Speedometer gearbox rotates with rear wheel

I recently replaced my speedometer gerabox and it rotates about 30 degrees with the wheel. The cable is tied to the swingarm so when it rotates it pulls the cable sheath out of the fitting and the cable out of the gearbox. The spring on the cable holds it together. The old gearbox stayed in place fine.

[ATTACH=full]88557[/ATTACH] [url=ht...otos/52577093@N03/9350660917/]Rear axel parts by niagaraz, on Flickr[/url]

I appear to missing Part#34 so maybe it is too loose? I saw it referred to as a top hat a thread search but the speedo gearbox has a top hat fitted into where the axel goes thru. Is it an ordinary washer or a top hat and how thick should it be? I have a washer that fits the axel but it is to thick to fit between the spacer (4) and the gearbox. I don't want to crush the gearbox.. I'm off to the hardware store to see if I can find a thin washer.

Any suggestions?

Thanks in advance

Yep sir been there done that and got the T-shirt with photo of cable wrapped around the axle till tire locked up, on pasture thankgoodness. Part 34 is what we both were missing and didn't know it till later. Its a top hat shape spacer not just the rim washer part. Its not something you can make up easy as pretty darn thin metal barrel so vendors can help you. Of course once refitted the jerked on speedo drive itself may dissolve and lock up to wheel to roll your own cable mess again. Commando's gotta love em or leave em.

I had the same thing happen when I changed the speedometer drive on my MK3. Turned out one of the spacers was stuck in the old speedometer drive and I didn't notice it.

Bill G

Part 34 crushes when you tighten your wheel down and is not supposed to. It is a bad design. It also literally welds itself into your old speedo box so it looks like it is not there. You have to drill them out.

It is there so you don't crush your speedo box when you tighten your wheel. That is why some Nortons have scores on their rims from the speedos rubbing. The speedo box should be able to rotate a bit when installed correctly. The speedo cable prevents from rotating too much. Buy a new part 34 and keep an extra on hand. They are not expensive.

Been my experience that the speedo box gets pushed towards the cover plate for some reason not explained to me yet. The top hat spacer helps, but the gearbox metal is real weak around that area and lets outer part of the box push up against the cover plate on the hub. If you can install a new top hat spacer and also push out the gearbox away from the hub cover plate it will help immensely. The object is to get the gearbox not to rub on any rotating part of the wheel. Only contact should be with the dogs in the gearbox and the drive on the wheel.

Be careful you don't ruin the gearbox by beating on it. Try pushing out the center of the gearbox with a plastic pipe or similar. Don't whack on it with a maul.

My gearbox is away from the cover plate about 1/4".

Later 850's are on the other side and completely different from what I understand.

Dave
69S

DogT said:

Be careful you don't ruin the gearbox by beating on it. Try pushing out the center of the gearbox with a plastic pipe or similar. Don't whack on it with a maul.

Dave
69S

Click to expand...

I believe I fell foul of that very action. My gearbox was rubbing on the cover, tried a new top hat washer, no better. Tried to ease the foul by slightly dishing the centre of the gearbox. I was actually very cautious, used a vice, rubber jaws, and an appropriately sized socket to push the centre of the gearbox until it did not foul. However even though the adjustment was slight, the gearbox has a "rough spot" as you rotate the gear by hand. Haven't run the bike yet, but I expect it will not be good news.........

Commandos come with a number of expected consumables, Amal slides and speedo drives have similar replacement cycles as front tire. One should never believe the odometer on any Commando. My Trixie speedo has lasted over 10K miles and still not loose inside nor dragging after being removed from Peel use a few 1000 miles but the cable broke like 2500 miles ago, ugh. So did the tach cable so just winging it by ear and wind and traffic flow sense. There are upgraded anodized slides now but nothing so far but DIY rivets on the speedo drive. Don't over tighten the RH axle eh.

Thanks for the insight, I'll order an # 34 up. The hardware store search came up fruitless, the washers were all too thick. Hardware stores don't carry the variety of stuff like they used to, casualty of the Home Depot / Lowes era I guess.

It is an odd design and have always wondered why the speedo wasn't run off the front wheel, maybe it had something to do with the front brake or 6 ft of cable is better than 3... I can judge speed by the tach and surrounding traffic but like to use the odometer to gauge fill up time. I picked up a Garmin Edge 200 bicycle computer which works well , flips between mph and kph with the push of a button and gives me a trip odometer. I have a Veglia speedo on the shelf with a trip odometer with a damaged ring but otherwise working, rebuild will happen some day.

Old Bloke said:

DogT said:

Be careful you don't ruin the gearbox by beating on it. Try pushing out the center of the gearbox with a plastic pipe or similar. Don't whack on it with a maul.

Dave
69S

Click to expand...

I believe I fell foul of that very action. My gearbox was rubbing on the cover, tried a new top hat washer, no better. Tried to ease the foul by slightly dishing the centre of the gearbox. I was actually very cautious, used a vice, rubber jaws, and an appropriately sized socket to push the centre of the gearbox until it did not foul. However even though the adjustment was slight, the gearbox has a "rough spot" as you rotate the gear by hand. Haven't run the bike yet, but I expect it will not be good news.........

Click to expand...

Mine just did the same thing. I noticed a rough ring on the cover tin where the gearbox had rubbed before (P.O.) and it did so with a vengence after assembling with the proper torque. The gearbox looked to be slightly dished outward, so I popped out #34 with an appropiately-sized socket, layed the gearbox face-down on the anvil, nestled the ball end of a 20 oz ball-peen hammer in the center hole, and gave it a light rap with a brass mallet. Yes the gearbox body is soft! :mrgreen: Now, I have about a 1/8' gap between the box and cover tin.

Gidday mate. . Someone wrote "The speedo box should be able to rotate a bit when installed correctly. The speedo cable prevents from rotating too much.".I cannot stress enoughTHIS IS WRONG, NOT TRUE. DONT TAKE MY WORD, get a second opinion IF THE CABLE SHOULD STOP THE SPEEDO DRIVE BOX FROM TURNING. the driving worm wheel inside the box rotates and drives the worm, , NOT THE BOX ITSELF. the cable should not be under stress.

I have been through this and offer the following. I will try to be clear. the top hat is a spacer and radial locater as well. the hole in the drive box is the same dia as the small outside diameter of the top hat and locates the drive box radially as well as being a spacer. the wall thickness of the ORIGINAL box is about 1/16th". the flange of the top hat is also 1/16th", giving total of 1/8th. The replacement box (not Smiths) already has a steel spacer (to stop the soft alloy from crushing) of about 1/8th" . add 1/16th to this and you have a length of 3/16th. this may have no effect or make the total length of axle assembly 1/16" too long. there may be some washers on the sproket side about 30 thou thick. if total distance is too much remove these washers as needed. otherwise shorten the spacer that goes up against the box by 60 thou if totall assembly is too long.

Do not attempt to bend a new box to get a good fit. If it has bent outwards the cause must be found and eliminated. when all is correct, the box itself should clamp tightly and not rotate. if the tophat is missing, the box cannot locate radially, and the lost clearence between worm wheel and worm may cause interference instead and lock the worm to the box. thus turning of the worm wheel will now try and turn the box itself and not the worm only. Any rubbing on the hub cover plate is caused by felt seal holder being too wide or not fitted properly.. if ya gotta bash something belt that a bit thinner.

The wheelhub drives the worm wheel. the worm wheel drives the worm. The worm drives the inner cable. NO torque should be transmitted to the box itself and the cable should not be under tension.This is how it should be.
Arguments to the contrary and corrections welcomed Bradley
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For my simple mind, but like Bradley says, the top hat bushing is tightened down with the axle and thus should be as stable or like a part of the swing arm/axle. The dogs on the worm gear engage the rotating 'hub bearing lock ring'. The cable is not involved except to transfer the rotation to the speedo.

Now why the inner face of the gearbox gets pushed up against the cover plate, that's a complete mystery to me, but it happened to mine and others seem to have it happen also. I wish someone could answer that one.

My speedo gearbox was so out of kilter, the riveted on plate inside the gearbox disappeared. I didn't replace it, it didn't seem to matter, just stiffens up the gearbox there as far as I know.

When riding the prototypes, we had a basic mismatch in the speedometer system. The hub units were 1600 revs/mile, like the Atlas, but the speedos were 1000 revs/mile. The indicated speed was 1.6x actual! Man, those things were quick! We just used to work off tacho readings - "Really, officer, there's a design problem back at the factory, I thought I was doing 50."