Knocking/tapping from underneath

[Hairyarse]

Was driving home earlier this evening and noticed a knocking/tapping noise from underneath the car - middle to rear.

However, it's not constant, it's only there when I accelerate. If I come off the gas there's no noise, if I am on the pedal just to maintain speed, again no noise but as soon as I accelerate then the knocking/tapping noise appears.

I wondered if it would be something to do with the torque tube but then thought the noise should be present the whole time I'm driving along.

I've not looked underneath as it's dark, just wondered if anyone has had this before or any suggestions? Other than the noise, the car is running absolutely spot on, no problems at all.

Cheers
Andy

 

[Riverside]

If it's a light, tinkly sort of noise it could be a loose heat shield or the exhaust hitting the body. A heavier knocking is probably the drivetrain hitting the body.

Check exhaust etc with a rubber mallet, if it's the drivetrain it could be caused by worn engine mounts.

I had the two engine mounts & the gearbox mount changed a couple of years ago, fixed no end of rattles & made the wole car feel more solid. Expensive but worthwhile imo.

 

[Hairyarse]

It's not the heat shield - that was already making a noise! [] that resonates at about 1500 rpm.

This new noise at first I thought was a large stone stuck in a tyre but soon realised it's not. Really baffled by it tbh!

 

[924nutter]

Reverse it off the traffic warden you have inadvertently driven over. []

 

[bmnelsc]

I wonder if it might be a CV joint? Haven't had a failure myself so just speculating. I know on front drive cars they start to "rumble" at higher speeds when worn. Just read a "tech question" in Exellence mag a while ago about an S2 without LSD losing drive when turning right - turned out to destroyed CV joint - surprised that wasn't making noise. On regular rear wheel drive cars - a clicking noise as you describe is often a universal joint on the driveshaft - as we don't have those - CV joint is the next suspect....

 

[Veerzigzag]

I had a noise like that soon after buying my car - people suggested drive shaft joints, wheel bearings etc etc. Turned out that one of the handbrake shoes had no linings on it at all.

 

[Hairyarse]

I don't think handbrake as it's not long passed the MOT. I don't think CV joint either as doesn't sound like that, it does sound under the car in middle. Sean on TIPEC said he had the same, it was a broken exhaust rubber hangar so I hope it's something that simple.

It's snowing here (again []) so not been under the car yet

 

[graham.webb]

ORIGINAL: 924nutter

Reverse it off the traffic warden you have inadvertently driven over. []

Well done John...just what I was thinking!

 

[graham.webb]

Andy
I'll be interested to hear what this turns out to be....I've always had a light rattle (ie not a knock) from the o/s/r. Northway had a good look and couldn't find anything obvious. I've been wondering if it's just something like a perished shock absorber bush. I guess I won't know until I fork out for new shocks (nothing obviously loose).

 

[DarrylH]

I had something like this a month ago, sounds stupid but it turned out to be the rear disk little cross head screw was loose and was making it make a noise when accelerating exactly like you have described.

I honestly don't have a clue HOW it allows the disk to move/make a noise but I can tighten it up and it goes and loosen it off and I get it back. If it's that it's a nice simple fix

 

[Hairyarse]

Well I jacked up the car this afternoon, I couldn't find anything untoward at all. Took the rear wheels off, brakes all fine at the rear. The only thing I could find as a potential was the exhaust shield by the centre section would easily push in to the transmission tunnel. After a little bending ensued there was a bit more clearance. I went for a test drive and no more noise, so I hope that's all it was.

Oh and a little rant - When tightening my wheel nuts my 19mm socket split! A quick drive to Halfords to buy another but oh my god, what a reminder at how appalling customer service is in Halfords, it never ceases to amaze me and it seems pretty common at any store I go to, not limited to my local store.

Anyway, rant over and hopefully the knocking noise is now banished! []

 

[Veerzigzag]

When tightening my wheel nuts my 19mm socket split!

Probably a bit late to say this, and you probably know already, but it is advisable to use a long socket to fit right down over the nuts, also best if it is a "wall-drive" 6-point one rather than 12 point. Alloy nuts at high torque and all that....

 

[Hairyarse]

Hi Mike, yes I did buy a deep socket as well as a normal one yesterday, thought the same that standard one was maybe a little too short!.

 

[Hairyarse]

Sussed it!

The knocking noise hadn't happened again - until yesterday (I'm sure she knows she's going to be sold!) Again it was only under acceleration.

I looked under the car again and couldn't find anything loose, or out of place. So I decided to take off the drive shaft. Turns out the inner CV joint was quite badly worn on the inner race - the outer CV joint was perfect though.

Waiting for the new one to arrive then job done and hopefully no more knocking noise!

 

[Hairyarse]

Ok so I re-greased and assembled the old CV joint (the good one!) and greased up the new one and had the whole assembly ready to fit to the car. However, the outer race on the new CV joint will not pivot around the inner race at all so I cant get it bolted to the flange on the side of the diff. I'm sure I'm missing something obvious, but is it just a case of new CV joints being very tight?

I did have it apart when greasing it - and when a ball bearing popped out I reassembled it and could pivot.

I will look to take it apart and reassemble again tomorrow night but anyone who's done this and got any thoughts, it would be appreciated!

Cheers
Andy

 

[zcacogp]

Andy,

Did you re-assemble with the inner spider in the same orientation to the outer part as when it came apart? If it came all the way apart it is possible to assemble it 'wrongly'. Although if all you did was to lose one ball bearing and then replace it then it should be OK ...

Are you sure it isn't just stiff?


Oli.

 

[Hairyarse]

Hi Oli

I think I must have reassembled it wrongly. I just saw an online feature about the same problem. It was stiff when it was new, I did take all balls out (well they fell out!) so must have cocked it up when i reassembled. Will take another look tomorrow night.

Cheers again
Andy

 

[zcacogp]

Andy,

It's hard to describe, but if you look at the grooves in the inner spider they don't run parallel; when viewed from the end, you can see that the raised areas between them alternate between being broad and narrow. The same goes for the grooves in the outer part - when viewed from the end, the raised parts alternate between being broad and narrow. When the joint is assembled it can be 'right' or 'wrong' ('wrong' being 1/6th of a turn out from 'right'.) Easiest way of doing it is to compare the stiff joint with one that works as it should, when viewed from one end.

(I had a joint from a Golf come apart while rebuilding it and managed to re-assemble it wrongly, and it was exactly as you describe - very stiff.)


Oli.

 

[Hairyarse]

That's it Oli!

I found a link on google last night which explained just that and had a nice pic too! - http://www.outfrontmotorsports.com/cv_assembly.htm

Got home from work and it was realigned, repacked with grease and all fitted to the car in about an hour! Problem now solved, no knocking noise []

Many thanks for the help

Cheers
Andy

 

[zcacogp]

Glad it worked Andy.

And thanks for the link - that's a really interesting page. I'm not sure I completely agree with all their comments (the 'clocking CV's' was interesting, but I think it's a good idea to reverse the side of the axles from time to time as it means you wear the CV's on their 'back face', thus extending their life.) Still, a great page and thank you.


Oli.