Diff n steering wheel questions..

They could mean backlash in the gears or something. Id get it clarified exactly what they mean and how serious the issue is. You might find its one of those minor issues that needs to be monitored but not have any cash thrown at it yet

 

It's a bit difficult to explain backlash to someone who doesn't have a good grasp of what's involved,(and I'm not having a shot at you when I say that). Your driveline comprises a number of components which can create the clunking you described. The transmission, tail-shaft and differential all have parts which are subject to high loads and wear out. The clunking is caused by excessive free movement between two or more parts which should not have that movement. It probably won't be the transmission, but the universal joints and differential are likely culprits.

You can test both yourself.

Jack the rear end of the car clear of the ground. PUT IT ON PROPER STANDS FOR SAFETY.

Crawl under the centre of the car. The tail-shaft on Commodores is a 2 piece unit, with a centre support and bearing. Starting at the front of the tailshaft, grab each side of the universal joint and try to twist the two sections in opposite directions. (You shouldn't be able to get any movement). Then do the same for the centre joint, then the rear joint. Universals in good condition shouldn't have any movement when you attempt to twist them - if there is freeplay there, the joint is probably knackered.

Now, with the handbrake off and the car in neutral, go back to the rear of the tailshaft and rotate it back and forth, about 10 to 15 degrees of rotation. If there is freeplay in the diff, you will feel a slight clunk as you rotate the shaft in each direction. The diff should have a very slight amount of freeplay but if the tailshaft moves freely by much and there is a perceptible clunk, your diff could need adjustment to get the backlash between the crown-wheel and pinion correct. That is a specialised job for a differential specialist. They will be able to diagnose the backlash and tell you if it needs to be fixed or not. You should also check your diff oil level while you're under there. It's at the right level when it just starts to run out when you pull out the rubber bung in the rear plate of the diff. If no oil comes out, put your finger in to check the level. Top it up to the correct level pronto - low oil = stuffed diff = moneyyyyy.

I would imagine the noise you hear is diff lash. Do the tests I have described, then get the problem fixed. You can ignore these things but they are important and will cost more to fix if ignored.

In relation to your steering shudder, it's probably the power steering pump and possibly old oil. Turning the wheels at very low speeds really puts a load on the pump, especially when they are getting old, and they can groan and shudder, which you feel as a vibration through the steering. It could also be old oil. You can drain the power steering and replenish the oil to the correct level. As long as the pump is in reasonable order and the oil is clean, any vibration you feel at slow speeds should not be a major consideration unless it occurs as the speed increases.