Analogue (moving coil) Electrical Speedometer Fault

[Citroënbender]

This is a question coming from my 164 look-a-like Peugeot.  It's got an electrical transducer speedo drive in the gearbox, which feeds a signal to an underdash splitter/amplifier box to independently supply speedometer pulse to suspension computer, steering pressure regulator solenoid, cruise control and of course the dash cluster. 

When the car gets hot inside the cabin (ie, summer!), the speedo sometimes starts flicking/hovering above the actual road speed by 10-20km/h.  The fluctuation increases with road speed, it's more subtle at 60 than 110.  I don't believe there's a problem with positive supply or ground to the cluster as the tacho stays rock solid. There doesn't seem to be any effect on the steering pressure, although at higher road speed the assistance is pretty low anyhow.  I can't say whether it affects the cruise or suspension, haven't had the presence of mind to try them when this fault comes up.

It's frustrating both because I like things to work as designed, and to be aware accurately of my speed - not cowed by fear of penalties.

The core question is, has anyone here experienced similar behaviour with an analogue/electric speedo, and was it difficult to rectify? I don't know if driving/balancing coils blow, or if they are prone to dry joints. The cluster is Jaeger, but I'd not be surprised if the needle drivers are actually the same across several brands.

[philpot]

Having just put back together the speedo/instrument binacle (again, again...) in my '85  33 QV,  I will bite with a response on this one.

The biggest pain in the butt with my 33 is the electronic speedo. Am forever having to disassemble and clean contacts with contact cleaner/isopropol alcohol. Just got it all back together again a few minute ago. IS working, for the moment...

Have bypassed flat connector block on back of binnacle,  direct wire to copper contacts in plastic electrical sheet/panel on back of same.   But, have to remove  actual speedo unit and then clean four prongs in back of speedo recess (male terminals) then spray contact cleaner into female slots in back of speedo unit back circuit board.

My speedo used to flick work then not, flick then not.  But, sometimes if put on headlights, reardemist, fan, it would reduce.  Theorise resistance at connectors/contacts reduced by lower power input?   Never had a prob with electronic tacho...

Trip meter clicks loudly, so maybe some mechanical resistance there as well, that in combination causes/exaserbates problem...?

With 33's, yes both are pains, the signal from electromag pic up is very, very small. Especially compared to other makes, so there is an amplifier to boost the signal on back of cluster behind tacho. This 'failed' on first cluster on 16V. After someone tried to fix it...

All I can offer by way of advice is to clean every connector you can find, then look for others (like mine, the pins that connect back of speedo unit into instument cluster) you may have not yet found.   Seems like the cleaning thing then becomes a very practised routine.

NB:  had 1.5QV  twelve years, 16V seven, so have some experience with them.  Do long for good old cable speedo drive that was on my '81 Sud sometimes!

[Citroënbender]

The "clean everything" approach is what I'm dreading...  Did the 164 have a similar cluster to the 33, with signal boost on the back - as opposed to a separate box?