TC lock up switch
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Joined: Feb 2020
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From: South Carolina
TC lock up switch
1980 Auto - After reading several post about a Torque Converter lock up switch I didn't know if my tranny was a TH350C. Inside the engine bay I found the electric/Vacuum switch and followed each. When I had replaced several Vacuum hoses while installing a PCV system I failed to reconnect a vac. line. I follow the wire down to the transmission and it is indeed hooked up. After driving the vette around town and the interstate I did not notice a drop in RPM while driving only when it actually changed into 2nd and 3rd.
My question is how do you go about checking to see if the switch is bad at the firewall before dropping the trans cover to check the internal switch? You guys have helped me identify several things that needed to be adjusted and I was doing a mileage check ride. Will finish today and post results, but if I can determine if the lock up switch is faulty or not would help me increase the mpg. Thanks
My question is how do you go about checking to see if the switch is bad at the firewall before dropping the trans cover to check the internal switch? You guys have helped me identify several things that needed to be adjusted and I was doing a mileage check ride. Will finish today and post results, but if I can determine if the lock up switch is faulty or not would help me increase the mpg. Thanks
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The lockup solenoid switch makes a click when you apply 12 volts. It's an easy test. The actual lockup clutches can fail in the TC. That can be tested with a manual 12 volt switch. Toggle on when driving level about 55 and see if the rpm drops a few hundred rpm
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From: Crossville TN
Your description sounds like it is working correctly. RPM drops a few hundred revs when 2nd range and 3rd range stabilize. Lockup should drop out (revert to converter mode) when the accelerator is depressed significantly (ie, going up a steep hill, etc).
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From: South Carolina
Drifting
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It would have a electrical connector going inside the transmission. I thought the T350 with Lock up came out in 81 ?
To check go steady 55 mph , then gas it a little bit , if rpm go up initially then it’s not a lock up , with lock up rpm will only increase with mph
another check is if rpm is steady with mph then tap the brake pedal should release TCC and gain 200 rpm
To check go steady 55 mph , then gas it a little bit , if rpm go up initially then it’s not a lock up , with lock up rpm will only increase with mph
another check is if rpm is steady with mph then tap the brake pedal should release TCC and gain 200 rpm
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From: St. Augustine, FL
" I thought the T350 with Lock up came out in 81 ?"......Correct. Unless someone changed out the transmission for a TH350C, your 1980 transmission does not have a lock up torque converter.
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From: South Carolina
I have followed the wire down and they are hooked up to the tranny and also the vacuum hose and found the hose disconnected. After I figure out the easiest and best way to hook up a toggle switch I will check it. Anyone have a hand drawn photograph that will guide me in the right direction.
Last edited by Quackster; Apr 13, 2020 at 11:01 AM.
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Joined: Feb 2020
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From: South Carolina
It would have a electrical connector going inside the transmission. I thought the T350 with Lock up came out in 81 ?
To check go steady 55 mph , then gas it a little bit , if rpm go up initially then it’s not a lock up , with lock up rpm will only increase with mph
another check is if rpm is steady with mph then tap the brake pedal should release TCC and gain 200 rpm
To check go steady 55 mph , then gas it a little bit , if rpm go up initially then it’s not a lock up , with lock up rpm will only increase with mph
another check is if rpm is steady with mph then tap the brake pedal should release TCC and gain 200 rpm
You guys correct me if I am wrong with potential wiring test of the TC lock up switch? I only have 1 wire going into my transmission and I am assuming that I can do a temporary tie in of 12 volts exiting the Elec/Vacuum switch into the wire going down to the transmission. Since there is only one wire to the transmission connector, the grounding is done inside at the TC lock up switch itself. Is this correct? Then from there, all I have to do is drive the car around 55 and 60 mph enable the switch and notice if the rpms drop a couple hundred rpm's?
Drifting
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MY 80 does have TCC , I said it didn't in an early post but it does upon further investigation , here's how a 80 TCC works ….. TCC and Cruise Control use the same 20 amp Fuse that goes straight to the Cruise Control /Brake light switch . Cruise and TCC both get 12Volt power provided the brake is off which is the exact opposite of how the Brake light switch works , hitting the Brake cancels TCC and Cruise Control …. From the Cruise Control/Brake light switch the 12 Volt power goes straight to the Vacuum switch under the hood , providing the Vacuum is between 7 and 2.5 inches of Vacuum the Switch will allow the 12 Volt power to go to the Transmission , Once the power is at the transmission the wire goers to 3rd gear pressure switch , if transmission is in 3rd gear the 3rd gear switch allows the 12 Volt power to go to the TCC solenoid which will Lock Up the Converter ,
Drifting
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I checked at 45, 55 and 60 mph and tapping the brakes today to monitor the engine rpms, noticed no change. I feel it is not working correctly.
You guys correct me if I am wrong with potential wiring test of the TC lock up switch? I only have 1 wire going into my transmission and I am assuming that I can do a temporary tie in of 12 volts exiting the Elec/Vacuum switch into the wire going down to the transmission. Since there is only one wire to the transmission connector, the grounding is done inside at the TC lock up switch itself. Is this correct? Then from there, all I have to do is drive the car around 55 and 60 mph enable the switch and notice if the rpms drop a couple hundred rpm's?
You guys correct me if I am wrong with potential wiring test of the TC lock up switch? I only have 1 wire going into my transmission and I am assuming that I can do a temporary tie in of 12 volts exiting the Elec/Vacuum switch into the wire going down to the transmission. Since there is only one wire to the transmission connector, the grounding is done inside at the TC lock up switch itself. Is this correct? Then from there, all I have to do is drive the car around 55 and 60 mph enable the switch and notice if the rpms drop a couple hundred rpm's?
To check vacuum sensor hook OHM meter up to both leads , apply vacuum and watch the Meter show continuity when the switch is "ON" between 2 and 7 inches of vacuum , also install vacuum gage on vacuum hose to make sure the vacuum system is working , any leak or bad thermal vacuum switch will not allow vacuum
Last edited by Eric P; Jun 26, 2020 at 09:38 AM.
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From: South Carolina
Thanks Eric, I appreciate the information. I have been put on hold a little while, you know how it is, fix one thing and then move onto another. Waiting to see a Doctor. Will update when I am able to continue the Rockets repairs.
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From: Crossville TN
The problem with a toggle switch is that you have to remember to flip it off EVERY TIME IT NEEDS TO DROP OFF. That means, when you slow down, or when you need to stop, or when you start going of a relatively steep hill, or when you go to pass someone on the highway, .....etc, etc.
If you leave the L/U clutch engaged when it should be "off", the L/U clutch can easily be damaged, It is not a 'full-power' clutch; it cannot handle a lot of torque. And, if the L/u clutch fails, not only will that clutch no longer work, but it could mean a torque converter replacement if any metallic components in the L/U clutch were to generate any debris.
The L/U clutch can save money on fuel costs; but only if it will drop out automatically when you tap or apply the brake (as a MINIMUM fail-safe).
If you leave the L/U clutch engaged when it should be "off", the L/U clutch can easily be damaged, It is not a 'full-power' clutch; it cannot handle a lot of torque. And, if the L/u clutch fails, not only will that clutch no longer work, but it could mean a torque converter replacement if any metallic components in the L/U clutch were to generate any debris.
The L/U clutch can save money on fuel costs; but only if it will drop out automatically when you tap or apply the brake (as a MINIMUM fail-safe).
Racer
Joined: Jan 2016
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If you really want to run the lock up from a toggle switch, simply run it in series through the brake switch and a WOT switch and continue throught the 3rd gear pressure switch. Personally, I would just get the factory control system working.
Team Owner
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From: Crossville TN
What is a "WOT" switch???? If you just run power to the lockup switch thru the brake switch (only), it will engage any time the brake pedal is released....like when you take foot off the brake from a stop light. It would be ON during transmission shifts. hmmmm.......