Posted By : Chris Taylor,
23-Feb-2007, 09:42am
Seems that there is a consensus of two areas to check:
1. Exhaust system. This could be anywhere on the system, even if it sounds to be at one end of the car. Although every car is different, in my
experience if the exhaust is fouling the back of the car it will be a thud, rattle or knock, whereas towards the front it sounds more of a
"ringing" or "clang". Favourite spots are the bottom of the downpipe, or the centre pipe against the narrowest point of the chassis rails. It
is almost impossible to see the exhaust make contact with the body or chassis, and it needs to be a pretty persistent occurrence to see any
shiny points of contact as to where this has been happening. Basically you need to shake and push the exhaust as far as it will go to see if
and where it makes contact. If the problem is when setting off, it would suggest the system is moving sideways rather than bouncing up and
down.
2. Propshaft. Some shafts, particularly those with no splines or strap drive, are just a hollow tube and will give a "ring" for any shock or
impact. While it is unlikely (but still possible) that something is striking the propshaft, it is more likely some form of transmission shock.
This could be in the clutch (a broken spring in the driven plate or a contaminated plate which is snatching), in the shaft itself (usually a
u/j), in the diff (backlash, play, wear) driveshaft u/js or even brakes (a sticking shoe that releases with a jerk).
Although it is the solid shafts that are the most prone to resonance from outside shocks, any play in a strap drive or in the splines of the
shaft itself.
If the problem is a u/j, sticking brake, or broken strap in a strap drive propshaft, then it clearly needs repairing. If the problem is
backlash in the diff, or wear in propshaft splines, then there is little you can do except live with it and look out for any further
deterioration. (Propshaft splines can be greased which will help, but of worn you will need a new shaft. Do not be tempted to disengage the
splines and reassemble with the two parts in a different position as although this will probably reduce any play, it will probably put the
shaft out of balance).