Anglefire Posted June 2, 2018 Report Share Posted June 2, 2018 I've taken the Spitfire (1500) out this afternoon to some friends and went past a speed radar sign and I'm pretty sure it said I was doing 35, when I was showing 30 on the speedo. So wondered what the rough speed should be for say 3000rpm in 4th (non OD)? When I'm at 3000rpm, the speedo is showing about 50, but based on the attached spreadsheet, 3000rpm should be about 55/56mph? gearspeeds.v2 lr.xls Link to comment Share on other sites More sharing options...
yorkshire_spam Posted June 2, 2018 Report Share Posted June 2, 2018 Have you tried comparing against a GPS speedo? I can't remember 100%, but I think I worked out that in 4+OD 2250 rpm is 50 mph and in 4th only 2750 rpm is 50 mph. Link to comment Share on other sites More sharing options...
Anglefire Posted June 2, 2018 Author Report Share Posted June 2, 2018 To be fair I haven't - it was only a passing thought really as I was driving back. Link to comment Share on other sites More sharing options...
yorkshire_spam Posted June 2, 2018 Report Share Posted June 2, 2018 I've had to use a GPS speedo recently as my Spitfire 1500 speedo is goosed.... it refuses to go above about 20mph (when you are actually doing about 50), another thing to repair! Link to comment Share on other sites More sharing options...
Clive Posted June 3, 2018 Report Share Posted June 3, 2018 Most of cars I have owned have had wildly inaccurate speedos. 10-20% out, and always under reading. Bizarrely the most accurate speedo has been with my type 9. Less than 1% out at 110mph (checked against GPS, and yes, it was on a genuine autobahn) Part/most of the issue seems to be with overdrives. Attention isn't paid to the speedo drive gear when fitting. Yes. I am guilty. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 3, 2018 Report Share Posted June 3, 2018 Way back in the 70-90s when I waas involved with in factory tachograph calibration we had a spec for speedo was +10%+4mph so it could read 70 at true 60 and be within tolerance they must not read slow Manual calibration measure 52.8 ft down the road, attach card pointer to speedo cable inner . push car exactly 52.8 ft count the turns. X the turns by 100 and thats the turns per mile needs to match the numbers under the oddometer rolls Pete Link to comment Share on other sites More sharing options...
JohnD Posted June 3, 2018 Report Share Posted June 3, 2018 Anglefire, In addition to the above points on the legal side of speedo readings, in Triumphs they measure the speed of the final drive, as it leaves the gearbox. This is then reduced by the differential, which of course has a range of ratios, from1:4.5 (?Courier van) to 1:3.27 (GT6, no overdrive). A 1500 Spifire left the factory with a 1:3.63 ratio diff and a speedo to match. If, as is quite likely, it has had a higher ratio diff fitted, or a speedo from a lower ratio car, then the speedo will under read, the car will be going faster than indicated. John Link to comment Share on other sites More sharing options...
thescrapman Posted June 3, 2018 Report Share Posted June 3, 2018 Spit1500 should have 1000 on speedo as it was from the standardised speedo era. About 20mph per 1000 rpm in 4th I think Link to comment Share on other sites More sharing options...
Anglefire Posted June 3, 2018 Author Report Share Posted June 3, 2018 Yes it has 1000 on the speedo. So when I’m doing 50 on the Speedo it’s doing nearer 60. Likewise 30 on the speedo is about 35. That would tie up. Link to comment Share on other sites More sharing options...
NonMember Posted June 3, 2018 Report Share Posted June 3, 2018 Hey ho. My first Vitesse, many years back, had a speedo that I could get to read 130 if I was really trying. Given that it was a perfectly standard Mk1 2L, with a factory top speed of 95, I don't think the speedo was terribly accurate. 1 Link to comment Share on other sites More sharing options...
thescrapman Posted June 3, 2018 Report Share Posted June 3, 2018 I have managed to get my 1200 Herald (fitted with Vit1600 speedo) well past IGN, so about 110. I need to offload some of that optimism onto the TR which the most pessimistic speedo I had ever owned. Link to comment Share on other sites More sharing options...
Mad4classics Posted June 3, 2018 Report Share Posted June 3, 2018 12 hours ago, Pete Lewis said: Way back in the 70-90s when I waas involved with in factory tachograph calibration we had a spec for speedo was +10%+4mph so it could read 70 at true 60 and be within tolerance they must not read slow Manual calibration measure 52.8 ft down the road, attach card pointer to speedo cable inner . push car exactly 52.8 ft count the turns. X the turns by 100 and thats the turns per mile needs to match the numbers under the oddometer rolls Pete Pete is right, the calibration requirements on the speedo were fairly wide; the speedo was only supposed to be an “indication” of your speed and must not read slow. However, that's not to say the operating principle of a NEMAG speedo is wildly inaccurate because they can be made to read a lot more accurately than they generally do; it was the calibration requirements which were loose and after decades of use, things will obviously have drifted further out. I decided to do something about my tacho and speedo neither of which was reading correctly, so I re-calibrated them based on the principles gleaned from TM9-1829A Ordnance Maintenance: Speedometers, Tachometers, and Recorders - 1944 a War Department document. It was my winter project! I built a lash-up consisting of a large electromagnet a power supply and a geared electric motor and managed to get very good results; you’ve just got to have a lot of patience. David Link to comment Share on other sites More sharing options...
Chris A Posted June 3, 2018 Report Share Posted June 3, 2018 The speedo on my 13/60 has been recalbrated by a previous owner and using GPS as a comparison it is as accurate as my modern so they can be adjusted to read correctly. How it was done I have no idea. Mind you sometimes it does fluctuate a bit at 60 ish. Link to comment Share on other sites More sharing options...
dave.vitesse Posted June 4, 2018 Report Share Posted June 4, 2018 On the UK 1500 Spit, 3.63 diff, the top gear speed at 1000rpm is 18 mph. This subject is a can of worms, this is because in 1974/5 the Speedo's on most Triumph models was standardised at 1000 turns per mile. This meant that other Triumph models, Dolomite, using the same gearbox and overdrive would have Speedo drive cog to match the diff ratio and not a different turns per mile Speedo. This meant 1500 Dolomite which up to 1980 has a 3.89 diff though it has the same gearbox/overdrive as the 1500 Spit has a Speedo drive cog gave less turns per mile. The 1300 Dolomite had a 4.11 diff so less turns per mile. So if somebody fits a Dolomite 1300/1500 gearbox into your 1500 Spit then you may have an under reading Speedo. The same goes for the 1500 Dolomite Overdrive unit. Late, 1980, 1500 Dolomite had a 3.63 diff so no problems. The 1850 and late, 1980, 1500 Dolomite Overdrive where OK as both cars had a 3.63 diff the same as the UK 1500. The problem may be the Speedo or the above. Check with a GPS. Dave Link to comment Share on other sites More sharing options...
Anglefire Posted June 4, 2018 Author Report Share Posted June 4, 2018 Thanks Dave - little bit more to add to my story! The engine in the car when I bought it was from a Dolly 1300 - but I'm 99% sure was rebuilt as a 1500. The flywheel was also a dolly flywheel so pre-engaged starter. It is therefore possible that the gearbox is from a dolly as well. In fact if you replace the diff ratio in the spreadsheet with 4.11 then the calculated speed at 3000rpm is about 50. I always knew the car was a bit of a triggers broom, but also looks to be a heinz 57 too 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 4, 2018 Report Share Posted June 4, 2018 For warranty testing I had a Smiths drive unit , had two humongous electro magnets that shut down the grid if used in anger, Giant rpm dial and stabilised drive motor.... when they closed us down it went on the skip along with a starter and alternator tester As a superb air valve test rig there Is limit on what you can acrue from the skip in hindsight could have set up a nice little earner Happy days .....gone Pete Link to comment Share on other sites More sharing options...
Anglefire Posted June 4, 2018 Author Report Share Posted June 4, 2018 Assuming the GPS proves its out of kilter, I guess the required speedo drive cog is the black one with 23 teeth? Link to comment Share on other sites More sharing options...
Steve P Posted June 4, 2018 Report Share Posted June 4, 2018 I went electronic route..mainly due to the saloon gearbox and angle drive. Link to comment Share on other sites More sharing options...
Mad4classics Posted June 4, 2018 Report Share Posted June 4, 2018 38 minutes ago, Pete Lewis said: For warranty testing I had a Smiths drive unit , had two humongous electro magnets that shut down the grid if used in anger, Giant rpm dial and stabilised drive motor.... when they closed us down it went on the skip along with a starter and alternator tester As a superb air valve test rig there Is limit on what you can acrue from the skip in hindsight could have set up a nice little earner The Smiths drive units are as rare as you know what! Double Do'oh oh Well David Link to comment Share on other sites More sharing options...
dave.vitesse Posted June 4, 2018 Report Share Posted June 4, 2018 23 teeth for 4.11 sounds near, maybe a bit on the fast side. A 4.11 with 155/80/13 tyres is 16 MPH per 1000 RPM. As a guide - 20 teeth (Grey) is for 3.89. and 19 teeth (Green) for a 3.63. Though some times the drive cog is also changed on the main shaft as a result I have seen 18 teeth (Brown) used on a 3.63. Dave Link to comment Share on other sites More sharing options...
Anglefire Posted June 4, 2018 Author Report Share Posted June 4, 2018 I was basing my no of gear teeth on the canley site - part number 219004 - but there is a 219003 which is 23 teeth Link to comment Share on other sites More sharing options...
dave.vitesse Posted June 5, 2018 Report Share Posted June 5, 2018 Mark, How many teeth does 219004 have as 21 or 22 would be closer. Dave Link to comment Share on other sites More sharing options...
Anglefire Posted June 5, 2018 Author Report Share Posted June 5, 2018 004 is 23 teeth. 001 is 20 teeth. The canley site suggests 004 is standard 1500 spitfire. 001 for the Swiss market and 005 for USA. https://www.canleyclassics.com/triumph-spitfire-mkiv/1500-rear-extension-and-speedo-drive-details/ Link to comment Share on other sites More sharing options...
dave.vitesse Posted June 5, 2018 Report Share Posted June 5, 2018 Mark, teeth numbers don't sound right, this is probability me . So back to part numbers. Standard UK 1500 Spit has a 3.63 diff. If you are using this ratio then yes you need 219004 as given by Canley. I have checked this number against the 1850 Dolomite which uses the same diff ratio and it is the same, so it looks correct. The Swiss 1500 Spit uses a 3.27 diff, 219001. The US 1500 Spit uses a 3.89 diff, 219005. Dave Link to comment Share on other sites More sharing options...
Anglefire Posted June 19, 2018 Author Report Share Posted June 19, 2018 I forgot to mention when I went out at the weekend I checked the speedo against a gps speedo on my phone - and it is reading about 10% low. So 32mph on the gps was about 30mph on the speedo. So how easy is it to change the gear? Link to comment Share on other sites More sharing options...
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