Switch Pitch TH-400 (was something else)

[Shannen Durphey]

Gwyn Reedy wrote:
> 
> Thanks for your response Max, and Shannen too.
> 
> Time to admit some ignorance. Haven't taken apart an automatic since I
> rebuilt a powerglide back in the 70's.  Have driven Buicks with Dynaflow,
> and a 66 Buick with 2 speed torque converter (my mom's car back then) and
> various TH350s and TH400s and the 4l60E in my Impala.
> 
> Was under the impression that you can't put a locking torque converter on a
> TH-350 or 400 because there is some kind of mechanical device (rod or
> sleeve) that is in the trans and activates the locking of the clutches in
> the converter. Seems like it would have to be that or else some kind of slip
> rings to get electricity into the converter to lock an electrical clutch.
> 
> So what I'm asking is if the mechanism to switch the variable pitch torque
> converter is similar enough to the mechanism of the locking torque converter
> to be used for the latter. Not concerned about how the decision to switch
> pitch or to lock comes about, but how does it get transmitted into the
> converter.
> 
> Reason for the interest: I have a big block pickup with TH-400 and 3.08 rear
> end. 4l80's are very expensive but is what I'd really like to have. If I
> could get a locking converter to work on the truck I might spring for an aux
> overdrive unit to mount behind the automatic and put in a 4.11 rear.
> 
> Do you have a reference to a site or book that explains the variable pitch
> setup?
> 
The reference of preference is "How to Work With and Modify the Turbo
Hydramatic 400 Transmission" by Ron sessions.  ISBN 0-87938-267-8 
Hopefully, there's an updated edition which includes the 4L80E.

Both the TCC and the variable pitch mechanisms are hydraulically
actuated through the stator shaft. The stall speeds in the VP are
changed by changing the angle of the stator blades.  The TCC is
applied by forcing a large piston with a thin layer of friction
material against the inside of the converter housing.  The  reason
that a THM350 tcc type converter won't work on the non tcc versions is
that the hydraulic passages and controls aren't present.  This is
assuming that the converter will even fit.  Hydraulically, there are
some similarities.  It's the mechanical problems you have to overcome,
like mismatched splines and drilling hardened shafts and making
auxiliary valve bodies.  I remember considering looking into using the
tcc type 350 converter on the variable pitch 400 pump, but I've since
found I'm satisfied with the v.p. converter.  In the 60's, the general
public didn't like the switch pitch, and GM dropped it.  Twenty years
later, the TCC was forced down our throats and we learned to live with
it.  Compared to the early TCC cars, the switch pitch is a dream to
run.

Now for your situation...  There's a THM350 with a TCC.  If your truck
is for fun and light duty usage, you could switch to a THM350. This
would also free up some horses.  Or maybe replace the trans gear set
for lower 1st and 2nd gear ratios.  They're available for both 350 and
400 trannys.  As far as putting a TCC on your non tcc trans, I don't
know of any easy solution.  If I were going to do it, I'd start by
finding out which parts differ between the 400 and 4L80E, and why, and
go from there.  I won't say it can't be done.  With enough time and
money, anything's possible.

Shannen

> Gwyn Reedy
> Brandon, Florida
> mailto:mgr at mgrcorp.com
> 
> > -----Original Message-----
> > From: owner-diy_efi at efi332.eng.ohio-state.edu
> > [mailto:owner-diy_efi at efi332.eng.ohio-state.edu]
> 
> On Behalf Of
> > Guenther,Max
> > Sent: Monday, January 25, 1999 1:05 PM
> > To: 'diy_efi at efi332.eng.ohio-state.edu'
> > Subject: RE: Switch Pitch TH-400 (was something else)
> >
> >
> > As for control I just used a cheap micro switch.  looked cheesy but
> > works great!
> >
> > >----------
> > >From:        Shannen Durphey[SMTP:shannen at grolen.com]
> > >Reply To:    diy_efi at efi332.eng.ohio-state.edu
> > >Sent:        Monday, January 25, 1999 11:56 AM
> > >To:  diy_efi at efi332.eng.ohio-state.edu
> > >Subject:     Re: Switch Pitch TH-400 (was something else)
> > >
> > >Gwyn Reedy wrote:
> > >>
> > >> Coupla questions.
> > >>
> > >> Does any aftermarket vendor provide custom stall ratios on the variable
> > >> pitch converters?
> > >>
> > >At one time Kenne Bell did.  Looks like rebuilt/strengthened factory
> > >converters, two styles.  1800/2600 rpm, and 1600/2400 rpm stall
> > >speeds.
> > >Kenne Bell, 10743 Bell Court, Rancho Cucamonga, California 91730;
> > >(909) 941-6646.
> > >
> > >> What mechanism is used to control the pitch switch? Could that
> > be adapted
> > >>to
> > >> allow control of the clutch in a locking converter?
> > >>
> > >Old stuff, used in 65-67 Buick and Olds.  Mechanical switches close
> > >circuit, switches to high stall at idle, and at 70%+ throttle
> > >opening.  Electrically, it's opposite the TCC.  Original switches and
> > >linkage are tough to locate, might as well use a manual switch.
> > >
> > >> Gwyn Reedy
> > >> Brandon, Florida
> > >> mailto:mgr at mgrcorp.com
> > >>
> > >> > -----Original Message-----
> > >> > From: owner-diy_efi at efi332.eng.ohio-state.edu
> > >> > [mailto:owner-diy_efi at efi332.eng.ohio-state.edu]On Behalf Of Greg
> > >> > Hermann
> > >> > Sent: Sunday, January 24, 1999 10:50 PM
> > >> > To: diy_efi at efi332.eng.ohio-state.edu
> > >> > Subject: Re: DFI, Batch Fire, and other myths
> > >> >
> > >> >
> > >> >
> > >> > >
> > >> > >Was just thinking yesterday that the switch pitch converter
> > should be
> > >> > >connected to tcc control , and detent solenoid should remain manual
> > >> > >control.  BTW, 350 Buick HEI works, but must use drive gear from 455
> > >> > >points dizzy.
> > >> >
> > >> > Ahh--dangerous thoughts, and hardware that gets
> > forgotten--Anybody know
> > >>of
> > >> > any experience racing with switch pitch TH-400's????  Or
> > whether such an
> > >> > idea ever got tried with turbo motors??? :-) (Like switching
> > the pitch to
> > >> > let it rev up into the boost QUICKLY???)
> > >> >
> > >> > Regards, Greg
> > >> > >
> > >> > >Shannen
> > >> >
> > >> >
> > >
> > >
> >