[Healeys] Overdrive pressure not releasing.

Mon Apr 18 10:08:20 MDT 2022

There is a very small bleed hole in the operating rod that if plugged will cause the overdrive pressure to be very slow at releasing.

Remove rod and see if you can blow thru the it. Look in about the middle just below the ribs and you will see the bleed hole. It is most likley plugged

David Nock
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From: Bob Spidell 
Sent: Monday, April 18, 2022 8:24 AM
To: Roger Grace ; simon.lachlan at alexarevel.plus.com 
Cc: Healeys 
Subject: Re: [Healeys] Overdrive pressure not releasing.

Wouldn't opening up an O/D with 500psi be kind of messy?

On 4/18/2022 8:03 AM, Roger Grace wrote:

  To confirm Michae's analysis, consider:
    remove ball, spring and plunger

    remove the valve push rod and inspect - I use a piece of steel wire of appropriate thickness to pry out.

    replace the push rod - it should go in smoothly

    insert the wire again and push down gently; with your other hand operate the cam and you should feel the operating rod move up and down on the cam.

  if not MS is correct and the pin/peg has failed....
  of course it could also be the cotter pin that goes through the setting lever - but less likely IMO

  BTW I have found that my OD (O rings) holds 400 psi for several days.
  rg

       Virus-free. www.avg.com  

  On Sun, Apr 17, 2022 at 3:21 PM Simon Lachlan via Healeys <healeys at autox.team.net> wrote:

    That’s the one I’ve got. I did get an increase in pressure. No question about that.

    I talked to Dave at OD Spares with regard to the various accumulators out there at the moment. I don’t recall exactly but he supplies all of them to his customers and, I think, to the suppliers.

    Simon

    From: Healeys <healeys-bounces at autox.team.net> On Behalf Of Bob Spidell
    Sent: 17 April 2022 23:06
    To: Michael Salter <michaelsalter at gmail.com>
    Cc: healeys at autox.team.net
    Subject: Re: [Healeys] Overdrive pressure not releasing.

    AH Spares has an accumulator and piston which uses an O-ring. It appears the pressure relief hole is chamfered:

    https://www.ahspares.co.uk/austin-healey/performance-parts/gearbox-overdrive/o-ring-conversion-accumulator-piston.aspx

    On 4/17/2022 12:03 PM, Michael Salter wrote:

      Actually Bob I've never used an  "O" ringed accumulator.  

      I spent a little time many years back looking into using "O" rings on the accumulator but couldn't resolve the issue of the ring being chaffed when passing over the radial drillings in the accumulator body. 

      Does anyone know how that has been solved?

      M

      On Sun., Apr. 17, 2022, 2:49 p.m. Bob Spidell, <bspidell at comcast.net> wrote:

        Michael, 

        Sounds like you're implying the O-ringed accumulator is superior to the metal ring (OEM) type? Wish I'd known about it when I rebuilt my O/D (I bought the DWM 'uprated' accumulator).

        I'll throw out another, very unlikely, potential cause: the cone clutch could be stuck together. I've heard of this happening, but have never experienced it my self--nor has anyone I know--but it's theoretically possible (esp. if the clutch is excessively worn). Could this be the reason the manual is adamant about replacing the 8 strong springs, of two lengths, that oppose the operating pistons on overhaul, regardless if they still seem robust?

        On 4/17/2022 9:31 AM, Michael Salter via Healeys wrote:

          Simon,

          Based upon your synopsis I conclude that the operating valve is NOT opening when either the solenoid lever or the setting lever is being moved to the position where the operating valve ball would normally be lifted off its seat.

          This conclusion is based upon your discovery that the pressure in the accumulator, as indicated on the gauge, does not leak away overnight.

          There is a small clearance between the operating valve push rod and the overdrive housing. If the operating valve ball was indeed lifted off its seat all the oil in the accumulator would, over time, leak past the operating rod thus discharge the accumulator. 

          This process would indeed take some time but would certainly completely relieve most, if not all the residual accumulator pressure overnight.

          If however the operating valve ball is still in contact with its seat (i.e. not being lifted) the oil pressure would not reach the small clearance between the valve push rod and the housing and, other than past the accumulator rings there is nowhere for that pressure to be relieved. 

          I would presume that Overdrive Spares installed an accumulator with an "O" ring rather than the original cast iron rings. If the original type accumulator piston was still fitted, oil would seep past the cast iron rings to relieve the pressure, albeit very slowly, and again the accumulator pressure would be discharged overnight..

          The cam on the operating shaft, the one which lifts the operating valve push rod and thus the operating valve ball, is locked to the shaft with a small taper pin. I would guess that the taper pin has either fallen out or sheared. 

          Bad news is that this pin cannot be accessed without removing and disassembling the overdrive.

          M

          On Sat, Apr 16, 2022 at 1:19 PM Simon Lachlan via Healeys <healeys at autox.team.net> wrote:

            My OD is driving me mad and I definitely need some inspired advice. A bit of background first. I’ll try to lay out all the facts in a logical sequence. (I’m increasingly reluctant to link ODs with logic!)

              1.. I’d say that the OD has done +/- 15k miles since a total rebuild by Overdrive Spares here in UK. 
              2.. The OD had issues before Christmas (21) and was sorted out by OD Spares. The accumulator was uprated and pressure issues sorted. 
              3.. OD functioned 100% on the few times I’d been able to take it out since then until.. 
              4.. One day, the OD stopped functioning. 
              5.. I checked the electrics. All fine there so I delved a bit deeper. 
              6.. It had fried its solenoid which I replaced. But… 
              7.. That did not fix the problem so… 
              8.. I decided that the operating valve’s adjustment might be off so.. 
              9.. I bought a dial gauge and hoped to sort it out precisely rather than by “feel”, which I lack in this area. 
              10.. Prior to using the gauge I decided to see if the OD was functioning at all so I raised the car on stands and fitted my pressure gauge. 
              11.. I get a reading of 500psi rising a bit when I rev the engine but I’d suppose that would drop when the oil warms up. 
              12.. BUT, and this is where things go pear-shaped…moving the little lever on the RHS up and down does not engage/disengage OD. There is no change on the gauge to show OD engaging or disengaging. 
              13.. AND, the gauge stays at 500psi even when the engine is off. Moving the lever 20 times has zero effect. Stayed at 500 overnight! 
              14.. Of course, I checked for dirt in the operating valve area. None. 
              15.. Likewise, the tiny hole in the “valve – operating” (the spindle thing which the ball sits on)….that’s clear. And surely, the pressure would diminish overnight if something in that area was partially obstructed? 
              16.. When I remove the pressure valve, there’s a small spillage – no more than you’d expect – but repeating the pressure gauge process only returns the same results. 
              17.. I see in the bible according to Norman Nock that “Holding this lever with your thumb and index finger, you should be able to push the lever down lightly about ⅜” until you feel a slight spring pressure resistance. The lever should go down another ¼” after encountering the resistance……” ie there’s about ⅝” movement up & down in that lever. Well, my lever does move and does lift the ball, but there’s not ⅝” movement there. Could that be the problem area??? 
              18.. Almost finished…keep reading! 
            So, I’m stumped. Every time I learn something new about the OD, it has a new trick to baffle me.

            I’ve no 100% sure way of telling whether it’s gone into OD  and stuck there or whether it’s simply not going into OD at all.

            I’ve done a lot of reading through my books and collection of advice from the various gurus and found reference to ODs being stuck but those seemed to be to do with “weak springs” which, particularly after a long lay-off, wouldn’t disengage. The cure for this being a good smack on the steel plate sandwiched in the OD from below. Well, that seems to be a stuck mechanism issue whereas I’m facing a hydraulic conundrum. Or am I?

            There is what is usually referred to as the “pressure relief valve” adjacent to the accumulator. The name suggested that pressure might be stuck in that area….but surely not overnight?

            Any ideas? I am particularly reluctant to take the gearbox and OD out. You’ll recall the ridiculous business of the defective clutch kit? Well, I forget whether we had the box in and out 3 times or 4. I’d hoped not to do it again so soon or ever for that matter.

            I’m hoping for a miracle of course but some sound advice would be a godsend…………

            Thanks,

            Simon

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