Originally Posted by
Chaz
Tony, your transmissions TCU will lock the converter in 3rd gear under the right conditions.
The reason for the brake switch relay is that the GU will stall if you forget that it’s locked and slow down or stop. I think the most important part of the circuit is the Park/Neutral relay which won’t allow the converter to lock in that state. If it does, you’ll destroy your transmission in a few seconds.
The Hold In relay is necessary for the momentary switch with brake release. Its only to make it more user friendly and fool proof.
I’ve setup and designed manual lockup circuits for a few different transmission types (GM TH700R4, BW45 etc) and they all differ slightly, but the principal is much the same. One thing to consider is that after fitting a manual TC lockup system it’s very advisable to increase your line pressure so that you can safely lock it at lower speeds. Our Patrol transmissions generate maximum line pressure at around 1800rpm depending on throttle position, so it isn’t wise to drive below that with the converter locked under considerable load. A Wholesale Auto’s valve body is the best way to increase it or fitting a shift kit helps, but the cheapest and easiest way is to change the transmissions line pressure dropping resistor to one of 1K ohms or more, depending on the shift firmness that you prefer.
This is an excellent mod for towing and it does more for transmission temperature that anything else that I’ve found.
NissPat, your circuit will work, but you'll need to be carefull when and how you use it, without the saftey features.