[Healeys] Overdrive pressure not releasing.
Bob Spidell
bspidell at comcast.net
Sun Apr 17 16:06:12 MDT 2022
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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