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Re: "Yes, springs wear out."
Correctly designed, manufactured and installed springs don't wear out.
Very occasionally they will suffer from fatigue cracking but that is rare
and a function of poor design.
Think valve springs or distributor point springs; millions and millions of
cycles and still as good as the day they were installed.
M
On Sat., Aug. 12, 2023, 2:25 p.m. Hank Leach via Healeys, <
healeys@autox.team.net> wrote:
> Bob-good point. I just got a set of springs from Moss (from OD Spares in
> UK, I imagine). The cost was $99 or about $12/spring which in the scope of
> things is really not relevant. Holding that clutch in tight contact to the
> brake ring is paramount and just imagine the number of miles in direct
> drive that the car has experienced...many at high RPM. The other side of
> the brake for overdrive position is the "lazy side" as the operating
> pistons under hydraulic pressure have plenty of clout driving mostly steady
> RPMs. Yes, springs wear out.
>
> I place them on the bench and line up the lengths. They should measure
> 4-1/2" for the long springs and 4-1/4" for the short ones but invariably
> there is differences in the resting length. After 50+ years of pushing you
> would tend to get tired. When in overdrive, the springs are greatly
> depressed. That is asking a lot for spiral metal to accomplish. So, yes
> they may look good, but have poor stamina-oops, I just describe all of us.
> Hank
>
> -----------------------------------------
> From: "Bob Spidell"
> To: healeys@autox.team.net
> Cc:
> Sent: Friday August 11 2023 9:19:34PM
> Subject: Re: [Healeys] Laycock overdrive
>
> 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 well
> > 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, relies
> > on adequate hydraulic pressure. The change from direct to overdrive
> > needs to be smooth, not harsh, and if pressures are high the unit will
> > snap into and out of OD rather than the smooth interchange we are used
> > 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 alloy
> > "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 not
> > 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
> >
>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"auto">Re: "Yes, springs wear out."<div dir=3D"auto">C=
orrectly designed, manufactured and installed springs don't wear out.</=
div><div dir=3D"auto">Very occasionally they will suffer from fatigue crack=
ing but that is rare and a function of poor design.</div><div dir=3D"auto">=
Think valve springs or distributor point springs; millions and millions of =
cycles and still as good as the day they were installed.</div><div dir=3D"a=
uto"><br></div><div dir=3D"auto">M<br><div dir=3D"auto"><br style=3D"font-s=
ize:12.8px"></div></div></div><br><div class=3D"gmail_quote"><div dir=3D"lt=
r" class=3D"gmail_attr">On Sat., Aug. 12, 2023, 2:25 p.m. Hank Leach via He=
aleys, <<a href=3D"mailto:healeys@autox.team.net";>healeys@autox.team.net=
</a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:=
0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>Bob-good point=
.=C2=A0 I just got a set of springs from Moss (from OD Spares in UK, I imag=
ine). The cost was $99 or about $12/spring which in the scope of things is =
really not relevant. Holding that clutch in tight contact to the brake ring=
is paramount and just imagine the number of miles in direct drive that the=
car has experienced...many at high RPM. The other side of the brake for ov=
erdrive position is the "lazy side" as the operating pistons unde=
r hydraulic pressure have plenty of clout driving mostly steady RPMs. Yes, =
springs wear out.<div><br></div><div>I place them on the bench and line up =
the lengths. They should measure 4-1/2" for the long springs and 4-1/4=
" for the short ones but invariably there is differences in the restin=
g length. After 50+ years of pushing you would tend to get tired. When in o=
verdrive, the springs are greatly depressed.=C2=A0 That is asking a lot for=
spiral metal to accomplish. So, yes they may look good, but have poor stam=
ina-oops, I just describe all of us. Hank<br><br><div></div><p>------------=
-----------------------------</p>From: "Bob Spidell" <u></u><br>T=
o: <a href=3D"mailto:healeys@autox.team.net"; target=3D"_blank" rel=3D"noref=
errer">healeys@autox.team.net</a><br>Cc: <br>Sent: Friday August 11 2023 9:=
19:34PM<br>Subject: Re: [Healeys] Laycock overdrive<br><br>
re: "... The health of the 8 springs that keep the unit in direct
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 pressure
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 his
writings<br>
> about the early transmissions "harsh shifting" revolved arou=
nd
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 the
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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