G'day,I worked with many drivers at Delec in the 60's and 70's also some from BMD who were specialists in operating the 46's in regen from Nth Strathfield through to Gosford providing you had the road all the way.
The 86 class had severely cracked frames due to being over the load with the 3300 tonner coalies climbing to Zig Zag.
Many of the cab doors would not stay latched shut, such was the extend of the stretch cracks.
The 85 class didn't seem to suffer as badly, but got kyboshed a year earlier.
Both the 85 and 86 class COULD NOT do something that the Metro Vickers butter boxes (46 class) could.
Motor in regen.
With a light load train and on easy grades, you could set up the 46ers in Series Parallel regenerative brake when going down the first hill.
And, then when they got to the bottom of that hill, they would drop out of regen and commence powering.
LOOK MUM, no hands.
This was only possible in Series Parallel and Series motor combos, not in Parallel.
And, you could not get weakies, just full field.
So, it was slow.
But, was fun when you had the time and could just sit there and enjoy the scenery.
Them butter boxes were naturally manual relays, where as the 85 and 86 class have pilot motor driven cam shafts for notching out of resistance, plus weakies and regen.
You could only get into regen on them by shutting off power and engaging regen.
Plus, you could not go back into resistance after having notched out with 85's or 86'ers without shutting off power.
That is unless train speed got down below the full field maintaining speed.
The old butter boxes were hideous toward the end of their use by date.
So modified that no two units were fully identical.
But, they were fun to drive.
On a slow haul up a steep grade, while in resistance, you could reinstate a bank to reduce power to the traction motors if a wheel slip or spin occurred.
The 85 and 86er controller notching was;
Notch One, starting full resistance, and step down notch.
Notch Two, holding notch.
Notch Three, step up notch.
Notch Four, full field.
Weakfield zone of equivalent of 4 weakfields.
Notch Five, motor combination transition.
So, to get going in Series, take notch one, and then notch two and up to notch three to remove a bank of resistance.
Then back to notch Two until motor amps steadies.
Then up to Notch three to remove a further bank, and back to Notch two to hold.
This being repeated until sufficient amps would hold the train after the brakes were released.
Release the train brakes and then continue to slowly notch out of resistance.
If a wheel slip occurs, the go down to Notch One to reinstate a bank of resistance to stop the slipping and return to Notch Two.
Once all resistance is notched out, it was either 9 or 10 banks of resistance, I forget, go for weakies.
On a light load train on a light grade, you could simply whip the controller around into Notch Four and let it step out automatically.
Once train speed has increased to permit transition, around 20 kph to attempt Series Parallel and around 40 - 50 kph for Parallel, go into Notch Five and return to Notch 4.
Better fun than simply whipping a diesel throttle up through the notches to get it to move.
They would set them up in Series Parallel as soon as they got near to 60Km/h and worked them in regen in power as well as regen down the river bank and down from WW tunnel.
Much care was taken as they watched the amps and the settings there. Worked with both single and doubles. One thing I found was the only the senior drivers would attempt it, meaning those with years of experience, most of them at Delec were also those who worked big engines in steam days, then on the mountains the only MP was the 46cl.
PS, it was totally against the rules though. Never heard of any getting bunged or in trouble with it though. I would suggest they were confident in what they were able to do, and it did not always work, especially if one of the 46's was down a bit. If that happened they reverted to normal driving as soon as they could, usually at Eastwood, Epping or Normanhurst.