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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