My first car, a 1949 Willis Jeepster, had a cable actuated o/d on the end of
the 3-speed tranny that would work in all gears. One unusual feature was
that it would coast when you let off of the throttle. It definitely took
some getting used to!
-----Original Message-----
From: Max Heim <mvheim@studiolimage.com>
To: MG List <MGS@autox.team.net>
Date: Monday, February 21, 2000 6:12 PM
Subject: Re: Why OD on 4spd and not just 5spd?
>Good explanation.
>
>As for the previous, broader question, look at it this way -- can anyone
>name any cars in 1962 that had 5-speed transmissions? Ferraris? No.
>Porsches? Don't think so, though I may be wrong. The reason MGs had 4
>speeds is that 5 speed technology was not widely available, at least not
>as a BMC parts-bin component. The reason they had overdrive instead is
>that OD technology had been common since the '30s, if not before. Someone
>commented recently that they didn't think OD saved any wear and tear on
>the engine or driveline components. That may be true, but I always
>assumed that the motivation was passenger comfort (reduced noise and
>vibration) and fuel economy, not wear reduction.
>
>BTW, the late OD only operated in 4th gear, for some reason. I've always
>wondered why they changed it.
>
>
>wizardz had this to say:
>
>>In essence, the O/D is a second transmission in series with
>>the 'stick' controlled tranny. The O/D unit replaces the tail-cone of your
>>stock tranny.
>>It's basically a giant 2:1 planetary gear cluster.
>>You don't end up with 5 speeds...you have 6!
>>O/D is usually configured to engage in both 3rd and 4th gear.
>>
>>This let's you control whether ...say in traffic or whatever...
>>you're cruising at the bottom end of the power band for any given speed,
>>or running near the top of the power band at the same road speed.
>>
>>It's also nearly an instantaneous gear change ( no lost clutch
>>dis-engagement/engagement time) , much like an automatic
>>rev'ed way up that finally kicks up/down a gear...but you have that
control
>>in your finger tips. (thumb tip whatever.)
>>
>>Paul Tegler wizardz@toad.net http://www.teglerizer.com
>>OBie - '73 BGT - daily driver
>>http://www.teglerizer.com/mgstuff/ob_description.htm
>>Punkin' - '78 Spitfire - corner ripping screamer
>>http://www.teglerizer.com/triumphstuff/spit78.htm
>>Lil' Greenee - '73 RWA Midget - lady killer
>>http://www.teglerizer.com/midgetstuff/index.html
>>
>>-----Original Message-----
>>From: Tab Julius <tab@penworks.com>
>>To: wizardz <wizardz@maxinter.net>
>>Cc: MGS@autox.team.net <MGS@autox.team.net>
>>Date: Monday, February 21, 2000 2:12 PM
>>Subject: Re: Why OD on 4spd and not just 5spd?
>>
>>
>>
>>Good point, though of course, half the fun is in the shifting.
>>
>>However, that brings up the other part of the question - is OD different
>>than 5th gear in ways other than the fact that it simply doesn't have a
>>stick position? Is pushing/sliding the little OD button effectively the
>>same as choosing 5th gear or does it do something very different?
>>
>>TIA,
>>
>>- Tab
>>
>>At 02:06 PM 2/21/00 -0500, wizardz wrote:
>>>Stop and think of the era in which the cars were designed.
>>>Yes the major market was the US but they didn't design them
>>>by driving around on US roads. No it was the small country
>>>lanes regional to the factory.
>>>The speeds are up and down, constantly through the gears.
>>>....not flat out cruising and 70+ like the US.
>>> The requirements for gearing were dictated by the design.
>>>
>>>Lightweight... high ratio drive line.. scoot down that crooked lane....
>>>missiles.
>>>with 10 to 50kph Accel. times of less than 3 seconds.
>>>
>>>
>>>
>>>
>>>Paul Tegler wizardz@toad.net http://www.teglerizer.com
>>>OBie - '73 BGT - daily driver
>>>http://www.teglerizer.com/mgstuff/ob_description.htm
>>>Punkin' - '78 Spitfire - corner ripping screamer
>>>http://www.teglerizer.com/triumphstuff/spit78.htm
>>>Lil' Greenee - '73 RWA Midget - lady killer
>>>http://www.teglerizer.com/midgetstuff/index.html
>>>
>>>-----Original Message-----
>>>From: Tab Julius <tab@penworks.com>
>>>To: MGS@autox.team.net <MGS@autox.team.net>
>>>Date: Monday, February 21, 2000 1:43 PM
>>>Subject: Why OD on 4spd and not just 5spd?
>>>
>>>
>>>
>>>I apologize if a greater mechanical background for me would have made
this
>>>obvious... but:
>>>
>>>I first saw OD on an automatic. My Toyota automatic has one, as have
other
>>>vehicles I've owned, and I've always thought of it as the equivalent of
5th
>>>gear (and a gear "over drive", fwiw).
>>>
>>>My Saab has 5 speeds, manual, and no OD. This reinforces my "OD=5th
gear"
>>>assumption.
>>>
>>>So, when I had a chance to think about it, I realized that the 4spd + OD
on
>>>MGs didn't fit into the equation. Is my understanding of OD wrong? Why
>>>not just have 5 speeds / stick positions? Why 4 speeds plus a switch?
>>>
>>>Any enlightenment appreciated...
>>>
>>>Thanks
>>>
>>>- Tab
>>
>>
>>
>
>
>--
>
>Max Heim
>'66 MGB GHN3L76149
>If you're near Mountain View, CA,
>it's the red one with the silver bootlid.
>
>
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