Speedo accuracy.

[DUF2 ‘65 Elf]

I have a 1965 Riley Elf with a 1275 engine and DAM 5626 gearbox from a 1989 Metro. The car is running 165/60r12 tyres
I have the original (maybe) central speedo with 1376 tpm.
I have no idea on the speedo gear. I suspect it may be DAM 2905 green 16 tooth
I need to change the speedo cable and may change the gear whilst in there (if this can be done with the engine in situ!)
Does anyone know which should the correct gear be to make the existing speedo as accurate as possible?

[Smiffy]

http://www.guess-works.com/Tech/ratio.htm

[1071 S]

Just being pedantic; you don’t need gears etc to get the speedo calibrated correctly... Its an adjustment available in the speedo head itself.

However, you will need gears to correct the

Cheers, Ian

[1071 S]

Just being pedantic; you don’t need gears etc to get the speedo calibrated correctly... Its an adjustment available in the speedo head itself.

However, you will need gears to correct the odo..

Cheers, Ian

[1071 S]

Duplicate post ... can it be deleted completely?

[timmy201]

I swapped the gears in my gearbox, but I had the radiator out at the same time as you'll need to access the gear under the engine mount bracket.

There's a couple of photos here of the process
https://mk1-forum.net/viewtopic.php?p=277817#p277817

[surfblue63]

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[Spider]

Just being pedantic; you don’t need gears etc to get the speedo calibrated correctly... Its an adjustment available in the speedo head itself.

However, you will need gears to correct the

Cheers, Ian

Some small adjustment is available in the head but only to calibrate the speedo.

You still need to change gears to get the Odometer correct, there's no way around that.

[timmy201]

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You can only delete your own post when it’s the newest post in the thread (I assume so you can’t change the post history after others have posted). Of course an admin can delete anything they feel necessary

[indigo]

You still need to change gears to get the Odometer correct, there's no way around that.

I found there is some adjustment in the head for the odometer.
The gear on the end of the odometer cluster can be changed but you need to scrounge second hand parts. I changed this to calibrate for a 3.44 diff fitted with my Mini Deluxe speedo.
The smaller red gear can also be changed. This appears to change the cluster from MPH to KPH but needs to be done as a pair.

ClusterGear.jpg

Red Gear.jpg

[Spider]

You still need to change gears to get the Odometer correct, there's no way around that.

I found there is some adjustment in the head for the odometer.
The gear on the end of the odometer cluster can be changed but you need to scrounge second hand parts. I changed this to calibrate for a 3.44 diff fitted with my Mini Deluxe speedo.
The smaller red gear can also be changed. This appears to change the cluster from MPH to KPH but needs to be done as a pair.

ClusterGear.jpg

Red Gear.jpg

Hey Indie !

Yes, you are correct and perhaps I should have been a more clear in what I wrote. I did say ',,, change gears,,,'. I should have added 'either in the speedo drive and / or the speedo head'.

All the same, we are changing gears !

There is a Screw Adjuster in the Speedo Head that is used for Calibrating the Speedo itself.

The way I've always gone about it is to do the necessary adjustments to get the Odometer correct and that should put the Speedo in the ball park. Then adjust the Speedo head to bring it in to calibration.

[indigo]

Yes, you are correct and perhaps I should have been a more clear in what I wrote. I did say ',,, change gears,,,'. I should have added 'either in the speedo drive and / or the speedo head'.

Thanks Spider, All makes sense now.

[DUF2 ‘65 Elf]

Spider, where is the adjustment screw?
My car is under reading, so I would like to be able to adjust it

[Peter Laidler]

When you say 'under reading....' what is under reading? The odometer or the speed meter? I used to work in an instrument calibration bay where we rebuilt these things and other instruments and gauges

A mechanical odometer can only be corrected by changing the gearing. And even then, it is only a '.....closest to' . And that fact had to be recorded on the certificate of accuracy
The speedo part, so far as we were concerned, could be corrected to take up certain smallish errors by............ I'm repeating myself here so I won't waste anyones time

[Spider]

Spider, where is the adjustment screw?
My car is under reading, so I would like to be able to adjust it

As Peter alluded to, the first thing to 'adjust' and correct is the Odometer. You need to get that reading correctly. That's done by changing the speedo drive gears, though, if you are good with fine work and can source the gears, those on the speedo head can also be changed.

This is necessary to do first as the Odometer is direct coupled driven from the gearbox. The Speedo though is a different kettle of fish, it has a magnetic coupling, but is made such that to be in the ball park to hold linearity with the Odometer at all speeds.

If you take the needle and face off the speedo, there's a small thin bar with a screw to one side of the spindle, that's the adjustment screw.

However, as I stressed above, the Odometer has to be done first. If you just go in and adjust the screw, then the speedo will only be accurate at what ever speed you used as a reference speed, it will still be out at other speeds.

[DUF2 ‘65 Elf]

Spider, my original post gives the details of my car.
I do not know for certain what the gears are in the speedo drive in the gear box, the car came with whatever configuration it is when I bought it.
I realise the gearbox is non standard, I’m guessing it is the original speedo, but who can say after 57 years!
I have only just got my car running on the road after a long drawn out rebuild. On Saturday I went for a short drive and checked the speedo against TomTom on a phone, at 43mph on the phone the speedo was reading 38/9 mph so it is approximately 10% out. Since the rebuild the car has only been driven around 10 miles. Other work needs to be done before the car is finished, I was just looking for a quick and easy way to correct the error, but it looks like it is going to be a real pain to sort.
I understand what you say about the odometer, but I will need to find a measured mile to check this, even then how accurate will a test over 1 mile be? ie start with 0 tenths, after 1 mile, the odometer could be reading 9, or changing from 9-0, 0 would be nice to see, but it could even be changing from 0-1
What would you suggest as the correct Speedo gears for this application?

[surfblue63]

If you are not worried about originality, I think the best way to sort you speedo accuracy would be to get a central speedo from a 1970s Mini with a TPM of 1280.

[timmy201]

There’s a very easy way to work out the speedo gears, and it was in the first reply

Go to this website:
http://www.guess-works.com/Tech/ratio.htm

Enter your tyre size, diff ratio and speedo TPM and it’ll tell you what speed drive gears you need

That’s the easy part. Normally once you have the right gears it’ll be close enough to not need any further adjusting for the odometer

As to calibration of the odometer, you might be lucky enough to find an odometer check zone near you (not sure if they do them in the UK). I have one on the way home from work!

[Ronnie]

Emergency phones on motorway's are 1 mile apart

[Spider]

Spider, my original post gives the details of my car.
I do not know for certain what the gears are in the speedo drive in the gear box, the car came with whatever configuration it is when I bought it.
I realise the gearbox is non standard, I’m guessing it is the original speedo, but who can say after 57 years!
I have only just got my car running on the road after a long drawn out rebuild. On Saturday I went for a short drive and checked the speedo against TomTom on a phone, at 43mph on the phone the speedo was reading 38/9 mph so it is approximately 10% out. Since the rebuild the car has only been driven around 10 miles. Other work needs to be done before the car is finished, I was just looking for a quick and easy way to correct the error, but it looks like it is going to be a real pain to sort.
I understand what you say about the odometer, but I will need to find a measured mile to check this, even then how accurate will a test over 1 mile be? ie start with 0 tenths, after 1 mile, the odometer could be reading 9, or changing from 9-0, 0 would be nice to see, but it could even be changing from 0-1
What would you suggest as the correct Speedo gears for this application?

I have read and re-read your opening post mate, but there's not enough info there to suggest any changes, anything would be a guess at best.

The longer the distance you do the Odo check over, the better the result will be, really, 1 mile isn't nearly enough, I'd say 5 as a minimum and preferably 10.