FYI. More from the Toro mailinglist on the switch pitch transmission setup.
Date: Mon, 7 Jun 1999 09:38:37 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] Switch Pitch
Alex, I agree with you: the switch pitch trans gives extra torque in some
situations. It also gives slightly better mileage in the economy mode.
What a combination! What most of you have not yet discovered is it can also
give smoother shifts and increased part throttle responsiveness when fully
utilized; I found this by accident myself. In 1968 Olds increased their V8s
from 330 and 425 cu in to 350 and 455. In my opinion they had to do this IN
PART to compensate for loss of the switch pitch feature (saving money?). Of
course we can have it both ways.
To retrofit a switch to a 68 or later TH400 rear drive trans you need
several things. First, a torque converter: these are available, including
super duty reinforced (against ballooning) units. You need the pump
assembly the converter slides onto. You need a restrictor plug for an oil
passage. And you need a 2 contact plug to bring the second wire out.
Kenney-Bell used to sell all the parts; now you have to scrounge them. Some
of the late 70s trans cases do not have the required oil passage, but I have
been able to drill it on a drill press. Even later cases left out the metal
in that area and can't be converted.
A front drive TH425 can be converted, but the pump assembly means the whole
chain sprocket assembly. You will also need the 66/67 valve body, with 2
solinoids. The restrictor is contained in the valve body.
My typical approach is to get 2 TH400 or TH425 transmissions, a 67 or
earlier and a 70 or later. Each year had its weaknesses, but by using the
best parts from each you can build a trans better than any the factory put
out. I could make a list of parts that I am likely to change out/have seen
failed in scrap units if someone asks. Some of these are still available,
and some I have saved up for whoever might need them.
It would probably be a lot easier to put a 3.21:1 final drive in a 68 Toro,
but I think you would gain more overall performance and some economy by
going to the switch trans (esp with the electronic controller). I like to
run a 2.41:1 to keep engine revs low at 70-75 mph in a 4100lb car, but this
will vary with your application.
The microswitch factory control on Olds (and I think Buick too) only
utilized the converter performance mode at full throttle and idle (to
prevent creeping). So you got no performance benefits in normal driving. I
still use the kickdown to second switch, but the converter is controlled by
the brake switch, engine torque (via manifold vacuum), kickdown, and timer
circuits.
The electronic controller puts all this together to give some extra
performance any time you could use it, then times out in a few seconds and
goes to economy mode. Manual override is possible, but I find it completely
unneeded. The linkage adjustment problems disappear, I use one of the later
kickdown switches mounted over the gas pedal.
The electronic switch pitch controller uses computer type logic to control
an unmodified switch pitch transmissions' torque converter. Only the wiring
is modified. The rest of the trans operates pretty much independently.
I am updating the write-up now to mail to interested parties; cost will be
between $100 and $200 when I figure it out. Bruce Roe
Date: Mon, 7 Jun 1999 09:38:37 -0500 (CDT)
From: bcroe (Bruce C Roe)
Subject: [Toro] Switch Pitch
Alex, I agree with you: the switch pitch trans gives extra torque in some
situations. It also gives slightly better mileage in the economy mode.
What a combination! What most of you have not yet discovered is it can also
give smoother shifts and increased part throttle responsiveness when fully
utilized; I found this by accident myself. In 1968 Olds increased their V8s
from 330 and 425 cu in to 350 and 455. In my opinion they had to do this IN
PART to compensate for loss of the switch pitch feature (saving money?). Of
course we can have it both ways.
To retrofit a switch to a 68 or later TH400 rear drive trans you need
several things. First, a torque converter: these are available, including
super duty reinforced (against ballooning) units. You need the pump
assembly the converter slides onto. You need a restrictor plug for an oil
passage. And you need a 2 contact plug to bring the second wire out.
Kenney-Bell used to sell all the parts; now you have to scrounge them. Some
of the late 70s trans cases do not have the required oil passage, but I have
been able to drill it on a drill press. Even later cases left out the metal
in that area and can't be converted.
A front drive TH425 can be converted, but the pump assembly means the whole
chain sprocket assembly. You will also need the 66/67 valve body, with 2
solinoids. The restrictor is contained in the valve body.
My typical approach is to get 2 TH400 or TH425 transmissions, a 67 or
earlier and a 70 or later. Each year had its weaknesses, but by using the
best parts from each you can build a trans better than any the factory put
out. I could make a list of parts that I am likely to change out/have seen
failed in scrap units if someone asks. Some of these are still available,
and some I have saved up for whoever might need them.
It would probably be a lot easier to put a 3.21:1 final drive in a 68 Toro,
but I think you would gain more overall performance and some economy by
going to the switch trans (esp with the electronic controller). I like to
run a 2.41:1 to keep engine revs low at 70-75 mph in a 4100lb car, but this
will vary with your application.
The microswitch factory control on Olds (and I think Buick too) only
utilized the converter performance mode at full throttle and idle (to
prevent creeping). So you got no performance benefits in normal driving. I
still use the kickdown to second switch, but the converter is controlled by
the brake switch, engine torque (via manifold vacuum), kickdown, and timer
circuits.
The electronic controller puts all this together to give some extra
performance any time you could use it, then times out in a few seconds and
goes to economy mode. Manual override is possible, but I find it completely
unneeded. The linkage adjustment problems disappear, I use one of the later
kickdown switches mounted over the gas pedal.
The electronic switch pitch controller uses computer type logic to control
an unmodified switch pitch transmissions' torque converter. Only the wiring
is modified. The rest of the trans operates pretty much independently.
I am updating the write-up now to mail to interested parties; cost will be
between $100 and $200 when I figure it out. Bruce Roe
