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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