de Normanville Safety Gearbox test drive. At last.
I appreciate that it is unusual of me not to mention a marque or model in the title of a post but this job has been all about the gearbox so I have to start with that. An article in MotorSport from 1935 is a good place to start if you've never heard of this device, suffice to say it was an epicyclic 4 speed with hydraulic control that was fitted to the top of the range Humber Snipe (for £30). It is connected to the engine with a regular clutch but with the addition of a dashpot that prevents the clutch pedal from rising when the car is in Neutral. Regular readers might remember that it came in with no second speed, on stripping it down I found the associated annulus was broken, a rather complicated part right in the middle of the main drive rotor that had been remanufactured by a high end engineering company for the previous owner. Sadly they had left no meat on the metal and the action of the v-shaped brake block had popped the end off. Long story short, my good friend Joe Carroll was able to repair the new annulus by pinning and welding a new outer edge onto the annulus and then machining the 'V' back to original. I got it all back together and in the car but the first test drive did not go well, it would go forwards, and second speed was definitely ok, but there was no reverse. Back to the drawing board but with a good idea, I'd mis-located the gear on the main cylinder block cam where it interacts with the shifter. Typically, with the fault corrected and with it all going back together nicely, the last fitting on the last oil pipe broke. Even more typically the broken tube nut was found to be a ⅜" x 26tpi thread, not something available off the shelf, but I could, and did, buy the taps. Joe made me a new nut this week, with the final pipe fitted I could put the sump back on, fill it with XL20, and today got it fired up and ready for a customer visit. Now the story turns down another avenue and I refer back to the aforementioned dashpot, the forward gears were all found to be fine, and neutral was working, but the pedal would also not rise when the selector was in reverse. I disconnected the actuator, basically a cam that holds a ball valve off its seat in all locations other than neutral, where it is notched, and reverse joined the rest of the box. I removed the dashpot assembly and was able to adjust the cam and the link rod and it now works as it should, remarkable as it's getting on for 90 years old and operated every time you move the shifter. I'm so glad I learned all of this, the owner tells me there might be 5 others. In the world.