850 T gearbox return spring

[JFerg]

I recently bought an 850T FB. This was imported from the USA to Australia about 9 years ago. I first saw it 6 or so years ago, when it showed 8,000 miles. Every indication is that this was genuine at the time. At the time it also had what appeared to be a Heath-Robinson arrangement of external springs to return the gear lever, a clear indication that the hairpin spring inside had broken.

Now mine, the bike shows 14,000 miles, and I am happy this is genuine. Prior to recommissioning it, in the process of sorting, I thought I'd fix the gearbox properly.

Once on the bench, there were two surprises. Firstly, the external return spring arrangement is far from Heath-Robinson; it's a bronze casting stamped "Patent Pending" and "31". Plainly it originally had two leaf springs, one for "up " and the other for "down", but the "up" spring had broken and been replaced roughly with a coil spring.

Inside the 'box there is no hairpin spring, broken or otherwise, and the eccentric spring tension adjusting screw was just a bolt filling the hole.

Pictures below, hopefully. Does anyone recognise this, or know exactly what it is?

 

[john zibell]

I had put one of those on an 850T that I owned in the 70s because the internal spring had failed. I think I fellow names Woods made them. For replacement springs, 4 each 0.025 inch feeler gauge pieces work well to replace the original. Use two up and two down. Or since the geabox is on the bench you can go back to original with the improved spring (two coils instead of one so it doesn't fail) and a new eccentric. Adjusting the eccentric can be a bit time consuming, but it isn't rocket science. Also this is a good time to properly shim the shift drum no matter which route you take. Since you are in Australia, Pete Roper is well versed on these 5 speeds if you want to get it to him. PM me for his e-mail address or check with fellow Aussies for his contact information.

 

[JFerg]

Thanks, John.

I've now acquired the proper bits and will fit them, but will keep the Woods external return spring as a workshop ornament.

I know Pete Roper quite well, and there's no way I'd reassemble a gearbox without shimming as per his instructions. He'd torment me forever if I didn't!

cheers,
JFerg