28-09-2019, 10:44 AM
Hi Tony, Bob, Chris - Here is the history of the two gearboxes which will answer a lot of the points you have raised.
Converted CR box - This was converted by a well respected A7 engineer about 20 years ago. It has always been noisy but in those days I didn't know any better until someone commented on it at one of the A7 rallies. Apart from being noisy it worked fine and and ran for a coupe of years and several thousand miles without getting any worse. I then rebuilt this box with new 1st, 3rd motion shaft bearings and a new plain inter-shaft bearing from a large A7 parts supplier. I still have one of the boxes the bearings came in and it is marked 6207 NR J. SKF. When I refitted the box it was, disappointingly, exactly the same. I have lived with the problem ever since.
Original close ratio box. This came with a second car I bought about 15 years ago and has sat around the garage until recently when I fitted it to the, finally, restored car. It makes the same noise as the other gearbox. I stripped this box last week and found the following;-
1) First motion shaft bearing is smooth, shows no sign of wear and spins quietly.
2) The gearbox has been fitted with a smooth inter-shaft bearing at some time which appears in good condition.
3) The 3rd motion shaft is gritty and needs replacing but is not turning when the noise occurs.
4) The lay-shaft end float is 20 thou and there is some scoring on the lay shaft but it spins quietly and smoothly by hand.
5) I fitted a temporary shim to remove the lay shaft end float, it might have been slightly quieter but still not right.
6) "the little teeny roller race in the nose next to the clutch release bearing" this seems in good condition and I have run the gearbox without it and there is no difference.
I will try the gearboxes in gear as Ian suggested and see if there is any difference. I will strip the original box again and check more closely for wear to the shafts, one thing I have not looked closely at is the front lay shaft bearing.
Converted CR box - This was converted by a well respected A7 engineer about 20 years ago. It has always been noisy but in those days I didn't know any better until someone commented on it at one of the A7 rallies. Apart from being noisy it worked fine and and ran for a coupe of years and several thousand miles without getting any worse. I then rebuilt this box with new 1st, 3rd motion shaft bearings and a new plain inter-shaft bearing from a large A7 parts supplier. I still have one of the boxes the bearings came in and it is marked 6207 NR J. SKF. When I refitted the box it was, disappointingly, exactly the same. I have lived with the problem ever since.
Original close ratio box. This came with a second car I bought about 15 years ago and has sat around the garage until recently when I fitted it to the, finally, restored car. It makes the same noise as the other gearbox. I stripped this box last week and found the following;-
1) First motion shaft bearing is smooth, shows no sign of wear and spins quietly.
2) The gearbox has been fitted with a smooth inter-shaft bearing at some time which appears in good condition.
3) The 3rd motion shaft is gritty and needs replacing but is not turning when the noise occurs.
4) The lay-shaft end float is 20 thou and there is some scoring on the lay shaft but it spins quietly and smoothly by hand.
5) I fitted a temporary shim to remove the lay shaft end float, it might have been slightly quieter but still not right.
6) "the little teeny roller race in the nose next to the clutch release bearing" this seems in good condition and I have run the gearbox without it and there is no difference.
I will try the gearboxes in gear as Ian suggested and see if there is any difference. I will strip the original box again and check more closely for wear to the shafts, one thing I have not looked closely at is the front lay shaft bearing.