Modified Mustangs & Fords
Ford C6 Transmission Upgrades - Built Tough
CK Transmissions upgrades a C6 three-speed with modern amenities
In 1966, Ford introduced a beefy three-speed automatic transmission that was stuffed into anything that required a strong transmission including trucks, high-performance Mustangs, and sedans. The Ford C6 transmission would go on to enjoy a 30-year service life as Ford phased it out in 1996 to make room for overdrive versions of its big transmission line-up. Today, the C6 is still the go-to Blue Oval piece when you are looking to harness big horsepower. Credit the beefy guts and many aftermarket upgrades for the tough label.
"I have a few customers who run our C6 behind supercharged Hemis in monster trucks, it holds up just fine in that application," says Chris Kokonis of CK Performance.
There is a downside to Ford's beefy three-speed, though--it weighs a lot, causing the loss of valuable horsepower in order to turn the parts and pieces. That is changing, though, as CK Performance offers a hybrid C6 package that merges custom parts made in-house with specific C6 components, and certain pieces from the modern 4R100 electronic-overdrive sibling. The result is a unit capable of withstanding abuse, but one that also negates the power-robbing antics of the original C6 design.
We use the adjective hybrid to describe the CK Performance C6 because Kokonis mixes and matches his way to C6 utopia. He has pulled apart and inspected almost every iteration of the C6 since its inception. The transmission was in production for 30 years, so there were several running changes to fit different applications, improve designs, and, of course, implement cost-cutting measures. Kokonis has seen the good, the bad, and the ugly, as well as figured out which 4R100 components can easily transfer over without any issues. The final result is a rollerized C6 that prevents a switch to the GM TH400 or forcing the expensive swap to an electronic-controlled 4R100 transmission.
A stock C6 features a 2.40:1 (First), 1.40:1 (Second), and 1:1 (Third) setup from the factory. A new wide-ratio gearset is installed providing a numerically greater First gear of 2.72:1 followed by a 1.54:1 Second gear, which finally leads into the standard 1:1 Third gear ratio. The higher First is a big help for those with a heavier car, as it makes the rear gear act larger without increasing the highway cruising rpm. According to Kokonis the company uses stock input shafts for applications up to 1,000 hp. Pushing past that limit requires the CK Performance billet input shaft. Other standard modifications are stronger C6 planetary carriers. The new planetaries bring the transmission's rating to more than 2,000 hp, provided the input shaft has been swapped. Like all aftermarket transmission builds, the new clutch packs have better surface material and additional clutches for greater gripping power. The thrust bearings in many of the rolling components are discarded in favor of needle bearings for less friction.
There are many small details that are upgraded, and a few key elements caught our eye, like the modified parking pawl gear. CK Performance machines it down to fit a needle bearing assembly instead of a thrust washer. The switch to a needle bearing prevents the case from getting beat up on deceleration. As the parking pawl gear accelerates, it pushes outward, which is fine until you left off the gas and go to decel. At that point, the input shaft puts a lot of pressure on the housing. The modified parking pawl prevents damage from the decel strains. The First and Reverse planetary gearset in a C6 features either a three- or four-pinion unit, each are made of aluminum. That is tossed into the recycling bin and a super heavy-duty, six-pinion steel planetary gearset is used. The extra pinions help disperse the load and the steel material is far stronger than its aluminum counterpart.
Kokonis made the decision many years ago to only use a Lincoln drum, which is the Third-gear/direct drum. The Lincoln drum features a higher snap-ring groove allowing more clutches to be installed. From the factory, the Lincoln drum uses four clutches, while the other Third-gear drums have three clutches. CK Performance fits six new high-performance clutches in the Lincoln drum for the ultimate in grip.
"I use a different aftermarket clutch that is 0.0065-inch-thick as compared to the 0.0080-thick stock clutches," says Kokonis. The thinner high-performance clutches allow more room for stacking. As a side note, Kokonis runs stock thickness steel plates. Going to a thinner steel plate would allow for eight clutches, but the thinner plates don't absorb the heat well and burns the clutches. The eight clutch/thinner steel plates setup holds less power than the six clutches/stock-thickness steel plates.
CK Performance also performs the usual ritual of upgrading the valvebody allowing for automatic shifting or manual action (forward and reverse). A trans-brake can be fitted for drag racers. We also can't forget that thicker high-performance bands are standard and a deeper oil pan is optional. An SFI-certified bellhousing could also be grafted on to the stock case for customers looking to go that route. Tallying it all up--1,000 hp, 2,000 hp, or even more; CK Performance has a C6 package ready to back your wildest engine combination so you don't have to turn orange to back your Blue Oval bullet.