oterpoter Posted May 15, 2022 Share Posted May 15, 2022 (edited) Hello. I am trying to figure out if my series 3 speedometer can be mated to the LT230. The LT230 has 1.003 ratio. The diffs are 4.7 ratio. And I have 33.1" tyres (255/85/16). The LT230 came without the speedo gears, so I need the proper parts as seen on this link Parts 16 to20. https://www.lrworkshop.com/diagrams/land-rover-defender-transfer-box/transfer-box-lt230/rear-flange_53758 My question is what gear would be most accurate. It is better if the result displays higher speed than actual, since I will not get the car approved if it is the opposite. Thx Best regards Mathias Bergen, Norway Edited May 15, 2022 by oterpoter Quote Link to comment Share on other sites More sharing options...
TSD Posted May 17, 2022 Share Posted May 17, 2022 (edited) The following is all from google and scribbling on a metaphorical fag packet, so a grown-up should check my maths. I used to run an LT230 with series speedo, but the wobble was so bad I have no idea how close the speedo was. I think the Series speedo exists in several different versions, according to build. There should be an identification number around the outside of the face, which ends with a number indicating the calibration. According to the internet, it indicates directly the revolutions per mile. I found values of 1376, 1408, 1504, 1536 mentioned, there may be others. That value will obviously affect your ideal gear. 33.1" tyres, so I make that about 610 revolutions per mile. 4.7 Diff, so the propshaft does 2867 revs/mile Speedo cable is driven by the output shaft, so LT230 ratio is unimportant. The output gear is FRC3162, which is (I think, from online photos) a 9T gear. Speedo drive gears are available as: FRC3310 / Blue / 20T / 90/110 with 235/85 or 750 tyres FRC3311 / Green / 21T FRC3312 / Yellow / 22T / 90 with 205 tyres FRC9939 / Black / 23T / V8 Middle East market vehicles FRC3313 / Red / 24T / LT77 Using the blue gear, 20T, the speedo drive is 2867 * 9 / 20 = 1290 revs/mile Using the Red gear, 24T, the speedo drive is 2867 * 9 / 24 = 1075 revs/mile So I think your best choice, without additional complication, would be the Blue gear, but even with the best speedo option from the list above, it would under-read by around 10% It is possible to get the speedo recalibrated of course, or fit a Td5 electronic speedo, or VDO universal programmable speedo (but the latter options lose the proper look, of course). EDIT : I'm wondering where the FRC9939 info in my notes came from, Google seems to deny it exists. FRC3313 has 23T according to the parts list linked in the original post. It's a typo when copied from : Edited May 17, 2022 by TSD added possible correction. Quote Link to comment Share on other sites More sharing options...
oterpoter Posted May 17, 2022 Author Share Posted May 17, 2022 WOW! that was one impressive reply! Thx. I will go for the suggested 20T blue. If it wobbles, I must replace it anyways thx! best regards Mathias Quote Link to comment Share on other sites More sharing options...
western Posted May 17, 2022 Share Posted May 17, 2022 5 hours ago, TSD said: The following is all from google and scribbling on a metaphorical fag packet, so a grown-up should check my maths. I used to run an LT230 with series speedo, but the wobble was so bad I have no idea how close the speedo was. I think the Series speedo exists in several different versions, according to build. There should be an identification number around the outside of the face, which ends with a number indicating the calibration. According to the internet, it indicates directly the revolutions per mile. I found values of 1376, 1408, 1504, 1536 mentioned, there may be others. That value will obviously affect your ideal gear. 33.1" tyres, so I make that about 610 revolutions per mile. 4.7 Diff, so the propshaft does 2867 revs/mile Speedo cable is driven by the output shaft, so LT230 ratio is unimportant. The output gear is FRC3162, which is (I think, from online photos) a 9T gear. Speedo drive gears are available as: FRC3310 / Blue / 20T / 90/110 with 235/85 or 750 tyres FRC3311 / Green / 21T FRC3312 / Yellow / 22T / 90 with 205 tyres FRC9939 / Black / 23T / V8 Middle East market vehicles FRC3313 / Red / 24T / LT77 Using the blue gear, 20T, the speedo drive is 2867 * 9 / 20 = 1290 revs/mile Using the Red gear, 24T, the speedo drive is 2867 * 9 / 24 = 1075 revs/mile So I think your best choice, without additional complication, would be the Blue gear, but even with the best speedo option from the list above, it would under-read by around 10% It is possible to get the speedo recalibrated of course, or fit a Td5 electronic speedo, or VDO universal programmable speedo (but the latter options lose the proper look, of course). EDIT : I'm wondering where the FRC9939 info in my notes came from, Google seems to deny it exists. FRC3313 has 23T according to the parts list linked in the original post. It's a typo when copied from : Those part numbers came from my 110 1987 on parts book. Quote Link to comment Share on other sites More sharing options...
TSD Posted May 17, 2022 Share Posted May 17, 2022 1 hour ago, western said: Those part numbers came from my 110 1987 on parts book. Yes, but the typos were all my own work 1 Quote Link to comment Share on other sites More sharing options...
western Posted May 17, 2022 Share Posted May 17, 2022 Ah I see 😂 at least you saw the errors & corrected them. Quote Link to comment Share on other sites More sharing options...
LiftedDisco Posted July 27, 2022 Share Posted July 27, 2022 Can I possibly jump in on this thread with an’ almost similar’ request for information? I’m building a Tornado, based on a RRC chassis with Borg Warner transfer box but currently have 33/12.50/R17 tyres on the vehicle which are reasonably close to the tyre size (235/85/R16) associated with a Defender. I believe that I can run a blue speedo drive - I will now confess that I haven’t yet had a root around under the thing, but how does the output from the speedo drive turn into the yellow transducer wire that i have feeding into the back of the instrument cluster - is there another box of tricks??? Thx! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 27, 2022 Share Posted July 27, 2022 Bolted to the inside of the RRC chassis rail is a transducer, connects via a short speedo cable to the LT230. Quote Link to comment Share on other sites More sharing options...
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