Muncie Four Speed Transmission Makeover Part 2 - Pontiac Tech

This photo was taken prior to installation on the mainshaft assembly and shows correct orientation of the front Reverse idler gear's forward thrust washer.

Carson then inserts the rear Reverse idler gear thrust washer and Reverse idler shaft. Note the position of the shaft's lock pin-it corresponds with a notch in the rear extension.

During disassembly, Carson removed the Reverse shift fork and drove the Reverse shifter shaft into the extension housing (the Reverse shifter shaft detent ball and spring will fall out). He replaces the Reverse shifter shaft seal before reinstalling the spring and detent ball assembly back into the housing (shown is the assembeld housing). With a small flat-blade screwdriver, he reinstalls the Reverse shifter shaft and shift fork, then removes the existing bushing in the rear extension and taps the replacement into place with a race driver. Next, he'll install the rear extension oil seal.

He slides the Reverse gear onto the mainshaft and drives the speedometer Drive gear into place using a length of steel pipe. According to the Pontiac Service Manual, the Drive gear's proper location is roughly 6.15 inches from the rear of the shaft. The rear extension gasket is also installed.

Pulling the Reverse shifter shaft outward, Carson slides the rear extension over the mainshaft while aligning all the internal components. He treats the six retaining bolts to a coating of blue thread locker and tightens them to the suggested torque spec. The upper three bolts receive 20 lb-ft of torque, while the lower three receive 30 lb-ft.

Carson installs the Reverse shifter shaft lock-pin and speedometer gear fitting (with a new O-ring).

He installs a new roller bearing and snap ring onto the main Drive gear.

After sliding both mainshaft synchronizer sleeves forward to lock the transmission into opposing gears, Carson threads the bearing-retainer nut onto the main Drive gear. While using the correct tool shown in Part I is preferable, a flat-blade screwdriver and hammer or a pipe wrench can also be used to gently walk it around the main Drive gear to tighten. Remember, it's left-hand thread, and the correct torque spec is 40 lb-ft. The nut can also be staked with the corresponding holes in the main Drive gear to securely lock it into place.

Carson treats the clutch gear bearing retainer to a new gasket before it's slid over the main Drive gear. Note the machined hole points toward the bottom. This ensures that the retainer's internal oil drain is positioned correctly. He applies thread locker to the four retaining bolts and tightens each to 20 lb-ft of torque.

As Carson assembles different points along the way, he manually places the transmission into each of its four forward gears and Reverse and turns the main Drive gear to ensure the unit is free of any internal binding. With a day's work and about $150 in parts, this completely rebuilt Muncie is now ready for service. The owner reports that it operates quietly and shifts with relative ease.

Carson removed the forward shift forks and shifter shafts from the case cover during disassembly. He drives new seals into place during reassembly.

With the shifter shafts and shift forks in place, Carson slides the Third-and-Fourth gear synchronizer sleeve into the neutral position while leaving the First-and-Second assembly in the forward position. He then positions the case cover gasket and lowers the case cover into place.

He tightens the case cover's seven retaining bolts to 18 lb-ft of torque using a crisscross pattern.

There are some transmission builders who feel that synthetic lubricant was never intended for use with vintage manual transmissions. Conventional lubricants such as this 75W-90 product from Valvoline seem to be the choice of those professionals. The M20 Muncie's capacity is 2.5 pints.