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Series 3 speedo mated to LT230. What gear?


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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 by oterpoter
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  • oterpoter changed the title to Series 3 speedo mated to LT230. What gear?

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 by TSD
added possible correction.
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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. 

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  • 2 months later...

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!

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