944 rear end knock diagnosis help

[dern]

Evening,

I've posted this to titanic but wondered if anyone here could offer any advice.

I've been commuting to a new job over the last 2 months
and the car (an 85 lux) was only getting a 3 mile journey each way so given the opportunity to give it a good blast this evening to fetch supplies was greeted more enthusiastically than usual

On the way back I notice a knocking/clunking from the back end while enthusiastically negotiating a roundabout. The noise is directly proportional to road speed and changing from 2nd to third doesn't alter the speed of the noise. The noise sounds exactly like the noise of a knackered driveshaft on a fwd car on lock but with less rumble. I've had rwd cars before but never had to change driveshafts on them only on fwd cars so don't know what rwd driveshafts sound like when they go. I get no usual sounds while reving the engine in neutral so assume it's not the torque tube. I get play in the drive train if I really come on and off the acc pedal but the noise comes from the back and not from the clutch so I'm discounting the failure of the rubber cush drive in the clutch.

I put the car on ramps (the back) and tried to find play in the driveshafts. With the wheels locked in place (handbrake and they are on the ramps) but with the car in neutral there is no play on the outer joints on the drive shaft on either side as you'd expect and no play on the middle shaft bit so I'm assuming the outer cv joints are ok. If I grab the inner cv joints (the ones nearest the gearbox) I can move them and there is play, the joints move by a good 1-2mm rotationally.

I took the car off the ramps and jacked up each side in turn. Now when I rotate the wheel slowly there is the same amount of rotational play until the inner cv joint starts to rotate.

Does that sound like the inner cv joints to you chaps or are there other tests I can perform to really nail it down?

If it does sound like the driveshafts need replacing what are my options? Can I swap them over for a while or is that a waste of time? How much are new ones? Is it an easy job or are there any good gotchas?

Thanks very much for your time.

Regards,

Mark

>>> Edited by dern on Monday 22 November 22:05

[Thom]

There should not be any rotational play in the CVs, at least there is none on mine. IIRC a single new CV costs £200.
Rear noises can also come from shot dampers, wheel bearings or gear box mount, but the CV seems to be the reason in your case.

[dern]

The shocks are new.

New inner cvs are about 50 quid from berlyn services so if it's those it won't be the end of the world.

Thanks,

Mark