Ford Tranmission, C6 Transmission, and a Transmission Rebuild

JET begins the rebuild by first disassembling the tranny and hot-tanking the larger pieces. Internal parts that are to be reused are cleaned with brake cleaner and dried with compressed air. This leaves the parts not only clean, but free of degreasing residue since the brake cleaner evaporates away.
JET begins the rebuild by first disassembling the tranny and hot-tanking the larger pieces

JET’s Fred Nungaray (one half of the flying-fingered Nungaray brothers) begins the reassembly with a new one-piece rear case bushing and the output shaft which is slid into position to hold the rest of the internals. The C6 low-reverse sprag is replaced with a stronger one-piece unit from an E4OD.
JET’s Fred Nungaray (one half of the flying-fingered Nungaray brothers) begins the re

The low-reverse clutch pack is installed, alternating JET’s high-energy friction plates with the clutch steels. JET resurfaces the clutch steels for better holding power unless they show evidence of hot spots, in which case they’re replaced. The first of several thrust washers is replaced with Torrington bearings. The bearings increase durability and decrease friction over the stock thrust washers.
The low-reverse clutch pack is installed, alternating JET’s high-energy friction plat

Moving forward from the rear of the case, the new E4OD low-gear assemblies are installed (see “A Case for Lower Gears” sidebar). After the rear ring gear and low-reverse planetaries comes the input shell, sun gear, forward planetary assembly (with another Torrington bearing), and another set of clutch packs which are stacked up and snap-ringed into the forward clutch drum. The drum gets a light resurfacing by hand for better bite. The input shell and forward clutch assembly is now ready to be slid onto the output shaft.
Moving forward from the rear of the case, the new E4OD low-gear assemblies are installed (

The intermediate band is slid into the front of the case and adjusted to specs. The front pump gets a new metal pump washer to replace the factory plastic piece before the pump is torqued down. A plug of silicone is squirted into the case front to keep fluid from seeping into the bellhousing and causing an external leak.
The intermediate band is slid into the front of the case and adjusted to specs. The front

JET installs a servo with a larger piston which increases the band’s holding power, helping the 2-3 shift. An adjustable vacuum modulator is also included to help fine tune shift points. To make shift points later and firmer, remove the vacuum hose, insert a small screwdriver, and turn the adjusting screw clockwise. Now it’s on to the brains of the automatic transmission, the valvebody.
JET installs a servo with a larger piston which increases the band’s holding power, h

The valvebody is disassembled and cleaned and the shift valve bores are polished to keep the valves from sticking during operation. JET reprograms the shift points using its own recipe of modifications. New springs are used on the regulator, scheduling, and accumulator valves. Other springs on the cutback valve and the servo modulator valve are exchanged for plugs or balls. Finally, one passage on the separator plate is enlarged. What all this means is you get firmer, later, quicker shifting from your C6.
The valvebody is disassembled and cleaned and the shift valve bores are polished to keep t

JET welded a drain plug on the pan before buttoning everything up, poured in some ATF, and got ready for the dyno. Every transmission that JET rebuilds is run on its dyno. Manuel Nungaray (second half of the now infamous Nungaray brothers) bolted the fresh C6 behind the dyno’s Chevy small-block, while JET technicians Steve White and Scott Neeley put the tranny through its paces. JET checks for proper operation, shift points, line pressure, and any leaks as the transmission is brought up to normal operating temperature. Driving the C6 is now a pleasure once again. The Bronco shifts with authority, yet without harshness, and will properly kick down when the driver plants his right foot. The low gearset (actually a wide ratio set, considering both First and Second gears are lowered) really helps the emissions-ladened 400 get out of its own way. We’re happy, and we’re looking forward to another 20 years with a better C6.
JET welded a drain plug on the pan before buttoning everything up, poured in some ATF, and

It was a good run. How long did your Ford C6 automatic transmission live? Ten years? Fifteen? After 20 years and 250,000 miles, ours finally slipped (pun intended) into mechanical unconsciousness.

We were lucky. Our C6 breathed its last gasp of tranny fluid pulling into the parking lot of the office instead of on some lonely trail on the edge of civilization. Now were aware that the risk of being stranded off-road with an automatic is always greater than with a manual transmission, but well wager that most of you reading this either wheel a fluid-shifted vehicle or have one in your driveway. Plus, weve recently seen more purpose-built 4x4s using autos as well.

Were not going to settle the auto versus manual debate here. In short, we decided against trying to retrofit an NP435 four-speed, and against all the modifying necessary to install a late-model auto overdrive (such as an E4OD) at this time. We just wanted the Broncos trusty C6 revived.

The Plan

Maybe revived is not a strong enough termwe wanted the tranny rejuvenated. We knew that gains could be had with a performance rebuild that included heavy-duty friction and band materials, valvebody modifications, and shift reprogramming, but, being 4-Wheel & Off-Road, we wanted more. We wanted big-time improvements in off-road capabilities. In 4-Wheel & Off-Road parlance, we wanted lower gears.

While well gladly tear into a transfer case or a manual transmission, setting an automatic on our workbench is like NASA shuttling Ray Charles up to correct Hubble optics.

So, after flipping through a JET Performance Products catalog we knew the company had the tools, techniques, and technicians to handle rebuilding the C6, but we didnt know if JET could also provide the lower cogs (see the sidebar A Case for Lower Gears) needed to satisfy the 4-Wheel & Off-Road gearing decree.

A phone call to JETs Paul Darden gave us the answer: No problem. Wonderful device, the telephone. A few days later the Bronco was up and running with improved driveability, on-road and off. If your automatic transmission is on its last legs, read this story, then use your phone and JET to put the juice back into that juicebox.