Switch Pitch TH400 Advice
February 9th, 2021, 07:06 PM
#1
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Join Date: Jan 2021
Location: Cleveland Ohio
Posts: 12
Switch Pitch TH400 Advice
Hello everyone!
I am currently working on rebuilding a switch pitch transmission out of a 1966 Oldsmobile 98. I'm looking for advice directly relating to the actual switch pitch system itself. I ran into a few problems during disassembly and have also heard a couple of mods that I was wondering if anyone had good instructions or info on.
1. During disassembly the two prong connector that goes through the housing broke. Luckily, I found a new one online so I think that problem is solved. However when taking the two solenoids out, the insulation on the wiring running between them from the connector completely crumbed because it was rock hard after 50 years in a transmission. I was wondering how I should go about fixing that wiring and checking to see if my solenoids work.
2. Assuming my solenoids work I do not have the factory trigger for the switch pitch which I believe was a "dashpot" or something similar that sent the electric signal to the kickdown solenoid and the switch pitch solenoid when needed (via vacuum? I don't really know). I have heard of people wiring up a manual switch to trigger the switch pitch whenever you want (i.e. hard drag race launch). How would I go about doing that and what do I need to do?
Also any known resources on the TH400 switch pitch system specifically would be awesome! (Books, internet links, etc) I already have a rebuild book that has been super helpful but it has no mention of the switch pitch.
Thanks in advance!
-Mike
I am currently working on rebuilding a switch pitch transmission out of a 1966 Oldsmobile 98. I'm looking for advice directly relating to the actual switch pitch system itself. I ran into a few problems during disassembly and have also heard a couple of mods that I was wondering if anyone had good instructions or info on.
1. During disassembly the two prong connector that goes through the housing broke. Luckily, I found a new one online so I think that problem is solved. However when taking the two solenoids out, the insulation on the wiring running between them from the connector completely crumbed because it was rock hard after 50 years in a transmission. I was wondering how I should go about fixing that wiring and checking to see if my solenoids work.
2. Assuming my solenoids work I do not have the factory trigger for the switch pitch which I believe was a "dashpot" or something similar that sent the electric signal to the kickdown solenoid and the switch pitch solenoid when needed (via vacuum? I don't really know). I have heard of people wiring up a manual switch to trigger the switch pitch whenever you want (i.e. hard drag race launch). How would I go about doing that and what do I need to do?
Also any known resources on the TH400 switch pitch system specifically would be awesome! (Books, internet links, etc) I already have a rebuild book that has been super helpful but it has no mention of the switch pitch.
Thanks in advance!
-Mike
February 10th, 2021, 12:45 AM
#3
Registered User
Join Date: Oct 2016
Posts: 33
1. The detent or kick down solenoid is inexpensive and widely available so no need to rewire that one. For the switch pitch solenoid, you will have to rewire as nobody is making them any more. I wasn't sure what kind of wire I could buy to work in there so I used wire from a newer transmission internal harness to replace the old busted up wire on the switch pitch solenoid. Remove the switch pitch solenoid from the back of the trans pump and make the splice into the old wire as close to the solenoid can as possible. You can't really wire all the way into the solenoid as you can't solder that close to the coil without melting the insulation and causing a short. You will need some proper metal crimps as I would not trust the ones with plastic insulators. You will also need some chemical resistant heat shrink tubing as I don't think electrical tape will survive in there either. Go to a local trans shop they will probably give you a junk internal wire harness to chop up and maybe they have the right materials and tools to replace the wire for you.
To test the TH400 solenoids out of the trans ground the case of the solenoid and put 12vdc on the wire. They make an audible click that shows they are working. You can even hear the click when they are buried in the transmission if you jump the contacts with the engine off.
2. As far as I know all the A/B/C/Toro 66/67 Olds switch pitch cars used a firewall mounted switch that was integrated into the throttle linkage. Are you sure it's not still there as somebody would have had to hack the throttle linkage to get rid of it? The contacts in those switches wear out but there are some good internet threads on rebuilding them. You can do manual switching via a toggle as well or buy Bruce Roe's modern vacuum/brake/timer based switch, which does a much better job than the original mechanical linkage switch.
3. For switch pitch references find the Sessions TH400 book as there are a few pages in there on the switch pitch. The more recent book by Cliff Ruggles has many helpful color photos for the guts of the TH400 but nothing on the early switch pitch versions. Best source of active user info I have found is on V8buicks.com under the "Juice Box" forum. Join that site and search up a storm as there is lots of good stuff in there for you.
To test the TH400 solenoids out of the trans ground the case of the solenoid and put 12vdc on the wire. They make an audible click that shows they are working. You can even hear the click when they are buried in the transmission if you jump the contacts with the engine off.
2. As far as I know all the A/B/C/Toro 66/67 Olds switch pitch cars used a firewall mounted switch that was integrated into the throttle linkage. Are you sure it's not still there as somebody would have had to hack the throttle linkage to get rid of it? The contacts in those switches wear out but there are some good internet threads on rebuilding them. You can do manual switching via a toggle as well or buy Bruce Roe's modern vacuum/brake/timer based switch, which does a much better job than the original mechanical linkage switch.
3. For switch pitch references find the Sessions TH400 book as there are a few pages in there on the switch pitch. The more recent book by Cliff Ruggles has many helpful color photos for the guts of the TH400 but nothing on the early switch pitch versions. Best source of active user info I have found is on V8buicks.com under the "Juice Box" forum. Join that site and search up a storm as there is lots of good stuff in there for you.
February 10th, 2021, 05:53 PM
#4
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Join Date: Feb 2019
Location: The Seasonally-Frozen Wastelands
Posts: 660
I got an electronic switch-pitch controller from Bruce Roe.
Has built-in timers for idle-to-off idle stator pitch change, and full-throttle pitch change. Has a vacuum switch so the torque converter changes pitch based on engine load. VERY slick unit.
I don't know if he's still making them any more. I got mine years ago. His e-mail address might have been bcroe@juno.com.
Tell him Schurkey sent you.
Has built-in timers for idle-to-off idle stator pitch change, and full-throttle pitch change. Has a vacuum switch so the torque converter changes pitch based on engine load. VERY slick unit.
I don't know if he's still making them any more. I got mine years ago. His e-mail address might have been bcroe@juno.com.
Tell him Schurkey sent you.
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