Morris Minor Owners Club

I have had the speedo rebuilt by JDO and fitted a new cable. Out of the car and tested with a drill using the new cable, the reading sits rock steady. When fitted in the car and driven it will sometimes appear steady but at other times, particularly after going over speed bumps, it will just sit at zero for a long period (up to 5 minutes) before going back to where it should be. When it is showing a steady reading, the reading seems to be around 8mph too low. All of the cable connections are tight. Could this be a problem with the pinion that feeds the speedo from the back of the gearbox? Has anyone had a similar fault?

Hi David,


I had the same trouble with my speedo. The problem turned out to be that the worm drive on the

third motion shaft in the gearbox was loose. The speedo pinion which meshes with it was just

spinning resulting in the speedo needle sticking and bouncing. If you disconnect the speedo cable

at the gearbox end, then carefully unscrew and remove the plastic pinion housing, you should be able

to insert you finger through the hole and feel if the worm drive is loose by trying to spin it.

If it is loose, I'm afraid the gearbox will have to come out.

Hope this helps.

Yes ^^^^ that's the most likely scenario. The 8mph low - did you tell them the final drive ratio - and tyre size?

Thanks guys. I will pull out the pinion and check the worm drive. If the gearbox needs to come out it could take a while. Once the sticking is sorted I can then check the calibration. It was calibrated to the original spec. I'll let you know how I get on.

The gearbox (transmission in my lingo) shouldn't have to come out to tighten the nut holding the worm drive. You should be able to pull the extension housing off the gearbox w/the gearbox in place. (Not 100% positive on this, but pretty sure.)

Katy, would I need to drain the gearbox oil before removing the extension housing?

Yes!