[Healeys] Overdrive pressure not releasing.

Michael Salter michaelsalter at gmail.com
Mon Apr 18 09:43:45 MDT 2022


*Wouldn't opening up an O/D with 500psi be kind of messy? *
Lots of pressure but actually very little volume of oil involved.

M

On Mon, Apr 18, 2022 at 11:25 AM Bob Spidell <bspidell at comcast.net> wrote:

> 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
>
>
>
>
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> 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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