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Author Topic: C12 Gearbox  (Read 261 times)

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Offline AdminPete

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C12 Gearbox
« on: December 06, 2008, 05:44:42 PM »
From: PeteRudge1  (Original Message) Sent: 27/07/2008 10:41
I'm finding it hard to engage 4th gear on my C12 gearbox. If I keep trying it will eventualy go in, but by then I've lost enough pace to drop back to 3rd. Any suggestions what I should be looking for when I strip it down?

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From: BSAC12ver Sent: 27/07/2008 17:12
Hi Pete,

I think you will soon spot the problem, it will either be the selector plate burred up in the slot at 4th gear position or a worn cog or something.
Its a fairly simple gearbox ( in fact its very neat) and any problem will soon show itself on inspection.

I have my spare gearbox in parts so if you need a photo or anything I will take pictures if required.


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From: PeteRudge1 Sent: 02/08/2008 16:43
Thanks Richard. I've just put the gearbox back together for about the forth time and now it's even worse. I couldn't see anything wrong with it. I tried leaving out the thrust washer (78 plate 4) and put the covers back with just a couple of screw, and I could select all gears when spinning the wheel, but when I put it back I could only get 1st. Could the problem be something to do with end float? With the inner cover on, I can select all gears by moving the selector (40 plate 4) , so could the problem be with the selector mechanism? I'm really running out of ideas now. Are there any service sheets with more details about trouble shooting and setting up for the light gearbox?
Any suggestions would be greatly appreciated.

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From: camman3 Sent: 02/08/2008 17:55
Hi Pete,
I have emailed you four pages I have on four speed lightweight gearbox.
I have never stripped mine, on a, "as it aint broke, dont fix it" basis, so dont know of anything peculiar to look for.
I hope the service sheets help.

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From: BSAC12ver Sent: 02/08/2008 17:56
Hi Pete,It seems a bit odd that its ok when you select the gears, yet when you put it back together only getting first?

I would not think it was end float unless someone has had the box out before and took shims out or something?
Its not something daft like too much wear on the bush of the gearbox cover where the shaft comes out for the gear lever canting it to an angle and making it jam or something?
If you lift the back wheel off the ground, can you select the gears then?

If you want, your welcome to try bits of my spare stripped out gearbox in yours if you can make the effort to come to Basingstoke to pick it up, if it gets it going then thats great and you can keep the bits

Meantime I will have a play with my stripped out gearbox and see if I can see a potential problem area selecting the gears.



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From: PeteRudge1 Sent: 02/08/2008 18:11
Thanks Graham and Richard. I'm on a run tomorrow so won't be striping the box again til Monday. The run is from Breamore House, 10 ish for an 11 o'clock start if anyone is interested in coming.
Cheers for now,

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From: BSAC12ver Sent: 02/08/2008 19:24

Took a little look at my gearbox and if as you say everything looks ok then............

It might be knackered bearings that the shafts go into, I think the shafts need to be perfectly parallel at all times.
Although it changed ok by hand, under load you may find it pulls the chain cog to one side due to a knackered bearing.

I think you should also put the washer back



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From: PeteRudge1 Sent: 04/08/2008 10:47
 I don't know if I should be posting this here or on the "Own Up" hall of shame page............I timed the gearbox wrong. I didn't realise how close the dots have to line up. Now everything is fine. At least running it on the stand. I'll take it for a test run later today to see if the original 4th gear problem is cured. Thanks for all your help lads.

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From: camman3 Sent: 20/08/2008 14:21
Hey Pete,
You all sorted now?
Is the Rudge/C12 on the road and run in yet?
You've been quiete lately, must be out there enjoying this glorious summer!

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From: PeteRudge1 Sent: 20/08/2008 17:48
Sorry I've been quiet. I always find the time to read all the messages on here but don't often get time to contribute. The gearbox is sorted, as are the oil leaks and valve gear rattles. I took it for a run on Sunday, had 4 gears, no oil leaks and quiet valve gear. I'm confident to take it for a proper run now, when the weather allows. I still need to find the right size carb, but the one I'm using isn't too bad.
Sorry I missed the Popham meet on Sunday, looks like you all had a dry day even with Owen being there. Lets hope he brings the sun to the 2nd Summer Run!