How can I test if my driveshaft splines or bearings are broken?

I have had a really loud grumbling resonating rumble come from the transmission rear end on ym indy for two weeks and I still cant locate what is at fault.

Its a XR4x4 3.62 LSD diff and bolt on drive shafts. Car is great under power and drives fine, its just when lifting off the gas does this sound start to build up when coasting down speed IN GEAR.

I cant get it to make the sound on demand, just does it now and again

really stuck and need it fixed in 3 weeks before I go 'ring.

Jack the back end on axle stands up, chock the front end securely, start it up and run it in gear. Then go underneath with either a stethoscope, solid iron rod or long screwdriver to your ear and listen to either end of the drive-shafts and then the three diff bearings. Should tell you the most likely place where the noise is coming from as a starter. If you detect a likely source for the knocking but can't pin it down try disconnecting driveshafts in turn. Failing that work your way forwards, knocking the propshaft off if necessary.
BE CAREFUL EXTREMITIES, CLOTHING, HAIR ETC DO NOT CATCH ON RECIPROCATING PARTS AND JUMP UP & DOWN ON THE CAR BEFORE SCOOTING UNDERNEATH TO ENSURE ITS GOING NOWHERE. Also helps to have an assistant standing by to switch it off and keep passers-by out of the way!
HTH.
Cheers, Pewe

Thats ^^^ probably not going to help a lot with a BEC. They tend to clatter and bang through the transmission if put in gear with no load (IE up in the air), so making it very hard to find any other noises.

The description doesn't sound like the typical desciption of a knackered shaft; Usually people hear knocks, bangs or clicks. Sounds more like the diff (sorry) or possibly a wheel bearing, although that'd vary more with cornering load that drive. However there are always exceptions. Can you get a second opinion from someone?

[Edited on 25/8/09 by adithorp]

you mention it makes the noise coasting downhill IN GEAR, and you put 'in gear' in capitals. does it not do it in neutral?

Is the sproket adaptor tight? I had a simlar sound when I had a bit of play in the adaptor

one item i have not checked is the sporcket adaptor onto the engine itself

the prop bolts seem fine though

its very hard to provoke the sound, and will try and see if i can do it in neutral