1. It had the dreaded ‘white spot’ disease.   Not just on the instrument cluster surround, but the inside of the glass too.
2. The outside temperature LCD was all cloudy and difficult to read.
3. The speedometer needle jumped around at low speed.

I assume the white spot is some kind of mould.  it seems to affect cars that have spent time in the tropics or humid environments the most – e.g. Hong Kong, Singapore, Queensland etc.   My car spent over 10 years in Queensland, so I guess that’s where it came from.

The other night I started replacing the front speakers in the car.   I will cover this separately, but this made it very easy to push out the instrument cluster from behind.     On doing this I noticed a fourth thing.   A previous mechanic or owner had used some kind of thick black bitumen like substance to hold the cluster in place.   It was really sticky and hard to get it off the dash surround.     I tried to get as much off the inside of the dash as I could.   It was also hard to get it off my hands.

I cleaned it off as best as I could and unplugged the cluster.    I put the cluster aside to take home.  My first task was to lubricate the speedo cable.   This should improve the jumpiness of the needle at low speed.   I used ATF in a syringe.  I wasn’t able to get very much in there, but I will have another go before I put the cluster back in.    The roll of tape was to keep the angle of the speedo cable up.

I really don’t know why the W124 uses a cable.   The earlier W126 is all electronic.  On the W124 they still have to convert it to an electronic signal for various accessories like the tempomat and the speed sensitive volume feature on some radios.    Seems kind of a step backwards.

The next phase of my W124 instrument cluster project will be to refurbish the outside temperature display.

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There are generally two ways of accounting for the differential ratio in the speedometer.   American cars have an easily changeable speedometer gear in the output of the transmission.   This allows them to have the same speedometer regardless of the differential ratio.   This approach simplifies things for their high production volumes.   It also simplifies modifications, although I doubt this is the aim.    European cars generally had a different speedometer for each ratio.      If the ratio is changed, then either the speedometer needs to be changed, or an inline Speedometer ratio box needs to be installed.

As Sydney is infested with speed cameras, I had the cable removed from the car and sent to a speedometer shop.    The original plan was to modify my cable to accept a ratio box.   However, my cable wasn’t able to be modified – it was too thick and the right fittings are no longer made for such a thick cable.    Therefore, a new cable and ratio box was made up.    Having the new cable made up was more expensive than I was hoping, but If I avoid two low range speeding tickets, I am ahead.

Helpfully, the Smiths speedometer actually lists how many revolutions per mile it expects.   In the case of an E-Type with a 3.54 ratio, this is 1312.    For a 3.07 ratio, it is 1120.   These ratios allowed the speedometer shop to correctly build the speedometer ratio box.    For reference, the 3.31 ratio should be 1216 revolutions per mile, and 2.88 is 1058.

The new cable was installed today and a small bracket fabricated to hold the speedometer ratio box.

I have not yet compared the speedometer and odometer to a GPS, but it was reasonably accurate before the differential ratio change, so I expect it to be ok.   This is a timely change as the NSW Government have just announced the speed camera warning signs are to be removed.

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The panel under the dash that protects all the wires is easily removed providing access to the back of the instruments.   The speedometer has two thumb screws that hold it secure against the dash board.   They are hard to see, but can be felt.  They had slowly worked loose, letting the bezel rattle loose.  The fix is simply to un-tighten them, so the speedometer can be pushed out 0.5 cm, allowing the bezel to be twisted back on, then tighten up the screws properly.

I found it easier to move the steering wheel forward, and sit outside the car, leaning my head and arms into the footwell to reach up and unscrew/screw in the thumb screws.  The speedo needs to be held in place during the tightening so it stays straight.

After that, since it was a beautiful summer’s night, what better than to make sure the fix was given a proper test drive!

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It is good to have a working radio in the car.   While on the test drive, the glass cover of the speedo fell off, which looks like it just clips on.   I have re-attached it, but it does not seem as secure as the tacho.   Will have to wait and see if the fix is good.

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