Smiths Electronic speedometer

[FatJon]

I fitted a Smiths electronic speedo today with the default sender they ship with it. It will NOT fit with the 90 degree drive still on the box, it has to be direct to the box. The pulses per mile figure to put into it for accurate reading is 5839. That's with standard factory wire wheels and tyres and a type A overdrive on a 1970 car. Since it measures the speed on the tail shaft the exact gearbox type will not matter but of course a non standard diff ratio will matter.

BTW don't be fooled by the PPM figure on the old mechanical speedo (1120), that will have you doing 60 as you pull off the drive and 140 within 30 yards!

Maybe at some point in the future this will save someone some work.

[stuart]

1 hour ago, FatJon said:

I fitted a Smiths electronic speedo today with the default sender they ship with it. It will NOT fit with the 90 degree drive still on the box, it has to be direct to the box. The pulses per mile figure to put into it for accurate reading is 5839. That's with standard factory wire wheels and tyres and a type A overdrive on a 1970 car. Since it measures the speed on the tail shaft the exact gearbox type will not matter but of course a non standard diff ratio will matter.

BTW don't be fooled by the PPM figure on the old mechanical speedo (1120), that will have you doing 60 as you pull off the drive and 140 within 30 yards!

Maybe at some point in the future this will save someone some work.

The figure of 1120 is actually Turns Per Mile so not actually the same measurement I dont suppose. Presumably your figure is for a 3.45 diff, do you have a figure for a 3.7?  Do you have a link to that Electric speedo?

Stuart.

[FatJon]

Stuart, Yes, after thinking about it for more than a few seconds at the roadside you quite right about the PPM number as the sensor sends more than pone pulse per revolution. Weirdly though the number I got is not even close to an exact multiple of the Smiths number. Sure it's correct though as I tested with a GPS speed application on my phone at various speeds and I know the app is very accurate.

 

These are the Revington part  numbers I used, not cheap but then a reconditioned original is not cheap either and at least you forget about knackered speedo cables after it's done..

RTR8558-1 Speedo Drive

RTR8558-D   SPEEDO TR250,5,6CC,CP ELECTRONIC MPH

According to my maths and assuming my diff is a 3.45 the correct number for a 3.77 diff is (3.77/3.45)*5839 so 6380PPM

 

If you choose to fit one there are a couple of tips on the wiring that you will find useful, especially the indicator telltale. 

 

 

 

 

[stuart]

17 hours ago, FatJon said:

Stuart, Yes, after thinking about it for more than a few seconds at the roadside you quite right about the PPM number as the sensor sends more than pone pulse per revolution. Weirdly though the number I got is not even close to an exact multiple of the Smiths number. Sure it's correct though as I tested with a GPS speed application on my phone at various speeds and I know the app is very accurate.

 

These are the Revington part  numbers I used, not cheap but then a reconditioned original is not cheap either and at least you forget about knackered speedo cables after it's done..

RTR8558-1 Speedo Drive

RTR8558-D   SPEEDO TR250,5,6CC,CP ELECTRONIC MPH

According to my maths and assuming my diff is a 3.45 the correct number for a 3.77 diff is (3.77/3.45)*5839 so 6380PPM

 

If you choose to fit one there are a couple of tips on the wiring that you will find useful, especially the indicator telltale. 

 

 

 

 

Thanks, interesting to note their price compared to everyone elses, regardless of the slight face difference.

Stuart.

[iani]

On 9/7/2021 at 10:59 AM, stuart said:

Thanks, interesting to note their price compared to everyone elses, regardless of the slight face difference.

Stuart.

RTR sell the conversions made by Speedy Cables, I went direct to the very inaptly named Speedy for mine but bought the sender from RTR, wherever you order from you will have a long wait, over six months in my case. The calibration process is very easy, I think I adjusted the setting three times before it was an accurate reading.

Ian

[Nigel Triumph]

1 hour ago, iani said:

RTR sell the conversions made by Speedy Cables, I went direct to the very inaptly named Speedy for mine but bought the sender from RTR, wherever you order from you will have a long wait, over six months in my case. The calibration process is very easy, I think I adjusted the setting three times before it was an accurate reading.

Ian

I did like Ian when fitting an electronic speedo to my GT6. The instrument electronic conversion was done by Speedy Cables and I bought the sensor from Revington.

The attached photo shows how the sensor fitted in the GT6, no problem despite space being tight. Calibration took me three attempts and now agrees with GPS to 1mph. I'm very pleased with the outcome.

Nigel

[Charlie D]

On 9/6/2021 at 2:52 PM, FatJon said:

Since it measures the speed on the tail shaft the exact gearbox type will not matter

I don’t think that’s strictly true.

The sensor measures the speed from the speedo take off point which  is geared to the tail shaft and the ratio of that gearing is not the same between boxes. (I think…)

I have a  feeling that saloon boxes that some people fit have a ratio of 2:1 whereas the regular TR box is 2.5:1 .

 

But I may be wrong……..

 

Charlie.

[FatJon]

On 9/12/2021 at 8:37 AM, Charlie D said:

I don’t think that’s strictly true.

The sensor measures the speed from the speedo take off point which  is geared to the tail shaft and the ratio of that gearing is not the same between boxes. (I think…)

I have a  feeling that saloon boxes that some people fit have a ratio of 2:1 whereas the regular TR box is 2.5:1 .

 

But I may be wrong……..

 

Charlie.

Valid point Charlie. I didn't think of that.

[SA948]

Have purchased new Smith Electronic Speedometer and Tachometer for my 1971 TR6.  Read directions and contacted Caerbonet for some suggestions.  Got back bunch of gobbly gook.  Bottom line is there a drawing, photo or diagram for the electric attachments for these gauges anywhere.  Instructions are just lame.  thanks in advance.

[RobH]

Welcome to the forums  "SA948" - do you have a name we can use?

If you can post a scan of what you have been sent we can perhaps make sense of it for you.  

( In future it would be advisable to start a new thread of your own rather than to tack the request into an existing one. It makes things clearer and prevents thread drift and confusion.  Go to the 'home' page and scroll down to the forum you wish to post in. Select it and then select 'start new topic' ).

Rob

 

 

Edited September 19, 2023 by RobH

[mleadbeater]

I fitted a GPS speedo to my TD, cheap, £45 or so,  dead accurate, needed to make a new face as it was too small, but works great.

ps why do my photos get inverted?

 

 

Edited September 25, 2023 by mleadbeater

[Mike C]

I thought about using something similar on another vehicle but I  lose my GPS signal in forests - does this speedo keep working under a heavy tree canopy?

My photos don't get inverted when I post them, are they correctly upright when you attach them?

 

[TRTOM2498PI]

2 hours ago, mleadbeater said:

I fitted a GPS speedo to my TD, cheap, £45 or so,  dead accurate, needed to make a new face as it was too small, but works great.

ps why do my photos get inverted?

 

 

Hi.

Do you mind me asking, where you purchased this from please ?

 

 

Cheers.

[mleadbeater]

re tree canopies, not sure as don’t have  many around here. You can always use the tacho until trees clear.
 

check out ebay, under gps speedometer, dozens for sale, although all seem to be limited to 85 mm diameter. Thats why I made an adapter and new face

I initially bought a low cost digital one , then realised my mechanical one was miles out (sorry).

My photos are fine on other forums, yes they are upright in my photos files.

 

Mike

[mleadbeater]

this was an early test mounting.