Question about Electric Speedo Drive

[Dale M.]

Have a VDO electric speedometer with Hall effect drive on end of cable (standard VDO unit).. What I am experiencing is some wavering needle variation causes by cable whip, I was contemplating a tone ring (chopper wheel) added to inner side of bearing hub and mounting a magnetic pickup in the backing plate... Sort of same concept as crank fire timing wheel (but no missing tooth) and pickup... The speedo will accent a magnetic pickup coil according to instructions ... The idea is to be rid of the cable drive and go full electronic...

Question is has any body actually done this sort of modification, I know the electronic part is possible but actually mount of a "tone ring" and pick up is questionable and wondering if any body here has experience do in this..

The other option would be mounting hall effect unit behind spindle and just using a short drive shaft (in brass lubricated sleeve) from dust cap to hall unit ....

I know there was a sensor and tone ring available at one time to connect to speedo if using a IRS rear suspension and tome ring went on inner CV joint, but unfortunately I have a swing axle so there is no practical access to axle shaft for mounting a tone ring...

Just brain storming here...

Dale

[Ol'fogasaurus]

I wish I could help you on this Dale but when I was going to make my black buggy street legal I did look into a GPS speedometer. The only real problem with GPSs were when I went into was tunnels, worried about maybe some heavy tree'd places like we have around here but so far with a GPS I have only the tunnel or tunnel under building that stop the GPS and even that isn't as bad as I thougt it might be.

I still might do it due to the law and park speed enforcement on the ocean beaches.

Lee

[Dale M.]

Yeah GPS unit for existing speedo is a possibility... And I have looked a it, but not real keen on dropping at least $100 for unit and having to put antenna someplace where it looks ugly (not sure I want ugly pimple on my smooth clean hood)....

Dale

[Ol'fogasaurus]

As I said, I haven't checked on them for a while but I thought the extra antenna wasn't needed any more.



I did a quick check using amazon (https://www.amazon.com/gps-speedometer/ ... peedometer) as a supplier and this is one of many I came up with. I don't see an antenna but then....

Lee

[Dale M.]

But that does not drive my existing speedo.... I was thinking something mire like this if I had to go GPS...

https://www.jegs.com/i/JEGS/555/41612/10002/-1

[sideshow]

I don’t think you have wavering cable whip and the problem is the cable drive. I think the problem is that the VDO speedos are kind of crappy. On mine I run the over the CV bolts flange, I have tried a couple different teeth sizes with a consistent random wavering that seems to occur at freeway speeds.

[Dale M.]

Maybe.... But I can fool with cable and get it into some position and its smooth for long time at any speed then as cable creeps back to where IT WANTS TO BE the radical needle movement begins again, cant seem to find the exact location it wants to be for smooth operation an secure it there (to lazy) so I just want to eliminate cable...

Also since the brain trust that designed the cable assembly has it made in such a way the cable can not be removed from sheath for cleaning and lubrication...Grrrrrrr!...

Dale

[Ol'fogasaurus]

Yeah,, a cable binding in it's housing can be a long running problem until it breaks. I seem to remember that there was some kind of dry lube for them but it has been so long... I did a quick search and what I saw was liquid Graphite types of lube; one of them was a spray bottle with a small hose to go inside of the cable housing.

Lee

[sideshow]

Well I started with that stupid length cable drive, wonky speed readings, direct off axle drive, wonky readings.
I'm also on my my third speedo head as they don't seem to last all that long.

My conclusion is that the VDO speedos are not for use as instruments, but they fill dash holes very well.

[Ol'fogasaurus]

[Kafer_Mike]

I had thought of mounting the below hall sender on the back of the spindle by welding a flange fitting over the existing cable exit hole and using a shortened cable or rod to drive it. Then I would just need to run the wires up to the speedo.

[Dale M.]

Kind, sorta of my concept but was thinking to just mount hall unit on back of spindle with a short straight drive shaft... probably use brass sleeve press fitted in spindle to "support" small drive shaft... with a flange (threaded portion) to support hall unit ... Just have to design it so it clears "link" when spindle pivots...

Dale

[GS guy]

Dale,
Might try pinging these guys:
http://www.speedometersolutions.com/
They seem to have a lot of experience with speedo's and electronic conversions. They provided me with an electric speedo adapter that worked off my 914 trans speedo angle drive (shelved when I decided on a GPS based speedo). That said, I think the optimum solution is the GPS speedo (Speedhut gauges). The antenna can be mounted underneath fiberglass bodywork - so non-visible. Programmable for tweaking true speed. Seems like anything (cable or wiring) coming off the back side of a spindle, with all the relative movement, is just made for eventual failure.
An alternative might be a custom cable drive - like you already have - but with higher quality (and serviceable) cable/sheath.
Jeff

[TZepeSH]

I have VDO Vision electronic speedo. The Hall sensor is at the and of a cable and it also wavers no matter what I do. I tested the speedo at work with a clean square signal and it is steady and precise according to the parameters set. Now that I change to Porsche 944 turbo front spindles, I do not have provision for a cable and I will use the ABS sensor instead (magnetic). I will first try to wire it directly to speedo, and if it doesn't work properly I will create a small adapter circuit using LM1815, as for Megasquirt VR circuit. I will post how it goes, I am now waiting to receive the sensor.

[Dale M.]

I have VDO Vision electronic speedo. The Hall sensor is at the and of a cable and it also wavers no matter what I do. I tested the speedo at work with a clean square signal and it is steady and precise according to the parameters set. Now that I change to Porsche 944 turbo front spindles, I do not have provision for a cable and I will use the ABS sensor instead (magnetic). I will first try to wire it directly to speedo, and if it doesn't work properly I will create a small adapter circuit using LM1815, as for Megasquirt VR circuit. I will post how it goes, I am now waiting to receive the sensor.

Aaah... That was sort of one of the concepts I had in mind of using toothed wheel like ABS sensor but being my spindles/drums are super old technology no ABS ring...

If I had IRS rear I know a sensor assembly could be attached to CV joint flange but again old technology of swing axle...

Let me know if you find solution in mean time speedo will probably keep waving at me...

Dale