Pontiac Muncie Transmission Rebuild Part One - Muncie Makeover

Midwest Transmission Supply in Omaha, Nebraska, supplied Carson with a rebuild kit (PN BK116WS) for '67-'74 Muncie units. It includes such pieces as bronze blocker rings, high-quality roller bearings, and all of the necessary gaskets and seals. It retails for $109.95.

Carson begins the rebuild by removing the four bolts that secure the clutch-gear bearing-retainer with a 9/16-inch wrench. The bearing-retainer nut, which is a left-hand thread, follows only after both shift shafts on the case cover are placed in the forward position, locking the transmission into gear. This photo from the Service Manual shows the specific J-tool designed to remove the bearing-retainer nut. Midwest Transmission Supply offers a similar tool (PN WT297-W) for $39.95.

Before removing the case-cover assembly, Carson places the transmission into Second gear by leaving the rear shifter shaft (on the case cover) in the forward position and moving the front shaft to center. He then removes all seven case-cover retaining bolts with a 1/2-inch wrench and lifts the assembly away from the unit, setting it aside. Here, the parts attached to the backside of the cover are identified.

He then removes the speedometer gear fitting. A 7/16-inch wrench is required to take off its retaining bolt.

Carson uses a 3/16-inch diameter punch to drive the Reverse gear lock pin upward and out of the rear extension (tailshaft).

After removing the case cover, Carson places the transmission in Neutral by manually positioning the rear synchronizer sleeve so the teeth of all four bronze synchronizer rings are visible.

He threads a bolt into the Reverse shifter shaft and pulls the Reverse shifter shaft outward about 1/2-inch, freeing the Reverse shift fork from the Reverse gear. The rear extension is attached to the main case assembly by six bolts, all of which he removes with either a 9/16- or 5/8-inch wrench. A few blows from a soft mallet separates the main case assembly and extension, which he rotates away and sets aside.

Carson extracts the rear bearing retainer and mainshaft assembly, including the Reverse idler gear, from the main case. Though still intact here, the main Drive gearshaft (or input shaft) simply pulls away from the mainshaft, but will most likely remain in the main case, where it can be gently tapped out of its main bearing and into the main case. It can also be tapped outward, along with its bearing, and be removed as a unit.

The speedometer's steel Drive gear is pressed onto the mainshaft and must be pulled off for complete disassembly. Carson uses a Bearing Separator tool from Mac Tools to complete the task. He then simply slides the mainshaft Reverse gear off the mainshaft and pulls the Reverse idler shaft straight out.

Focusing on disassembling the mainshaft, Carson uses a pair of high-quality external snap-ring pliers to remove the rear bearing retainer snap ring located on the rear end of the mainshaft.

He then inserts the mainshaft assembly into a hydraulic press, supports the rear bearing retainer, spreads the snap ring, and presses the mainshaft through the rear bearing, separating the two. The procedure is the same as the one illustrated here in the service manual.

Complete mainshaft disassembly follows. Using snap-ring pliers and working front to rear, Carson removes the front snap ring that retains the Third and Fourth gear synchronizer sleeve, and Third gear. (The synchronizer sleeves and hubs are matched pairs, so be sure to keep them oriented correctly.)

Supporting Second gear, Carson inserts the mainshaft into the hydraulic press and, applying pressure from the rear, removes Second gear, the First and Second gear synchronizer hub, and First gear to gain access to the Second gear synchronizer-block ring.

Using a 3/4-inch diameter metal dowel and the hydraulic press, Carson removes the Countershaft gear pin by applying pressure from front to rear. This allows removal of the Countershaft gear, its 112 needle bearings, and its thrust washers, as well as the front Reverse idler gear and its thrust washers. All parts are then set into the parts washer for a thorough cleaning. (The main Drive gear and its bearing were already removed from the main case in this photo.) Carson will reassemble the trans in Part II.

P9E01A identifies this transmission, broken down as follows: P-Muncie Plant; 9-1969; E-May; 01-1st day of the month; A-M20 Wide Ratio.

The original vehicle's VIN is typically stamped on the top of the main case in Muncie applications and, in this particular instance, it's broken down as follows: 2-Pontiac Motor Division; 9-1969; R-Arlington, Texas, assembly plant; 175134-Vehicle Identification Number. This unit appears to be from a '69 Pontiac A-body.

A factory service manual like this from the '70 model year contains exploded views and detailed instructions for a complete transmission overhaul. Since the M20 Muncie was available that particular year, it could be considered an invaluable resource during any rebuild. Myriad reprints are available, but used manuals can often be found reasonably at swap meets or popular Internet auction Web sites.