Spit_2.5PI Posted September 4, 2019 Report Share Posted September 4, 2019 21 hours ago, john.r.davies said: PS Duncan, when changing gear from 4th O/d to 3rd O/d, or the opposite direction, the O/d does not disengage and re-engage. The O/d stays in operation. J. John, while there's no interruption in the OD signal changing between 3rd & 4th in Triumph's "Small Car" gearbox, is the same true for the TR/Saloon box? I have this nagging feeling it might not. Can anyone tell me which it is please? Cheers, Richard Quote Link to post Share on other sites
john.r.davies Posted September 4, 2019 Report Share Posted September 4, 2019 (edited) 12 hours ago, Mike C said: Check the O/D interlocks work still in the lower gears /reverse. Some boy racer wired mine to engage in all gears to help him climb hills faster in the 1970's/80's That's what I meant by "getting busy with a jumper wire"! Richard, "The OD signal"? This technonology is pre digital, pre electronic and just, but only just, electric! The OD is a epicyclic gear box behind the constant-mesh, helical drive gearbox in front, and works completely separately. It would be possible to 'switch' the OD on and off mechanically. But for convenience and simplied constuction, the 'signal' is a voltage in a simple circuit with two switches, one to the driver's hand on the steering column, the other an "inhibitor" switch on the front gearbox . Both must be 'On' for the volts to get to the solenoid (which provides the mechanical switch!) to engage the overdrive . If it is engaged, it stays engaged, unless it is disengaged, either by the driver turning off the voltage from the switch on the steering column, or by changing to a lower gear, interrupting that voltage by the inhibitor switch on the gearbox. There is no provision for disengaging and re-engaging OD when changing between 3rd and 4th, or the other way as the inhibitor switch on the front gearbox is arranged to stay 'on' in both gears. John Edited September 4, 2019 by john.r.davies Quote Link to post Share on other sites
Spit_2.5PI Posted September 4, 2019 Report Share Posted September 4, 2019 3 hours ago, john.r.davies said: "The OD signal"? Apologies John. Yes, by OD Signal, I meant the 12V which goes to the solenoid via the driver's OD switch and the gearbox inhibit switch. On the small car box the inhibit switch does not interrupt (inhibit) the signal (i.e. 12V) to the solenoid between 3rd & 4th. Is this the case with the saloon / TR box? Is there more than one OD inhibit switch on the big box? I thought I remembered it might be different, especially as someone on page 1 had mentioned dropping out between the gears. I hope I've explained myself now. Cheers, Richard Quote Link to post Share on other sites
Mike C Posted September 4, 2019 Report Share Posted September 4, 2019 There's always an inhibit switch on reverse. Quote Link to post Share on other sites
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