Any ideas what this knocking is?

[roj62]

Hi

Going across town this afternoon I started to hear a knocking sound that got progressively louder as time went on but calmed down a bit after half an hour - its still there though and doesn't sound nice.

Its a slow knock that seems to match road speed not engine speed, starts as you pull away so its once a second then when you get up to about 20mph its 4 x a second roughly. LHD and it sounds like its coming from the left rear (louder out my window). once speed is steady and around 30mph it goes.

For all the world it sounded like something was being dragged along behind the van and bouncing off the road. It's not so loud when you decelerate apart from when you stop and theres one loud clunk.

Any ideas what it could be and if so are there obvious things to look at that don't involve taking it to bits

[dugwiththevwbug]

check very quickly for loose wheel nuts or cv joint on its way out. Either have severe outcomes if not dealt with.
with cv joint grab drive shaft and wobble it if there is movement then probably had it.

[silverbullet]

Loose wheel! I'm amazed you got up to 30 A knacked CV will soldier on for ages (I should know...) and the noise will be there all the time you're rolling and at a higher rate than 4 times a second. More of a rumble.

[roj62]

managed to get under the van - its a bit tricky as were on quite a busy road!

the CV joints don't feel that bad - theres movement in one direction (in and out) but nothing else that i can feel. The one concern though was the amount of oil around the bottom of the gearbox. There was a lot around the seals and the start of a drip at the bottom of the unit (nothing on the ground though)

Theres a dipstick that runs down to the gearbox. I checked the level - there are two circles on the dipstick but the level was way above both of them at the turn on the stick

[dazzzer1]

heres a check for the cv thing--

the drive shafts will move back and forthsort of in and out of the gear box, so ONE AT A TIME move thenm in and out. give it a giggle to redistribute the grease a bit, then see if the sound stops, if not then do the other one. this way you can tell which side it is. the trick then is to sus which one is worn, its hard to tell if they arent really shot but as a rule the outers usually go 1st in my experience

sometimes you can repack them with grease and this will stop it, other times they are a tad beyond that. if you are a real skin flint like me you will turn the shaft over, leaving the inner as the outer and the outer as the inner, this way the shaft is rotating in the opposite direction and is using the less worn driving surfaces

as has been said in a previous post the bolts on the cvjoints do come loose

daz

[CovKid]

I added a chunk on upgrading the bolts in the WIKI recently: https://club8090.co.uk/wiki/Ge ... nts_repair" onclick="window.open(this.href);return false;

If its a dry CV joint, stuffing it with fresh grease will generally shut it up as said.

[silverbullet]

It's not so loud when you decelerate apart from when you stop and theres one loud clunk.

I read right through this...you might have a damaged diff. The clonk would be the pinion trying to jump across a broken crownwheel tooth...which it would be able to jump across at higher speeds, until it goes bang and leaps out the side of the gearbox case as shrapnel.
One for Aidan, but it doesn't sound good. Drain the gear oil and see how much iron filings you get.

[buteux]

I'm not a mechanic, but i had a noise which would fit this description. Very loud, speed related but not rev related and only when moving.
It was my heat exchanger, just the outer part on the drivers side exhaust, flapping against the driveshaft. My local mechanic pulled it from the exhaust and said he rarely sees them still attached. Anyway, it was quiet as a mouse after this, but now i have a whole new problem with funny noises.

Worth checking.

[toomanytoys]

If you have a gearbox oil dipstick, you must have an auto gearbox??? that dipstick only shows the autobox part, NOT the final drive oil level.. I would be checking the oil level in there (sounds low) and if its leaking bad.. then its more likely a bearing failing or poss diff unit.. you DONT want to be driving it anywhere unless local to have it fixed.... It WILL break...

Aidan doesnt do Autoboxes. Although if the final drive has the same parts in it as the manual boxes he will be able to supply parts..

[roj62]

Ok thanks for the tips guys.

There is someone local I've got the number of through the LVWC. Will give him a call today, fingers crossed.