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 Posted: 10-05-2015 08:58 pm
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NigelK
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Dear forum users

After the W58 gearbox swap in my GT, I've noticed that my speedo is reading about 15% low. I've done some calculations, as follows:

Circumference of standard 185/70/R13 wheel is 72.88". This equates to 63360 / 72.88 = 869.4 wheel revolutions per mile. Which in turn equates to 869.4 x 3.44 (diff cwp ratio) = 2990.9 prop shaft revolutions per mile. This means I need a 3:1 speedo driven gear ratio to match the Smiths speedo 1000 tpm rating. The standard speedo driven gear ratio in the W58 gearbox as fitted to the Lotus Excel is 3.5:1.

This difference in speedo driven gear ratios could account for why my speedo is reading low. The question is what to do about it? Some internet research suggests the nearest available alternative speedo driven gear ratio for W58 boxes of the correct vintage is 31:10, so I'd need to recalibrate the speedo as well as swapping out the driven gear at the gearbox.

How have you guys with W58 conversions handled this issue?

Many thanks in advance.

Best wishes,
Nigel

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 Posted: 10-05-2015 09:31 pm
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t4brew
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Hi Nigel,

I am looking into a W58 conversion as well. I have replaced the speedo gears (one in the transmission tail housing and one on the speedo cable assembly). Below are the Toyota W58 speedometer gear ratio sets and part numbers I found when looking at different gears:

Ratio Gears Plastic Gear#               Metal Gear#
2.7   30:11  33403-29105 30 teeth   33481-14020 11 teeth
2.8   31:11  33403-19245 31 teeth   33481-22020 11 teeth
2.9   32:11  33403-19255 32 teeth   33481-22020 11 teeth
3.0   33:11  33403-29115 33 teeth   33481-14071 11 teeth N/A
                                                    33481-35100 11 teeth N/A
                                                    33481-20090 11 teeth (possible replacement)
3.1   31:10  33403-29145 31 teeth   33481-22030 10 teeth (for 31 teeth plastic gears)
                                                    33481-35130 10 teeth (not sure if this is a match)
3.2   32:10  33403-29125 32 teeth   33481-22130 10 teeth (for 32-33 plastic gears)
                                                    33481-35130 10 teeth (not sure if this is a match)
3.3   33:10  33403-29135 33 teeth   33481-22130 10 teeth (for 32-33 plastic gears)
                                                    33481-35130 10 teeth (not sure if this is a match)
3.4   34:10  33403-39075 34 teeth   33481-14031 10 teeth
3.5   35:10  33403-19235 35 teeth   33481-14031 10 teeth

I hope this helps,

Jerry

Last edited on 10-05-2015 09:42 pm by t4brew

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 Posted: 10-06-2015 04:25 am
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NigelK
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Thanks Jerry. Do you know if all these gear sets would fit any W58 gearbox? My local Toyota dealer could not be 100% sure, because their parts database is driven by vehicle code and not gearbox type, and clearly I couldn't give him a vehicle code (as my W58 came from a Lotus). I do know that later W58 gearboxes came with electronic speedo drivers, which I don't think would work with the stock Smiths speedo on my GT (at least not the odometer)...

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 Posted: 10-06-2015 02:47 pm
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t4brew
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Hi Nigel,

It has been a while since I looked into the part numbers but they should all fit the W58, at least the ones that don't mention "not sure if this is a match".  If I remember correctly there may have been some changes for Lexus W55 transmissions in the early 2000's but the W58's seemed to be a good fit.  The two differences I remember are the electronic speedometer which uses the same plastic gear as the cable speedometer and the ABS sensor that mounted into the front/top of the tail section of the W58.

Getting the electronic speedometer to work with the stock Smith's speedo would not be easy.  I am switching from the Smith's to an EVO speedometer and a W58 electronic speedometer assembly.  I needed to do this because I am adapting an EFI from a Lotus Esprit and a GM Quad4 (both used the same ECU with different PROM's) to fit a 912. The ECU needs the speedometer signal from the transmission and then it sends it on to the EVO speedometer. I also needed to change the speedo gears from stock to something close to what you would like to do. If I remember correctly I used Toyota part# 33403-29115/33481-14071 for a 3.0 ratio and it seems to work fine.

Let me know if you have any other questions.

Jerry

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 Posted: 10-06-2015 03:16 pm
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NigelK
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That's good advice, many thanks!

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 Posted: 02-09-2017 10:06 pm
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Rick Willard
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Hey Jerry, Nigel, T4Brew, and anyone else reading this....

Sorry to bring up an old string here, but I'm in the middle of my W58 conversion and could use your help with the speedometer gearing. I'm struggling with finding the right speedometer drive gear (10-tooth metal one).

I ordered the following part: 33481-35130. It's clearly labeled to fit the 33-tooth plastic gear, so I was excited about installing it. Unfortunately, this particular part is too big in diameter to fit the shaft. BTW, my tranny came from Lotus Bits and is out of an Excel.

I see that the likely part number is 33481-22130, which I would guess has the right diameter and right pitch to fit the tranny. Unfortunately, Toyota is advising that this part is NLA. Given the rear end on my car, tire size, etc., I'm shooting for a 3.3:1 set-up. Do you guys have any suggestions for me to either find this part or possibly use a different set-up??

Any advice would be GREATLY appreciated. Thanks, all!

Rick

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 Posted: 02-10-2017 06:38 am
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NigelK
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Hi Rick

In the end I kept the stock Lotus / Toyota speedo gear, and had my speedo recalibrated to the appropriate tpm. It now reads relatively accurately.

Best wishes,
Nigel

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 Posted: 02-10-2017 02:14 pm
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t4brew
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Hi Rick,

If you want to stay with the stock speedo you have two options that I can think of:

1) Try to find the next closest gear pair available.  You might try to use 33481-14031 (a 10 teeth metal gear that is supposed to be mated to a 34 teeth plastic gear) and see if it works with the plastic 33403-29135 33 teeth gear.  If that does not work you will need to choose the next closest gear pair you can find and live with it.  Probably the 3.4 gear ratio set.

2) Have the stock speedo recalibrated to work with a gear ratio you can find. I am not sure where you would go to do this.

If you are willing to replace your speedo, I believe there are newer ones that can be
configured to different gear ratios.

Jerry

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 Posted: 02-10-2017 02:27 pm
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NigelK
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Nisonger (http://www.nisonger.com) can calibrate Smiths mechanical speedometers. Worth checking with them beforehand whether the range of re-calibration you require is within the range of what's possible with the stock J-H speedometer. I had my speedometer recalibrated by Speedy Cables here in the UK, and they were able to achieve the required 15% correction in calibration without any issues.

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 Posted: 02-10-2017 04:49 pm
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Rick Willard
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Thanks for the quick feedback here, guys. I really appreciate it! I've talked to a couple of specialists who do recalibration right here in Colorado (even classic speedos). They've confirmed that they can handle this recalibration with no problem (very familiar with all Smiths gages), so that's the way I'm going to go. More to follow, we move forward with the conversion. Will let you know if I run into any more challenges. Thanks!

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 Posted: 02-12-2017 01:15 am
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Esprit2
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Google GPS speedometer. I recommend the SpeedHut line. They even have a vintage-look gauge that doesn't look out of place with vintage Smiths gauges. Dead simple installation, super accurate speed indication, and no calibration required. GPS only knows how fast the car is going, and doesn't care about electronic ignition, tire diameter, or transmission choice.

Regards,
Tim Engel

Last edited on 02-12-2017 01:15 am by Esprit2

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