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Hi Folks

i would normally use speedy cables to recalibrate my Speedo since I’ve changed my diff ratio.

but I thought I’d check to see what others do. 
H

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There are two things to change the speed readout, this can be done by playing the magnetism of the spinning magnet, either de-magnetising it a little (slower) or increasing it (faster) I have used a tape head de-magnetiser for this job, & stroking the spinning magnet with a much more powerful one to increase it magnetism.

however to alter the odometer you need to change the gearing which, unless you have access to lots of different gear set is not really somthing the user can do.

When I fitted my saloon gearbox to the TR I found that the speedo drive was a different ratio (3.5:1 where as TR is 2.5:1) I got over this (after lots of research & calculations) by sourcing a 2.5PI Mk2 saloon speedo which had the correct turns per mile for my new setup. even though the speedo was made approx 20 years after the TR one, the innards fitted more or less directly. 

Bob.

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Hi Hamish,

thank you for throwing that ball, a VERY interesting question (for one of my other projects).

Would a "gearbox" inline of the speedo cable not also work.

Two sprockets with teeth A / teeth B as needed and another one between then both to keep the correct spin?

Any idea who makes something like this?

Ciao, Marco

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Marco,

I can see you now, toiling over your gear-cutting lathe and producing a detailed write up with loads of pictures.

The only problem I can see is that the ratio needed will be something that will not translate easily into two sets of gears. For example, if the up (or down) ratio needed to be 3:1 you could produce one gear with 24 teeth and the other with 8 teeth. But if the ratio was 3.375 to one it would need a hell of a lot of teeth on each gear that the size would make the gearbox too big.

 

But I may be wrong.

And the actual ratio will be something more like 0.9512 to 1

I suppose, in Hamish’s case you just need to work out the ratio difference between th two back axles. (I’ll let you do the calculations…)

 

Charlie

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I've used Speedy Cables to refurbish my TR6 speedo and convert the tacho to electronic. They calibrate every speedo they refurb, and will set it for non-standard turns per mile, according to customer's requirement. The speed indicating is re calibrated by adjusting magnetically and believe they can use different gear sets to adjust the odometer. Very happy with their work.

Nigel

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Thanks for the replies everyone. 
 

I think I need to send it off to be done properly. 
I wouldn’t have a clue where to point a magnet in a Speedo.

I have non standard but 15” alloy wheels

non standard tyres 185/70x15 tyres.

a TR6 gearbox with A type od 

and now a 4.1:1 cw&p with LSD.

 

Speedy want this info

https://speedycables.com/speedometer-calibration/

 

So whilst it may take a while (6weeks) it will be right. 
 

just need to push the car down the road to get the info they want.

thanks again  

H

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I have a saloon gearbox plus O/D in my TR3a and a 3.45:1 axle and as luck would have it my speedo is pretty much spot on.  Certainly the odometer is, I have calibrated it on a 50 mile circuit to within 3%.  The speedo is over reading by about 7% at 70mph but for cars in the sixties (let alone the fifties) that was standard.

The rev counter also over reads by about the same amount.

Rgds Ian

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3.5/2.5=1.4    3.45*1.4 = 4.83     not   3.7   so I'm surprised it is that close.

Bob.

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Well I did have the o/d converted to TR spec by ORS so maybe they changed the speedometer drive. 

Certainly before I changed the back axle ratio it over read by much more. 

Rgds Ian

Edited by Ian Vincent
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  • 3 weeks later...

Hamish, if you haven't sorted this yet let me know, I may have a free/easier solution which worked for me. Regards Mike.

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3 hours ago, Mike 5 fan said:

Hamish, if you haven't sorted this yet let me know, I may have a free/easier solution which worked for me. Regards Mike.

Hi Mike

no I haven’t got around to the Speedo recalibration yet.

always interested in cost effective mods.

H

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  • 2 weeks later...

Hello Hamish, firstly you need to get an idea of how accurate the Speedo is now using Google maps or similar and travelling at say a constant 50mph. Best to have someone help you for safety's sake to check your Speedo reading at an actual 50mph. If the reading was 44mph, you remove the Speedo, take off the back and turn the needle to 44mph from the back. Now holding the spindle steady at the rear, gently push the needle to 50mph and hey presto, it's recalibrated. As I say, this worked for me, hope it does for you too. Regards, Mike.

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That will only be accurate at the speed you have chosen. the correct way is to "adjust" the strength of the magnet.

Bob.

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Hello Hamish,

Bob has more technical understanding than I do, so is probably right but I have found that it's pretty close at 30, 50 and 70, so I'm satisfied with my adjustment.

I was adjusting because it was reading under when I replaced low profile tyres with standard size Michelin. I don't know if it will work as well for you having changed the diff.

If, like me you don't have the equipment or knowledge to use the magnet adjustment, and you have time on your hands at the moment, you could try it.

Regards, Mike.

 

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Thanks guys. 
my Speedo was about 10% out with modern tyres and tr6 gearbox but now a long way out with the 4.1:1 diff as well.
I’ll use a sat nav until I get the Speedo done. 
but in this lock down I’ve not taken the car out of the garage so not even rolled it down my v quiet road to get the calculations for speedy cables to re-calibrate the Speedo. 

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1 hour ago, Hamish said:

Thanks guys. 
my Speedo was about 10% out with modern tyres and tr6 gearbox but now a long way out with the 4.1:1 diff as well.
I’ll use a sat nav until I get the Speedo done. 
but in this lock down I’ve not taken the car out of the garage so not even rolled it down my v quiet road to get the calculations for speedy cables to re-calibrate the Speedo. 

You can get the relevant information needed for them in the garage by jacking up the rear (As you have an LSD) and disconnect the speedo and fit a piece of card to the stub end of the cable with a mark on it and then measure the circumference of the tyre and then turn the rear wheels  20 times and count how many times the mark on the card turns.

Stuart.

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Posted (edited)

Hi Stuart 

Does the lsd make the jacking method possible as speedy cables are pretty definite that it’s NOT done by jacking 

https://speedycables.com/speedometer-calibration/

Rolling it down the road is do-able I just need to ask My wife to do the counting of the revolutions

(don’t think it’s fair to get her to push the car !!)

 

Edited by Hamish
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2 minutes ago, Hamish said:

Hi Stuart 

Does the lsd make the jacking method possible as speedy cables are pretty definite that it’s NOT done by jacking 

https://speedycables.com/speedometer-calibration/

Rolling it down the road is do-able I just need to ask My wife to do the counting of the revolutions

(don’t think it’s fair to get her to push the car !!)

 

I see your Speedy Cables method and raise you the JDO one http://www.jdo1.com/speedo_calibration_1.html

As you have an LSD you need both wheels off the ground.

Stuart.

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1 hour ago, stuart said:

I see your Speedy Cables method and raise you the JDO one http://www.jdo1.com/speedo_calibration_1.html

As you have an LSD you need both wheels off the ground.

Stuart.

Looks good Stuart. I didn’t know of them. 
May be able to do the job quicker too 

do you use them ?

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1 hour ago, Hamish said:

Looks good Stuart. I didn’t know of them. 
May be able to do the job quicker too 

do you use them ?

I have used them.

Stuart.

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