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BN1 Overdrive

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Bentley3

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I have a friend's BN1 in my shop with an overdrive problem that I have not seen addressed, or if it has, I've missed it.

The overdrive works. The problem is it works all the time. About 20-25 mph the overdrive kicks in, in second or third, as it should, albeit at too low a road speed. It does this regardless of the position of the dash switch. There is no kick-down. The overdrive solenoid will kick out under 20 mph when the shifter is put in neutral.

I have done the following tests according to the factory manual and several on-line procedures: Checked the relays; this is a two-relay system. They are operating as the various tests indicate they should. Tested the gear switch, both in and out of the gearbox. Checked the throttle switch and carefully adjusted it...several times. The test on the switch seemed to be a bit inconclusive so it disconnected it. I tested the overdrive operation with the throttle switch wires both off the switch and connected together without change in the overdrive operation. The centrifugal switch had been bypassed some years ago and the system was working properly until last fall. I removed the bypass to check the centrifugal switch operation without any change. The dash switch is new and I have checked its operation also, knowing that even new electrical components might be faulty. The solenoid is working very well, obviously. The owner bypassed everything and wired the dash switch directly to the solenoid so the car can be used with and without the overdrive, engaging it when needed. Of course, there is no kick-down and he has been careful to turn the switch off before using reverse...so far.

Most all the on-line discussions i've read concern a system not working. This one won't stop working. Any clues as to what I've missed? Suggestions are greatly appreciated.
 
Have you checked to see that power to the solenoid is being applied/removed when the solenoid activates?

Maybe the solenoid is powered all the time and the OD is switching off the centrifugal switch only.
 
Power to the solenoid switches on as soon as the gear lever is moved to 2nd or 3rd gear. Maybe it's picking up that power through the centrifugal switch? It's been bypassed with a wire across the terminals but not otherwise isolated.
 
If the switch is bypassed with a wire across the terminals then it is no longer a switch it’s just a wire junction .
 
I wrote an article on the BN1 overdrive electrical, soon to be published in the HEALEY MARQUE magazine. I made a logic diagram for the BN1 wiring (attached). You will see the overdrive solenoid is energized through overdrive relay #1 contacts C1-C2. Is relay #1 picking up when the gear lever is in 2nd or 3rd? Perhaps the relay contacts C1-C2 are welded closed? With the wiring modifications, maybe there is some errors in the connections. Looks like the solenoid is always energized and the overdrive enables when the pressure builds up?


Screen Shot 2024-05-28 at 10.23.16 AM.png
 
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