Ford C4 Transmission External Reseal Kit 1968-1986

A Mustang, Falcon, Maverick, Comet, early Bronco or F-100 with the C4 automatic that marks its parking spot needs seals, not a rebuild. This kit covers the leak points on the outside of the Ford C4 three-speed for 1968 through 1986: the oil pan gasket, the front pump seal, the rear extension housing seal, the pump and case gaskets, both band adjusting screw lock nuts and an assortment of O-rings for the external fittings. The seals are NBR rubber.

What these seals do in a C4

The C4 was the first automatic Ford designed and built itself, a lightweight aluminum case with a Simpson planetary gearset. It uses two bands, intermediate and low-reverse, and both are adjusted from outside the case through threaded screws with lock nuts. Those lock nuts do double duty: they hold the band setting and seal the threads, so an old nut that has lost its seal weeps fluid down the side of the case. The front pump seal rides on the torque converter hub, and the extension housing seal rides on the driveshaft slip yoke. The pan gasket seals the bottom of the case under the valve body. Lose enough fluid past any of them and the C4 starts slipping and running hot.

Symptoms that point to this kit

• Fluid dripping from the bellhousing area or a wet converter (front pump seal)
• A wet driveshaft yoke or drips at the back of the tail housing (extension seal)
• Seepage around the pan rail
• Fluid trails from the band adjusters on the side of the case (lock nuts)
• Low fluid at every check, delayed engagement when cold, or a flare between shifts once the level drops

How to confirm it before you order

Clean the case and the underside of the car, run it, and find the highest wet spot; fluid runs back and down, so the drip point is rarely the leak point. Red fluid is the transmission; brown oil at the bellhousing is often the engine rear main seal. If the C4 also slips under load or bangs into gear even when full, external seals will not fix it, and a shift kit or an overhaul is the better path. The TransGo 40-2 shift kit for 1970-1981 C4s includes a pan gasket and separator plate gaskets for that job.

Fitment

This kit is listed for the Ford C4 from 1968 to 1986 in Ford, Lincoln and Mercury cars and light trucks. Ford redesigned the C4 case and valve body for 1970, and production of the C4 itself wound down in the early 1980s, so the late end of the range is where you should be most careful about what is actually under the car. Check the ID tag on the case and compare the pan gasket and seals against your parts, or send us the year and VIN and we will confirm it before shipping. A 1967-1969 car with the earlier valve body pairs with the TransGo 47-3 C4 reprogramming kit instead of the 40-2. Other C4 parts are on our Ford C4 rebuild parts page.

Install notes

• Pan: drain, drop the pan, scrape both the case rail and pan flange clean and dry, and check the flange for dents at the bolt holes before hanging the new gasket. Snug the bolts evenly in a crisscross; overtightening bends the flange and starts a new leak.
• Extension seal: pull the driveshaft, pry the old seal out, and drive the new one in square. Look at the slip yoke surface first, because a grooved yoke wears a new seal out fast.
• Band adjusters: set the intermediate and low-reverse bands to the spec in your shop manual and lock them with the new nuts.
• Front pump seal: this one needs the transmission out, or at least the converter pulled, so do it when the C4 is already out of the car. Lube the seal lip and the converter hub before the converter goes back on.
• Fluid: most C4s were built for Type F, such as Valvoline Type F ATF. Ford says Type F must not go into a transmission that calls for MERCON V, so read the dipstick, and if the unit was rebuilt, use whatever the rebuilder specified.

While the car is up, worn shifter linkage can also leak at the manual lever and make the gear selection sloppy; a ratchet shifter for the C4 is a common upgrade at the same time. This is an external reseal kit only. It does not include frictions, steels or internal piston seals.

Does this kit fit a 1966 or 1967 C4?

The kit is listed for 1968-1986. Early C4s, including the 1964-1966 Dual-Range units, used different valve bodies and some different hardware. If yours is a 1967 or older, compare the pan gasket and seals to your parts or send us the year and VIN before ordering.

Can I replace the C4 front pump seal without removing the transmission?

Not really. The front pump seal sits behind the torque converter, so the transmission has to come out, or at least move back far enough to pull the converter. Most people reseal the pan, band nuts and extension seal in the car and save the front seal for when the C4 is out.

What fluid goes in a C4?

Most C4 units were built for Type F, Ford spec ESW-M2C33-F. Ford warns not to use Type F in a transmission that calls for MERCON V or later fluids. Check the dipstick, and if the C4 was rebuilt, follow what the rebuilder used.

Why does the kit include band adjuster lock nuts?

The C4 has two bands, intermediate and low-reverse, adjusted from outside the case. The lock nut holds the adjustment and seals the threads, and old nuts lose that seal and weep fluid. Fresh nuts let you set the bands and keep them dry.

Will this kit stop my C4 from slipping?

Only if the slip came from low fluid and the bands and clutches are not damaged. If the C4 slips with the level correct, it needs internal work such as a band adjustment, a shift kit or an overhaul with frictions and steels.