Hamish Posted April 15, 2020 Report Share Posted April 15, 2020 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 Quote Link to post Share on other sites
Lebro Posted April 15, 2020 Report Share Posted April 15, 2020 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. Quote Link to post Share on other sites
Z320 Posted April 15, 2020 Report Share Posted April 15, 2020 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 Quote Link to post Share on other sites
RobH Posted April 15, 2020 Report Share Posted April 15, 2020 (edited) Speedo correction gearboxes are available from Speedograph Richfield, Marco: http://www.speedograph-richfield.com/html/minature_gearbox.html Edited April 15, 2020 by RobH Quote Link to post Share on other sites
Charlie D Posted April 15, 2020 Report Share Posted April 15, 2020 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 Quote Link to post Share on other sites
Nigel Triumph Posted April 15, 2020 Report Share Posted April 15, 2020 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 Quote Link to post Share on other sites
Hamish Posted April 15, 2020 Author Report Share Posted April 15, 2020 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 Quote Link to post Share on other sites
Ian Vincent Posted April 15, 2020 Report Share Posted April 15, 2020 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 Quote Link to post Share on other sites
Lebro Posted April 15, 2020 Report Share Posted April 15, 2020 3.5/2.5=1.4 3.45*1.4 = 4.83 not 3.7 so I'm surprised it is that close. Bob. Quote Link to post Share on other sites
Ian Vincent Posted April 15, 2020 Report Share Posted April 15, 2020 (edited) 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 April 15, 2020 by Ian Vincent Quote Link to post Share on other sites
Z320 Posted April 15, 2020 Report Share Posted April 15, 2020 7 hours ago, RobH said: Speedo correction gearboxes are available from Speedograph Richfield, Marco: http://www.speedograph-richfield.com/html/minature_gearbox.html Hi Rob, thanks for that, this is what I need! Have to check what I need and will contact him. Ciao, Marco Quote Link to post Share on other sites
Z320 Posted April 16, 2020 Report Share Posted April 16, 2020 Tho' (after sleeping a night over it)..... Quote Link to post Share on other sites
GT6M Posted April 17, 2020 Report Share Posted April 17, 2020 Errrr wots wrong with a different drive coming oot the gearbox. or am i missing some thing Quote Link to post Share on other sites
Mike 5 fan Posted May 5, 2020 Report Share Posted May 5, 2020 Hamish, if you haven't sorted this yet let me know, I may have a free/easier solution which worked for me. Regards Mike. Quote Link to post Share on other sites
Hamish Posted May 5, 2020 Author Report Share Posted May 5, 2020 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 Quote Link to post Share on other sites
Mike 5 fan Posted May 14, 2020 Report Share Posted May 14, 2020 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. Quote Link to post Share on other sites
Lebro Posted May 14, 2020 Report Share Posted May 14, 2020 That will only be accurate at the speed you have chosen. the correct way is to "adjust" the strength of the magnet. Bob. Quote Link to post Share on other sites
Mike 5 fan Posted May 15, 2020 Report Share Posted May 15, 2020 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. Quote Link to post Share on other sites
Hamish Posted May 15, 2020 Author Report Share Posted May 15, 2020 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. Quote Link to post Share on other sites
stuart Posted May 15, 2020 Report Share Posted May 15, 2020 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. Quote Link to post Share on other sites
Hamish Posted May 15, 2020 Author Report Share Posted May 15, 2020 (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 May 15, 2020 by Hamish Quote Link to post Share on other sites
stuart Posted May 15, 2020 Report Share Posted May 15, 2020 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. Quote Link to post Share on other sites
Hamish Posted May 15, 2020 Author Report Share Posted May 15, 2020 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 ? Quote Link to post Share on other sites
stuart Posted May 15, 2020 Report Share Posted May 15, 2020 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. Quote Link to post Share on other sites
AlanG Posted May 15, 2020 Report Share Posted May 15, 2020 I've used them twice now. No problems and fast turnaround. Alan. Quote Link to post Share on other sites
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