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Borg Warner speedo drive


jad
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Morning having now got my project on the road I have found the speedo is substantially out... When driving at 60ish it says 40ish. I am using a Borg Warner tbox with dicso 1 3.54 axles and currently a 235/70 tyre. I will be moving to a 7.50 or 235/85 tyre however which should make things a bit worse! My speedo is a series 3 109 unit.

I have looked on rimmers and they only note 1 "black 23 tooth" drive gear for the Borg Warner. The lt230 ones look very similar is it possible to fit these? If so will they correct my speedo enough? If it is too far then I was wondering if it could be adjusted so the kph scale was correct for my actual mph...

Are there any clever people that can give me the answer?

Thanks

Jad

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  • 2 weeks later...
  • 2 weeks later...

The problem lies not with the drive gear in the Borg Warner, but with the Series 3 109 speedometer. The 109 speedo will require 1408 turns per mile (tpm) of the cable input whereas a Defender unit is nearer 1000 tpm, hence the 60mph > 40mph relationship. There should be some small lettering around bottom dead centre of the speedo face to confirm 1408 - 1536 is for SWB on 205R16 tyres.

Simplest approach would be to fit a speedo out of a Defender - less radical than dropping to 4.7 diffs! I have managed to fit an early RR two door speedo (~1000tpm) in to a SIII housing when 3.54 diffs were fitted to my SIIA.

Once on 253/85 tyres then a Blue drive gear should be correct.

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I would like to keep the standard speedo if possible just for the looks. I think I calculated I would need a 14 tooth speedo drive gear to make it correct which obvioulsy doesn't exist! How did you fit the RR two speedo into the s111 housing. Did you keep it looking original? Alternatively could you use the gears from an early Defender speedo?

Won't be changing to lower ratio diffs if anything would like gearing slightly higher.

Thanks for your help.

Jad

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Picked up a speedo binnacle from a scrap RR Classic 2 door, dismantled the housing and extracted the speedo head.

Series IIA / III speedo head is easy to open - examine the back of the black bezel to locate tags that are hooked over the lip cylindrical body. Rotate bezel until bezel and glass separate from the body, exposing the face of the speedo. Remove two screws from the back of the housing to release speedo head. RRC speedo head fits straight in and is secured by the same two screws. Align bezel and glass with body, and rotate to secure. RRC speedo cable fittings are the same as SIIA (but slightly longer) and will fit to drive on LT230 transfer box.

I would recommend starting with a SIIA speedo housing as I know from doing mine that everything fits together.

post-249-0-02341400-1436814614_thumb.jpg

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Hmmm that looks good! just so happens my dad has a classic sitting in the drive.... Might try and get another series 3 speedo and see if they can be amalgamated.

Thanks

Jad

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