[Healeys] Overdrive pressure not releasing.
Bob Spidell
bspidell at comcast.net
Sun Apr 17 12:48:32 MDT 2022
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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