do speedo cables shrink in use - solved!
 

The speedo on my 87 300E stopped working recently, all I hear is a clicking from behind the cluster. I removed the cluster, checked that the inner cable wasn't broken and reconnected. The speedo and odometer worked for another 7km and then stopped again.

I removed the speedo and checked that the unit was working by inserting a 2mm Allen key and twirling to check that the internals worked.

My mechanic took one look at the position of the inner cable in the collar and announced that it had shrunk in use, presumably due to the constant revolutions, and it wasn't the first time he'd seen the problem. He recommends replacing the cable.

OK, so I've ordered a new cable but I'm curious as to whether anyone else in the forum can back up this assessment of the situation.

As I said, the inner is still turning, it does seem to be seated low in the outer cable, the cable collar and locking ring at the speedo end are in good order and the connection at the gearbox looks, from a cursory visual inspection, to be OK.

So, do speedo cables shrink over time or is it just another mechanic's myth?

OK, that sounds more reasonable. Number of times I've pulled the cluster has probably stretchd the outer cable but I'll check the routing as well

Look for the little brass clip that holds the cable to the steering column near the brake pedal. You are supposed to slip the cable out of the clip before removing the instrument panel, which makes it easier.

DS

Fixed. The outer cable was broken at the gearbox end so I replaced the cable

Speedo needle now smooth, no jumping