Just wondering if any body can offer suggestions as how I can sort my 7's problem. I own a 1930 Austin 7 special has a 4 speed gear box fitted, since I purchased the car I have done quite bit of work on it. The problem is that I my car did not have a speedometer. So I managed to find 1 at a swap meeting, got it repaired. This is a Smiths PN which has weights, well the other day after 5 years after fitting it, thought would check it out only 2 find that it reads slow at first blamed the cable as the joint became detached, repaired it, now I have worked out that the cable is to slow as the speedometer should be a magnet type. So at a 1000 revs in top gear the speedometer reads 5 mph, were it should be around 13mph...Can I change the gear drive in the g/box. Might be able 2 get a step up drive to fit to the cable.

One of the pleasures of driving an A7 Special is trying to remember what the relationship is between indicated speed and actual speed. Mine is easy, 20 = 30, 30 = 40. Or use a satnav. Those flashing 'your speed is' signs are quite useful, or you could try going past the speed camera at ever increasing speeds until it flashes.

Location: The Isle of Wight - the Wight place to drive old cars.

Electronic bicycle speedos work well.

Location: Buxted

Paul,
I fitted a 4 speed synchro box on my RN saloon and found that the Smiths PA speedo was reading slow. It had originally a 3-speed box.I think it was Vince Leek who provided me with a new skew gear for the 4-speed box( the larger one that fits in the speedo take-off on the rear of the gearbox) which was spot on. This is all from memory from 9 years ago. Vince is one of the "Cherished Suppliers" on this website. Not sure what a Smiths PN speedo is.
Dave.

Location: Sheffield

Hi Paul,
Speedos on "bitsa" specials are always a problem; without knowing your diff. ratio and wheel/tyre size it is hard to know what to suggest.
However, the blackfaced PN (graduated 5 to 60mph with 30 mph at 12 o'clock)and PA speedos fitted to the A7s with 3 speed boxes and 4.9:1 diffs. needed 2240 revs per mile of the speedo cable to match their calibration.
The later (2" diameter) speedos as fitted to some Rubys with 4 speed boxes and 5.25:1 diffs. needed 1040 revs per mile to match calibration.
If I were you I would sell on the PN and watch eBay for a 2" dia. MA needle type ruby speedo (see photo) and start from there. If you are using a different final drive ratio or little wheels etc. you may need to recalibrate that but, you will be starting from somewhere much nearer to where you need to be eventually.



Ian Mc.

Location: Shropshire

I had a similar problem: 4 speed box, PA speedo. It was reading approx half true speed.

The weights act against a spring - I changed the spring for a softer one, it took a couple of goes to get it right, but has worked ever since.
Tends to flick up and down over bumps.

It is a fiddly job, but perfectly do-able.

Before you start, though, check the cable connections again. They can look ok but still be fractured - my speedo is currently driven by a tapered cable end jammed in a cone shaped hole in the connector thingy.
It did that itself and I only found out by accident.

S

Location: On a hill in Wiltshire, currently surrounded by water.

PS

Of course, the odometer readings are useless. On my original speedo the numbers were all rusty and I couldn't read them anyway.

My Dad, a bit of a model maker, would have made an intermediate gearbox using nylon gears. If you get the direction of rotation wrong, the speed will be right but the odometer will run backwards

S

Location: On a hill in Wiltshire, currently surrounded by water.

The following article by Ced Verdon originally appeared in the 2004D A7CA Magazine and may be of interest to this topic...

Location: Shropshire

You'd need to speak to Ced about that Ian. He does state that it works well in his article and I see no reason why he would write that if it didn't. An intermediary gear would sort the direction out wouldn't it?

The PA speedometer and odometer mechanisms both work irrespective of direction.

R

Ian McGowan

The gearbox pictured in that article, Ruairidh, patently reverses the direction of rotation of the speedo cable not, I would think, a good idea.
Ian Mc.

Location: Brittany

renaud

Ian McGowan

The gearbox pictured in that article, Ruairidh, patently reverses the direction of rotation of the speedo cable not, I would think, a good idea.
Ian Mc.

Hmmm, I'm sorry Ian n but no, it does'nt!
Renaud

Location: Shropshire

Sorry Ian, Im with Renaud on this one.

One of those gearboxes could be very easily made out of the plethora of aftermarket Meccanno gears. with 3 gears to keep the rotation the proper way.

Am I blind, or is everyone else? two coupled gears, fed from the same end do, by necessity rotate in opposite directions.

Ian Mc.

Location: Shropshire

Yes, but you are looking at one cable from the drive (input) end and the other from the driven (output) end.

R

and all becomes clear!

Thank you Rob

Location: Shropshire

All in all, I retain that idea. Could adapt any gearbox output to any speedo (even a CCW one Ian! )and not too much difficult to make. Nice.
Thanks Ruairidh!
Renaud

Location: Brittany

There used to be a company in London that would modify any speedo for a reasonable cost, if you tell them what turns-per-mile you want.

Location: United Kingdom ooop norf

Thanks for the feed back, now I can ponder over it. The axle ratio is 5.625 with 16' wheels,overall dia with Tyre is 25'. I may look at gearing up the cable speed, as I have invested into speedo quite a bit, had it reconditioned,(as I found it at a swap meet), also cut a hole to fit it in the dash. Perhaps I could as suggested change the spring weight.
Thanks

Paul,20 odd years ago for my pretend Ulster,I bought 2 Ford 10 Speedos and used one for tacho and one for speedo. I did not want to alter the dials so I borrowed a workmates lab. tachometer,found out what reduction ratio/clock/anticlock and obtained Meccano gears from a place called Frizzinghall Models I think.They sold(still sell?) many Meccano parts and they were sending me a newsletter about 5 years after I had bought anything from them.The gearboxes are two sideplates made from 1/8" aluminium sheet with brass bushes pressed in and the whole assembly bolted to the back of the speedo.They both have done many revs over the last 19 years with no problems.

Location: Sheffield

Frizinghall Models & Railways (note, one 'Z' not two) trading as:

http://www.meccanoshop.co.uk/

Jeff.

Location: Almost but not quite the far North East of England

No speedo so bought a smiths motorcycle copy (made in india!) from ebay (£4.99)! tried it against the garmin and found it 50% fast (read 45 when doing 30) so built a reduction gearbox using meccano gears.Now I have checked it reads ok I will put sides on it and give it a "dollop" of grease. phil.

Location: on the settee

As it is a "through" type gear box I used an idler gear (three gears).

Location: on the settee