Electronic Speedo Conversion

[camperman]

For all of those people who need to use an electronic speedo but dont want a horrible mis-matching modern speedo in their dash.

 

Note - I offer no solution to a speedo sensor pick up - my 02 has the E30 medium case diff in the back with built in speedo sensor. There are threads knocking around discussing solutions to this elsewhere. 

 

 

 

1) Buy a used Motometer E30 speedo (must be Motometer one not a VDO one).

2) Replace the Odometer gears with new ones - these always fail if they havent already (google suppliers)

 

Note - if you have access to a square wave signal generator it is possible to bench test the speedo by wiring it as per below and using the generator to give it a signal - I didnt do this so im not 100% certain how to do it.

 

3) Prise off the needle from the front - do it carefully

4) Take your 02 speedo, prise off the needle and remove the face

***removing the needles is not easy and if not done carefully you can break the speedo itself and the needle - this is your fault not mine***

Note - you will notice the needles are very different weights - this does not matter.

 

5) Remove the backing plate from your 02 speedo and drill holes in it to get it to screw onto the back of E30 speedo centrally.

6) Take the 02 face you want to use (all 3 designs work fine) and drill 2 holes in it to mount the face onto the E30 Speedo. (if the back of the face is touching a big silver cog that turns the odometer numbers you will need to shim it slightly to allow the cog to turn freely)

7) File/grind out the 5 digit odometer slot on both sides to accomodate the 6 digits of the E30 odometer. You can file out the lower slot to show the 4th odometer number but I didnt bother with this and left it hidden.

8.) In order to get the speedo to fit in the cluster you have to hack off redundant bits of plastic around the edges including the trip reset arm (you will lose this functionality unfortunately). I also took about 2mm off the edge of the speedo face on one side to allow me to install and remove the speedo easily with the rev counter and fuel gauge still installed. Use trial and error cutting off bits until it generally fits. Try not to scratch the face of the speedo on the metal ring holding the glass inside the cluster covering the face with masking tape is probably a good idea.

9) Get some M5 threaded stud or cut the head off a bolt. Screw them into the 4 holes used to mount the speedo into the cluster. Put nuts on them to hold in the rev counter and fuel gauge in place. Use further nuts to mount the speedo in place.

10) There are 4 marked "plugs" in a line on one side where on the E30 the speedo plugs into the rest of the cluster somehow (I dont have a cluster to look at). Solder wires onto each "plug" and hook them up as necessary.

 

"+" goes to 12V live - I piggy backed the rev counter

"31" goes to earth - I piggy backed the rev counter

"31b" goes to one side of the speedo sensor, the other side of the sensor goes to earth.

"A" is redundant.

 

11) Once all of this is done you are ready to install the needle. The E30 spindle is smaller than the 02 needle so wont just press on. Glue it on with superglue or the like. Use something to space the needle off the face when you do so (cardboard). Make sure it is level so that it doesn't come away from the face as it goes around or drag on the face. Obviously glue it on resting against the 0mph stop.

 

12) Reassemble it all and put it in the car. The cluster just about fits even with the extra depth of the speedo. However the two long threaded shafts used to screw the cluster in that come off the back of the speedo now sit much closer to the slots they go through. This necessitates these slots being extend downwards significantly for the cluster to go in fully (file or grind them out) and the shafts need to be cut down in length by quite a bit then threading to the base using a die nut. Alternatively just cut them off altogether - the cluster will happily stay in place quietly without needing to be fixed in from the back anyway. 

 

13) Go for a drive and test it all works. The speedo should read in the ball park of correct straight away (that was my experience) but the Motometer speedo has a bonus feature that the VDO unit does not, there is a round potentiometer on the PCB board on the back of the speedo that can be adjusted in order to "calibrate" the speedo. So if it is reading under or over you can adjust this to correct it. Use a GPS Satnav system to determine this. I cant remember now which way to turn it to make it read faster or slower, sorry. Be careful when turning it as it has a tendency to bend over on the board and might break off if you are heavy handed. The potentiometer is positioned as such that you can just about access it to turn it without having to remove the speedo from the cluster altogether. I could not get the speedo to read absolutely perfect it reads a bit fast at first then a bit slow at higher speeds. Currently my readings are around about this...

 

Actual         Speedo

   30                 33

   40                 42

   50                 51 

   60                 60

   70                 69

   80                 78

   90                 87

 

If I tried to get lower speeds reading perfectly it would throw out the higher speeds even more, its a compromise. Overall it is certainly close enough and much better than a digital modern speedo in my dash!

 

Heres some pictures, I didnt take that many though when doing this. I'll add more later if I can find any.

 

Note - I drilled the holes in the face slightly out of level so the numbers look a bit wonky in the slot 

 

 

Note - This is part way through, no wiring done here and those 2 long mounting shafts are unaltered here.