Help me diagnose a knock
Discussion
So my car has a knock. I've been trying to diagnose it myself for a week or two but failing miserably.
Initial thoughts were CV joint but I'm close to dismissing this now.
Symptoms are as follows : Knocking sound appearing to come from the front drivers side wheel. Knocks with rotation of the wheel. Only knocks when turning right, driving forwards, under acceleration. Does not knock when rolling or slowing down, only under acceleration. Does not knock accelerating straight or turning left.
I've been under the car tonight rotating the wheels at various degrees of lock, shaking joints and shafts. There seems to be no play in any of the joints. All bushes look in good condition. I can't recreate the knocking with the wheels off the ground.
As said, I suspected CV joint initially but surely if it was the CV joint, it would knock when rolling and not just under acceleration?
The car just passed its MOT and didn't fail on anything so in theory, it can't be anything major, although it can be felt through the steering so something must be knocking fairly bad.
The only points on the advisories that could be related at "o/s inner drive shaft universal joint has slight play" and "Steering column slight play".
I've had a tug and a fiddle with the universal joint but can't find any play myself. Could a worn UJ cause the knocking I'm experiencing?
Cheers!
Initial thoughts were CV joint but I'm close to dismissing this now.
Symptoms are as follows : Knocking sound appearing to come from the front drivers side wheel. Knocks with rotation of the wheel. Only knocks when turning right, driving forwards, under acceleration. Does not knock when rolling or slowing down, only under acceleration. Does not knock accelerating straight or turning left.
I've been under the car tonight rotating the wheels at various degrees of lock, shaking joints and shafts. There seems to be no play in any of the joints. All bushes look in good condition. I can't recreate the knocking with the wheels off the ground.
As said, I suspected CV joint initially but surely if it was the CV joint, it would knock when rolling and not just under acceleration?
The car just passed its MOT and didn't fail on anything so in theory, it can't be anything major, although it can be felt through the steering so something must be knocking fairly bad.
The only points on the advisories that could be related at "o/s inner drive shaft universal joint has slight play" and "Steering column slight play".
I've had a tug and a fiddle with the universal joint but can't find any play myself. Could a worn UJ cause the knocking I'm experiencing?
Cheers!
Deluded said:
The only points on the advisories that could be related at "o/s inner drive shaft universal joint has slight play"
This must surely be the prime suspect - MOT testers tend to be good at finding play in things; it's their job. Have you tried putting the car in gear and rocking the o/s wheel forwards and backwards whilst looking to see if the driveshaft rotates relative to the inner joint (i.e. the one at the gearbox end of the shaft)? I wouldn't be too surprised if it doesn't clonk - the angles will be different with no weight on the wheels and you won't be applying as much force as the engine does. If that doesn't find it, try asking the tester - he'll probably remember what he did.
Does the sound disappear when driving straight? If when turning the steering it does appear and it appears only on the steering being turned I reckon it is a drive shaft.
If it goes on when the vehicle is running straight then the bearing/hub is probable.
All my experience suggests drive shaft for any regular thumping/knocking which only occurs when the steering is turning.
If it goes on when the vehicle is running straight then the bearing/hub is probable.
All my experience suggests drive shaft for any regular thumping/knocking which only occurs when the steering is turning.
Only knocks when turning right and accelerating. Turning left is silent, as is driving straight.
Will try turning the wheel with the car in gear and see what happens. Might notice visible play in the joint. Hope not though as driveshafts are as rare as rocking horse s
t and very, very expensive from the dealers...
Surely it wouldn't be a constant thud, thud, thud as the wheel turns though? I would have thought it would be a thud as you press on the pedal and then smooth until you ease off the pedal?
Will try turning the wheel with the car in gear and see what happens. Might notice visible play in the joint. Hope not though as driveshafts are as rare as rocking horse s
t and very, very expensive from the dealers...Surely it wouldn't be a constant thud, thud, thud as the wheel turns though? I would have thought it would be a thud as you press on the pedal and then smooth until you ease off the pedal?
Deluded said:
Surely it wouldn't be a constant thud, thud, thud as the wheel turns though? I would have thought it would be a thud as you press on the pedal and then smooth until you ease off the pedal?
Maybe if the shaft was operating in a perfectly straight line, but it won't be. If you removed the gaiter, the joint would look something like this:
...so those ball bearings will be rolling up and down in their grooves as it rotates (the ones on the bottom come up to the top as it turns). If there's any kind of edge or rough bit the balls will make a noise every time they run over it.
Bump.
Ok, been out again.
Put the car in gear and rocked it back and forth. No knocking at any degree of lock. Watched the U joint as I did it too and can't visually see any play.
Can't really see the knocking I'm hearing coming from the U joint anyway. Its pretty loud like a proper clunk. Not just a knocking from some play in a joint. Imagine someone tapping the front wing with a hammer. Sounds like that.
Ok, been out again.
Put the car in gear and rocked it back and forth. No knocking at any degree of lock. Watched the U joint as I did it too and can't visually see any play.
Can't really see the knocking I'm hearing coming from the U joint anyway. Its pretty loud like a proper clunk. Not just a knocking from some play in a joint. Imagine someone tapping the front wing with a hammer. Sounds like that.
Seems like it's the CV joint to me, especially your description of it making the noise under acceleration on full lock. Does it make a fairly loud clicking noise as you accelerate on full lock? Or just a single knock? If it's just a single knock then start looking at suspension arm inner rubber mountings or possibly anti roll bar linkage, again possibly a steering joint is wearing, very difficult to diagnose without hearing it myself so hope some of this helps.
I'll try and get a recording of the sound tomorrow.
Its a repetitive knock that seems to sound once on each rotation of the wheel. It doesn't only sound on full lock. Even turning to the right by a few degrees makes it sound. but only under acceleration. Can go from full lock to straight without a sound if just rolling.
Its a repetitive knock that seems to sound once on each rotation of the wheel. It doesn't only sound on full lock. Even turning to the right by a few degrees makes it sound. but only under acceleration. Can go from full lock to straight without a sound if just rolling.
Eggman said:
aybe if the shaft was operating in a perfectly straight line, but it won't be. If you removed the gaiter, the joint would look something like this:
...so those ball bearings will be rolling up and down in their grooves as it rotates (the ones on the bottom come up to the top as it turns). If there's any kind of edge or rough bit the balls will make a noise every time they run over it.
True it will look like that but utterly caked in grease! Is it something simple like the anti rollbar drop link? Not easy to diagnose without taking the weight off the wheels but piss to change and cost bugger all - they tend to knock like f...so those ball bearings will be rolling up and down in their grooves as it rotates (the ones on the bottom come up to the top as it turns). If there's any kind of edge or rough bit the balls will make a noise every time they run over it.
k when going round corners if the ball joints on the link are shagged Deluded said:
.....Symptoms are as follows : Knocking sound appearing to come from the front drivers side wheel. Knocks with rotation of the wheel. Only knocks when turning right, driving forwards, under acceleration. Does not knock when rolling or slowing down, only under acceleration. Does not knock accelerating straight or turning left.
CV joint, almost certainly. Absolutely typical symptoms.Thought I would update this thread rather than make a new one.
I had the CV joint replaced. Was going to do it myself but couldn't source the part anyway. Called a local garage who said they could supply and fit for £90 so went for it.
Took the car yesterday and it was done this morning so went to collect.
New part, new bolt but still knocks. It's exactly the same.
Was sure it was the CV joint but obviously not, so, anyone have any other ideas?
I'm lost.
I had the CV joint replaced. Was going to do it myself but couldn't source the part anyway. Called a local garage who said they could supply and fit for £90 so went for it.
Took the car yesterday and it was done this morning so went to collect.
New part, new bolt but still knocks. It's exactly the same.
Was sure it was the CV joint but obviously not, so, anyone have any other ideas?
I'm lost.
Just a little update.
Not done much in trying to find the knock again. Been meaning to get round to changing the wheels around but haven't got a deep 17mm socket (my standard one isn't quite deep enough) so can't undo the wheels at the moment.
Anyway, drove down to my Mums over the weekend in the swift. 300 miles there and back and some extra mileage inbetween. Drove great, not a problem at all. The car was fully loaded though with 2 adults, a child, 2 dogs and a roof box too, full of stuff. The knock wasn't present. Could feel it though as you can feel the car bumping up and down at low speeds. Only slightly but its noticable. Also the tracking is out a fair bit so I'm assuming a previous owner has hit a kerb and bent something.
The garage that did the CV didn't pick up on anything though, and nothing looks bent to me. Maybe its just the wheel? Although that doesn't account for the knocking!
Any ideas?
Not done much in trying to find the knock again. Been meaning to get round to changing the wheels around but haven't got a deep 17mm socket (my standard one isn't quite deep enough) so can't undo the wheels at the moment.
Anyway, drove down to my Mums over the weekend in the swift. 300 miles there and back and some extra mileage inbetween. Drove great, not a problem at all. The car was fully loaded though with 2 adults, a child, 2 dogs and a roof box too, full of stuff. The knock wasn't present. Could feel it though as you can feel the car bumping up and down at low speeds. Only slightly but its noticable. Also the tracking is out a fair bit so I'm assuming a previous owner has hit a kerb and bent something.
The garage that did the CV didn't pick up on anything though, and nothing looks bent to me. Maybe its just the wheel? Although that doesn't account for the knocking!
Any ideas?
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