Speedo Signal

[Cabrio_Simon]

I've got to the stage now where I need to complete the wiring for the dashboard and particularly the speedometer. Although I've got a magnetic sensor kit that came with the (CAI instruments) speedo I was wondering wether you can use the toothed wheel and ABS sensor from the disc brake Sierra axle?

I'm thinking that this will be a much better method (assuming it will work) as there are alot more 'teeth/rev' than the magnetic sensor (ie more accurate) and will save me having to make up all the various brackets etc.

I've tried contacting CAI gauges about this but not got a reply. Does anyone else have any experience or thoughts on this?

Thanks. Simon

[pdm_engineer]

Re: Speedo Signal

Simon
I too thought about using the ABS sensor but after doing some calculations I concluded that it cannot work with the Smiths instruments. Firstly if you calculate the pulses per mile you will find that the result is a long way off the highest number available on the calibration table.
Secondly if you think about it when cornering sharply you could end up with a very slow or zero mph reading.This is because you will be using only 1 wheel to monitor the road speed.
The magnet sensor, from my experience, is also hopeless with 4 magnets but you may wish to experiment with 2 or 3 on the propshaft. My feeling here is that the reed switches supplied cannot switch fast enough to be reliabl/stable.
The proper solution is to use a 4 slot disc on the propshaft in conjunction with a poximity sensor like the ABS sensor. I have writen an artical on how to do this and set it up. If I have'nt sent this to you (I can't remember if I have or not) then let me know and will forward to you via E-mail. (Too much info to put here)

Peter

[goldwill]

Re: Speedo Signal

I had a lot of problems obtaining a stable reading (failing the SVA twice), initially with a reed switch and magnets mounted to the prop shaft at the gearbox end, and subsequential with a proximity sensor using either the magnets or the head of the prop shaft bolts. Using the latter approach I managed to pass the SVA, but only just and the speedo stopped working on the way home!
The final solution was to pick from the edge of the prop shaft bolts (the senor is mounted at 45 degrees to the bolt), this gives a sufficiently stable signal and the speedo has work well since.

[Cabrio_Simon]

Re: Speedo Signal

Thanks all for the very usefull information and for the article that you sent me Peter. I will definitely rule out using the ABS sensor ring because, as you say, the number of teeth/mile are too high for the speedometer.

Since I've already bought the magnetic sensor kit I think I'll give it a try using a disc on the propshaft but will bear in mind that the proximity sensor seems to be a much better method (at least the magnets coming unstuck and flying off at high speed will be 'entertaining'?!!).

Simon

[teazle]

Re: Speedo Signal

Hi Simon,
I would agree with your conclusion.Although I used ETB intruments the principle's the same; I positioned the sensor directly off the gearbox holding bracket and the 2 magnets onto an alminium spacer in between the g/box flange and p/shaft.With usual calculations it worked out at 69 mph @ 70 on speedo which pleased the SVA fellas! Couple of tips - get magnets @ 180 and to prevent losing them I drilled holes for them so they ended up flush with metal; the sensor doesn't bash them on first attempt and you've got a much better bond. I used Araldite.Good luck.
Chris

[milliemarlin]

Re: Speedo Signal

Hi Simon,
I carefully crafted a strong steel bracket to hold my sensor rigidly in perfect position to pick up four magnets positioned around the differential propshaft flange. This completely failed to work at any speed. In fact it did not register the magnets at all. After some mucking about I discovered that it was the steel bracket that was causing the problem. I made up a much simpler bracket in Al-alloy and that has works perfectly.

Paul