I've been told my '67 has a "switch-pitch"
transmission. What does this mean?
Lockup Torque Converters
Beginning in '81, I believe, GM started providing most automatics with
what's called "locking" torque converters. These do not change the
turbine blade pitch; rather, when the converter "locks", an
internal clutch is applied much like a manual transmission clutch so
that the output of the torque converter is "locked" to the engine. It's
not like the switch-pitch concept...it's a totally different thing.
In these transmissions (TH200C, TH350C, TH200-4R, TH700-R4 in the case
of that other brand), the computer (ECM) detects the road speed and the
Throttle Position Sensor plus other sensors on the vehicle. When the ECM
decides that the vehicle is being driven at a constant road speed above,
typically, 38 mph (44 mph or so for most A/G-bodies), the ECM will
output an electrical signal to the torque converter to cause it to lock
up. When the TC locks, you usually can tell that the engine RPM drops
typically several hundred RPM, which can sound exactly like another
gear. If you have to release the throttle such as cresting a hill and
coasting down the backside, the ECM will detect that you've released the
throttle and will then command the TC to unlock. You usually can't hear
fell this unlock-action. Then when you get back onto level ground and
throttle's been steady for a few seconds, the ECM will again lock the TC.
When the TC is locked up, the torque-multiplication provided by the
blades is effectively "short-circuited" and the engine torque, alone,
drives the transmission.
Think of a torque converter as two fans set one in front of the other.
As one turns (the engine), air from that one will cause the other to turn. A
converter does this with fluid. By switching the pitch of the blades one
fan turns the other more efficiently.
its a variable vane torque converter that uses a electric
actuating rod to operate the variable vanes
controlled through a switch mounted by the carburetor or under the dash, depending on
the engine. The purpose is to provide higher stall speed for acceleration then switch
(angle) of the vanes to achieve a lower stall speed once acceleration is attained.
TC has a control switch which is connected to the throttle linkage. When it
detects that the throttle has been opened to a certain point, an electrical
solenoid inside the tranny will cause tranny fluid to flow through a path into
the TC, and this will cause the turbine blades of the switch-pitch TC to
change pitch. When this happens, the torque multiplication of the TC is
INCREASED, compared to the locking TC in the 1980's and later vehicles, which
effectively eliminates the internal torque multiplication of the TC by locking
torque multiplication helps the engine drive the vehicle easier, much like an
additional gear. A locking TC, on the other hand, causes a slight reduction in
the engine RPM and eliminates the energy loss due to the slight RPM difference
between the turbines inside the TC. The combination of lower engine RPM and
less wasted energy within the TC increase fuel mileage and lower emissions.
The elimination of this energy loss within the TC also helps keep the
transmission much cooler since the transmission's fluid is pumped through the
TC and thus is heated by the TC. Locking the TC eliminates the heat that is
otherwise generated by a slipping TC.
Is this a
The switch pitch
(a great feature, IMO) was only produced '65-'67 for Olds before the GM bean
counters killed it. The control system was a bit primitive, but the
basic idea was great. It was, however, expensive to produce.
converters were available as options on most vehicles that used the TH400,
including the Toronado and some GM trucks. However, I don't believe that
Chevrolet had it as an option although Pontiac, Buick, Cadillac and GMC all
did (depending upon the vehicle). Locking TCs appeared sometime in the very
early '80s, I believe, and are still in use. They were available on most
vehicles in the first years, perhaps as an option, I don't know... but were
standard on most vehicles, regardless of engine size or tranny type. Other
manufacturers, such as Ford, have their own versions.
"Switch Pitch" refers to the
type of torque converter used with that tranny. The
switch pitch (a great feature, IMO) was only produced '65-'67 for Olds before
the GM bean counters killed it. The control system was a bit primitive,
but the basic idea was great. It was, however, expensive to produce.
As you may know, there are horsepower advantages to keeping an engine in a higher
rpm range. Now-a-days, that is done by making the torque converter "looser" (or
higher-stall, as it is called). Torque converters are designed to actually multiply torque
when they slip. It's almost like another set of gears. Thus, you have the advantage of
both more torque multiplication and putting the engine in it's optimum rpm range.
The switch pitch converter was an earlier method used to keep the engine at higher
As you start out from a dead stop, it would slip more than usual. Then at higher speeds,
the vanes inside it would switch to a different angle so that it wouldn't slip as much. I
believe the switching point was electrically controlled. The disadvantage of a switch
pitch converter is that it doesn't provide any extra torque multiplication when in the
looser mode -- you only get the benefit of higher engine rpm.
If there is some
kind of throttle linkage between the carb and some sort of electrical switch
mounted behind the carb (on the firewall, I think); and if there's an
electrical cable plugged into your TH-400; then you have a switch-pitch
TH-400. If you EVER get it rebuilt, you want to make ABSOLUTELY CERTAIN
that the rebuilding shop doesn't simply switch transmissions or torque
converters on you, giving you an ordinary TH-400 without SP. Let them know
that YOU know you have a SP, and that you fully expect your rebuilt tranny and
TC to BE a SP when you get the car back
What color should my restored TH400 be?
The TH400 was left bare aluminum from the factory. Once you degrease it, a good method
to remove any corrosion is to use mag wheel cleaner (the one for
UNPAINTED wheels). Be
sure to completely cover any openings (tranny cooler lines and input and output shafts).
If you want to put a protective coating on afterwards (it really isn't necessary), use a
flat finish clear.
How does a torque converter work?
A torque converter is a fluid coupling device which transfers torque. It does this by
the use of a sealed case and a turbine, stator, and impeller. Basically 3 fan blades, to
put it more simply. One is attached to the crankshaft on the engine (impeller) and one is
attached to the transmission (turbine). The stator is there to aid in the fluid forcing
against the turbine to multiply torque (increase the amount of fluid striking the blades
of the turbine). The impeller spins forcing the fluid in the case to spin the turbine. The
way the fans are shaped and the angle of the blades causes, at certain rotational speeds,
the fluid to "miss" the blades on the turbine which will let the engine
freewheel and not turn the transmission. This is known as stall. If you shape/angle the
blades just right you can keep the impeller from turning the turbine even at moderately
high rotational speeds. At this point the stator really doesn't do much of anything since
at high speed the fluid moves too fast for it to do its job of forcing more fluid against
the blades of the turbine effectively (so no torque multiplication). You would want to
increase the stall to let the engine rev up to a certain point very quickly since there is
no resistance. For an engine with a very hot setup, good only for high RPM output, this
allows the engine to rev up to that point before engaging the transmission. It
you start off the line at the engines best RPM range. For stock engines, or lower tuned
engines, its best to keep the stall at a very low RPM range because that is where the
optimal engine torque will be.
Example 1: If you had a 3000 RPM stall converter on a engine that has its peak torque
at 2200 RPM, upon hitting the gas the engine will jump to 3000 RPM before moving the car
so you would have lost all the torque the engine was putting out up to that point. Since
the engine is low tuned it doesn't put out as much torque past 3000 RPM, the car will lose
every single race.
Example 2: An engine which has a torque peak at 3500 RPM but little torque under 3000.
A 3000 RPM stall converter would allow the engine to "skip" the RPM range with
the least amount of torque before spinning the wheels. A stock converter with a stall
rating of 1600 RPM will cause the wheels to engage very early (when there is little
torque) and the car will lose the race.
These are the basics anyway. There are a lot of variables when attempting to select a
performance torque converter, one of the major factors being the torque of the motor.
For a more detailed torque converter lesson, go to http://www.bmracing.com/noflash/tech/torque.html
All '68-up Olds gasoline engines used the same flywheels and vibration dampers. The
flexplates are drilled for both big and small torque converter bolt patterns. The large
pattern couples to a TH400 and 200R4, and the small pattern fits the ST300 (Jetaway) and
TH350. All 64-67 flexplates are similarly the same, but the crank flange bolt pattern
changed between 1967 and 1968.The only exceptions with dampners are the 350 W-31s which
uses a bigger damper and the 260 and 307 Y which use smaller ones. Anyhow, they are all
balanced the same. I'm not sure what you're doing there, but if you're putting a 350
flywheel on a 455 in place of a flexplate, it will be fine. The lack of pilot bearing hole
in the crankshaft is what you need to worry about if converting from automatic to manual.
One owner reports running a 425/350 turbo with a T.C.I. Saturday nite special in a 1965
Cutlass ragtop. The converter will stall to 2400 rpm according to the factory tach. With a
3.08 posi. it will burn the tires till you let up. He says "the beauty of the
converter is that there no loss of streetability; it stalls just a little over
What flywheels will work on my Olds engine?
There is no difference from SBO to BBO flywheels, but '64-'67
flywheels are different than the '68-'79 units. There is no interchange with Pontiac or
Buick for this one.
However, make certain that you don't have a diesel flywheel. They have heavier, coarser
teeth and the gasser starter will not match, unless you also had access to a diesel
starter...then the diesel flywheel would be a great addition. You wouldn't believe the
improved cranking the diesel starter gives. There were two (or more) models of starters on
the diesels: a 'direct drive' unit and a 'reduction' model. The 'reduction' version is the
premier unit. If you ever pick one up in a boneyard, be certain it works. The diesels
started hard and most starters get cooked due to prolonged cranking.
I want to put an overdrive-equipped transmission in
my car. What are my options?
My first choice would be to go with an
overdrive unit. Allows you to keep the TH400, and it
is a bulletproof unit that can handle 1000HP. I think it is the best way to go
for a high horsepower application. Not cheap, but
bulletproof and well worth the fun. It works as an regular overdrive, or a
"gear-splitter", doubling your existing 3 gears. Nuthin' like chirpin' the
tires thru 6 gears, lemme tell ya! It's a blast!!
OEM OD auto trans I'd trust behind a big block is the 4L80E. This trans is used in
big block trucks and is effectively a TH400 with an OD gear. Unfortunately they only come
in Chebby bolt pattern, so you'll need an adapter plate. Several companies sell them
configured for musclecar use with a standalone computer. Expect to pay about $2600, plus a shortened driveshaft. On the other
hand, you'll pay that much for a Gear Vendors OD unit, plus the cost of beefing up the
TH400. (Jet Automotive also sells a valve body mod for the
4L80E that allows the OD to be engaged in first and second gears, turning the trans into a
Another popular transmission swap in TH350/TH400-equipped cars is the overdrive TH200-R4
unit which has an overdrive (4th) gear. The 700R4 uses a deeper first gear (3.08), but the
RPM drop is too excessive between gears. The TH-700-R4 is only for Chevy motors, anyway.
It won't work unless you get an adapter and modify your trans crossmember and
driveshaft. The 200R4 has better gearing (2.75 first gear). Gains on the strip of 1/2
second are reported when going from a 700 to the 200.
I believe this is one of the most underrated GM late-model parts out there, but by no
means is it bulletproof. Even with heavy-duty mods, GNX/T-Type guys over 400hp usually
switch to something else. If it can die behind a 350 diesel (think torque) it WILL die
behind a built 455.
(If you are not
sure what it is look at the pan. If it is large and irregular-shaped
it is a 2004r. If it is square it is a 700r4.)
In stock form these 200R4 transmissions are not equipped to handle the torque of a larger V-8,
but there is a good aftermarket for performance parts...and keep in mind these trannies
are also used in the Turbo Buicks, so with a heavy-duty rebuild, these can be safely
installed behind stock or even modified 350s and 455s. GN's are pushing 600HP, and 500+
ft/lbs with much success. Just get a rebuild kit, shift kit, larger servo, 10 vein front
pump, and a hardened stator shaft if you plan to lock up the TC @ WOT. Art Carr sells a
kit, and you use some Buick GN parts. Make sure you put a TCC (torque converter clutch)
solenoid in it when its apart if it hasn't been done already; (more on this below) If you
can't find a specialist who can do the heavy-duty rebuild, you can try the new Original Parts Group. Their catalog lists
them for $1300 and are rated at 450 ft/lbs. torque. Kenne
Bell also sells all of the upgrade equipment to beef up the 2004R. Just
remember it ain't no Turbo 400...and won't take the abuse a TH400 will.
You can hook up the 200's linkage with a little fabrication and some ingenuity, when you
take the tranny out of the donor car, before you do any thing watch closely to how the TV
(throttle valve) is pulled by the arm on the Quadrajet. See how much "throw" is
needs. Measure and take notes. Its so important that this movement is duplicated
the 200R4 doesn't use vacuum to change gears or a kick down cable. The TV cable directly
controls line pressure in the valve body. Its takes some work to get any swap like this to
work but it can be done. For info on how to adjust the throttle valve, go to
Be sure to put in a 4-speed auto shifter out of an '80s Cutlass. When swapping this
transmission into a Jetaway-equipped, it turns out the floorshift mechanism is only set up
for the old Jetaways P R N D L and won't let you get out of overdrive because there isn't
room for enough "throw" to reach P R N OD D 2 1. You can take the detent stops
out and to at least get 3rd, which greatly reduces the soggy WOT feeling.
Be sure you pay attention to those wires from the side of the transmission.
(I think the
wire may be the 4th gear clutch pressure switch or the TCC(torque converter clutch) wire.)
I believe these are a 4-terminal connector on the side of the case. (Not all of the
connectors are used.) You may want to get your hands on a factory service manual for that
model year to be sure. Anyway, it controls the torque converter lock-up function in
overdrive and in some cases third (towing?). This was originally a function controlled by
the computer in the donor car. Lock up is very necessary, without it the
tremendous heat at freeway speeds. Heat is bad... it will burn your tranny up very quickly.
There are a couple ways to go:
1) get a TCC solenoid lockup kit from a company like B&M or TRANSGO or
2) read the FAQ at www.442.com about how to make do with a switch and some electrical
know-how. (I'm pretty sure that's where I saw that info.)
You can get help with the wiring from the Buick guys at www.gnttype.org.
I think they are really THE authority on 200r4s. Some of them run 10's with this
supposedly "weak" transmission.
In the case you go with a kit, the B&M kit costs about $185.00 and works off the
speedo cable output on the right rear of the tranny. This is the kit they used in the
HotRod article that prompted me to do the swap. The full bore street/strip kit produces
neck snapping 1-2 and 2-3 shifts. However, in my opinion this kit is inferior to the
TRANSGO kit. The TRANSGO kit operates off engine manifold vacuum and has an adjustable
vacuum switch, which is pretty neat I think, since you can really get it perfect. Also I
don't know if the B&M kit allows you to hook up a toggle switch to turn on and off the
lock-up function like the TRANSGO kit does The TRANSGO kit is around $65. I would
recommend you get that sorted out first.
Once you get that sorted out, add an external transmission cooler in conjunction with the
one in your radiator. Adequate cooling is the key to automatic tranny longevity. As far as
insalling a shift kit in a tranny, it is messy but not hard. Most kits come with very
detailed instructions, only hand tools needed. Of course I did it with the tranny out of
the car. something you might want to consider, laying on your back with AT fluid
everywhere. When I was installing the shift kit I found a broken spring In the 2-3 shift
servo replacement from AAMCO $2 but without it could have been a disaster.
The 200-4R OD's final drive (4th gear) ratio is 0.67 when locked up, 0.67 plus some slip
when not locked up. (That makes 3.73's act like 2.50 gears.) That means when you turn the
input shaft .67 of a rotation then the output turns 1 rotation. Now lets throw a locked-up
torque converter (no slip) in the mix. It'll act like (and really is) a direct link to the
engine. So for every .67 revolution of the engine the output turns 1 revolution. Now if
the TCC isn't engaged (torque converter slips) then the engine will spin a little faster
to turn the input shaft .67 of a rev. This ratio would be higher than lock-up. Maybe .8/1
or 1/1 or who knows?
I'm sure some will disagree but I would recommend you do the junkyard swap route and see
how nice an overdrive is (or not, depending on your driving style) before you invest $600
plus in an ovrdrv/undrdrv unit or $1000 in a 10 sec spec pro-built super-duper 200R4. I
went to the local pick and pull and got a 200R4 out of and '87 Cutlass with a smashed rear
end and 89k on the clock for $75...add a lock up deal for $65 out of PAW and a shift kit
from same place $25, a little elbow grease, a little good ol' fashioned American ingenuity
and viola!...overdrive! Some say that it's a weak tranny but the turbo part of the BOP
family doesn't think so. Key to making this tranny live behind 300-350 hp include putting
in a shift kit, (this will give you an opportunity to inspect the insides of it. If the
clutch packs are dust, you will find lots of friction material and metal in the pan.)
Also.. replace the 1-2 and the 2-3 shift servo springs shift. These things break (my 2-3
was busted) 2) add a tranny cooler 3) make sure you add some form of lock-up function 4)
make sure you can grab all of the gears 1-2-3-od-n-r-p cuz the 2.74:1 first is well...fun
The following related articles/websites are recommended reading:
Are there any automatic transmission besides the TH-400
that can handle the power of a built 455?
Well, if you can afford to "build" a 455, then you may be able to afford to
"build" a tranny. In particular, a TH350 could be built to handle it.
Drag racers with 1000+ HP engines use a variety of trannies. But they buy them already
"built", from shops which specialize in racing trannies.
One option, however, is the 4180e transmission. A 4l80e is an electronic overdrive
transmissions that is based on the TH400. It should be able to handle the power. The
downside is, it is very expensive, requires a computer, and requires an adaptor plate. It
comes behind Chevy late-model full-size pickups and full-size SUV's (Chevy Tahoe) and has
the Chevy bellhousing pattern.