73 mgb overdrive issues

The 1973 MGB continues to have more issues to deal with. I start addressing the turn signals, and after getting most of the other mechanical issues taken care of a test drive reveals another issue. The overdrive engages itself at times and won’t disengage most of the time, which can be very costly if not addressed

[@majorscope]

Hi, We were always told here in the U.K. to only ever use something like castrol 20-50 classic in an overdrive gearbox with definitely no additives. Always worked for me. Well done sorting it out.

[@W0uter1992]

Non detergent 30w is what I use in my B's with an overdrive, never had an issue. 20w-50 could also work but I found that it is difficult to get hold of non-detergent 20w-50 (only low-detergent). As the workshop manual states not to use anti-friction additives I won't take a risk.

[@simongilbert9955]

I had a Laycock J type O/D in a Triumph and I used Shell E3766 gear oil to avoid harshness when engaging/disengaging. It was 40 years ago, no idea if the oil is still available; it did seem to have a low viscosity compared to EP90.

[@stanbest3743]

The friction brakes on the epicyclic rely on you using straight 20/w50 engine oil in the gearbox. i always do that and have only ever had electrical problems with the OD.

[@jcx5659]

I always use 20 - 50 wt in my 74 with OD. No issues.

[@spurgear4]

Just suscribed, I have burnt out three overdrive coils in my car over the last few years, getting kinda frustrated and wondering if you have any idea's .

[@mgbgtguy]

Maybe theres a bad wire/connection with high resistance in the circuit? You could rig a new wire and switch to control it and see if it burns out again.

[@spurgear4]

@@mgbgtguy Thank, I will meter the rest of the circuit and check the resistance, I kinda thought since its getting power it was ok, but if resistance is high somewhere else in the circuit it will likely be felt in the coil as it is the weak spot. Thanks again

[@hueyhoolihan582]

ya, always good to know the typical RPM in top gear and MPH when an overdirve is engaged and when not.

[@mgbgtguy]

The speedometer is way off on this car, so I wasn’t looking at that😁

[@ronmackie3127]

Sorry should have said when o/d is NOT engaged can I still use reverse normally?

[@mgbgtguy]

As long as overdrive is not engaged, no problem using reverse. When overdrive is engaged and won’t disengage you do NOT want to use reverse. Hope this helps 👍🏻

[@ronmackie3127]

Hi, just looking at your info about o/d on mgb, having problems with my 68 GT have isolated problem to inhibitor switch, have isolated switch and o/d is working again,so can I still use reverse normally when o/d is engaged.temporary till I figure what to do next with inhibitor switch

[@ronmackie3127]

Thanks for that, just wanted to make sure,now to work out how to change switch without removing engine/gearbox