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Help me diagnose a knocking noise please?
smart51 - 1/6/14 at 02:34 PM

In the last week, my project car has developed a slight knocking noise. The frequency of the knock is directly related to road speed and happens under power, in neutral and with the engine off. It is most obvious below 20 MPH and you can't hear it at all at above about 40. The sound is a dull ker-LUNK noise like something loose is knocking against a panel. I seem to get one knock for every 2.5 turns of the road wheel or 0.5 turns of the prop. I'll go out again later and time it more accurately.

I've jacked the car up at both ends. The wheels turn freely and without stickyness. There's not noticable play in the whele bearings. All the suspension is good. There's only a little play in the rear drive shafts. The prop coupling to the diff looks fine. You have to take the exhaust and two cover plates off to inspect the diff joint at the gearbox end, so I haven't inspected that yet.

Any ideas what the cause of the klunk may be?

[Edited on 1-6-2014 by smart51]

Sam_68 - 1/6/14 at 02:50 PM

quote:
Originally posted by smart51...I seem to get one knock for every 2.5 turns of the road wheel or 0.5 turns of the prop...


Logic suggests that this makes a worn UJ in the propshaft favourite?

renetom - 1/6/14 at 04:39 PM

Sound like props or drive shafts.

Sam_68 - 1/6/14 at 05:14 PM

Drive shafts you'd expect to be at least once per revolution of the road wheel - hence propshaft UJ seems more likely in this case.

whitestu - 1/6/14 at 05:47 PM

Check your wheel nuts are tight.

smart51 - 3/6/14 at 08:01 PM

Thanks everyone. I've taken off the prop and the UK at the gearbox end is a bit notchy. But there' said further problem. The centre and rear UJs have circlips holding in the bearings, but the front one, which is the dodgy one, has the bearings sort of preened in.

Are there specialist places that will replace them for me, or is it the sort of thing my local friendly garage can do?

smart51 - 8/6/14 at 09:14 PM

I took the prop off and it was notchy at the one end. So I bought a second hand replacement where all the UJs moved freely and smoothly. It is much better but not completely solved. The noise is not only apparent below about 10 or 15 MPH. It's hard to tell if it is coming from the gearbox end or the diff end. Any more ideas?