<VV>Overdrive

[Tony Underwood]

At 08:17 hours 08/11/2006, tkalp at cox.net wrote:
>Chrysler made an overdrive 4-speed back in the '70's or '80's.


Both.   That would be the A-833OD gearbox, which is externally 
identical to the A833.


>They used their standard 4 speed, left "fourth" as 1:1 but put 
>overdrive gears in the third gear position.


They did this by pretty much swapping the sizes of the 3rd gear on 
the syncro hub with the 3rd gear on the countergear.   Thus, 3rd gear 
was overdriven instead of underdriven.


>Then they flipped the third/fourth shifting arm 180 degrees so when 
>you drove and put the shifter in to third position, it actually 
>selected the 1:1 "fourth gear" and the shifter's fourth gear 
>position selected the overdrive "third gear".


It was rather ingenious, since it meant no changes to the gearbox 
case or most of the other hardware that went into the 
assembly.   They did change the cluster gear and the 2nd gear idler 
so as to make a wider spread between 1st and 2nd, to keep from having 
such a big gap between 2nd and "3rd" which was actually 1:1.

With a torky engine, this gearbox was the best of both 
worlds.   There's one of these gearboxes in the Dodge Ram pickup in 
the driveway.    Works well.   The truck has some gotohell rear end 
gears in it which would make it terrible on the highway if not for 
that OD gearbox.


>With the single rail shifter in a Corvair it would be trickier to 
>get the correct pattern.


Actually, it would be almost impossible.   No external linkage for 
the 'Vair gearbox...  you'd have to swap out 3rd and 4th via the gear 
shift, which means shifting from 1st to 2nd, then to "4th" and then 
"3rd" according to the standard shift pattern...  and you'd need to 
be prepared for a rather steep drop between 2nd and the new "3rd" 
gear.   But it would sure help out if the Vair has 3:55 gears and 
short tires and runs the highways often.

My '60 buzzes like a weed-eater in traffic on the Interstate, keep 
finding myself looking for another gear.

>The effect would not be much different then using a 3:08 and wide 
>ratio transmission.


The modifications to the Vair gearbox would involve some cutting and 
welding on the cluster and synchro idler gears...  which has already 
been done by the racers to change gear spacing etc.   No reason 
someone couldn't do this to a Vair gearbox to add an overdrive ala 
the Chrysler A833OD gearbox trick.

What you would have in effect would be a three speed with 
overdrive...  and what's more, if someone wanted to actually do this, 
a kit could be cooked up to convert a "typical" Vair gearbox (you'd 
have to make sure which one) into an OD variant.

Now, if someone could conjure up a means to keep the 3-4 shift the 
way it started out...  ;)



tony..