support plate and Back Plate are held in place by 4 m6 hex bolts. Still a faff but doable 

Dave

PS. When your in there check all the area in case it is a heat shield loos or something on the driveshaft

[oldnotbroken]

Good morning greydog and thanks for the reply.

As soon as it stops raining I'll get the jack out and have a look at the back plate. I've had this issue on a previous car where the back plate had started to hit the disc as it rotated, but it was pretty constant and not effected by the weight or lean applied to the car. It was for this reason that I had kind of discounted it as a likely suspect. With the backplate being fixed to the hub, does it not move in the same plane as the disc and wheel regardless of extra weight or sideways load on the axle? If this is the case, wouldn't there have to be some play in the hub assembly that causes the hub and disc to move from their fixed plane and strike the backplate? Its this thinking that made me suspect bearing or cv. 

I doubt I'll get to look at it today as the rain here is torrential, and fortunately I don't need it on a daily basis (lucky enough to have a works van) but I'll certainly start where you suggest and let you what I find. If it gets to complicated, it'll have to go to a garage as I don't have the space or time for a major strip down.

I would ask this however. The x5 is 17 years old with approaching 150k on the clock. If it turns out to be a garage job with expensive beamer parts, how far do I go?

Thanks again

Paul

 

 

[oldnotbroken]

So, the rain let up for a short while and I had the opportunity for a quick look.

The back plate seems really secure with no damage, no slack on the mounts and well clear of anything that rotates past it. The car is parked on the road so couldn't do any more than a quick visual around the prop, but nothing jumps out at me as obvious. I couldn't feel any rotational slack or play on the wheel either, which I would expect to find if the cv was worn or damaged enough to create such a loud knock.

Kinda stumped for ideas now. I think I may just drive it until the noise becomes as constant as it was while towing and have another look.

[Greydog]

Hi Paul

Well 1 down main prop shaft and centre bearing to check next also diff mounting bush in case the diff is moving under load. The air suspension takes up any slack in bushes which makes finding worn stuff harder

Great teachers these cars 🤣 like they say every days a school day

Good luck 

Dave