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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1116
Registered: 5-2012
Posted on Thursday, 24 March, 2016 - 03:31 am:   Edit PostDelete PostView Post/Check IP

Hi Folks

I have just replaced the speedo cable (gearbox to cruise control regulator) as the old one was frayed. I was hoping this would cure a fault in which the speedometer needle would jump around accompanied by an annoying clicking sound.

With the new cable the problem is much better but not solved. At any speed above 20 mph there is a clearly audible click-click every three seconds. The speedometer needle drops 5mph and then immediately returns - click click. At above 60 mph the clicking is less obtrusive.

It is the type of sound that would occur if a tooth was missing from a gearwheel somewhere. I have checked the cruise control regulator and the gearwheels are ok and nicely re-greased. So the fault must be either in the speedometer gauge or in the drive in the gearbox.

Since I'm not a great fan of rolling around in the dirt and oil on the garage floor, with two tons of car just above my head, I've decided to check the speedometer gauge next.

My question is whether the speedo gauge can be easily dismantled or is this a specialist job? Has anyone tried to do this before? Given the symptoms I have described, is there anything else I should check first before destroying my speedo gauge?

Geoff
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1486
Registered: 6-2006
Posted on Thursday, 24 March, 2016 - 03:38 am:   Edit PostDelete PostView Post/Check IP

Hi Geoff,

Have you greased the upper cable as well?

The speedo comes apart quite easily . It's tricky to drive and hold it and listen though, so being on a ramp is best for testing.

If not, jacking the rear up onto stands and running it in gear will do.

Don't be tempted to just jack it up.

Paul.
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Omar M. Shams
Grand Master
Username: omar

Post Number: 555
Registered: 4-2009
Posted on Thursday, 24 March, 2016 - 03:44 am:   Edit PostDelete PostView Post/Check IP

Dear Geoff,
Try holding the trip meter reset button and when you hear the clicks see if you can also feel it with your finger.
I have had exactly the same symptoms in the past on my Wraith IIs and both times it was the plastic gear that drives the trip meter inside the speedo.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1117
Registered: 5-2012
Posted on Thursday, 24 March, 2016 - 04:11 am:   Edit PostDelete PostView Post/Check IP

Paul and Omar

Thanks for the advice.

I have visually checked and greased the upper cable with the special cable grease. It rotates freely. When I fitted the lower cable I was able to turn it from the gearbox end, with little resistance, before fitting it to the gearbox drive.

It's good news that the speedo gauge comes apart quite easily. This will definitely be my next job. It is interesting that Omar had the same symptoms. I will carry out the trip meter test later today.

Geoff
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Vladimir Ivanovich Kirillov
Grand Master
Username: soviet

Post Number: 439
Registered: 2-2013
Posted on Thursday, 24 March, 2016 - 04:23 am:   Edit PostDelete PostView Post/Check IP

Geoff I suspect it is something inside the speedo. Also, you did grease all of the speedo drive inner cable didn't you?

Attempting to pull apart the speedo and repair it yourself is something only a lunatic like myself would try. The easier and less painful path is to send it to an instrument specialist.

Another problem may be that you only replaced the inner cable and that previously the frayed inner cable had damaged the outer cable inside as well and now the outer cable is going to work maiming your new inner cable.

Omars suggestion sounds on the money too.
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Omar M. Shams
Grand Master
Username: omar

Post Number: 556
Registered: 4-2009
Posted on Thursday, 24 March, 2016 - 04:53 am:   Edit PostDelete PostView Post/Check IP

Dear Geoff,
look at one of the older threads from 2011 headed Odometer - Silver Spirit. meanwhile here is a photo of the gear that i had to replace on my speedo.

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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1118
Registered: 5-2012
Posted on Thursday, 24 March, 2016 - 05:09 am:   Edit PostDelete PostView Post/Check IP

Hi Vladimir

I agree it is almost certainly the speedo gauge.

I was very careful about greasing the upper cable and am happy with it.

As you said, the lower outer cable was frayed as well as the inner. It was catching as the inner rotated, which is why I thought it may be solely the cause of the fault. I have fitted a brand new outer and inner lower cable from Flying Spares.

As for attempting to pull apart the speedo, I am definitely on the lunatic end of the spectrum.

I have this crazy notion that when I try Omar's test the fault will magically go away. Maybe a small speck of grit will become dislodged and everything will work again. Of course, we all know that is not going to happen.

Geoff
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1119
Registered: 5-2012
Posted on Thursday, 24 March, 2016 - 05:14 am:   Edit PostDelete PostView Post/Check IP

Hi Omar

Thanks for that, but my speedo is the earlier mechanical type. I should have made this clear. The test you mention is still valid. The trip reset is operated by a short cable and it hadn't occurred to me to try resetting it and feeling for any tell tale signs of the fault.

Geoff
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1487
Registered: 6-2006
Posted on Thursday, 24 March, 2016 - 05:14 am:   Edit PostDelete PostView Post/Check IP

Omar is quite right for the later type speedos (Shadow II on) but the earlier cable driven speedos are slightly different.

Hopefully you'll find something obvious.

Good luck with her.
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Jean-christophe Jost
Yet to post message
Username: jc_jost

Post Number: 1
Registered: 3-2016
Posted on Thursday, 24 March, 2016 - 06:25 am:   Edit PostDelete PostView Post/Check IP

I've solved a clicking noise (but with no needle issue) yesterday by just greasing both cables ends and also the two slots. .

I took a picture of the rear end of the speedo and I am curious about what are the two screws with blue washers (picture) ?

PS I'm new on this forum and truly happy to join. Hope you'll pardon my English.

speedometer rear side wiew
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1488
Registered: 6-2006
Posted on Thursday, 24 March, 2016 - 06:35 am:   Edit PostDelete PostView Post/Check IP

Great picture and timing J-C. And welcome :-)

The screws hold the mechanism and the washers damp any noise.

Turn the bezel around the glass so the slots line up and remove the bezel and glass.

Put it face down on some soft sponge.

Undo the two screws with the sound insulating washers on and the mechanism will come out of the front.

Do not try and take the needle or the face off.

You will find a round magnet that spins around with the cable and a spring loaded magnet that's connected to the needle. There may be some rust or debris between them.

There is also the gears that drive the mileometer and trip counter.

Have fun :-)
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Vladimir Ivanovich Kirillov
Grand Master
Username: soviet

Post Number: 441
Registered: 2-2013
Posted on Thursday, 24 March, 2016 - 06:46 am:   Edit PostDelete PostView Post/Check IP

Jean-Christophe - welcome to the forum - your English is fine but your Russian is bad.

I hazard a guess that those two screws hold the permanent magnet to the frame but I say that as a guess only.

Then again it could be a sinister English trap which you discover after you loosen the two screws off and find its a feral pig to get back together so don't loosen those screws until you are total certain what is going to happen.

My brother in Russian Federation says Russian people love French people. I asked him why and he said "Napoleon". I am still puzzled.
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Jean-christophe Jost
New User
Username: jc_jost

Post Number: 2
Registered: 3-2016
Posted on Thursday, 24 March, 2016 - 09:56 pm:   Edit PostDelete PostView Post/Check IP

Thank you very much for the welcome messages and the answers about these two screws.

Off-thread from here :
To answer Vladimir (which also happens to my second first name don't ask why) there is indeed an interesting question for historians about Napoleon's reputation in continental Europe, still today. He could carry liberty with him (as Goethe saw him first) but he definately was a butcher.

Best regards!
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1120
Registered: 5-2012
Posted on Friday, 25 March, 2016 - 06:10 am:   Edit PostDelete PostView Post/Check IP

Hi Folks

Welcome to the forum Jean-christophe.

I removed the speedo and have taken a look inside. As Paul said, it's just a case of turning the bezel until the slots line up and pulling off the front glass. Then undo the two screws shown in Jean-christophe's picture and the speedo mechanism just pulls out.

I have included a picture below to give an idea of what a mechanical speedo looks like, in the nude.

I have found the fault, but correcting it will be another matter. On turning the cable I found there was a stiff spot every so often. On close inspection it corresponded to one full rotation of a nylon gear wheel that is driven by a worm gear on the cable input shaft. This gear wheel is cracked and the adjoining cog is worn down. The lower picture attempts to show this, but the resolution at the 640-480 pixel setting may not show it clearly.

So, I need to replace this gear wheel. I cannot think of any way of repairing it. I could remove the gearwheel and lose the odometer (which may be illegal) but at least I would have a non-ticking speedo and there would be no stress on the cable (as the worm gear forces itself over the broken cog).

There is a speedo for sale on ebay for $115, however I do not like buying second hand parts as they may well develop, or even have, the same fault.

I think I will do some searches of the web to see if anywhere sells these gearwheels.

speedo1

speedo2

Thanks for all the help.

Geoff
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Omar M. Shams
Grand Master
Username: omar

Post Number: 558
Registered: 4-2009
Posted on Friday, 25 March, 2016 - 06:21 am:   Edit PostDelete PostView Post/Check IP

Dear Geoff,
Your problem is exactly the same as the one I encountered. Even though the speedos are different, essentially it is the same gear that has gone.
Your job is easier than mine was - yours is just one gear not two.
I have a collection of little plastic gears that I once bought from a video repair shop many many years ago. They are all new. If i have a gear that is the same as the one you want - I will gladly pop it in the post to you. In return I would want you to put one Dollar towards making a disabled person happier.
let me have the sizes and i will look into my box of gears.
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Jim Walters
Frequent User
Username: jim_walters

Post Number: 71
Registered: 1-2014
Posted on Friday, 25 March, 2016 - 07:02 am:   Edit PostDelete PostView Post/Check IP

Omar, that gear is integral with the shaft and has an eccentric pin on the end to drive the odometer.

Geoff, I'll have one but I won't have the chance to dig it out until later today. Email me your address and I'll drop it in the mail. Jim.

SRC18015 SRE22493 NAC-05370
www.bristolmotors.com
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 903
Registered: 5-2015
Posted on Friday, 25 March, 2016 - 10:41 am:   Edit PostDelete PostView Post/Check IP

If one has a lathe.

This gear car be made. By first turning and then indexing using another gear with the same number of teeth as an index.

The index gear is placed behind the gear being made in the chuck. A blade is used in the teeth of the index gear to hold position.

With out turning on the lathe work the saddle to and fro so a tool in the tool post gradually cuts a tooth shaped slot. The tool is the shape of the tooth and is called a form tool. When turning the tool is generating a shape not forming.

Once tooth is cut unlock lathe headstock turn chuck by hand to next tooth.

Splines can be done like this as well.

Also because only a couple of teeth are missing the broken cog could be used as a index gear with care full re alignment when the gaps come up.

The back lash is probably not a problem so the gear could have a "generous" clearance to make life easy.

Also model shops have gears like this and you may be lucky.

Maybe it's a generic Smiths speedo part and available from speedo repair guys.
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Bob Reynolds
Grand Master
Username: bobreynolds

Post Number: 369
Registered: 8-2012
Posted on Friday, 25 March, 2016 - 10:55 am:   Edit PostDelete PostView Post/Check IP

This is an obvious job for a 3D printer.

You can get programs that 'construct' gear wheels. Just put in the diameter, PCD, No.of teeth, etc. and print it out.

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