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Old 03-26-2015, 11:42 AM   #16 (permalink)
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Originally Posted by oil pan 4 View Post

When towing something heavy my plan is to put the shifter in 3 making it like a TH400 since they share the same 3rd gear ratio of 1:1. And because my 700R4 is an 1984 the torque converter lockup will lockup in 3rd gear. Later 700R4 transmissions will not lockup in 3rd gear unless you modify them.
Plus I added a torque converter lockup control switch. I can turn the lockup off, run it like normal or turn it on when ever I want.
All 700R-4s can lock up in 2nd, 3rd, and 4th, if you wire the pressure switches correctly. Forget the manual switch, just wire in a vacuum switch for engage / WOT disengage, and a brake switch so you don't stall your engine or hurt your lockup in a panic stop, when you'll forget a manual unlock.
Any torque converter the average guy can easily afford isn't built to hold WOT while locked up. There are $900 race converters that can, but neither a mild 454 nor any diesel can run a 4400-stall converter.
Too many guys with manual switches are either too bold or too cautious about when to use lockup.
The biggest problem with lockup in 2 / 3 is getting it to unlock for shifts, plus seldom are you cruising at an RPM less than the converter's stall speed except in OD.
Stock stalls start around 1400 for the 700, and around 1200 for the TH350 / TH400, but as I referenced earlier, a GM 1200 will slip more at cruise than a good aftermarket 2000.
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