4l80e sloppy transbrake (3rd gear spool mod)

Now, I had alot of help getting this working from LS1 tech members and tons of info from a trans guy, wanted to let you know that first! thank you for the community for helping me out, i wired it in, tested it and ill show you how i did it.

First of all I will explain, I am using this for foot brake turbo cars, 4l80e transmissions, i use tighter circle D stall converters for my street cars that will come up if you have really good brakes and other situations, what sucks is most of the time i am using 80s shitboxes, with poor brakes,

when i bring the car up into a brake stand i will push the back or front tire before i can get the boost and rpm i need to leave hard.

well what happens here is you hit a switch and it forces the trans into high gear, removing the mechanical advantage you have over the tire, forcing the converter to hit its highest stall capability easily, and also when dropping back into 1st helps bump the tire and leave harder than just letting it roll off the brakes.

i used a 5 wire relay, what it does is leaves the trans connected and working normally, when you hit a switch it throws the 2-3 shift solenoid to ground, activating it.

then when you turn the switch off, (or monetary button etc) it will go back to normal and select first gear. and you will take off.

here is the wiring diagram i wrote up for how i have it working on a 5 wire relay

also when you do this, the stock PCM will have a fit, and put the trans in limp mode, i had to disable codes for it to work correctly, you might have the same or different problem just be aware.

These are the codes i had to disable.

• [] P0719 - Brake Switch Circuit Low Input (Old) (History) (Current) (Immature)
• [] P0748 - Pressure Control Solenoid Circuit Electrical (History) (Immature)
• [] P0753 - 1-2 Shift Solenoid Circuit Electrical (Old) (History) (Immature)
• [] P0758 - 2-3 Shift Solenoid Circuit Electrical (Old) (History) (Immature)
• [] P1810 - TFP Valve Position Switch Circuit (Old) (History) (Current) (Immature)
• [] P1860 - TCC PWM Solenoid Circuit Electrical (Old) (History) (Current) (Immature)

now for a car that would have trouble hitting 2300 in my garage i could easily get to 3700+ and boost on the foot brake on smooth concrete

as shown here in this datalog...

and here is a video of it working at the track.

i come up to the line and then start to foot brake, hit the switch and feel the 3rd gear clunk.

then i am free to easily build rpm and boost. then when i hit the switch there is a delay and i am still on the brakes, it thuds hard into first gear and takes off easily blowing through the brakes.

more testing and unsure of the longevity or damage it might cause, but its basically power downshifting, wich people do all day long.

more to come and revisions etc just wanted to get this put up!