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Re: MGB Overdrive/Driveshaft

Subject: Re: MGB Overdrive/Driveshaft
Date: Wed, 4 Dec 1996 14:29:40 EST
JKearman wrote:

>I notice that MGBs with Type-D overdrives had vacuum switches, as well as the
>driver's switch and the switch in the transmission that inhibits the o/d
>unless you're in 3rd or 4th gears.

>Cars with Type-LH overdrives don't have the vacuum switch.

>I assume the vacuum switch made the o/d switch out when you got on the
>throttle, and let the o/d kick back in when you let off the throttle, like
>"passing gear" on a automatic transmission. This seems like a "good thing." I
>wonder why it wasn't used in the later cars?

>Also, anyone in the Northeast US have a driveshaft for an O/D car (73)? I
>guess it's a little shorter than the shaft used on a non-O/D car.

>Also need the column-mounted combination wiper-O/D stalk.

Sorry mate - wrong on both your assumption and your guess!  The 
vacuum switch inhibited shifting out of overdrive under high manifold 
vacumm conditions, i.e., you have taken your foot off the throttle, 
coming down from relatively high rpm.  This switch, and the 
protection it was supposed to provide, was deemed unnecessary with 
the newer overdrive unit.  And the driveshaft is the same length for 
all models from 1968 on.



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