[Healeys] Overdrive pressure drop

simon.lachlan at alexarevel.plus.com simon.lachlan at alexarevel.plus.com
Fri Jul 30 08:11:57 MDT 2021


I've been having issues with my OD. Similar to someone else quite recently..

The OD would engage and disengage properly at high revs but once the car was
cruising along at low revs, the OD would somehow act like it was on the
verge of dropping out &/or dropping back in.

It may be electrical, but I doubt it. The solenoid goes in with a nice
robust click.


I was thinking that it would be pressure related. So.....

I've bought a gauge from OD Spares here in UK and got the car up on axle


I did the test procedure much per the Del Border article which I sent out
the other day.

1.	Pressure is good, at the top end of 470 to 490 with gearbox oil
cold. ie 470 to 490 psi at 1500 rpm in 4th and then same in 4thOD after a
momentary drop. (40wt non-detergent).
2.	When I go out of OD, brake and switch off, the pressure drops to nil
at once. Which is, apparently and according to the article, WRONG.

I am now leaning towards something in the so-called "ball valve", items 33
to 37 on page 2 of attached. 


Does the above seem like a good place to start? 

Could, say, a worn spring or a piece of dirt in that area cause these


The names of these valves, "Operating valve" at top and "Ball valve" at
bottom seems to vary with every article I read.

The "non-return valve" and the "check valve"..are these the same thing and
are they what BMC calls the "Ball valve", item 37.


Thanks, hopefully!




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