4L80E Transbrake Installation Instructions

The internal mods that need to be performed are:

Drilling a bleed/release hole in the direct drum.

We recommend drilling a .055-.060" hole at a slight angle as outboard as possible on the drum as seen here:

We also leave the center seal off the direct drum as part of the "dual feed" process.

The seal seen here should be removed:

This is the ring in the 2nd position from the front of the transmission on the center support. There are 4 rings on the 4L80E center support. Center support removal from the case is not required for this. Simply use a pick or other sharp object to remove the ring.

We recommend the installation of a billet forward drive hub and input shaft in any transbrake equipped 4L80E or any used with 750+ HP/TQ. Please see our components page for these items.

The case needs one 5/16" set screw supplied installed at the rear servo location.

Tap the hole shown in red to the RIGHT with a 5/16" course thread tap, blow out the chips thoroughly, and install the set screws.

A 3/8 inch cup plug must also be installed in the reverse feed passage to the center support.
This will be to the right of the center support bolt as shown in the picture below.

The rear servo pin needs to be removed from the servo piston, and a "flat" milled or ground on the portion of the pin that goes through the case bore. A small flat or groove is all that is required.

Omit the two seals on the 1-2 accumulator piston (inner piston).

We recommend flat sanding the servo cover to ensure the surface is flat for better sealing.

Re-install the servo assembly, checking for band clearance as follows.

Disassemble the rear servo. Place appy piston on pin with washer between them but no return spring, accumulator piston, or seals. This gives you the overall length with no interference. Check band clearance by installing piston and pin in case. You should feel it engage the band, when it is in the bore push by hand firmly to judge travel. If it goes into bore deep, you need a longer pin. Rotate output shaft both directions to judge band engagement. Ideally you want no drag when the servo is JUST in the bore but drag as soon as you start to depress further into bore. This helps prevent a possible no reverse condition and faster transbrake setup. Once the proper clearance is acheived you can assemble the rear servo.

You can now install the checkballs in the case at the blue locations shown. Omit the red locations.

You can install the Jake's Performance Transbrake valve body at this time.

Once the VB is bolted to the case you will install the "sandwich plate", checkball, spring, and manifold pressure switch.


Install the internal harness, filter, and pan.

Wiring the transbrake consists of tying into the B wire, typically yellow wire, that controls the B (2-3) shift solenoid on the control harness going to the transmission.
Go through a momentary switch to a good ground.
Activating the switch in the manual low position will engage the transbrake.

Note:
PCM tuning required. You must program the controller to not allow a 1-2 shift while the transmission is in manual low.
The transbrake will engage if the PCM commands an upshift causing parts damage or injury.
We also do not recommend downshifting into manual low while moving.
Our transbrake design allows for very fast transbrake setup and release times as well as minimizes circuit volume in several circuits in the transmission. This makes it very quick acting and capable of holding more HP on the transbrake and clutches.  As a byproduct of the design, it applies the low gear band quicker than the intermediate (2nd) gear clutches can release, creating a slight bind on a 2-1 downshift. We can alter this for those that need the ability to do 2-1 downshifts.