<html><body>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.<div><br></div><div>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.</div><div><br></div><div>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.</div><div><br></div><div>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.</div><div><br></div><div>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<br><br><div class="reply-new-signature"></div><p>-----------------------------------------</p>From: "Simon Lachlan via Healeys" <healeys@autox.team.net><br>To: "Healeys"<br>Cc: <br>Sent: Friday July 30 2021 7:32:48AM<br>Subject: [Healeys] Overdrive pressure drop<br><br>
<div class="WordSection1">
<p class="MsoNormal">Hi,</p>
<p class="MsoNormal">I’ve been having issues with my OD. Similar to
someone else quite recently……</p>
<p class="MsoNormal">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.</p>
<p class="MsoNormal">It <i>may</i> be electrical, but I doubt it.
The solenoid goes in with a nice robust click.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I was thinking that it would be pressure
related. So……………</p>
<p class="MsoNormal">I’ve bought a gauge from OD Spares here in UK
and got the car up on axle stands.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I did the test procedure much per the Del
Border article which I sent out the other day.</p>
<ol style="margin-top:0cm;" start="1" type="1"><li class="MsoListParagraph" style="margin-left:0cm;">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<sup>th</sup> and then same in 4thOD after a momentary
drop. (40wt non-detergent).</li>
<li class="MsoListParagraph" style="margin-left:0cm;">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.</li>
</ol><p class="MsoNormal">I am now leaning towards something in the
so-called “ball valve”, items 33 to 37 on page 2 of attached.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Does the above seem like a good place to
start?</p>
<p class="MsoNormal">Could, say, a worn spring or a piece of dirt
in that area cause these issues?</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The names of these valves, “Operating valve”
at top and “Ball valve” at bottom seems to vary with every article
I read.</p>
<p class="MsoNormal">The “non-return valve” and the “check
valve”….are these the same thing and are they what BMC calls the
“Ball valve”, item 37.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thanks, hopefully!</p>
<p class="MsoNormal">Simon</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"> </p>
</div>
</healeys@autox.team.net></div></body></html>