Unidentified Knock

[Maccer 0]

I have a knock on my pug. It knocks when I step on the gas, and again when I come off it - pronounced if this is a sharp let off and then stamp back on, you can make it knock going down the road by doing this. If I'm very smooth it won't knock again until I move off having stopped. Both the driveshafts are brand new, and it went thru the Mot like this too so I don't know what it could be? The MOT usually picks up worn bushes etc so I'm at a loss. I can't pinpoint where the sound is coming from either, sometimes it sounds like the back, sometimes the front!

Any ideas? Btw there was one MOT advisory was that the n/s rear wheel bearing was slack but not a fail, this couldn't be it could it?

[mattbenselin 0]

From what you wrote it sounds like the knock only happens when you accelerate hard or lift off the gas hard. When this occurs the engine rocks back and then forwards. So it sounds like under hard accelerating something is hitting something else. I would check the exhaust is not knocking on the subframe or bulkhead and that all the engine mounts are in good condition. The lower one could be at fault check it thoroughly for wear in the bush and the mount. The upper mount may have come loose or the bump stops in the mount may have failed. The gearbox mount could have come loose from the battery tray yet still look ok. Check them all and tighten them up.

 

I'm sure other people will have their opinions but was just what I was thinking I would do first.

 

Matt

[Maccer 0]

Hi Matt thanks.

I did the shafts with a friend and have swapped the gearbox since I got the car a few months ago and the mounts are done up pretty tight and 'seem' to be ok, although this is one area I knew people would suggest. I should explain that the knock will only happen once under acceleration, however hard, and once I'm moving at speed then you can let off as hard as you like and it won't knock, its only at low speed you can make it knock back and fourth.

Its like something is moving side to side, like a knackered bush might sound with a pin moving between sides of a mount.

Also when it is stationary I can rev it up as much as you like and there is no knocking - it seems to be linked to the forward backward motion of the actual car not so much the engine….

[omega 82]

same as matt check engine mounts most likley bottom one

[Namder 0]

again check all mounts :-

 

get a freind to sit in the car with handbrake on engine running any bring the clutch up to bite piont quickly a few times over

if the listen for knocking and look for excess play aswel

 

 

could be gear linkage on transmisson tunnel?

 

 

don't take the fact it passed an m.o.t meaning all the bushes are ok either get it off the ground and look for play in these too

 

 

 

happy hunting

[Namder 0]

again check all mounts :-

 

get a freind to sit in the car with handbrake on engine running any bring the clutch up to bite piont quickly a few times over

if the listen for knocking and look for excess play aswel

 

 

could be gear linkage on transmisson tunnel?

 

 

don't take the fact it passed an m.o.t meaning all the bushes are ok either get it off the ground and look for play in these too

 

 

 

happy hunting

[Maccer 0]

Ok, will do. Just to check, is there anything on the back that could knock at all or should I be concentrating on the front end?

[jackherer 543]

Make sure all the subframe bolts are tight, even a slight looseness on these can cause a clunk when coming on and off the power. Also the inner wishbone bush bolts but its more likely to be the subframe in my experience.

[omega 82]

if its at the back cud b the exhaust/silencer moving which cud b moving due 2 worn mounts

[Maccer 0]

Hmm, subframe sounds interesting. The bolt that holds the gear selector to the subby was so slack I had a super, super sloppy stick before I did the linkages. There was a fair amount of oil from previous leaks so I suppose some of the main subframe blots could be loose too. I'm a little bit frightened now! Visions of the entire front end of the car just falling off and coming through the bulkhead! A little extreme perhaps, but think I must check this out asap!

[jackherer 543]

if its at the back cud b the exhaust/silencer moving which cud b moving due 2 worn mounts

 

Please don't use text speak.

[jackherer 543]

Hmm, subframe sounds interesting. The bolt that holds the gear selector to the subby was so slack I had a super, super sloppy stick before I did the linkages. There was a fair amount of oil from previous leaks so I suppose some of the main subframe blots could be loose too. I'm a little bit frightened now! Visions of the entire front end of the car just falling off and coming through the bulkhead! A little extreme perhaps, but think I must check this out asap!

 

It doesn't need to be very loose at all to knock so I wouldn't worry about it coming off! There are six bolts, one in each wheel arch and two on each side going into the front footwells. The pairs of bolts going into the footwells tighten into threaded flat bars, one on each side with two bolts going into each one and if these are even slightly loose (a quarter turn in one case I solved) they can clunk badly.

[SeanO'Connor 0]

This may sound to simple, but have you got something rolling around in your boot perhaps?