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Thanks for the advice, I have verified the small hole in the valve is not
obstructed and I have increased the hole up one size larger as advised by
another mechanic. I will remove the valve as suggested to verify it's not
pressure locking it engaged.
DW
On Sun, Aug 13, 2023 at 6:01=E2=80=AFAM Michael Salter <michaelsalter@gmail=
.com>
wrote:
> Assuming that you have confirmed that the bleed off hole in the operating
> valve is not blocked, something to try would be to remove the operating
> valve plug (cautiously) while the unit is stuck in overdrive.
> This would determine if the problem was being caused by residual oil
> pressure or a mechanical fault.
> If the overdrive does not slip whilst disengaged it's very unlikely that
> there is anything wrong with the 8 clutch springs.
> Incidentally I have rebuilt dozens of "A" type overdrive units and have
> never encountered the need to replace those 8 springs.
>
> M
>
> On Sun., Aug. 13, 2023, 1:33 a.m. Bob Spidell, <bspidell@comcast.net>
> wrote:
>
>> Two possible causes of this that I can think of:
>>
>> 1) O/D clutch is so worn it becomes jammed together (FWIW my BJ8's clutc=
h
>> was still serviceable at 205K miles)
>> 2) something is preventing pressure on the operating pistons from
>> bleeding down; not sure how this would happen, hopefully someone will ch=
ime
>> in
>>
>> bs
>>
>>
>> On 8/12/2023 2:19 PM, David Wirken wrote:
>>
>> Now that we are on the OD topic, I have a Healey 100 whose OD
>> won't disengage after I switch it off, it's not an electrical problem an=
d
>> I'm really cautious about not putting the transmission in reverse. The o=
nly
>> way I can release it is to rock the car back and forth in neutral until =
it
>> pops out .
>> It's probably time to rebuild, I presume.
>>
>> Any thoughts would be appreciated
>>
>> DW
>>
>>
>>
>> On Fri, Aug 11, 2023 at 11:11=E2=80=AFPM Bob Spidell <bspidell@comcast.n=
et>
>> wrote:
>>
>>> re: "... The health of the 8 springs that keep the unit in direct drive
>>> is important to keep the clutch from slipping...."
>>>
>>> I believe the shop manual admonishes owners to replace these when
>>> overhauling the unit, even if the old ones look and feel fine (some say
>>> not so). I think my old ones are in a box on a shelf somewhere if
>>> anybody wants them.
>>>
>>> Note the O/D pump is a positive displacement pump that will continue to
>>> produce pressure--driven by the full power of the engine--unless there
>>> is a pressure relief mechanism.
>>>
>>>
>>> On 8/11/2023 10:34 AM, Hank Leach via Healeys wrote:
>>> > Guys-this is a very lively topic and one of sometimes great mystery
>>> > and confusion. The unit is complex but the end result is working wel=
l
>>> > or not functioning at all.
>>> >
>>> > On the subject of pressure required to operate the shift into
>>> > overdrive there are many schools of thought. Some people replace or
>>> > stretch springs or add washers to increase the pressure needed. The
>>> > health of the 8 springs that keep the unit in direct drive is
>>> > important to keep the clutch from slipping. The pressure supplied to
>>> > overcome the strength of these 8 spring , and effect overdrive, relie=
s
>>> > on adequate hydraulic pressure. The change from direct to overdrive
>>> > needs to be smooth, not harsh, and if pressures are high the unit wil=
l
>>> > snap into and out of OD rather than the smooth interchange we are use=
d
>>> > to while driving.
>>> >
>>> > When applied to the Austin Healey 100, the Laycock overdrive was
>>> > initially a 32% reduction unit. It was soon found out in these early
>>> > Warwick cars that 32% was too much reduction. DHMC swapped units
>>> > three times in the original DMH tour car until they finally found a
>>> > combination that produced the smooth shift and complimentary gearing
>>> > desired.
>>> >
>>> > It is difficult, today, to find any information on this original 32%
>>> > gearbox, however if you examine the booklet (attached) supplied by
>>> > Laycock for the early cars, you will notice that the casting allowed
>>> > for a large accumulator piston (seen on p6 in brochure). After some
>>> > research and modified engineering, the company came up with this allo=
y
>>> > "sleeve" called the piston housing (photo) which partially filled the
>>> > chamber of the original large accumulator casting and allowed for a
>>> > smaller accumulator piston that we see in all the later 28% reduction
>>> > units. That size piston, in proper condition, produced from 350-450
>>> > lbs of needed hydraulic pressure to overcome the springs influence.
>>> >
>>> > I'm confident that the remark made by Geoff Healey in his writings
>>> > about the early transmissions "harsh shifting" revolved around this
>>> > huge accumulator piston producing too much pressure. Additionally,
>>> > there were three various accumulator springs supplied which adjusted
>>> > the pressure. The early boxes produced about 350lbs and the later
>>> > about 450.
>>> >
>>> > Today, Overdrive Spares supplies that sleeve housing with only one
>>> > rubber O-ring as it is basically a filler part and not under extreme
>>> > pressure. The accumulator piston within is under that pressure. They
>>> > supply a modified piston using O-ring technology. So, it is not
>>> > unusual to get good pressures over the normal 450 lbs required. If it
>>> > works well don't fix it. The only concern is if the pressure does no=
t
>>> > release when overdrive is not called for. A clean unit, with proper
>>> > 30W oil, will allow that to happen. All this some old theory and
>>> > history to ponder. Hank
>>> >
>>>
>>> _______________________________________________
>>> Support Team.Net http://www.team.net/donate.html
>>> Suggested annual donation $12.75
>>>
>>> Archive: http://www.team.net/pipermail/healeys
>>> http://autox.team.net/archive/healeys
>>>
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>>> http://autox.team.net/mailman/listinfo/healeys
>>>
>>> Unsubscribe/Manage:
>>> http://autox.team.net/mailman/options/healeys/dmw@wirkenphoto.com
>>>
>>>
>> _______________________________________________
>> Support Team.Net http://www.team.net/donate.html
>> Suggested annual donation $12.75
>>
>> Archive: http://www.team.net/pipermail/healeys
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>>
>>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr">Thanks for the advice, I have verified the small hole in t=
he valve=C2=A0is not obstructed and I have increased the hole up one size l=
arger as advised by another mechanic. I will remove the valve as suggested =
to verify it's not pressure locking it engaged.<div><br></div><div>DW</=
div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_at=
tr">On Sun, Aug 13, 2023 at 6:01=E2=80=AFAM Michael Salter <<a href=3D"m=
ailto:michaelsalter@gmail.com">michaelsalter@gmail.com</a>> wrote:<br></=
div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bor=
der-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,20=
4);padding-left:1ex"><div dir=3D"auto">Assuming that you have confirmed tha=
t the bleed off hole in the operating valve is not blocked, something to tr=
y would be to remove the operating valve plug (cautiously) while the unit i=
s stuck in overdrive.=C2=A0<div dir=3D"auto">This would determine if the pr=
oblem was being caused by residual oil pressure or a mechanical fault.</div=
><div dir=3D"auto">If the overdrive does not slip whilst disengaged it'=
s very unlikely that there is anything wrong with the 8 clutch springs.</di=
v><div dir=3D"auto">Incidentally I have rebuilt dozens of "A" typ=
e overdrive units and have never encountered the need to replace those 8 sp=
rings.</div><div dir=3D"auto"><br></div><div dir=3D"auto">M</div></div><br>=
<div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Sun., A=
ug. 13, 2023, 1:33 a.m. Bob Spidell, <<a href=3D"mailto:bspidell@comcast=
.net" target=3D"_blank">bspidell@comcast.net</a>> wrote:<br></div><block=
quote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left-w=
idth:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding=
-left:1ex">
=20
=20
=20
<div>
Two possible causes of this that I can think of:<br>
<br>
1) O/D clutch is so worn it becomes jammed together (FWIW my BJ8's
clutch was still serviceable at 205K miles)<br>
2) something is preventing pressure on the operating pistons from
bleeding down; not sure how this would happen, hopefully someone
will chime in<br>
<br>
bs<br>
<br>
<br>
<div>On 8/12/2023 2:19 PM, David Wirken
wrote:<br>
</div>
<blockquote type=3D"cite">
=20
<div dir=3D"ltr">Now that we are on the OD topic, I have a Healey
100 whose OD won't=C2=A0disengage after I switch it off, it'=
;s not an
electrical problem and I'm really cautious about not putting th=
e
transmission in reverse. The only way I can release it is to
rock the car back and forth in neutral until it pops out .
<div>It's probably time to rebuild, I presume.</div>
<div><br>
</div>
<div>Any thoughts would=C2=A0be appreciated</div>
<div><br>
</div>
<div>DW</div>
<div><br>
<div><br>
</div>
</div>
</div>
<br>
<div class=3D"gmail_quote">
<div dir=3D"ltr" class=3D"gmail_attr">On Fri, Aug 11, 2023 at
11:11=E2=80=AFPM Bob Spidell <<a href=3D"mailto:bspidell@comca=
st.net" rel=3D"noreferrer" target=3D"_blank">bspidell@comcast.net</a>>
wrote:<br>
</div>
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex=
;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,20=
4,204);padding-left:1ex">re:
"... The health of the 8 springs that keep the unit in direc=
t
drive <br>
is important to keep the clutch from slipping...."<br>
<br>
I believe the shop manual admonishes owners to replace these
when <br>
overhauling the unit, even if the old ones look and feel fine
(some say <br>
not so). I think my old ones are in a box on a shelf somewhere
if <br>
anybody wants them.<br>
<br>
Note the O/D pump is a positive displacement pump that will
continue to <br>
produce pressure--driven by the full power of the
engine--unless there <br>
is a pressure relief mechanism.<br>
<br>
<br>
On 8/11/2023 10:34 AM, Hank Leach via Healeys wrote:<br>
> Guys-this is a very lively topic and one of sometimes
great mystery <br>
> and confusion.=C2=A0 The unit is complex but the end result =
is
working well <br>
> or not functioning at all.<br>
><br>
> On the subject of pressure required to operate the shift
into <br>
> overdrive there are many schools of thought. Some people
replace or <br>
> stretch springs or add washers to increase the pressure
needed. The <br>
> health of the 8 springs that keep the unit in direct
drive is <br>
> important to keep the clutch from slipping.=C2=A0 The pressu=
re
supplied to <br>
> overcome the strength of these 8 spring , and effect
overdrive, relies <br>
> on adequate hydraulic pressure. The change from direct to
overdrive <br>
> needs to be smooth, not harsh, and if pressures are high
the unit will <br>
> snap into and out of OD rather than the smooth
interchange we are used <br>
> to while driving.<br>
><br>
> When applied to the Austin Healey 100, the Laycock
overdrive was <br>
> initially a 32% reduction unit. It was soon found out in
these early <br>
> Warwick cars that 32% was too much reduction.=C2=A0 DHMC
swapped units <br>
> three times in the original DMH tour car until they
finally found a <br>
> combination that produced the smooth shift and
complimentary gearing <br>
> desired.<br>
><br>
> It is difficult, today, to find any information on this
original 32% <br>
> gearbox, however if you examine the booklet (attached)
supplied by <br>
> Laycock for the early cars, you will notice that the
casting allowed <br>
> for a large accumulator piston (seen on p6 in brochure).
After some <br>
> research and modified engineering, the company came up
with this alloy <br>
> "sleeve" called the piston housing (photo) which
partially filled the <br>
> chamber of the original large accumulator casting and
allowed for a <br>
> smaller accumulator piston that we see in all the later
28% reduction <br>
> units. That size piston, in proper condition, produced
from 350-450 <br>
> lbs of needed hydraulic pressure to overcome the springs
influence.<br>
><br>
> I'm confident that the remark made by Geoff Healey in hi=
s
writings <br>
> about the early transmissions "harsh shifting" rev=
olved
around this <br>
> huge accumulator piston producing too much pressure.
Additionally, <br>
> there were three various accumulator springs supplied
which adjusted <br>
> the pressure. The early boxes produced about 350lbs and
the later <br>
> about 450.<br>
><br>
> Today, Overdrive Spares supplies that sleeve housing with
only one <br>
> rubber O-ring as it is basically a filler part and not
under extreme <br>
> pressure. The accumulator piston within is under that
pressure. They <br>
> supply a modified piston using O-ring technology. So, it
is not <br>
> unusual to get good pressures over the normal 450 lbs
required. If it <br>
> works well don't fix it.=C2=A0 The only concern is if th=
e
pressure does not <br>
> release when overdrive is not called for. A clean unit,
with proper <br>
> 30W oil, will allow that to happen. All this some old
theory and <br>
> history to ponder. Hank<br>
><br>
<br>
_______________________________________________<br>
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