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GPS Speedometer

PostPosted: Tue Oct 31, 2017 6:15 pm
by 1owner69Elan
After a number of speedometer failures due to snapped cables and angle drive failure I stumbled across another approach: a GPS based unit that drives the original Smiths speedometer. While I am not particularly concerned about the speedometer it's nice to have everything working.

In the process of a complete rebuild of my S4 I had purchased a new speedo cable as well as a new angle drive(not cheap). With these new units the speedo worked for about 25 miles when the cable snapped. I think the cable failure in this case was probably my fault as I had managed to pull the crimped end off of the cable (speedo side) during installation. I had put the cable back together but obviously not good enough.

Rather than get another cable I chanced upon a story about a GPS unit for classic cars in Classic Motorsports magazine. This GPS approach would also potentially yield a more accurate speedo as well, as I have changed tire sizes from original. The unit is not dependent on tire size or diff ratio.

I thought I would share my installation. (I'm not promoting this, just a customer).

The "Classic Speed" kit from Classic Auto Innovations comes with the following (motor unit, gps antenna, calibration dongle). I also purchased a custom 36" speedo cable (this can be ordered to length). The cable is standard so you can use your existing one if you can.

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The install was quite easy. I chose a location for the motor unit just under the bonnet (hood) bracket on the left side (I have a LHD car). This allows a relatively straight run for the cable. The unit is quite hidden, for the purists.

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I drew power off of the fan thermostat (ignition switched). I affixed the GPS antenna out of sight on the underside of the nose body. A nice advantage of the Elan is the fiberglass body which allows placement of the antenna virtually anywhere internally.

Calibration of the unit was very easy, just temporarily plug the dongle in. My unit was already very close and only required a minor adjustment.

Removed the existing cable. Capped off for now the angle drive (using cap supplied).

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When I next change the transmission oil I will remove the angle drive and speedo gear and use the aluminum plug below (from TTR):

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What I have found in use is that the GPS unit responds faster than the phone speedo apps. At a steady speed both the CAI unit and the app are the same. The CAI unit apparently has a 5 hz sample rate vs 1 hz for a cell phone. Advanced, accurate units used for motorsports and testing have 20 hz rates. The advantage of the CAI unit is that it drives the original speedo.

Re: GPS Speedometer

PostPosted: Wed Nov 01, 2017 1:04 am
by SENC
Fantastic, thanks for sharing! This fits a need for me (I rely on my cell phone and knowing my rpms for various speeds) and is a slick solution!

Re: GPS Speedometer

PostPosted: Wed Nov 01, 2017 9:21 am
by jimj
On the other hand; with your new angle drive you could fit a new cable and have the speedo. head rebuilt and recalibrated by a specialist. Less complication, probably cheaper, would still work driving though forests, and would probably outlast most of us.
Jim

Re: GPS Speedometer

PostPosted: Wed Nov 01, 2017 9:28 am
by gjz30075
1owner69Elan wrote: a GPS based unit that drives the original Smiths speedometer.
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This is key to anyone wanting to change gearbox to a different type, for the fifth or sixth gear. That's usually
a part of the engineering which may require chassis mods, et al. This unit looks looks like it
avoids all that. Thanks for this find.

Re: GPS Speedometer

PostPosted: Wed Nov 01, 2017 12:13 pm
by TomR
I agree. On my first T5 conversion I had to modify the chassis and cut a hole in the fiberglass to make room for a speedo drive. Now I am using an electronic classic Smiths speedo and a small GPS unit which sends it an electronic signal. Looks original, no mechanical cables. And modern GPS doesn't easily lose a signal once locked in. TomR

Re: GPS Speedometer

PostPosted: Wed Nov 01, 2017 1:14 pm
by wotsisname
Interesting device. I looked on the Classic Auto Innovations website and it appears out of stock - would you share a ball park cost ?
An advantage I can see is that you could change the diff ratio without having to then change the speedo gearing in the gearbox.

Re: GPS Speedometer

PostPosted: Wed Nov 01, 2017 5:50 pm
by 1owner69Elan
The price was $275 plus shipping ($15).

jimj wrote:On the other hand; with your new angle drive you could fit a new cable and have the speedo. head rebuilt and recalibrated by a specialist. Less complication, probably cheaper, would still work driving though forests, and would probably outlast most of us.
Jim


I would say this GPS approach is less complicated. No removal, reinstall of speedo (I found that a real pain when I redid my dash, clearing the odometer reset stalk). No careful measurement required of Turns per mile for the specific configuration (tire and wheel size, transmission gearing, diff, ...). Not counting this effort I am not sure what the recalibration costs would be plus shipping (or hand delivery) to and from the specialist.

Really, installation of this unit was trivial, once the location is decided. Took very little time. Maybe an hour (wiring, cable hookup, calibration). For calibration, when you first start the unit up it registers ~40 mph (car at rest). With the dongle you adjust this up or down to exactly 40. Mine registered 41 so just a minor change.

On balance, the cost and time involved makes the GPS solution relatively attractive to the alternative. And if there are any downstream changes (tires, gearing) no recalibration required.

As far as signal loss (tunnels), the speedo doesn’t drop out to zero, but uses some averaging algorithm to indicate an approximate speed until the signal is reacquired.

Re: GPS Speedometer

PostPosted: Fri Nov 03, 2017 4:02 am
by Chrispy
wotsisname wrote:Interesting device. I looked on the Classic Auto Innovations website and it appears out of stock - would you share a ball park cost ?


$275 is the price on their website. Looks like a good unit!

Re: GPS Speedometer

PostPosted: Fri Nov 03, 2017 11:29 pm
by 1owner69Elan
Thought I would add a picture showing the location of the unit and antenna. Quite hidden.

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Re: GPS Speedometer

PostPosted: Fri Dec 22, 2017 2:48 pm
by patrics
Hi
There is a company very close to me that does GPS speedo's for classic cars. Last time I talked to them (2 years a go) they said they were going to concentrate on Mini, but just looked on the web site and they now have more options.

https://www.digital-speedos.co.uk/

If I get chance I will talk to them after Christmas.

Regards
Steve

Re: GPS Speedometer

PostPosted: Sat Dec 23, 2017 1:08 am
by 1owner69Elan
If you happen to be interested in the CAI Classic Speed product you can get free shipping from now until April 30, 2018. This pertains to US deliveries only. If you are out of the US you might ask them to give you $15 off anyway - I don't know if they will honor that. But, no harm in trying.

https://www.classicautoinnovations.com/shop

Just enter on checkout:

PROMO CODE = FreeShipReferral

And enter the note "referred by 1owner69elan".

FWIW, in full disclosure, I get a Starbucks coffee card (I don't even drink coffee). Really just trying to save our members a little money. Not enough to influence your buying decision, but if you are ordering anyway might as well take the small discount.

Here's the page that shows the Elan install:


https://www.classicautoinnovations.com/picture-gallery