FYI. More subject info from the Toro mailinglist.
Paul Bartz
Date: Wed, 9 Jun 1999 09:46:45 -0400
From: "Bartz, Paul"
Subject: [Toro] Switch Pitch Transmission
Bruce:
My application/interest with the subject would be in the GMC Motorhome.
I've always been told that when the switch pitch feature was "engaged", the
torque converter would begin to heat up the transmission fluid , which in
time would be dangerous to the life of the transmission. Therefore, time of
engagement is considered critical??
What is your understanding about the heat buildup in the transmission during
"engagement"?
What GM models by year used the switch pitch transmission?
Are you aware of any publications available on the switch pitch
transmission?
Date: Tue, 8 Jun 1999 09:22:45 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] Cost
Thanks for confirming that Fred: the switch pitch feature was dropped
because of cost. About all it did for normal driving was slightly increase
mileage, by allowing a smaller engine to provide the same performance, and
by locking up a little tighter than a "compromise" torque converter.
In 1968 Olds apparently decided it was cheaper to bore the engines bigger
than to make a switch pitch, not a good way to help mileage. I was
designing electronic circuits in 1966, and the technology was there to build
a really good switch pitch control that would enhance all driving modes, for
a lot less than the cost of a radio. I always wondered if their development
team used one. Instead the cost cutters gave us a microswitch, one step
away from dropping the feature altogether. The whole TH400 design must have
been a great source of aggravation to the GM bean counters. Over designed
to the extreme (by their estimation, not mine), how can they sell new cars
when the old ones refuse to wear out and break down? They did try to
substitute some plastic and otherwise "cost reduced" parts over the years,
all of which I have found broken in junkyard units. Fortunately again for
us the "good" parts will directly swap in.
A computer controlled overdrive version (4L80E) has been serving in big
block trucks since the early '90s, and perhaps one day will show up in my
cars. Before the TH400, transmissions were the weak link at my house.
TH200, 350, 125, slim jim, power glide, 4 speed manual (German, the worst!),
I broke them all. The TH325 (79 Toro) has held up surprisingly well (must
be the shift kit), but once I get the TH425 in I can stop pampering it.
Date: Wed, 9 Jun 1999 10:09:28 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] trans
Your switch pitch experience pretty much matches mine. Lots of extra torque
(perhaps 25%) without downshifting, good results with low ratio axles, and
cool running (less heat means better mileage). The switch pitch will reduce
your need to downshift and it is far smoother than shifting gears. The
switch pitch operation WILL affect engine RPM (perhaps 500 RPM increase when
activated), but it WILL not affect shift points relative to road speed.
That is because the trans governor is on the driveshaft, not the engine
input.
My controller really helps the part throttle lugging you mentioned; that is
the key to its "driveability improvement". By sensing lose of manifold
vacuum, it activates the switch pitch without full throttle or down shifts.
It also helps to "pull away" after breaking situations. It is activated
here by the brake switch (far more reliable than that finicky linkage).
After the brake is released, it continues in the performance mode for a time
before going back to economy. The time is easily adjusted, I usually set it
to 14 seconds. This not only generates more torque in part throttle
situations, it makes shifts considerably smoother.
Paul, you are absolutely right that any high stall torque converter
including a switch pitch in the performance mode, will generate a lot more
heat than a tight converter (such as a switch pitch in economy mode). This
heat buildup is not instantaneous (like a slipping clutch), it takes some
time. That is one reason my controller uses adjustible timers to limit time
in the performance mode to a dozen or seconds. These are intended to cover
speed and gear change situations, before changing back to economy mode.
This is not long enough to be a problem for a car.
Transmission heating in a motorhome can be a problem, because the hard pulls
last so much longer. A trans temp gauge is a good idea, and it should be
considered mandatory for a switch pitch motorhome. The Caspro unit comes
with a gauge setup, and of course a big trans cooler should be used. The
electronic controller for this application has much longer timer duration on
the order of half a minute. This seems to cover most situations without
overheating. In extremes the converter can be manually set to economy,
still a huge improvement to the original method of ALWAYS controlling it
manually. Remember, a switch pitch in the dominant economy mode runs
somewhat COOLER than a regular converter.
Date: Wed, 9 Jun 1999 10:37:18 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] More swp
Also to Paul Bartz's questions: There were quite a few pages of the
Kenney-Bell catalog dedicated to description of the switch pitch feature in
1985; I could mail you some of this. Kenney-Bell dropped that line several
years ago.
The Caspro catalog has some info for front drive apps.
I believe the first switch TH400s came out about 1964/5 in Buicks; the
design was somewhat modified and offered across the GM big block for 66/67.
The front drive TH425 shared most of the same parts starting in 66.
Starting in 68 the trans did not include switch pitch. Others could perhaps
detail this out better
Date: Wed, 9 Jun 1999 14:12:13 -0400
From: "Frederick Nissen"
Subject: Re: [Toro] Switch Pitch Transmission
Paul,
Heat build up when the converter is "engaged" (in high stall mode) is no
different than you would encounter in a normal trans fitted with a higher
stall speed converter for increased acceleration. Running an adequate trans
cooler takes care of it.
The TH 400 used in all '64-'67 Buick, Oldsmobile and Cadillac models as well
as the '66 and '67 versions of the TH 425 (FWD Toro/Eldo) featured the
switch pitch converter. The two speed trans used in the Cutlass and F-85 V8
models from '65 to '67 also had a switch pitch converter. Buick may have
shared this as well, but I have never paid attention to the Buick A bodies
of this era.
Paul Bartz
Date: Wed, 9 Jun 1999 09:46:45 -0400
From: "Bartz, Paul"
Subject: [Toro] Switch Pitch Transmission
Bruce:
My application/interest with the subject would be in the GMC Motorhome.
I've always been told that when the switch pitch feature was "engaged", the
torque converter would begin to heat up the transmission fluid , which in
time would be dangerous to the life of the transmission. Therefore, time of
engagement is considered critical??
What is your understanding about the heat buildup in the transmission during
"engagement"?
What GM models by year used the switch pitch transmission?
Are you aware of any publications available on the switch pitch
transmission?
Date: Tue, 8 Jun 1999 09:22:45 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] Cost
Thanks for confirming that Fred: the switch pitch feature was dropped
because of cost. About all it did for normal driving was slightly increase
mileage, by allowing a smaller engine to provide the same performance, and
by locking up a little tighter than a "compromise" torque converter.
In 1968 Olds apparently decided it was cheaper to bore the engines bigger
than to make a switch pitch, not a good way to help mileage. I was
designing electronic circuits in 1966, and the technology was there to build
a really good switch pitch control that would enhance all driving modes, for
a lot less than the cost of a radio. I always wondered if their development
team used one. Instead the cost cutters gave us a microswitch, one step
away from dropping the feature altogether. The whole TH400 design must have
been a great source of aggravation to the GM bean counters. Over designed
to the extreme (by their estimation, not mine), how can they sell new cars
when the old ones refuse to wear out and break down? They did try to
substitute some plastic and otherwise "cost reduced" parts over the years,
all of which I have found broken in junkyard units. Fortunately again for
us the "good" parts will directly swap in.
A computer controlled overdrive version (4L80E) has been serving in big
block trucks since the early '90s, and perhaps one day will show up in my
cars. Before the TH400, transmissions were the weak link at my house.
TH200, 350, 125, slim jim, power glide, 4 speed manual (German, the worst!),
I broke them all. The TH325 (79 Toro) has held up surprisingly well (must
be the shift kit), but once I get the TH425 in I can stop pampering it.
Date: Wed, 9 Jun 1999 10:09:28 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] trans
Your switch pitch experience pretty much matches mine. Lots of extra torque
(perhaps 25%) without downshifting, good results with low ratio axles, and
cool running (less heat means better mileage). The switch pitch will reduce
your need to downshift and it is far smoother than shifting gears. The
switch pitch operation WILL affect engine RPM (perhaps 500 RPM increase when
activated), but it WILL not affect shift points relative to road speed.
That is because the trans governor is on the driveshaft, not the engine
input.
My controller really helps the part throttle lugging you mentioned; that is
the key to its "driveability improvement". By sensing lose of manifold
vacuum, it activates the switch pitch without full throttle or down shifts.
It also helps to "pull away" after breaking situations. It is activated
here by the brake switch (far more reliable than that finicky linkage).
After the brake is released, it continues in the performance mode for a time
before going back to economy. The time is easily adjusted, I usually set it
to 14 seconds. This not only generates more torque in part throttle
situations, it makes shifts considerably smoother.
Paul, you are absolutely right that any high stall torque converter
including a switch pitch in the performance mode, will generate a lot more
heat than a tight converter (such as a switch pitch in economy mode). This
heat buildup is not instantaneous (like a slipping clutch), it takes some
time. That is one reason my controller uses adjustible timers to limit time
in the performance mode to a dozen or seconds. These are intended to cover
speed and gear change situations, before changing back to economy mode.
This is not long enough to be a problem for a car.
Transmission heating in a motorhome can be a problem, because the hard pulls
last so much longer. A trans temp gauge is a good idea, and it should be
considered mandatory for a switch pitch motorhome. The Caspro unit comes
with a gauge setup, and of course a big trans cooler should be used. The
electronic controller for this application has much longer timer duration on
the order of half a minute. This seems to cover most situations without
overheating. In extremes the converter can be manually set to economy,
still a huge improvement to the original method of ALWAYS controlling it
manually. Remember, a switch pitch in the dominant economy mode runs
somewhat COOLER than a regular converter.
Date: Wed, 9 Jun 1999 10:37:18 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] More swp
Also to Paul Bartz's questions: There were quite a few pages of the
Kenney-Bell catalog dedicated to description of the switch pitch feature in
1985; I could mail you some of this. Kenney-Bell dropped that line several
years ago.
The Caspro catalog has some info for front drive apps.
I believe the first switch TH400s came out about 1964/5 in Buicks; the
design was somewhat modified and offered across the GM big block for 66/67.
The front drive TH425 shared most of the same parts starting in 66.
Starting in 68 the trans did not include switch pitch. Others could perhaps
detail this out better
Date: Wed, 9 Jun 1999 14:12:13 -0400
From: "Frederick Nissen"
Subject: Re: [Toro] Switch Pitch Transmission
Paul,
Heat build up when the converter is "engaged" (in high stall mode) is no
different than you would encounter in a normal trans fitted with a higher
stall speed converter for increased acceleration. Running an adequate trans
cooler takes care of it.
The TH 400 used in all '64-'67 Buick, Oldsmobile and Cadillac models as well
as the '66 and '67 versions of the TH 425 (FWD Toro/Eldo) featured the
switch pitch converter. The two speed trans used in the Cutlass and F-85 V8
models from '65 to '67 also had a switch pitch converter. Buick may have
shared this as well, but I have never paid attention to the Buick A bodies
of this era.
