Rattling at low revs

Post by **airhead** » 23 Apr 2007, 00:47

Ive been getting this insanely annoying metallic rattling sound coming from somewhere outside the van when Im driving and the engines at low revs. It makes the van sound crap, and also Im afraid whatever it is that rattles is one day going to clang onto the road. Im sure its not the exhaust cause I only recently got the exhaust repaired and got the brackets replaced. I removed the tinware on either side of the engine on the underside. Any other ideas?

1.6Td Syncro.

Post by **kevtherev** » 23 Apr 2007, 16:28

Metal water pipes?

can you get some one to drive with the engine lid off and have a listen?

dalmationman · Post by **dalmationman** » 23 Apr 2007, 17:09

Check the alternator. When mine was not on tight it rattled at low revs.
The sound came out of the rear ventilation grills.

Post by **toomanytoys** » 23 Apr 2007, 18:05

Just cause the exhaust has been "repaired" doesnt mean it isnt it.. check it..
But also the tin around the engine (on D/TD makes the things a lot quieter so removing it may have "uncovered a noise that was already there...

Post by **skell** » 23 Apr 2007, 19:44

mine started a horrible low revs rattle about 50 miles from home coming back from bus types, exhaust fractured immediately behind flange to manifold...

Post by **futurecut** » 24 Apr 2007, 15:30

first plan would be to check most recent weork done

Post by **airhead** » 25 Apr 2007, 00:17

Hmm, maybe Ill take the exhaust silencer off and see if it helps. Of course then with the van sounding like a truck I wont hear it anyway.

I dont have metal water pipes, but fair question. Would be that kind of sound to be honest. I must check all my bash plates are on good and tight too in fact.

Post by **HarryMann** » 25 Apr 2007, 08:13

Sure it's not from within engine, my TD used to make a highly metallic tap, tap at low revs, but not heard from within cab...

Sometimes, standing at roadside while someone drives it past helps, or reverses it and drives it forward..

You have checked the drivehsaft bolts I presume

Post by **airhead** » 25 Apr 2007, 10:13

I havent checked the driveshaft bolts. Its not the engine. Im sure of that. Ill check the driveshaft soon so. Since you mention the driveshaft I do sometimes get a sort of vibration at around 40mph. Maybe theyre related.

Post by **HarryMann** » 25 Apr 2007, 11:11

Is this when the engine is under high load at low revs... its the propshaft ringing surely... very common, if it is that, don't lug it and there is a partial remedy at least.

Does it sound like someone hitting the propshaft with a spanner? Try it..

Post by **Louey** » 25 Apr 2007, 12:14

best described as a clattering sound??

i get it - I think DH thought it might be something to do with a vacumm something, I'll have to contact him and see

Post by **airhead** » 25 Apr 2007, 23:31

Its not so much a ringing, more a clattering. I would believe it was the propshaft though. It does happen when Im moving off and the engines just idling. Whats the proper cure for this problem? Retorque the shaft bolts?

Post by **HarryMann** » 26 Apr 2007, 08:07

No, if they're loose you are in trouble! But as with everything driveline you should check they're OK... all the driveshaft bolts and the prop bolts.

If it is the prop 'ringing', which sounds like a clattering, it's usually ascribed to the propshaft's bushing where the rubber spider fits. There's also a poly plug aftermarket fix to damp down the prop resonance... here's Aidan's article on this area of the prop, from the Wikepedia...

http://wiki.80-90.co.uk/index.php/Syncr ... eplacement

Mine does this when I let the revs drop too much by changing down too late on a hill or tight corner, the engine/driveline starts snatching and excites the resonance - and I have a new non-VW propshaft - I live with it and try to change down before it starts - and use more revs when pulling away. Its probably a combination of wear in the gearbox and front-diff to some extent as well, and like a lot of Syncro foibles, some do it and some don't and doubt if its cured by a single fix... if its only when pulling a way and not when lugging, then it might be partly to do with the clutch not taking up particularly smoothly - but its just an inherent resonance, howsover caused.

Post by **airhead** » 21 May 2007, 09:02

OK Ive now established that it definitely is the driveshaft making the clattering sound. I got under the van and twisted it both ways with my hand and theres a fair bit of play there and it does make the same sort of sound when I do it as well. All the bolts are tight and its not the UJs on the shaft. The PTO on the nosecone of the gearbox turns as well, as does the input shaft of the front diff.

Its worth also mentioning that recently when Ive been driving after a bit of city driving or on a long drive (basically once the gearbox gets hot) the gearchange becomes a bit stiff and is a bit more difficult to get out of gear. It goes into gear fine though with no crunching or stiffness. It just requires a bit of pressure to get it out of gear. Would a change of gearbox oil help in this instance? I dont think its ever been changed.

Post by **HarryMann** » 21 May 2007, 12:29

The PTO on the nosecone of the gearbox turns as well, as does the input shaft of the front diff.

Shouldn't that be permanently disengaged or is it actually in use?

Gerabox doesn't sound good, you have checked the oil level though?