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My continuing woes with a 5 inch speedo - now 10 cables gone - help????????

BlackLightning998

Well Known and Active Forum Website User
VOC Member
:mad:

Afternoon all.

Well, I had an absolute ball at the Manx Grand Prix - 35 minutes and 28 seconds does not seem fast for a Parade Lap I guess, but it sure felt it for me! I have the entire lap on high definition head cam fixed to my helmet and so will be uploading that in two sections to You Tube when I get the necessary skills sorted.

Having completed 800 miles to and fro the French Rally faultlessly for my speedo I was pretty hacked off to snap speedo cable number 8 just 2 days into the Manx GP whilst out on track at Jurby. I found that the vertical gear in PR32 (the one with the slot in the top that the spade drops into) had dropped down the gearbox and the spade was only just touching/engaging - so I drove it further up and fitted the split pin that had been missing for some long time (like all of my ownership since 2007). Then, in less than 12 miles of light duty (0-40 mph) it snapped again. Then one more time within 4 miles. So, all in all now, 10 cables - all in exactly the same spot, the lower end of the cable where it is squared and drops into the spade connector.

The 5 inch clock has been back to David Woods at least twice and been all checked out.
The right angle gearbox at the head end has been regeared.
The PR32 wheel drive shafts are sloppy and worn, but the gears seem to engage.
The spade connector does not run true when you raise the front wheel off the ground and leave just the spade in the drive and spin the front wheel, it runs very out of true.

Having spoken today to David Woods at Netley he recommended that the spade must be made to run true and trying an original spade might help as the thickness of the spade section is materially thicker than the reproductions being used. I have an original so have popped one in and it is still running quite out of true, and the thicker original spade is a sloppy fit in the slot on top of the vertical gear shaft.

So............3 questions:

1 - Do you agree with my analysis so far that likely cause is:
1.1 An intermittent seize fault somewhere in the Speedo head or right angle drive (not likely as the tension required to snap the cable would likely do some damage in the speedo)?
or
1.2 The spade running out of true and causing a friction fracture of the cable at it's weak point where the round is made into square?

2 - If 1.2 is rightThen has anyone got any bright ideas on how I could have the PR32 overhauled and repaired? A new one appears to be listed at £200 PLUS 20% VAT - no thanks!!!!! Can anyone recommend someone to me to do the work?

3 - Has anyone got a spare PR32 I could try?I wonder if anyone has a spare PR32 that I could borrow to try and run on my bike to see if this solves the problem - a little challenging as the 800 miles of faultless run to and fro the Loire Valley suggests it is an intermittent fault. BUT substitution is the best route perhaps to nail down the problem.

Regards

:mad:
 

BlackLightning998

Well Known and Active Forum Website User
VOC Member
Not really Bill.

Moving it around the garage perhaps.

All have broken at exactly the same place, the lower end of the cable, where the round wire of the cable is compressed into a square section for fitting into the spade - just at the junction of the round to square section.

I have used at least 5 outers, and had them re-innered all by JnJ cables.

Regards
 

Hugo Myatt

Well Known and Active Forum Website User
VOC Member
Hi Stuart,

My early Shadow speedo (second version) did this on pushing the bike backwards. As I recall it took 17 turns of the wheel and then the cable would cease turning. It always broke at the lower end, i.e. brake plate end. I believe this always happens when the problem is at the other end of the cable. If the gears in the speedo head gearbox (or the housing) are worn they try to climb up each other and jam solid against the end plates. This only happens in reverse. I had the speedo head gearbox rebuilt by Speedograph Richfield. They modified it in some way and fitted new gears. That was some years ago and to date no further breakages.

Hugo
 

BlackLightning998

Well Known and Active Forum Website User
VOC Member
Hi Stuart,

My early Shadow speedo (second version) did this on pushing the bike backwards. As I recall it took 17 turns of the wheel and then the cable would cease turning. It always broke at the lower end, i.e. brake plate end. I believe this always happens when the problem is at the other end of the cable. If the gears in the speedo head gearbox (or the housing) are worn they try to climb up each other and jam solid against the end plates. This only happens in reverse. I had the speedo head gearbox rebuilt by Speedograph Richfield. They modified it in some way and fitted new gears. That was some years ago and to date no further breakages.

Hugo

Hi Hugo,
Thanks for that and good to see you both again today - another year and another Series D meet with no rain during the event. I have heard of the "going backwards" problem, on this occasion though I think it is not my problem, I rode the bike on the Isle of Man quite happily, no problems (and I had ridden it 800 miles in France to without effect) and then we loaded it into a van, unloaded it (yes pushing backwards out of the van and down the ramp) and then it snapped out on track at Jurby. Then I fitted a new one, and on the way to Glen Maye it snapped at circa 12 miles (with no pushing backwards) and then a new cable again and it snapped 4 miles later (again no going in reverse).
I stripped the right angle gearbox last night and found four or five small shards of metal in the grease, so there is always the possibility of these getting themselves in the mesh of the gears I guess, they look shiny and mangled under a magnifying glass.
I must admit I am a bit stumped - but I do think there is something intermittently sticking or seizing up at the top end and holding the cable fixed sufficient for the front wheel to continue to rotate and twist the cable and snap it.
I will lift the front wheel off the ground and run it backwards and do your 17 turns and see what happens though just to check that and either confirm or dismiss it. Thanks for the advice.
It is one of those things, the intermittent type problem is a pain, I had several cables brake and then had 1500 or more miles fine, then 3 cables in quick succession.
Ohh well - I will persevere.
Many thanks for your interest, and advice.
Cheers
 

Hugo Myatt

Well Known and Active Forum Website User
VOC Member
I think I've just had a senior moment. I now think it was 17 turns of the cable in the reverse direction not 17 turns of the wheel that locked up the cable. Apologies to any nervous types carrying their bike bike backwards after 17 backward turns of the wheel.

Hugo
 

nobby

Well Known and Active Forum Website User
VOC Member
For the third time now I refitted and checked the gearbox and the cable, front wheel from the floor, spinning, and yes the speedometer works...
But as soon I am outside and ride away, the thing does not work anymore. Thanks to Hugo I maybe found the cause! I have a very little workspace at the end of a store. When I get the Vincent out, I have to ride it backwards for about 16 meters. I have no possibilities to turn the bike in the shop or put it there backwards. So next time, probably this week, I will do the refitting outside and see what happens.
 

Stretch

New Forum Website User
VOC Member
ROGER STRETCH

Stewart, what about running the cable disconnected from the head ?.

Then disconnected from the angle drive.

You may have already done this, but process of elimination.

Good luck, Stretch.
 

Hugo Myatt

Well Known and Active Forum Website User
VOC Member
For the third time now I refitted and checked the gearbox and the cable, front wheel from the floor, spinning, and yes the speedometer works...
But as soon I am outside and ride away, the thing does not work anymore. Thanks to Hugo I maybe found the cause! I have a very little workspace at the end of a store. When I get the Vincent out, I have to ride it backwards for about 16 meters. I have no possibilities to turn the bike in the shop or put it there backwards. So next time, probably this week, I will do the refitting outside and see what happens.

Hi Cornelis and Nobby,

I have the same problem. My garage is down a steep slope with no possibility of turning round at the bottom so I have to wheel the bike backwards 20 meters or so. The cable does not always break at the time. It gets wound up like a spring and can break later. I have just sent the following to Stuart in a PM but I'm sure he won't mind my putting it on the forum. Pardon the lack of technical vocabulary.

'I’ve been thinking about the speedo head gearbox. I may have misled you as memory is possibly playing up. It may have been 17 turns of the cable rather than 17 turns of the wheel in the reverse direction. I have just dug out the old gears, which were returned to me by Speedograph Richfield. This is what I have discovered and now I begin to remember what they said.

First this is the gearbox that has a protruding worm gear for insertion in the speedo. Let’s call this the speedo gear and call the other into which the cable is inserted the cable gear. Both are supposed to have a minute (3/32”?) ball bearing between the gear end and the end plate to take up end thrust. The speedo gear always has one but it seems that sometimes on the cable gear it is missing. Whether it was omitted during manufacture or lost at a later date is unknown but is found to be common with these gearboxes.

Now the helical pinion on the speedo gear has a nicely machined chamfer on the ball bearing end however the cable gear pinion was not originally chamfered and was machined straight across. In practice this means that when the cable is turned in reverse the cable pinion tends to ride up the speedo pinion towards the endplate. Should the ball be missing, or if there is even a minute amount of wear in the pinions or housing, it allows the pinion to tilt slightly so that the sharp corners of the helical teeth dig into the end plate and the gear jambs. This can be witnessed by scuff marks on the end plate. Another way to check if this is happening is to compare both helical gears. The cable gear may at first sight appear to have a slight chamfer but compared with the properly machined chamfer on the speedo gear it becomes apparent that this blunting of the edges of the helical teeth on the cable gear is due to wear as it is forced against the end plate.

As I said Speedograph Richfield returned the gearbox with new gears saying they had modified it. In retrospect I think they must have machined a proper chamfer on the cable gear.'

Hugo
 
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