[Healeys] Overdrive pressure drop

[Bob Spidell]

Sounds to me like your hydraulics are OK; sounds more electrical to me. 
I had similar symptoms with an intermittent OD relay; I fixed it in a 
hotel room in Canada by opening up the relay and filing the points (and 
replaced it when I got home).

I suspect--and it's only a guess--that you get the drop out/in symptom 
at lower revs because most of us--racers aside--spend the vast majority 
of time cruising at 2-2.5K RPM, so you get that symptom in that regimen 
more often.

Bob

On 7/30/2021 10:04 AM, Henry G Leach via Healeys wrote:
> Simon-yes, there are two balls which control the pressure in the unit. 
> In the operating valve which is engaged by the action of the solenoid, 
> dirt is a possible issue. There is a very tiny hole drilling in the 
> stem of the valve which allows the oil to circulate.  That opening can 
> plug with debris and stop the flow. Oil from the accumulator goes thru 
> this valve and lifts the ball allowing the operating cylinders to move 
> forward on the clutch producing the overdrive. When the ball is seated 
> (solenoid off) oil does not pass and is dumped into the OD sump.
>
> You can see that this tiny drilling is very important and must be kept 
> clear.  Often rebuilders suggest to enlarge the hole to 1MM. It may 
> change the dwell time of the OD action, but its has a better chance of 
> staying clean...a theory not proven.
>
> The other ball is on the oil pump and that is the one that Del 
> suggested needed a new spring or extended plunger  to enhance 
> pressure-another theory.
>
> As you measured no pressure when out of OD, that is due to the ball 
> properly seating on the valve and reliving the pressure that operates 
> the two pistons. If you move the lever or engage the solenoid you 
> should get 470 lbs. again.
>
> I would suggest cleaning the valve-use a magnet to get the parts out 
> and don't use a shop rage to clean them (no lint). If all is ok in the 
> valve body you need to look further into the accumulator and o-rings 
> and piston rings. I suggest you contact David at OD Spares for some 
> additional advise. Hank
>
> -----------------------------------------
>
> From: "Simon Lachlan via Healeys"
> To: "Healeys"
> Cc:
> Sent: Friday July 30 2021 7:32:48AM
> Subject: [Healeys] Overdrive pressure drop
>
> Hi,
>
> 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 stands.
>
> 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 4^th 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 
> issues?
>
> 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!
>
> Simon
>
>

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