Speedo not reading

#1
After months of working on the car (dashboard removed) replacing wiring and sorting out gauges where they make electrical contact with the PCB with everything back in place now, I decided to take my car for a short drive and everything behaves as it should do aside from the speedometer is no longer working which before removal, it did so, perfectly. So back home and removed the complete dashboard assembly and double checked the correct insertion of the speedo cable which enters the small gearbox on the rear of the speedo and it seems fine.
So removed again and inserted a small screwdriver into the gearbox which sits on the back of the speedometer and turned counter clockwise and the needle moves off zero as expected but when looking at the square drive within the rear of the speedo gearbox, this looks nice and square, but the cable which goes into this, the squareness seems to be smaller. Should there be some form of step-up which slips over the cable which would then insert into this gearbox? I can't imagine the cable from the gearbox is damaged. It is certainly not snapped as I tried to rotate the cable and it won't, which would indicate it is fine. Everything worked before.
I welcome any suggestions.
Thanking anyone in advance for any assistance.
Best regards, Dave
 
#3
Stick in top gear and rock the car back and forth keeping an eye on the cable. It should turn slightly back and forth.
Thanks for your advice. I will try this tomorrow as I can't believe there is anything seriously wrong. I will let you know how I get on. I was going to disconnect the cable at the gearbox end which would be easy enough as I have no carpets in the car (yet to be ordered) and then put the end in a drill and slowly turn the cable inner shaft to see what happens to the speedo.
 

PeterZRH

Well-Known Member
#4
Goodness. That sound like a lot of work - I'm an electronics engineer by training and I hate fault finding old cars. I converted a strip speedo car to round dial. With the ends of the wiring loom with the 2 multi plug connectors I did this in a weekend without cutting the original loom at all. What was the issue you had to need all this electrical work? If the PCB is all all defective then really replacement is the best option because it could mean the board itself is delaminating or has been stressed causing trace fractures meaning you could get breaks in future.
 
#5
Goodness. That sound like a lot of work - I'm an electronics engineer by training and I hate fault finding old cars. I converted a strip speedo car to round dial. With the ends of the wiring loom with the 2 multi plug connectors I did this in a weekend without cutting the original loom at all. What was the issue you had to need all this electrical work? If the PCB is all all defective then really replacement is the best option because it could mean the board itself is delaminating or has been stressed causing trace fractures meaning you could get breaks in future.
The main problem was the car before I got my hands on it was kept in a dry garage for 7 years and no matter how dry, moisture will always penetrate and anything copper will oxidize which covers just about everything electrical.
My background is similar to yours, which was aerospace (fault finding and repair at component level) on cockpit avionics kit, 90% Rockwell Collins both here in the UK with 4 years in Canada. A long time ago.
I would rather keep the car original, not introduce anything electronic, aside from the original Lumenition Optronic Mk12 system which was fitted in the early 70's and is still working.
The board is essentially ok after cleaning the contacts, along with the pins, connectors. I did have to replace some cables and spade connectors, but then expected with a car of 49 years of age.
 
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