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Old 06-19-2007, 10:43 AM   #1
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TC lockup

OK....I think I've got a handle on why the torque converter is there, and what/how it does it's job. My question is this: I can wire my TC to a switch, allowing me to manually control lockup. If I do this, I'm concerned about possible damage to my transmission.

The possible scenario for use is something like this: I pull away from a stop, and let the car shift through the gears. In 3rd, I hit the switch for TC lockup. The transmission decides that it wants 4th gear, and shifts (with the TC still locked) Do you think I'll see a problem with that??

The stopping scenario is similar: I would go from 4th gear w/full lockup -> to N on the shifter. I would have to unlock the TC before starting, or risk the motor stalling (at full stop). Do you think I'll see any problems from this situation??


Let me know what you think...I'm considering this because in the 34-45 mph range, my Jeep has a hard time holding a gear. She'll go from 3rd unlocked all the way through 4th locked, and back and forth until I either slow enough for 2nd, or speed up enough for 4th to stay locked. Big problem with city driving......
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Old 06-19-2007, 12:14 PM   #2
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In 3rd, I hit the switch for TC lockup. The transmission decides that it wants 4th gear, and shifts (with the TC still locked) Do you think I'll see a problem with that??
This won't hurt it. This is one thing the transmission will do by itself to protect itself in overheat condition (i.e. never unlocking the converter above say 35 mph and possibly also doing partial lockup in 2nd gear as well.)

I'm interested in the rest of the questions though.
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Old 06-19-2007, 02:08 PM   #3
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Originally Posted by savoF3 View Post
This won't hurt it. This is one thing the transmission will do by itself to protect itself in overheat condition (i.e. never unlocking the converter above say 35 mph and possibly also doing partial lockup in 2nd gear as well.)

I'm interested in the rest of the questions though.
Transmissions tend to shift harder when they're in lockup. I have an annoying hill-logic control transmission that does a partial lock on steep hills (say in 3rd) and then once it calculates level ground -- ker-thunk: 4th (top) and locked quickly.

I've really looked over the operation of my auto in the Shop Manual. Stopping with the TC engaged manually could stall the engine, similar to a manual -- when not engaging the clutch. Shifting to N shouldn't be a problem.

Starting out from a stop, you'll need the torque multiplier action of an unlocked converter for efficient acceleration -- then lockup can help with that direct connection when you're ready (generally around 35 mph). With something like this, I might install a Transmission Temp. Gauge to monitor any potential overheating.

RH77
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Old 08-20-2008, 02:11 PM   #4
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Hey, I know that this thread is a lil on the old side... but how did you wire that switch?

I have been wanting to do this but how?

Let me know, Thanks!
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Old 10-07-2008, 05:40 PM   #5
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do they make a tc over ride switch for a 95 jeep cherokee obd1 4.0 auto
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Old 10-07-2008, 05:44 PM   #6
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They don't make a kit for it, you buy a switch and install it yourself.

-Jay
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Old 10-07-2008, 05:59 PM   #7
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sorry jay dumb question can you send me a link
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Old 10-07-2008, 06:43 PM   #8
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There isn't a link that I know of, there are several threads around here where people have talked about it. What you really need is to determine which wire going to your transmission controls the lockup, and splice in there. I was thinking on doing something similar on my Buick as there's some computer problem in the car and the TC no longer gets a signal from the computer to lockup. Of course its easy on my Buick because there is only one wire going to the transmission. My plan is to get an "old fashioned" floor mount high beam switch and use it to control the TC lockup. This way I can just tap the switch and control the lockup.

-Jay
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Old 10-07-2008, 09:19 PM   #9
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Keep in mind the TC lock up clutch is relatively small compared to a manual shift car clutch and the auto trans is designed to unlock the clutch anytime the torque demand from the driver is likely to exceed the limits of the clutch.
This is to give a longer life to the clutch unit.

Pete.
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Old 10-08-2008, 04:14 AM   #10
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Yes, but when you're hypermiling you're generally not demanding a lot of torque from the engine anyway. Also note that I had mentioned previously that my TC is currently not locking at all.

-Jay
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