+- Austinsevenfriends (https://www.austinsevenfriends.co.uk/forum)
+-- Forum: Austin Seven Friends Forum (https://www.austinsevenfriends.co.uk/forum/forumdisplay.php?fid=1)
+--- Forum: Forum chat... (https://www.austinsevenfriends.co.uk/forum/forumdisplay.php?fid=14)
+--- Thread: Noisy gearboxes (/showthread.php?tid=3351)
Noisy gearboxes - daveg - 27-09-2019
I have got a couple of gearboxes that I think have the same problem - they are both noisy, particularly noticeable when the engine is idling and the gearbox in neutral. The noise disappears if the clutch is pressed. Both gearboxes are 4 speed 2 syn with Nippy close ratio gears, one original and the other modified to close ratio.
The gearboxes have shown the same symptoms on two different engines so I don't think the problem is engine or flywheel related. The only things turning in the gearbox when in neutral are the first motion shaft and the lay-shaft. The first motion shaft and inter-shaft bearings are both in good condition so I am thinking it must be related to the lay-shaft.
I have measured the lay-shaft end float on one box as 20 thou which is a lot more than recommended but the lay-shaft bearings look in reasonable condition. Could the end float be the cause of the noise or is there something else that I should be looking at?
I have an MPEG 4 audio file of the noise - does anyone know if it is possible to upload it here?
RE: Noisy gearboxes - Chris KC - 27-09-2019
I think the starting point Dave has to be 'what sort of noise?' - I've never tried an MPEG but lots of people upload short videos - same way you upload photos I suppose.
RE: Noisy gearboxes - daveg - 27-09-2019
Hi Chris - it was good to meet you on Tony Betts stall at Beaulieu. I can't upload a video like a picture so will try a link to it on youtube:-
https://youtu.be/x-vH0WuwhAA
The noise can be heard between approx 6 and 14 secs when the clutch pedal is released
RE: Noisy gearboxes - Mike Costigan - 27-09-2019
Could be the clutch thrust bearing ...
RE: Noisy gearboxes - Ian Williams - 27-09-2019
If the noise is when the clutch is released, the first motion shaft and lay shaft will be spinning so It is likely that the constant mesh gears are producing the noise. This could be as a result of worn bearings causing them not to mesh correctly or badly cut/worn gears, seems strange that both boxes are making exactly the same noise though.
When you drive the car and the gears are loaded what is the noise then like through the gears, is it less or worse in top than the lower gears?
RE: Noisy gearboxes - daveg - 27-09-2019
Thanks for the ideas:-
Mike - I am fairly confident it is not the clutch thrust bearing as it not spinning when the noise occurs - I have checked on both gearboxes that it is not moving when you can hear the noise.
Ian - when driving the engine noise drowns out the gearbox noise so I can't be sure if it is better or worse under load.
Modified to close ratio gearbox - it is possible the after market gears were badly cut but I don't think wear is the problem as it has always been noisy. I replaced the 1st, 3rd motion and inter shaft bearings on this box and it made no difference. This box is in a car so I could check if the noise is better or worse in different gears by jacking up the rear axle.
Original close ratio gearbox - this is connected to an engine on a test bed. The 1st motion shaft and inter shaft bearings are smooth and shows no sign of wear. The gears do not seem worn to me but I am not an expert. I could try this box in different gears but not under load.
RE: Noisy gearboxes - Tony Betts - 28-09-2019
Hi dave.
We're the gearboxes used in the car after you replaced the bearings.
Or were the boxs left after fitting for a period of time.
And what manufacture were the bearings.
It seams strange both have the same noise, so it's unlikely orig and new gears have the same problem.
Tony
RE: Noisy gearboxes - Bob Culver - 28-09-2019
A lot of parts are whirring around.
The usual suspect is the 1st/3rd shaft bearing. The spigot is often spalled and the bore ridged but you have checked that, and may have a plain bearing anyway.
It is rare for helical gears to "wear" except after obvious spalling usually at colossal mileage or due faulty manufacture, not an Austin feature.... Even then not noisy running free dipping into oil. Gears with no backlash might be noisy but that would not apply to the Nippy ones. Have encountered noisy helical gears on other makes due mixed manufacturers, but not at idle.
Sevens do have that extra 1st shaft roller but usually seem OK.
RE: Noisy gearboxes - Chris KC - 28-09-2019
Hello Dave :O) Yes I recall, sorry, I didn't connect you at first.
The fact that you have the same thing going on with two different boxes does my head in a bit. Is there a connection? For example have they both recently been rebuilt by the same person?
Am I correct in understanding one is an original Nippy gearbox? i.e. not a gearbox which has had Nippy ratios installed?
Is the intershaft bearing a needle roller or plain bronze bush? The needle rollers do wear badly and the indentations on the shaft may not be obvious, plain bushes work well and ride on the high spots.
How about the little teeny roller race in the nose next to the clutch release bearing (or 'throwout' for the benefit of our colonial chums)?
I've heard that fitting CR gears can shrink the intershaft bearing bore, which may need honing back to size, could that be the issue? (makes more sense for the CR conversion, not sure about the Nippy box if original).
On the topic of gearbox end float it is a good idea to address it before it gets excessive as bad things can happen.
RE: Noisy gearboxes - daveg - 28-09-2019
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.