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YJ enthusiast
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Discussion Starter · #1 ·
I spent a lot of time trying to figure out how to get my 700r4 to lockup in a way that I liked. I have been running a TCI kit for a long time. The manual on/off works just fine. But the stupid little vacuum switch never worked right. Constantly kicking on and off at times I don't want it to.

So I finally came up with a solution that I LOVE and I thought I would share it. My design allows lockup under the following conditions.
- The brakes lights are NOT on
- The trans is in either 3rd or 4th gear (TCI kit provides those outputs)
- 8 seconds have passed after the above conditions have been met (Provided by the digital timer).

You may be asking, why 8 seconds? Well it gives you some time to accelerate before the lockup drops your RPMs. Some people hook up straight so that it always locks up in 4th. I HATED THAT. 4th becomes soooo doggy.

I ran a relay that brakes the lockup circuit when the brakes are pressed. I then ordered a digital timer from Amazon sold from 3rdbrakelight.com. The one I got is the "Multi-Functional 5V-20V Time Delay Relay (Timer) 5 amp". Very cool little product. It's durable and works amazingly well, better than I even expected. Programming takes a little getting used to, but they have YouTube videos that are very well done and walk you through each step. I hooked my 3rd/4th lockup signal to the ground of the timer (its a ground signal), this turns the timer on and after 8 seconds it sends a power signal to the trans to lockup. I highly recommend this solution and product.
 

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What's the trans in? I'm running a 700 in my jeep and just have the lockup on a dash switch, but it rarely sees any road miles anymore. I find it does cut the trans temps in about half while locked up at higher speeds though.
Would it make sense for you to eliminate the brake light condition? This way it'll stay locked up while decelerating/braking and act like an engine brake in 4th/3rd? Then it'll come unlocked as soon as it hits 2nd.
 
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