[Healeys] Laycock overdrive

Roger Grace roggrace at telus.net
Sun Aug 13 11:03:21 MDT 2023 

Yes totally agree that hi carbon spring steel does not age if not abused.
Having said that, it would be good practice to compare free lenghts against
a known good quality one

Found this on a spring manufacturers site.

*The first question is ‘could a spring last forever?’ and the answer is
yes, it could do if*

   - *The operating stresses are not too high*
   - *The working temperature does not cause the spring to lose too much
   load*
   - *The environment does not cause corrosion*
   - *The spring is not abused*
   - *The spring is well-made and free from imperfections.*

*If a spring meets the above requirements, yes it could potentially last
forever!*

rg

<http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
Virus-free.www.avg.com
<http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Sun, Aug 13, 2023 at 9:40 AM Michael Salter <michaelsalter at gmail.com>
wrote:

> 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 at 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 at 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
>> >
>>
>> _______________________________________________
>> Support Team.Net http://www.team.net/donate.html
>> /> Suggested annual donation $12.75
>>
>> Archive: <http://www.team.net/donate.html%3Cbr>
>> http://www.team.net/pipermail/healeys
>> http://autox.team.net/archive/healeys
>> />
>> Healeys at autox.team.net
>> <http://autox.team.net/archive/healeys%3Cbr>
>> http://autox.team.net/mailman/listinfo/healeys
>> />
>> Unsubscribe/Manage: <http://autox.team.net/mailman/listinfo/healeys%3Cbr>
>> http://autox.team.net/mailman/options/healeys/gradea1@charter.net
>> />
>> <http://autox.team.net/mailman/options/healeys/gradea1@charter.net%3Cbr>
>> _______________________________________________
>> 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
>>
>> Healeys at autox.team.net
>> http://autox.team.net/mailman/listinfo/healeys
>>
>> Unsubscribe/Manage:
>> http://autox.team.net/mailman/options/healeys/michaelsalter@gmail.com
>>
>> _______________________________________________
> 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
>
> Healeys at autox.team.net
> http://autox.team.net/mailman/listinfo/healeys
>
> Unsubscribe/Manage:
> http://autox.team.net/mailman/options/healeys/roggrace@telus.net
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/healeys/attachments/20230813/3b74d4ab/attachment.htm>

More information about the Healeys mailing list