Digital Dash Mod

lastRebel's Digital Dash Mod

Makes readouts of over 130 mph possible on your digital speedometer...

Ok guys and gals, here it is... the digital speedometer mod. I don't yet have a way of testing this 100% without it being in the car, but it checks out from the tests that I can do. Also, some members on Zcar.com have tested this in their running vehicles, and it works out fine with the exceptions mentioned below (keep reading).

The stock ZX digital speedometers only go up to 85mph, and it's pretty annoying. Here in the US, we don't need to know how fast we're going in kilometers an hour, and since 85mph = 137km/h (or close to it, anyway), why not use the km/h scale and set it equal to mph? After this mod, we'll have done away with the cluster's km/h feature, slowed down the speed sensed by the unit, and increased the top speed shown from 85 to 144 (that's the highest km/h readout available on the dash). On the negative side, the changes made by doing this mod include a small hole in the face of the cluster where the km/h - MPH selector button used to be, and when the speed sending wheel is modified, the speed will tend to jump around by a couple of MPH at a very few various speeds below 20 mph and at a couple of speeds above 20 mph, BUT ONLY IF THAT PARTICULAR SPEED IS MAINTAINED. This can be corrected by doing 2 things... first, find a way to remove the old speed sending wheel... then, find a way to attatch a new wheel with the proper amount of gaps on it (you'll have to make it or have it made - sorry, I have no info on this).

Now, for the legal stuff... the disclaimer: This is a semi-permanent modification to the original gauge cluster... while this modification can be reverted to let the cluster function normally again, I can NOT assume responsibility for any damage done, nor the responsibility of reverting the modification. Blah blah blah, yadda yadda. In other words, do this modification at your own risk. Anyway, on to the good stuff...

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First, start by removing the gauge cluster from the car (see your Hayne's manual if you need help), then by taking the front cover off the gauges. There are 6 screws on the back of the unit that hold the front cover on. This is what we've got:

There are 2 small screws on the back of the unit that hold the odometer assembly in place. Take those out and the odometer will come out of the cluster. 3 screws hold the odometer assembly together, take those out and the odometer will pull apart - be careful not to lose the blue worm gear from between the two halves. There are also two wires, red and green, that go to the switch at the top of the odometer. Unless you just don't mind cutting them loose and resoldering them later, make sure they don't break off (like mine did).

The piece that has the black wheel and little black C shaped box on it is what we're interested in. This is the speed sending unit. The C shaped box shoots an infrared beam into an IR reciever, and the wheel turns through it's path, only letting it shoot through the gaps in the wheel. To make MPH = km/h, the sensed speed needs to be slowed down by about 5/8 from it's normal sensed speed. There are 24 gaps total in the wheel as it is now. To trick the sensor into thinking that the car is going slower, we'll have to cover up 9 of those gaps on the wheel, leaving a total of 15 gaps still in the wheel. Using small cuts of electrical tape, cover up the gaps on the wheel in the pattern in the picture below (In the diagram, an X on a gap indicates covered). As a more accurate alternative without the bounce in low speeds, you can purchase a unit from the local speedometer shop that adjusts the speedometer according to wheel size, transmission gearing changes, or rear end gearing changes. You're on your own for that one though.

You'll need to find two small washers to use as standoffs to move the sensor about 3/32" away from the center of the wheel. This further increases accuracy of the sensed speed. I used the mounting ears from a plastic wire strap. Take the sensor off of the sending unit chassis by removing the 2 screws that hold it on. Now put the washers between the sensor and the chassis one at a time. The order is shown below:

Now take out the 3 screws from the speedometer circuit board so it can be pulled out of the cluster. Locate the long push-button that selects km/h or MPH... and pull it off (just a quick tug, it comes right off).

On the back of the circuit board, directly behind this push-button, there are two pins that stick up about 3/8". You can use a red or blue female spade connector to make a jumper that is perfectly sized to connect these two pins (just cut the crimp part of the connector off). When this jumper is in place, it keeps the speedometer in km/h so the rest of the world knows how fast they're going. You'll have to crimp the jumper to make it stay on the pins:

Looking at the gauge readouts from the driver's view, there are two visible rows of pins that go to the LED speed readout from it's circuit board... one row on the top side of the LED, one row on the bottom side. On the bottom, pins 18 and 19 (counting from the left, starting at 1) are the pins that send power to the LED, lighting up either MPH or km/h. You'll have to cut (or desolder) these pins and make sure they're not touching anything, then solder a small jumper wire from pin 18 on the LED to pin 19 on the circuit board. Now instead of km/h being lit up all the time, MPH will be instead. You could just leave the pins cut, and it wouldn't say anything but the numbers... this is what I've chosen to do with mine (at least for a while).

Well folks, that's all there is to it! Not too bad, eh? Like I mentioned before, if anybody wants to do some tests and let me know the results, data from running it in the car would be great. All I had was various small motors at different RPMs to conduct my tests (just don't let the results be in the form of a fast driving award).