G80 Speedo Gearbox

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G80 Speedo Gearbox

Postby thornebt » Mon Jul 09, 2018 2:57 pm

My speedo gearbox failed today - fell apart. I've had some problems with it before. The stepped chrome spacer outside the gearbox (021591) appears to have wear and burrs on both ends. I've tried uploading a photo but without success. Anyway it now measures about 0.825" in length and I'm fairly sure it's shorter than it used to be! Possibly not helping is that the cutouts in the adjusting ring are misshapen - not the nice square shape they should be.


I will need a new speedo gearbox. Can anyone please tell me:

- if the Indian made speedo gearboxes on Ebay work OK? They are closer to £10 instead of the 'proper' ones at more like £45.

- if my stepped spacer is best replaced - I'm not sure what the correct length of it should be or if that is critical. I could just file off the burrs.

- if it's worth me getting an engineer to sharpen up the square cutouts in the adjusting ring or maybe even cut two new ones at 90 degrees to the existing ones.


Cheers. Bruce.

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Re: G80 Speedo Gearbox

Postby Mick D » Mon Jul 09, 2018 3:26 pm

Hi

The critical parts are 021591, 021608 and the speedo gearbox body, if these don't 'clamp up' when the wheel spindle is tightened you will have problems.

Some damage to the bearing adjuster slots will be OK, (there should be little load on them if all is working correctly), however if you're going to strip it apart I'd replace it, or as you suggest, cut another pair of drive slots.

Can't comment on pattern gearboxes but it would be helpful to know how yours has failed.

Regards Mick

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Re: G80 Speedo Gearbox

Postby thornebt » Mon Jul 09, 2018 7:50 pm

Thanks Mick. The failure of my speedo gearbox took the form of the speedo locking nut staying in place but a fracture all the way round the gearbox which left a small margin under the locknut and the remainder of the casing dangling on the spindle with the internal gear wheel fallen out! Maybe the gearbox just came apart as it is only pressed together and it had been apart before.

I think I will probably square up the leading faces of the bearing adjuster slots using a hacksaw and Dremel. If I don't have much luck with that I'll see if I can get an engineering shop to cut two new slots. I've removed the burr from both ends of the stepped spacer but I can't see why these burrs formed as this spacer shouldn't move. The burr was preventing the locking nut from sliding on easily as it was fouling the nut threads. I also had a burr on the edge of the bearing adjuster around the slots which I've now removed. This is due to me using a hammer and screwdriver on the slots in the past. I know I shouldn't have done this and that it shouldn't need much force to adjust the bearings!

I might order a pattern speedo gearbox but I'll wait to see if anyone on here has had any experience of how good they are.

Cheers. Bruce.

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