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[oletrucks] Switch Pitch Transmissions

To: Old Trucks List <oletrucks@autox.team.net>
Subject: [oletrucks] Switch Pitch Transmissions
From: J Forbes <jforbes@primenet.com>
Date: Fri, 07 Apr 2000 18:41:18 -0700
Sure, Bob!

The switch pitch was used in mid 60s NON-Chevy GM cars, such as Buick,
Olds, and Cadillac.  The torque converter has moveable vanes on the
stator, and is controlled by hydraulics, actuated by an electric
solenoid.  The TH400 and SuperTurbine 300 used this system.  The 300 is
an obsolete 2 speed tranny, similar to the Powerglide, and probably not
something you want to mess with.  The TH400 that used the switch pitch
had a special restrictor plug installed in the case, and used a
different front pump assembly, and input shaft, as well as the special
torque converter.  The TH400 case had a special passage that was
eliminated in the 1970s, so the newer Chevy cases won't work with this,
but Chevy cases from the 60s and early 70s can be adapted to use the
Switch pitch guts.  The wiring is simple...I have a toggle switch on the
shifter to send 12v to the tranny when I want it to be in high stall.  I
get about 2000 in low stall, and 2500 in high stall, using a "loose"
ST300 torque converter (the 400 converter is bigger, and gives lower
stall speeds, usually about 2000 rpm in high stall).  Some torque
converters are tighter than others, and there are high performance
switch pitch converters available, but they aren't cheap!

If you want to pursue this, you first need to find the parts...which are
getting very scarce.  The switch pitch TH400 was used from 1965-67, and
mostly in big boats that have all been crushed by now.  You might get
lucky and find the parts at an old transmission shop, or perhaps you
will find a tranny at a junkyard.  Look for a short outer spline, and
smooth area, on the outer input shaft.  Also, look at the tag on the
tranny, which will give the year, if it's a likely candidate the year
will be 65, 66, or 67, and the case will have the non-Chevy bolt pattern
with a valley at the top of the bellhousing, instead of a peak (Caddies
and Buicks had a different case, so look for a 2 letter code that does
NOT begin with a C).


"R. Welch" wrote:
> Jim, can you provide a little more info on the switch pitch converters?  Are
> they factory only?  Still available? What transmissions will they fit in?
> What is the stall rpm?  How do you wire them up electrically - what mods are
> necessary to the trans?  -Bob
> >
> > I run high stall converters behind my higher performance engines because
> > it really makes a difference in how the truck accelerates, especially if
> > the cam has a long duration, and not much low end torque.  Of course, I
> > cheat and use switch pitch converters (a special feature of non-Chevy
> > TH400s from 1965-67) so I get the benefits of low stall speed while
> > cruising, plus the greater acceleration....I just have to flip a toggle
> > switch.
> >
> > Jim
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