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Q & A: Over Drive- Sticks On

Hi John,
are you in America?! I have a 1978 MGB Roadster (UK)(90,000 genuine miles)with a Laycock Overdrive which works in 3rd and 4th. It has an overdrive problem:- it gets stuck on. It works fine when I first set off and if I continue to click it in and out every 10 seconds or so it still works fine but if I leave it in for any length of time it sticks on. I've tried changing the solenoid o rings and the oil (20/50) but it makes no difference. Once I stop the car it takes about 30 minutes for the o/d
clutch to come out by itself. If I work at it when driving by continually flicking the switch every few seconds I can extend the time that the overdrive can remain in and then come out but when I do this and leave the overdrive engaged for several minutes when I switch it out it can take up to 30 seconds to kick out. The next time I use the car it seems as bad. I haven't used the car very much over the past two years and I wonder if
this problem is because of lack of use and it will gradually get better? It doesn't seem to me to be an electrical fault and I doubt it is hydraulic (why would it work at all if it was?) It seems more like the clutch is getting stuck on. Do you know what the clutch looks like? Does it have friction material which might be worn out? Can it get warped (it goes in and out smoothly when its working)? Could I try another type of oil? Is there anything else it might be? I don't think the problem is too far from being fixed as its not as if the overdrive is not working at all or is always engaged but I want to get it sorted before I try to drive it in reverse...

Incidentally your other comments about overdrive faults are absolutely spot on! Some years ago the cintred (how do you spell that word?!) bronze thrust washer broke into pieces which I found in the o/d sump. I replaced it with
a copper one when the gearbox clutch needed changed. The solenoid cable took a dead short on the body of the car at the gear lever and set the main loom on fire. It must carry quite a current. I've replaced the loom but it
hadn't occurred to me to fit a fuse. Great idea, I'll do that very soon. You mention yellow and white cables, I wonder what the colour is for me? Is it the live feed for the solenoid? I'll try to find it. What should the
fuse rating be?

Lots of questions!

Many thanks,

David

David!

Yes, I'm in sunny Grand Rapids, Michigan.

The OD can become stuck for two reasons -- failure to purge the oil pressure -- and failure of the springs to push the cone clutch from the annulus. You can fix th... read more