Hi Steve,
Best wishes for a Happy and Prosperous New Year.
Yep those symptoms mostly make sense.
*"The first time it would engage when cold, but not when hot. The
accumulator walls were severely gouged, probably from too much debris in
the oil from not having been changed frequently enough before I got the
car. I found no other problems. I concluded that the massive leakage
prevented the accumulator piston from moving back far enough against the
spring to direct the oil to the metering pin."*
In this case unfortunately you don't mention the pre-repair test pressures
but they would have been quite low, probably 300 odd cold and below 250
hot, meaning that there was not enough pressure to move the clutch against
the springs. I would imagine that as your drove and the oil heated up the
unit would have started to slip and then dropped out of overdrive
altogether.
*The second time, the overdrive was slow to engage, felt like it was
slipping, and would make a whirring noise as it tried to do so. I put a
gauge on the O/D and went for a drive. I was reading 350 psi before the
O/D switch was flipped, dropping to 100 psi at it tried to engage and back
up to 350 - 365 psi after engagement. I found a broken accumulator piston
ring and a loose ring in the bottom of the accumulator bore. After
correcting that (and a broken thrust washer behind the planetaries), I read
450 psi before flipping the O/D switch and 250 psi as it engaged. I
neglected to record the recovery pressure. This was done on a test rig and
I did not repeat the test on the road since the O/D worked perfectly after
reinstallation in the car.*
In this case the pressure during engagement is a little low but that is, as
you found, probably due to damage in the accumulator. I'm surprised to hear
that it slipped with a 350 -360 engaged pressure but that may have had
something to do with the broken thrust preventing full travel of the clutch
member...not sure about that one.. I have experienced that whirring noise
on some units as well I suspect it is the unidirectional clutch slipping..
I envy your test rig...I always intended to build one but I never got a
round tuit...
M
On Wed, Jan 4, 2017 at 10:46 AM, BJ8Healeys <sbyers at ec.rr.com> wrote:
> Mike, what I mentioned to Neil is that both times I have had problems with
> my overdrive failing to engage, or engaging sluggishly, the problem was the
> accumulator. The first time it would engage when cold, but not when hot.
> The accumulator walls were severely gouged, probably from too much debris
> in the oil from not having been changed frequently enough before I got the
> car. I found no other problems. I concluded that the massive leakage
> prevented the accumulator piston from moving back far enough against the
> spring to direct the oil to the metering pin.
>
> The second time, the overdrive was slow to engage, felt like it was
> slipping, and would make a whirring noise as it tried to do so. I put a
> gauge on the O/D and went for a drive. I was reading 350 psi before the
> O/D switch was flipped, dropping to 100 psi at it tried to engage and back
> up to 350 - 365 psi after engagement. I found a broken accumulator piston
> ring and a loose ring in the bottom of the accumulator bore. After
> correcting that (and a broken thrust washer behind the planetaries), I read
> 450 psi before flipping the O/D switch and 250 psi as it engaged. I
> neglected to record the recovery pressure. This was done on a test rig and
> I did not repeat the test on the road since the O/D worked perfectly after
> reinstallation in the car.
>
>
>
> Steve Byers
>
> HBJ8L/36666
>
> BJ8 Registry
>
> AHCA Delegate at Large
>
> Havelock, NC
>
>
>
>
>
> *From:* Healeys [mailto:healeys-bounces at autox.team.net] *On Behalf Of
> *Michael
> Salter
> *Sent:* Wednesday, January 04, 2017 9:53 AM
> *To:* Neil McDonald
> *Cc:* Healey List
> *Subject:* Re: [Healeys] BN6 Overdrive
>
>
>
> Hi again Neil,
>
> With all due respects to Steve I would not suspect the accumulator because
> it is in the hydraulic circuit ahead of the operating valve.
>
> If the accumulator was leaking badly enough to prevent the overdrive from
> engaging you would never see 390 p.s.i. if you are testing at the operating
> valve plug with the ball and spring in position.
>
> Although the specified pressure for our units is 470 - 490 p.s.i. I have
> never seen one achieve 490 p.s.i. and have found units that operated quite
> satisfactorily with pressures as low as 300 p.s.i. hot.
>
> Someone suggested running the car on stands and manually lifting the valve
> setting lever. That is how I test for correct operation BUT PLEASE be ware
> of that driveshaft spinning next to your right hip. Getting yourself
> tangled up in that will ruin your day.
>
> Michael S
>
> BN1 #174
>
>
>
> On Wed, Jan 4, 2017 at 6:05 AM, Neil McDonald <nmcd10 at gmail.com> wrote:
>
> Yesterday I wrote "I have concluded that the most likely cause of my
> problems are low OD fluid levels and/or inadequate opening of the actuating
> valve. Both I can readily deal with."
>
>
>
> In off line discussions with Steve Byers I have added a third and ominous
> possibility, a defective accumulator. The good hydraulic pressure already
> confirmed only indicates that the pump is OK because testing was not done
> while trying to engage the OD. My understanding is that OD engagement is
> the accumulator's function and the pump's role is to pressurise the
> accumulator for this task *before* OD engagement. A definitive test of
> accumulator condition seems to be how well it holds pressure after the
> engine is switched off!
>
> _____________________
>
> Neil McDonald
>
>
>
> Email: nmcd10 at gmail.com
>
>
>
>
>
>
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>
--
*If you can't fix it with a hammer, you've got an electrical problem.*
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