Resolving BN1 overdrive issues,

Since I started putting miles on my BN1,  I've been continually working to resolve some ongoing overdrive issues..
  
To start off, I should mention that my gearbox and overdrive were professionally rebuilt by our local expert here Tom Munro, and after purchasing another original donor gearbox from my friend Trevor, (for a better set of gears, and a better gearbox casing as mine was badly corroded and cracked around the clutch rods)..
Tom was  finally able to reassemble my gearbox & overdrive with some good quality original parts, replacing bearings, seals and gaskets with new.
Tom bench tested it, including the overdrive, and so far his work has been wonderful - it doesn't even leak!

However, when I first finished the car, and took it home from the insurance office for its first proper drive, the overdrive wouldn't work at all.
- Which I correctly assumed must be something electrical...
 
After checking the oil level, the first step I took was to replace the gearbox switch...
My original top gear switch with the screw in terminals, was already leaking a ton of oil from the front cover.
So when I replaced the switch with a new one, my overdrive suddenly worked!..  briefly...   until it started jumping out of overdrive on its own..

So I rigged a test light to the overdrive power feed, coming off of the c2 of the R1 relay that feeds the solenoid, so I could see that when the overdrive jumped out - so too did the power to the solenoid...   A-ha! 
So that meant that the issue was definitely electrical and not a hydraulic/mechanical issue... Good news!

My next step was to test and readjust my throttle switch to open at 1/5 throttle...

When that didn't seem to make much difference, my next culprit was the Centrifugal switch on the back of the gearbox (BN1's only) - 
This switch closes when the wheels are spinning approx. 30-40 MPH, thereby enabling the overdrive to be selected...
Most owners of BN1's that I know just bridge this switch off as it's a bit redundant and tricky to adjust properly ...

As each switch seemed to slightly improve the situation, the overdrive would still disengage after a prolonged period of driving...   

My next culprit was the relay switches, the BN1 uses 2 of them, whereas all later Healeys used just one.
I replaced both relays which seemed to solve the issue for a little while... until it started happening again!!

So I decided to disassemble my original relays and, clean and compare them to the new ones I'd purchased...

As it turned out the new ones actually showed signs of arcing at the points & had soot around the points, so I decided to clean and retry my originals, which worked, but still didn't solve the problem!

Finally I decided to replace the solenoid itself - it's the only piece other than the dash switch that it could be.

It struck me that because the solenoid completes the circuit to ground when it's engaged, perhaps my test light going out with the overdrive could also be a symptom the solenoid losing it's connection to ground and not something feeding the solenoid..

The solenoid actually has 2 windings in it:
-one that engages the overdrive,
-the other is to hold it engaged... I suspect the holding winding is what's failing...
So I replaced it with a new solenoid and voila!
I'm very happy to say that after a nice long test drive today along the coast and up and down the highway, the Overdrive finally seems to be working beautifully now! 

With that sorted, I've decided to go back and rebuild my original gearbox switch and get it back into service.
It was an easy restoration of just cleaning and resealing with a new rubber O-ring to keep oil sludge out of the switch and off the contacts...

So that finally seems to have solved it!
What a good (though sometimes expensive) learning experience, I feel like I've learned a lot, and have replaced and/or rebuilt every electrical switch on this car by now!

At least it's now functioning as it should...Now the driving gets even more exciting!

Until next time -