Recently I’ve dealt with several speedometer heads – some I’d fixed before; some new to me – that worked fine but either

i) quit and won’t restart with a dash-tap; or
ii) suddenly started quitting – usually on bumps; but restart with a dash tap.

The puzzling part is restarting with a tap on the dash above the cluster.

Recap of the problems I've seen and some solutions (1986-93 240s only):

1. I’m excluding speedo/odometers that didn’t work when I got them eg. someone buys a 240 with a non-working speedo and/or odo.. This can be a wire failure at the axle; bad circuit board; looseness at the L-shaped clip; bad gear; cracked solder joints – all discussed in threads here.

2. When the speedo and odo quit together and restart by themselves – tap on dash doesn’t help – this is often frayed wires at the rear axle and/or a bad plug.

3. If the odo quits and restarts – sometimes on bumps or with a dash tap – I’ve found too much solder on reflowed joints – the gear hits it and sticks. You can test for this by assembling the unit and turning the odo-gear motor with a needle. Sometimes a piece of debris has worked it’s way into the odo-gear mechanism.

4. If the odo and speedo quit and restart on bumps or a dash tap, this can be a poor connection where the L-shaped wire clip attaches to the back of the speedo board: a) The board contacts may be worn/ dirty/ corroded; b) the prongs in the clip may be loose and sometimes can be re-bent to offer more pressure on the board strips - or the clip can be replaced.

I’ve had to replace boards and clips.

All this done – board contacts cleaned, L-clip prongs re-tensioned, joints re-flowed - I still have 2 speedo-odo units that cut out on bumps and restart with dash taps.

I drove one 1990 this week. Speedo cut out/on rough back roads; then worked as it should for ~50 miles; then cut out when I hit bump pulling into a parking lot.

I believe this has to be a problem where the L-clip connects to the board – a loose prong, bad contact surface.


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240 drivers / parts cars - JH, Ohio