Speedo gurus... any reccomendation for Sydney?

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Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Harv »

Thanks Neil. I'll try the simple "change the gears" fix first... hoping that will cure it.

Cheers,
Harv
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Blacky
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Blacky »

Google TCI transmissions , they have a great page that you just punch your info into and it will tell you what gears you need 👍
When you're faced with an unpleasant task that you really don't want to do, sometimes you just have to dig deep down inside and somehow find the patience to wait for someone else to do it for you.


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ardiesse
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Re: Speedo gurus... any reccomendation for Sydney?

Post by ardiesse »

Harv,

I'm interested to see how well I remember the guts of a Holden speedo. I think my memory starts to fail at about the "zero adjust" bit. So it's the outer end of the hairspring which attaches to the dogleg arm thing, and probably that's where the taper pin is (holding the outer end of the hairspring in place).

But the fact that your speedo doesn't return to zero means that the shaft which carries the "vivid-arc" (aka needle in a normal speedo) and the eddy-current cup is binding in its pivots. Or the vivid-arc is coming into contact with a stationary part. Or the pivots are flogged out (less likely). Or your speedo has "moving coil meter movement disease" - magnetic particles or fragments of Alnico in the air gap between the pole faces.

See the black slotted screw in your "double-arrow" photo? There are two of them. They allow you to take the pointer shaft/hairspring/eddy current cup off the diecast frame of the movement, leaving the bar magnet exposed. Warning: you'll have to take the vivid-arc off the shaft, and it'll be pretty bloody tight. Craig A's Seagull Grey thread has a speedo teardown and rebuild illustrated in it.

If you move the pointer by hand and let it go, it should return to zero smoothly and sharply, and then bounce off the zero stop like a dropped tennis ball.

If, when the pointer is stuck at a non-zero reading, turn the input shaft with your fingers. if the pointer then drops back to zero, or wants to rotate in the same direction as the input shaft, I'd be inclined to look for foreign particles inside the magnet-plus-cup part. You could also see whether the tendency to bind is orientation-related.

Rob
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Errol62
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Errol62 »

If you don’t get to the bottom of it or want another victim to torture Harv, I can send you a spare speedo. You may already have one, do I recall? I’ve got a couple of spares (read: I’ve been greedily hoarding these things since the eighties).


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Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Harv »

Blacky wrote: Wed Feb 13, 2019 8:54 pmGoogle TCI transmissions , they have a great page that you just punch your info into and it will tell you what gears you need 👍
I tried their site last week (and today), but something is screwy. The home 'puter gives me virus error warnings, and the work 'puter refuses to load their page.
ardiesse wrote: Wed Feb 13, 2019 9:34 pm If, when the pointer is stuck at a non-zero reading, turn the input shaft with your fingers. if the pointer then drops back to zero, or wants to rotate in the same direction as the input shaft, I'd be inclined to look for foreign particles inside the magnet-plus-cup part. You could also see whether the tendency to bind is orientation-related.
I suspect the particles may be the culprit. The vivid arc ,moves relatively smoothly with a drill, and easily by hand. When it sticks, it wants to turn with the input shaft. I'll see how it goes once I'm back home again.
Errol62 wrote: Wed Feb 13, 2019 10:07 pmIf you don’t get to the bottom of it or want another victim to torture Harv, I can send you a spare speedo. You may already have one, do I recall? I’ve got a couple of spares (read: I’ve been greedily hoarding these things since the eighties).
Thanks mate. Yes, I've got one spare speedo. It came off an EK sedan that had hibernated under a tree near Tamworth for several decades. Given that I had "butchered" the wagon speedo by painting it white, I was hesitant to gut another one if I could fix it. I got the spare one down last week, and it runs pretty well off the drill. If the wagon one wont repair, I'll use the spare one and swap the white faces over.

Cheers,
Harv
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Craig Allardyce
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Craig Allardyce »

Andrew from memory too there was a change to the speedo design mounting or the assembly in the head (VDO/AC). Nut or screwed I think. One had some resilient mounts also. I did find that if the speedo cable was not laid correctly behind the dash that it would pull down or sideways on the joint coupling area. This in turn distorted the speedo internally and caused the cup over the magnet to touch in areas. One type was more prone to this hence maybe the change. Point would be to make sure the speedo cable isn't tight or putting any stress on the speedo head in its mounting. As Rob indicates, fragments on ya magnets! That's what I've usually found.
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Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Harv »

I left the speedo guts soaking in WD40 for two weeks. Got back home again, and spun the guts up with a length of busted speedo cable. No change - speedo still doesn't want to return to zero, and quite wobbly in operation. I figured it probably needs the internals pulled apart and the speed cup/rotating magnet cleaned of any debris.

I looked at the intricate guts of the speedo, and then at my fat, greasy fingers. I then wussed out.

I swapped the guts of my spare speedo into the fancy repainted gauge faces. The spare speedo internals look a lot cleaner than the other one, though the externals were filthy (country car). The speedo now returns to zero. There also seems to be more resistance in the spinning, but perhaps that is just my imagination. Got it back together and back in the car, but have not road tested it yet.

Interestingly, the old gutted speedo is sitting on the bench with no small plate/chrome trim (with odometer slot) that mounts to the guts. Without the plate/trim, the guts return to zero nicely (with the little "bounce off the stop" that Rob mentioned). Perhaps when I removed/painted/refitted the plate/trim 6 months ago I peined over the little ally tabs poorly, and put the speed cup under tension. For now the gutted speedo has been packed up out of harms way. Something to play with once I get the wagon on the road.

Next step: get home again, road test the new speedo, and buy some new TH350 gears.

Cheers,
Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Blacky »

Ringwood cant repaint the numbers in the original colour :esad:
When you're faced with an unpleasant task that you really don't want to do, sometimes you just have to dig deep down inside and somehow find the patience to wait for someone else to do it for you.


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BILLY BLACKARROW
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Re: Speedo gurus... any reccomendation for Sydney?

Post by BILLY BLACKARROW »

Harv
Iam going to have the same trouble with my speedo Harv when you do all the ground work it will give me something to go wrong by, I think we have to know roll dia & diff ratio anything eles ? could you let me know your diff ratio / roll dia & where you get the gearbox gears & what gearborx ratio
Thanks Billy
BILLY BLACKARROW
MY Father always said do the hard part first --because when you are OVER IT you only have the easy part left to do THINGS I HAVE TRIED TO LIVE BY
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Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Harv »

BILLY BLACKARROW wrote: Thu Mar 14, 2019 1:22 pm Harv
Iam going to have the same trouble with my speedo Harv when you do all the ground work it will give me something to go wrong by, I think we have to know roll dia & diff ratio anything eles ? could you let me know your diff ratio / roll dia & where you get the gearbox gears & what gearborx ratio
Thanks Billy
In theory, you can use this website:
http://www.tciauto.com/tc/speedometer-gear-calculator

It needs your tyre info from the sidewall (eg. 205/65/15), and will then calculate the rolling diameter for you (in that case, it calculates 25.49" diameter). You then plug that diameter into the calculator above.

It also wants diff ratio - for my VP Conformadore LSD, it's 3.08 (i.e. 3.08:1). Standard grey is 3.89.

It then wants the number of speedo drive gear teeth. This is the ring-shaped gear that lives inside the box on the main output shaft. In my case, I have an orange drive gear, which is 8 teeth. I worked that out by popping out the driven gear (it just bolts into the box), and peering through the resultant hole with a torch. I then googled the teeth colours... they change with different box types.

So when I plug 25.49", 3.08 and 8 teeth into the calculator, it tells me I need a driven gear with 19.475993602317654 teeth. For my TH350 box, that means I need either a 19-tooth gear (natural colour) or 20-tooth (blue colour). At the moment I have a 22-tooth (grey coloured) driven gear).

This is where it got funky for me. The calculator says I need to make my speedo read faster... my road-test showed the speedo was already reading too fast. This is where I learnt that my speedo guts were probably crook.

Rocket Industries is not too far away from my place, and they stock the speedo gears for a number of gearboxes.

Cheers,
Harv
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BILLY BLACKARROW
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Re: Speedo gurus... any reccomendation for Sydney?

Post by BILLY BLACKARROW »

Thanks Harv
That is just what I needed :smile22: :smile22:
BILLY BLACKARROW
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Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Harv »

Techo geek question for today. It is keeping me awake at night. I have tried putting my tinfoil hat on, but it is not helping.

The speedo works by spinnng a magnet inside the speed cup. The spinning magnet is like a generator, and makes current in the speed cup. The current has nowhere to go, and "eddies" around (it is often referred to as eddy current). The eddy current makes the speed cup want to turn, moving the speedo needle with it. A hairspring stops the speed cup spinning. As the car goes faster, the magnet spins faster. The eddy current increases, making the speed cup have more force. The hairspring extends more, letting the needle show a faster speed.

If the speed cup construction or magnet strength changed, I'd imagine that the eddy current would change - this should affect speedo reading. If the hairspring was stiffer, this would also affect speedo reading. There are lots and lots of speedo manufacturers, making waaaaaay different components. I would have thought that would mean that each speedo showed a different reading for a given cable speed.

But.... using the TCI website above, you enter only wheel size, diff ratio and drive gear. This gives you a driven gear, and hence a cable speed. This infers that for a given cable speed, every speedo in the world reads the same.

How can every speedo in the world do this, given the internals can change so much (eg stiffer hairsprings)? Is there some universal standard that every speedo manufacturer uses (e.g. 5rpm = 60 mph), and has since speedos were first invented?

Cheers,
Harv the Curious
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ardiesse
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Re: Speedo gurus... any reccomendation for Sydney?

Post by ardiesse »

Harv,

Speedometers are calibrated individually by the manufacturer, because, yes, variations in components. But a work colleague told me that all speedos read the same road speed for the same cable rpm, which is probably 1000 rpm for 60 mph indicated, thus 1000 revs/mile for odometers.

Rob
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Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Harv »

Its incredible that until lately we cannot seem to standardise anything in this world (batteries, globes, bolts etc), except speedos. Pretty cool though.

Cheers,
Harv
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Re: Speedo gurus... any reccomendation for Sydney?

Post by Craig Allardyce »

Harv wrote: Mon Mar 18, 2019 8:41 am Techo geek question for today. It is keeping me awake at night. I have tried putting my tinfoil hat on, but it is not helping.

The speedo works by spinnng a magnet inside the speed cup. The spinning magnet is like a generator, and makes current in the speed cup. The current has nowhere to go, and "eddies" around (it is often referred to as eddy current). The eddy current makes the speed cup want to turn, moving the speedo needle with it. A hairspring stops the speed cup spinning. As the car goes faster, the magnet spins faster. The eddy current increases, making the speed cup have more force. The hairspring extends more, letting the needle show a faster speed.

If the speed cup construction or magnet strength changed, I'd imagine that the eddy current would change - this should affect speedo reading. If the hairspring was stiffer, this would also affect speedo reading. There are lots and lots of speedo manufacturers, making waaaaaay different components. I would have thought that would mean that each speedo showed a different reading for a given cable speed.

But.... using the TCI website above, you enter only wheel size, diff ratio and drive gear. This gives you a driven gear, and hence a cable speed. This infers that for a given cable speed, every speedo in the world reads the same.

How can every speedo in the world do this, given the internals can change so much (eg stiffer hairsprings)? Is there some universal standard that every speedo manufacturer uses (e.g. 5rpm = 60 mph), and has since speedos were first invented?

Cheers,
Harv the Curious
Not sure your over doing it Harv. I think its only the magnetic attraction of the cup to the spinning magnet that causes the rotation.
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