There's a specific procedure, for fitting the prop-shaft, which requires the use of some special alignment tools. I think this is designed to give the correct angle between each prop-shaft section. The alignment is achieved through slotted holes and packing washers.
Unfortunately Alfa don't tell you what the alignment values are
. My father had a Jaguar XJ6 and the manual gave specific dimensions for prop-shaft alignment so that our own special tool could be made
The prop-shaft should be set up so that UJs have to work at an an angle. This angle will be sufficient to allow the bearings in the UJ to rotate. If adjacent sections of prop-shaft are aligned so that they are co-axial then the UJ bearings would not rotate. This condition would lead to the UJ failing through high bearing pressure on the same points of the UJ bearing needles and cups.
Thank you O.E. and Ken,
I appreciate your comments and the detail. I hope you won't put your heads in your hands when I tell you how I progressed this - I have to say with considerable trepidation.
I have to have a new near side rear trailing arm; with the shot hydraulic bush, replaced. So until I get this and the rear mounting bushes, I will be going no further.
Ken, your comments reference the need to ensure rotation of the UJ's to minimize the risk of failure are a great reminder of how much goes into what is essentially a rotating tube. And an appropriate comment being Alfa have not had a rear wheel drive car for years, so clearly the expertise is there in the company.
On this basis, I make the broad assumption this issue was addressed in production and given my car has 102,00 miles on the clock and the Prop is sound, I will put that issue to one side for the moment. O.E. is bang on about the exhaust acting as a microphone/pick-up for any low frequencies generated by the run-out of a miss-aligned prop shaft and this has been born out in the procedure I adopted.
Yesterday morning was miserably wet and windy, not the kind of day to work on the car, let alone venturing into unknown territory. But however, this is how I approached the problem.
1), rear wheels on the pavement.
2), Undid the four bolts on the Differential, Front Bush Mounting Bracket.
3), Degree of loosening, just enough to anable me to move the plate/bracket to which the front bush is mounted.
4), Knowing the prop shaft would attempt to rotate around it natural axis, I went for a drive down a long, flat, straight road; Not too fast.
5), Gently got as far as third gear, ignoring the thunk's.
6), Dipped the clutch and came to a halt in a straight line.
7), Stopped the car, handbrake on and switched engine off
8), Got back under the car and retightened the bolts.
9), Went for another drive and bingo, V8 TVR drone reduced. Quite clear now however, there is an exhaust resonance at 2500 RPM. But above and below that, resonance falls off.
10), Clunk/low thud on pulling away and changing to second can be provoked, but making a conscious effort to engage the clutch smoothly, it can be avoided.
I do believe there is a problem with the two rear mounting bushes and Paul thinks they may be "Rose - Joints". Difficult to say as they are obscured by rear suspension components. Could make out a square/four-sided nut on the inside; facing the drive shafts, very similar to the kind one used to get with one's "Mechano" and he thinks this is typical of some rose joint construction. I can't comment on that. However, until I have the near side arm and the bushes in my hand, this is as far as I go.
It is very difficult to be objective, as one can attribute improvements where hitherto there was no problems. However, first and second gear, particularly when cold, would baulk on selection. The gears would not grate, more the cones were a offering resistance, if you know what I mean. Not now, it would appear!! Or is it my imagination? Must re-check today, but we were out in her last night and when leaving friends after several hours, engaging 1st and second gear, did not draw my attention. Could a miss-aligned prop shaft cause "Stiction" with the selectors?
I had been getting a little depressed over the negativity that surrounds this car. It's frustration when people can't see the big picture and one can no-longer talk in engineering "Short-Hand" and have to resort to the "Once Upon a time" approach. I continue to find it amazing that the second most expensive item people buy, after their house, is largely a mystery to them and make no effort to understand their workings. I sometimes think they are the kind of people who would most likely visit a "Witch Doctor" for a cure.
So when the bush was replaced, "Black - Dog" set in and I was beginning to question my wisdom, or otherwise! That I chose adopt the procedure I did rather than wait till Paul could have another look seems bizarre. However, having spent many years abroad on proto-type systems that did not work, I suppose it was inevitable I would choose to do something like this. Still, I would be interested to know, although de-coupled from the gearbox, if indeed there could be some relationship with prop - shaft miss alignment? Given, it is always difficult to select first in a rolling car situation, because of the effective "Turns-Ratio", I'm extremely curious. Or is it just my imagination, given I wanted a degree of success to lift me?