ALFAGTV6.COM

[Bruce]

What is the forth picture down?

[mjr]

can you get your hands on a stroboscope? its basicaly a flashing light, very similar to a timing gun. It is used to spot inbalance in propellor blades. if you can get your hands on one of these little units, simply start the car on stands, get underneath and point the strobe at the propshaft. if the shaft is bowed in any way at all, it will show up instantly, under the strobe light. A good balancing shop , should have one of these anyway, since they should be checking the shaft is not bowed before even considering adding weights.

[Alessandro]

PROBLEM SOLVED

My very first suspicions ended up being correct > it was the Hanger all along!

I kept thinking of the 1970's when the first alfetta's came out > Alfa Romeo couldn't have knocked their head so many times with complex machinery trying to balance the shafts.....

[*] I took the propshaft out again today and decided to grind off all the massive weights (about 1/2 kg in total) the balancing centre had put on.
[*] I replaced the new (and very rigid) hanger bearing with the original (and much softer) hanger bearing.
[*] Started the car first with just the front half of the prop on and only slight vibration at high revs > probably due to tail end not being firmly fixed (hanger only) and bouncing around.
[*] Removed prop, joined back half, and reinstalled.
[*] Started the car and to my greatest surprise > no more vibration!

I went for a drive and the car is very smooth. There is just a very slight vibration felt at about 1500rpm and then it disappears and is smooth all the way up. This is now running with no weights on both propshaft halves. I will try the trial/error hoseclamp trick for balancing when I have a chance to see if it can get even better.

When underneath the car and looking at the prop there is bouncing movement at the centre at idle, but as soon as you accelerate the propshaft tends to straighten up and move slightly upwards at the centre. The new hanger was not allowing it to do this natural movement.

Anyway from my experience I have learn't that in these cars there is lots of movement from both engine and gearbox when accelerating / decelerating / coasting. The propshaft geometry is constantly varying when driving and for it to do this you need to have a soft rubber hanger bearing. If you have a hanger bearing with a stiff rubber this acts as a firm support/pivot at the centre of the prop and causes all sorts of misalignment/vibration issues!

A pity I don't have a shore hardness guage as I would have liked to know the difference between the original and new hanger.

Below are a few pictures of the type of hanger bearing you should avoid at all costs!

[kevin]

Well spotted, who would have thought. Where did you buy these hangers.

[Alessandro]

AK Components. 011 - 708 7240.

Try and give them a call (speak to Kevin) > they might have centre coupling for gtv6 if you are looking for one....

If you are looking for a soft rubber gtv6 hanger bearing I do have an new one which I bought and will not use - I can post this locally (ZA) if anybody needs one.

[kevin]

The centre hanger i just put was from AK and no problems. The centre couplins are not Alfa ones but from BMW which are 5mm bigger thats why I shortened my prop(back end as you cant take it up on spines) . Where did you get the bad hangers from.