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Overdrive

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C

canuck

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Recently in an unrelated thread that I cannot find, John Morralees I think asked a question about overdrives, and as mine was not working at the time, I put my doubts about the answers aside. Now that it is, I have experimented with what the responses said, and the behaviour of mine is not what was described.

As I recall it, the post said that the overdrive switch could be left on, the overdrive would stay on but a blip of the accelerator would switch it off.

Mine works this way: you turn it on, you drop revs, you have good but less aggressive acceleration. If you want to take it off, you have to switch it off, and I use the clutch on the way down to ease the transition (anyone else think this makes sense?). If you leave it on and wind up downshifting to second or first, when you go back up, the car will shift into overdrive right away upon engaging 3rd and top.

I don't think any harm can be done by inadvertently leaving it in overdrive in the lower gears, but as I prefer to accelerate through to third and fourth in normal and shift to overdrive at my option, I do try to remember to turn it off.
Chris
 
Hi Canuk, I think you misunderstood the comment. turning the swich off does not normally diengage the overdrive,However, if you pop the throttle with the overdrive swich "off" it will disengage. If this does not happen I would check the setting of the throttle switch.-Cheers Keoke P.S. The updown shifting you described is as it should be. /ubbthreads/images/graemlins/yesnod.gif
 
[ QUOTE ]
I don't think any harm can be done by inadvertently leaving it in overdrive in the lower gears, but as I prefer to accelerate through to third and fourth in normal and shift to overdrive at my option, I do try to remember to turn it off.
Chris

[/ QUOTE ]

If everything else is working faultlessly then yes, but if the gearbox interlock switch or wiring fails in the on state and you reverse in overdrive the chances are that you are in for an expensive overdrive repair
 
In my car, flipping the switch to normal disengages the overdrive, immediately. If you don't use the clutch, you get a bit of a lurch, probably not good for lots of things.
C.
 
Chris, switching the switch to normal should not immediately disengage the overdrive. I think your throttle swich is defective or most likely misadjusted.-Keoke
 
/ubbthreads/images/graemlins/savewave.gif Criss, Normally there is no requirement to use the clutch in conjunction with the overdrive.If yours lurches without using the clutch PO's may have modified the accumulator by removing the sleeve and installing a Triumph Piston. However, keep on using the clutch until you get things sorted out.---Keoke
 
In a previous post we discussed the jerking motion on disengaging the OD. I was a clutcher until the posts. I learned that if I give even a SLIGHT (all that is necessary)increase in RPMs while shutting off the OD there is no lurch. Try it, you will be amazed at the smothness. It becomes natural after 3 or 4 shifts.
 
Now THAT makes sense. I am still a little confused by the idea that the overdrive would not disengage on flipping the switch, per Keoke. The overdrive and engine were completely and thoroughly rebuilt by a Healey aficionado with a great reputation over the winter...All PO modifications were returned to original, and the car runs and behaves sweetly, and this overdrive behaviour seems to make sense to me. This may be a communications issue rather than a real one: perhaps the throttle blip is the way to match revs, avoiding the need for clutch, rather than the way to engage the OD?

Chris
 
The overdrive control circuit has a control relay with a seal-in contact that holds the relay energized after the drivers switch is turned on. The only way the relay is de-energized is by depressing the throttle far enough to open the throttle switch. Consequently, if you switch off the drivers switch and shift out of third or fourth without depressing the throttle sufficiently the relay stays energized. It will re-energize the overdrive solenoid when you go back to third or fourth. If you switch off the drivers switch and depress the throttle sufficiently while in any gear the relay will de-energize so overdrive will disengage. From your description of how your overdrive operates I think it is working correctly.
 
Thanks...that is really clear and I agree, I think my overdrive is working as it should. Nice to understand how it does it!
Chris
 
Stretch, You are correct, However Chris has stated that his OVD turns off immediately when he turns the dash switch off. That sequence is not correct.- /ubbthreads/images/graemlins/nonod.gif-Keoke
 
Keoke,
I read chris's description the same as you & agree that the throttle switch is out of adjustment. In fact, factory recommendation is that OD does not disengage until the throttle is depressed 1/4. I think this is a bit much - 1/8 depression should do the intended job.
D
 
Dave: /ubbthreads/images/graemlins/savewave.gif
I wondered where you were /ubbthreads/images/graemlins/smile.gif--OK ---Keoke
 
I went on a three day trip with our local car club. Snow capped mountains, snow drifts on the roads, lots of beer, good food, BS. Back home to 90 degree plus.
D
 
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