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**pjmoreland** · 06-03-2021, 07:50 PM

There are two limitations I'm seeing with my current setup:

1) If I'm driving down the highway in 4th gear and with the TCC locked, and I lift my foot off the accelerator to coast, the TCC unlocks since the vacuum switch is connected to the timed vacuum port on the carb. This is good because coasting is more fuel efficient than engine braking. The issue is when I reapply the accelerator, I have to wait unnecessarily for eight seconds for the TCC to lock up again. During this period of eight seconds, I have to press down farther on the gas pedal than I was before coasting because the engine has to spin up to a higher RPM. Then, when the TCC re-locks after eight seconds, I have to let back off the accelerator. One possible solution would be to connect the current vacuum switch to manifold vacuum, and then add a second vacuum switch connected to timed vacuum that cuts off 12V to the TCC upstream of the delay relay. This would allow the TCC to re-lock immediately after resuming from coasting.

2) If I am driving at a moderately slow speed (~40MPH) up a hill, the TCC will lock, putting too much strain on the engine at a low RPM, causing the need to press down on the accelerator. This causes the TCC to unlock, resulting in undesired acceleration. These two scenarios come and go every 8 seconds, or until the hill ends. A possible solution for this might be to add an RPM-controlled switch to the circuit that requires the RPM to be over something like 3000 before the TCC is allowed to be engaged. The RPM-controlled switch would need to have an off trip point at a lower RPM than the on trip point so that it wouldn't immediately unlock the TCC due the the RPM drop that results from locking the TCC. The MSD 8969 RPM-Activated Window Switch might work this way. The $200 price tag is painful though.

I may just try connecting my vacuum switch to manifold vacuum to see if having engine braking when coasting is more tolerable than the delayed TCC lockup after resuming from coasting.

Increasing the time delay of the relay may help reduce the annoyance of repeated locking and unlocking on a hill at lower speed.

06-03-2021, 07:50 PM	#13
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,332	Re: 700R4 TCC Wiring There are two limitations I'm seeing with my current setup: 1) If I'm driving down the highway in 4th gear and with the TCC locked, and I lift my foot off the accelerator to coast, the TCC unlocks since the vacuum switch is connected to the timed vacuum port on the carb. This is good because coasting is more fuel efficient than engine braking. The issue is when I reapply the accelerator, I have to wait unnecessarily for eight seconds for the TCC to lock up again. During this period of eight seconds, I have to press down farther on the gas pedal than I was before coasting because the engine has to spin up to a higher RPM. Then, when the TCC re-locks after eight seconds, I have to let back off the accelerator. One possible solution would be to connect the current vacuum switch to manifold vacuum, and then add a second vacuum switch connected to timed vacuum that cuts off 12V to the TCC upstream of the delay relay. This would allow the TCC to re-lock immediately after resuming from coasting. 2) If I am driving at a moderately slow speed (~40MPH) up a hill, the TCC will lock, putting too much strain on the engine at a low RPM, causing the need to press down on the accelerator. This causes the TCC to unlock, resulting in undesired acceleration. These two scenarios come and go every 8 seconds, or until the hill ends. A possible solution for this might be to add an RPM-controlled switch to the circuit that requires the RPM to be over something like 3000 before the TCC is allowed to be engaged. The RPM-controlled switch would need to have an off trip point at a lower RPM than the on trip point so that it wouldn't immediately unlock the TCC due the the RPM drop that results from locking the TCC. The MSD 8969 RPM-Activated Window Switch might work this way. The $200 price tag is painful though. I may just try connecting my vacuum switch to manifold vacuum to see if having engine braking when coasting is more tolerable than the delayed TCC lockup after resuming from coasting. Increasing the time delay of the relay may help reduce the annoyance of repeated locking and unlocking on a hill at lower speed.