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14-09-2020, 06:12 PM
(This post was last modified: 14-09-2020, 06:35 PM by DavidL.)
When I built mine 30 years back I picked up a nice Ruby speedometer with a needle, looks the part, works a treat.
My godson is getting close to having his on the road, perhaps with my engine and box (and speedometer) but ideally with his mag engine and three speed box.
Q1 - is there a way to use my speedometer (or same type) with his three speed box?
They appear from time to time at what looks to be sensible money, but do they always need a rebuild and what sort of money should we expect for that?
Q2 - if not, is there a gearbox that connects to his engine and that type of speedometer?
Q3 - any other ideas for a "we're not building an Ulster rep, just having fun with a special" speedometer?
We'd really like to be able to look the MOT man in the eye and at least think we comply with "construction and use". A bicycle trip computer is an idea but not very period, a phone app is sort of an option, and I've fitted one of the dash cubbies with a duel USB so can keep it powered but don't really want to have it clipped up on the dash the whole time. I've seen some "self contained" GPS speedometers in kitcar catalogues, and perhaps an evening on photoshop would have one refaced?
I've several Reliant Robin speedometers that could be sacrificed to the cause...I refaced a very similar (goes in the same hole) Triumph rev counter for mine "back in the day" and another thread mentioned bespoke cables and gearboxes...
Just remembered that a "speedometer" has two purposes - first to avoid a speeding ticket, second to count the miles for the insurance company.
Joined: May 2018 Posts: 2,107 Threads: 110
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Location: Llandrindod Wells
Car type: 29 Special, 30 RK, 28 C Cab
Hi David
Three speed box generally had a Smiths PA mechanical governor speedo rated at 2240 revs per mile. If you can find one of these that are correctly rated for the three speed box it is not difficult to clean the mechanism and replace the ball bearings (although you need good eyesight as the 30 ball bearings are just 1/16” diameter). I paid about £100 for mine some time ago.
However if the rear axle ratio is not 4.89 to 1 then the only way of using it is to use a correction box (several companies make these although they are not too difficult to make if you have the right tools). Mike Flannery of Magnetic speedometer repairs does repairs to governor speedos but tells me that he is not able to recalibrate the PA.
The other alternative is to buy a new “reproduction” speedo. Willie Mackenzie sells both electronic and mechanical ones I think? You can also find cheap ones on eBay manufactured in India. I have a cheap Indian rev counter that seems to work albeit 2x too fast (that might be down to me assuming a 2x take off from the drive on the bottom of the distributor?)
I’m sure others will add their experience which is probably better than mine.
Good luck
Howard
Joined: Aug 2017 Posts: 782 Threads: 26
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Location: On a hill in Wiltshire
It would be nice to use a period PA, but they are usually horribly expensive.
Other versions, often with an angled drive (not the vertical one the PA has) are usually cheaper.
The PA can be fudged to work at non original revs by changing the spring that controls the movement of the governor weights - the add-on gearbox is a much better way, but I never got round to that on my special, and the home made spring is still in there.
Maybe a simpler way, to get you going, is to fit (say) a Ruby needle type, which are usually cheap and working, and swap the face for(a home made) one with digits in the right place if you need to.
Or, if its a rough one, move the face around until it is correct at 30mph.
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Royal Enfield speedos are about £20. Speedy cables can make up cables to order.
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Interesting to know a governor type can be fiddled with.
Ruby needle type is what I have and 100pct acceptable for his car, and they're a few about, but the concerns are drive and calibration from a 3 speed box, and what "a bargain one" might take and/cost to get working. Am also intrigued by the REALLY cheap motorbike units...
Joined: Aug 2017 Posts: 782 Threads: 26
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Location: On a hill in Wiltshire
It should be easy to cobble a drive, and see how wrong the speedo reading is.
Simple for my car, the speedo is above the end of the box (four speed, with the end casting inverted), so the cable is straight up and down and maybe 18" long, if that.
For the inner cable: one end soldered and filed square, and a brass or copper tube soldered on the other, then hammered over the appropriate square shape to form the female end.
The outer (as far as I can remember) wasn't attached to anything at the gearbox end, and spirals of stiff copper wire fixed the other end to the back of the speedo.
Which worked until I could save up and buy a "proper" replacement. Which still looks horribly new.
You could use little bits of sticky label on the glass of the face to re-calibrate, until you have worked out a final solution.
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15-09-2020, 11:47 AM
(This post was last modified: 15-09-2020, 11:48 AM by Michael D.)
when considering using a speedo being cable driven from the 'box you'd not only need to have the 'right' final diff ratio to go with that box and speedo-drive; you'd also need to fit the right (i.e. 'correct') size of wheels + tyres. Personally I'd advice against all sorts of contraptions that need to be fixed by silly wires as that's all not very dependable... working out re-calibration also requires some skills to reface the dial... and I do not suppose your godson actually aspires driving something that would make him the laughing stock at the first event he enters even though it's 'his' special and he is doing things 'his way' regardless of what other people think... So try to get a (the) speedo that can be driven from the box and fit the correct diff and types ... why make life more difficult and spend money on a 'solution' that is actually not a solution but more hassle ?
Joined: Aug 2017 Posts: 3,391 Threads: 106
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Location: Darkest Bedfordshire
An accurate speedo is a praiseworthy aim but I'm guessing many among us simply do a mental correlation!
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Location: Near Cambridge, UK
Car type: 1928 tourer (mag type), short chassis Gould Ulster
Assuming the special has a registration from an earlyish A7 it will be pre 1936. It was only in 1936 that speedos, brake lights and possibly other items became construction and use requirements. As far as I know there is no retrospective enforcement for early cars. There is the principle that 'if fitted must work'. Presenting a pre 1936 registered car for MOT without a speedometer should not create a problem. Unfortunately there are still plenty of testers who do not know all the details, so sometimes you have to ask to see chapter and verse. They can be surprised to discover their ignorance of the details.
