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Why is my overdrive slow to engage?

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Jedi Warrior
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I have a problem with the overdrive of my 100 BN1 taking up to 20 seconds, sometimes more, to engage when at cruising speed (over 2,500rpm in top gear).
But, if I leave the dash switch in the o/d position, the o/d engages almost as soon as the appropriate gear is selected.
Recently the unit was rebuilt with a new accumulator and worked perfectly for a while. It still works perfectly now, once engaged, but it is frustrating waiting for that comforting surge as the o/d drops in.
I am using Penrite Gearbox Oil, 40 weight for our warm Queensland climate. The makers of this oil state that it is suitable for overdrive gearboxes. Any suggestions?
 
[ QUOTE ]
I have a problem with the overdrive of my 100 BN1 taking up to 20 seconds, sometimes more, to engage when at cruising speed (over 2,500rpm in top gear).
But, if I leave the dash switch in the o/d position, the o/d engages almost as soon as the appropriate gear is selected.
Recently the unit was rebuilt with a new accumulator and worked perfectly for a while. It still works perfectly now, once engaged, but it is frustrating waiting for that comforting surge as the o/d drops in.
I am using Penrite Gearbox Oil, 40 weight for our warm Queensland climate. The makers of this oil state that it is suitable for overdrive gearboxes. Any suggestions?

[/ QUOTE ]

It appears that the OD clutch is not fully engaging. Thus the "slip" when you engage it under load. When it engages as you shift with OD engaged, there is no load on the OD clutch & so you don't notice the slip.

I would contact the rebuilder first. There could be several reasons why you are having problems. Control valve adjustment, the valve that the solenoid operates, would be the first thing on my list. The control arm should be adjusted to lift the ball about .030" when the solenoid is fully operated. The factory alignment lever/test pin method of setting the valve is not very accurate as the various parts wear & or develop slack. Next would be the control valve ball not properly seating. It has to seat when it is both the up & down positions. Next would be the pump's non-return valve not sealing. Next, the accumulator piston seal.

It's pretty hard to really diagnose anything without attaching a pressure gage to see what's happening.

Maybe you can get some ideas here:
https://www.britishcarforum.com/lore/article.php?id=064
https://www.britishcarforum.com/lore/article.php?id=073
D
 
Thanks Dave,I think you may have something there. Prior to all my recent O/D troubles (I have owned this Healey since 1968)I always found feathering the throttle helped when engaging overdrive. Now when I do that I get clutch slip.
 
For the sake of "closure", which is becoming as popular a term here in Australia as it is in the USA, I have to tell you all that I have solved the problem of the slow engagement of my overdrive.
It was the darn solenoid lever all the time!!
This has been an intermittant problem for some months and being basically slack & lazy I took months to getting around to trying to sort it. Before I drained the oil to try another viscosity I had another go at adjusting the solenoid lever. It snapped off when I tried to release it from the shaft. I tried welding it back together but couldn't get a satisfactory repair. Fortunately another 100 owner came to the rescue and donated the correct type of lever (my 100 is a July '54 car with the removable cover on the solenoid housing. The later, exposed type of lever is actually a different length). I suppose the moral is: be thorough about checking the simple things first.
 
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