Re: A833 OD questions

[Doug Ahern <D170A833@xxxxxxxxxxxxxxxxxxx>]

you'd want the truck/van OD unit.  it is b-body length and has the shifter
provision in the same location as b-bodies.

the 3/4 gear set is at the front of the 4spd.

these are constant mesh transmissions..,  all gears are always meshed.
the only thing that moves or engages are the clutch sleeves that slide
forward and backward to lock a gear to the mainshaft.

on a regular 4spd,  3rd gear is engaged when the clutch sleeve goes 
backward and locks the 3rd gear on the mainshaft to it's counterpart 
3rd gear on the lower countershaft.  still on a regular 4spd,  4th gear 
is engaged when the clutch sleeve moves forward and locks the mainshaft
to the input shaft. 1:1.  hence "direct drive".  the counter shaft bears no
load and simply free wheels...  is is why manuals are considered to
be efficient transmissions.  this where the tranny is 90% of actual
vehicle operation time.. the only HP drain would be what it takes to
move the tranny fluid around the box.

on an OD 4spd,  the 3-4 lever on the outside of the transmission
is flipped over, so a normal shift pattern from the perceptive of
the driver and his Hurst 1-2-3-4,  actually shifts the tranny 
1-2-4-3.,,  so the driver's 3rd gear is "direct drive" (most 
efficient) 1:1.  when shifted to the driver's 4th gear, the 833 actually
engages the traditional 833 3rd gear set by sliding the clutch sleeve
backward over the the traditional 3rd gear lock.  To make it an OD,
Chrysler and New Process simply  designed the 3rd gear set to be 
an overdrive gearset where by the larger tooth count gear was on the
countershaft and the smaller tooth count gear was on the mainshaft.
to facilitate the small gear on the mainshaft,  Chrysler and New Process
used a smaller diameter mainshaft at the 3/4 gear area, hence "OD weak
spot #1".

since the tranny spends most of its time in "top gear",  the new OD
unit would spend most of its time with the countershaft engaged and
thus, be directing torque through 4 gears and the countershaft 
instead of a simple direct drive.  to offset the added "side" load
of the input shafts direction of torque down to the counter shaft
a larger input bearing was used.   "OD weak spot" averted!  but the
countershaft is now directing torque for 90% of the driving time,
and its centering bores in the main case are now under a lot more
stain.  hence "OD weak spot #2".  this is why Passon's aluminum 
case bushes this countershaft bore.

the truck OD to B/RB requires machining a 4spd bellhousing.

so..,  those are the weaknesses of the OD and how they work.  If
you are a mild mannered driver,  the OD will stand up.  If you bang
gears, shread tires all the time, your OD unit will be at its limits.

If you want a built proof OD unit, you should look at Passon's 
OD unit.  this is a beast.  its the same basic design that New Process
and Chrysler used for their OD, but he fixed the weak spots.
It uses a specially designed OD gear set that uses a regular 
non-OD mainshaft (not a narrowed mainshaft),  and he bushes the
main case.  plus he uses an 18 spline input shaft.  

For my $3K, this is the hot ticket.   Keisler's Tremec 5spd is cool,
BUT its a rail shifter and it feels like a rail shifter.  the new
automatic is cool too, but thats an automatic!


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