Wes Duenkel
June 17, 2019
Contributers: Wes Duenkel, Mike Morgan Photos By: Mike Morgan

Building a high-horsepower dragstrip Mustang used to mean sourcing a beefed-up, old-school two-or three-speed automatic transmission. While great for the quarter-mile duty, the older slush boxes don't have overdrive and aren't compatible with today's high-tech vehicles.

Fortunately, Ford's 2011-2017 Coyote-powered Mustangs came with a surprisingly stout transmission from the factory: the 6R80. Racers are finding that, with a few choice modifications, the automatic six-speed unit is a solid partner for serious drag race duty. This means a beefy, computer-controlled automatic transmission with highway-friendly overdrive is finally a reality!

As we prep our ProCharger-equipped 2011 Mustang for 8's in the quarter, we knew the 6R80 needed some attention to handle our expected 1,000-plus horsepower. To that end, we fortified our slushbox with a Power by the Hour (PBH) Performance Intermediate Shaft, Exedy Stage 2 clutches, and a Sonnax Zip Kit.

The PBH 6R80 Performance Intermediate Shaft was developed in partnership with Boninfante Friction, a supplier of drivetrain parts for Top Fuel dragsters—so if we break this thing, we're doing something wrong. Rated for over 1,000 rwhp, the shaft is machined from aerospace material and finished with Boninfante's "Nitrofinish" process to remove stress risers and improve product durability.

The strongest shafts won't mean anything if the transmission's clutches slip and burn up, so we chose Exedy's Stage 2 Clutch Pack kit for 6R80 transmissions. Exedy claims a 40% increase in clutch capacity over their Stage 1 kit. This increase in holding power and transmission durability is essential at the horsepower levels we're planning.

We're about as useless as an LS-swapped Fox-body when it comes to automatic transmissions, so we enlisted the expertise of Chino Hills Transmission to help us with the install. As you'll see in the photos and captions, we're glad we knew professionals handled this job!

Greg at Chino Hills Transmission began disassembling our 6R80 by removing the trans pan.

 

With the pan off, the case connector was disconnected and the valvebody was removed.

 

Then, the 6R80's front pump was removed.

 

With the critical guts of the 6R80 on the bench, we were glad we had the professionals at Chino Hills Transmission doing this job.

 

Exedy's Stage 2 clutch kit upgrades all of the critical clutches in the 6R80.
Through careful material selection, surface treatment, and design, Exedy's Stage 2 clutch kit increases clutch capacity 40% over their Stage 1 kit.
Before reassembly, all our transmission's internals got a bath in the parts washer.
Reassembly began by installing the planetary gears and repacking each clutch with the Exedy plates.
Assembly continued by alternating the steel and friction plates around each planetary set.
The stock intermediate shaft was replaced with the Power by the Hour Performance Intermediate Shaft.
With the Power by the Hour Performance Intermediate Shaft installed, transmission assembly resumed.
The final drums were dropped in the 6R80 transmission before installing the front pump.
With the front pump installed, we were ready to button up the mechanical guts of this 6R80.
We chose a Sonnax Zip Kit to improve the shift action of the 6R80's valvebody.
The valvebody is the circulatory system of the 6R80, and the Sonnax Zip Kit improves sealing of the critical valves in the transmission to keep our shifts smooth and crisp.
The Sonnax Zip Kit is comprised of upgraded sleeves, plugs, and seals that replace the original components in the valvebody. Fortunately, detailed instructions are also included.
Here are some of the valves that were removed and upgraded with parts from the Sonnax Zip Kit.
The Sonnax Zip Kit's aluminum valve spools replace the original plastic parts.
The plastic valve parts were removed from the 6R80's valvebody.
The Sonnax Zip Kit's aluminum valve spools were slid in the valvebody and the shift solenoids reinstalled.
With the Sonnax Zip Kit installed, the valvebody was reassembled.
After manually checking the clutch operation, the valvebody was bolted back in place on the bottom of the transmission.
This 6R80 six-speed overdrive transmission is ready for the 8's!

 

Chino Hills Transmission

14182 Central Ave #L
Chino, CA 91710
909-591-0449

Exedy USA
800-346-6091
exedyusa.com

Power by the Hour
561-737-2331
pbhperformance.com

 

 

Photos By Mike Morgan