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Racing Transmission Build - Make It A MuncieBuilding yourself an inexpensive two-speed manual From the February, 2009 issue of Circle Track All contributors: Jeff Huneycutt
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This Muncie is in the final... This Muncie is in the final stages of its conversion to a lightweight two-speed racer. Although it isn't as popular as the T10 among Saturday night racers, when properly prepared, the Muncie can make a capable racer quite economically. It may not be as popular in Saturday-night stock car racing circles as the Borg Warner T10, but the classic Muncie four-speed manual transmission can be made into a capable racer. Like the T10, the Muncie is compact, uncomplicated, capable of withstanding a moderate amount of abuse and easily modified. It is the modification part of that list that pricked our ears when gear specialist Jim Cook of Jim Cook Racing Transmissions told us he was modifying a Muncie for a short-track racer. Cook's race-ready Muncies go through a lightening program that cuts over five pounds of rotating weight by eliminating First and Second gears. Third gear becomes the pit and restart gear while Fourth gear at 1:1 is for racing. Other modifications are also made to help the transmission live under racing abuse and even break the Muncie's annoying habit of popping out of gear at precisely the wrong times. The Muncie--which is also sometimes referred to as the Rock Crusher--was produced and installed in GM vehicles between 1963 and 1974. That wide time frame means a lot of Muncie transmissions were built, and a lot are still available out there. But, it also means that the design is over 30 years old, and while new replacement parts are still being produced, they aren't in big demand. In effect, the case and core components of the Muncie are cheap, but some select replacement parts--namely bearings--can be quite expensive. But Cook says that by intelligently swapping out components a race-ready Muncie can be built for around $500, which is just under half what a T10 would cost. Very few components from the T10 will work on the Muncie, but Cook has designed adaptors to use T10 bearings when the stock Muncie components are either hard to find or too expensive. When built properly, Cook says a Muncie two-speed can reliably handle 450-500 horsepower, making them a realistic alternative for many different racing classes. If you decide to hunt for one in a junkyard, just remember that they appeared between 1963 and 1974 in several GM vehicles, but your best bets are Chevy performance cars like Novas and Camaros as well as the bigger cars. The cases of the Muncie, Saginaw and T10 transmissions are almost indistinguishable to the untrained eye, and they are not interchangeable. Thankfully, however, there are easily identifiable features you can use to determine what you are looking at without hunting around for identification numbers. The Saginaw is the only one of the three that has the reverse shifter mechanism on the case. It is on the tail housing on the other two. On the Saginaw, it is easy to see because all three control rods on the shifter mechanism connect to the main case, while on a Muncie and T10, just one of the three control rods connects ends at the tail housing. The T10 and Muncie are identifiable because the bottom of the side cover on the T10 is curved while the bottom on a Muncie is straight. If you're a racer who is on a budget (and who isn't?) a modified Muncie may be just the ticket to save you some money. An extra $500 will go a long way.  Gear specialist Jim Cook begins...  Gear specialist Jim Cook begins by modifying the side cover and shifter forks to work properly after First and Second gears have been removed. Here, you can see that the shifter fork on the left side has been removed. The hole is plugged with a standard one-inch freeze plug. Cook also drills a hole in the cover and installs a bolt to give the shifter mechanism a positive stop after the shifter fork has been removed.  Cook also cuts the shifter...  Cook also cuts the shifter mechanism. Here, the stock unmodified lever is placed on top so you can see the difference.  Here is what becomes unnecessary...  Here is what becomes unnecessary when First and Second gears are removed. That's approximately five pounds of weight you are looking at, and most of it is rotating weight. Third gear becomes the pit/restart gear, and Fourth, which is a 1:1 ratio, is the race gear.  The T10 replaced the Muncie...  The T10 replaced the Muncie transmission in many GM cars in the early '70s, and although they look nearly identical to the untrained eye, they actually have very few interchangeable parts. Here is a T10 case; you can identify it because the bottom of the opening for the side cover is curved.  Here, the Muncie's bottom...  Here, the Muncie's bottom side cover opening, however, is straight.  For almost every rebuild Cook...  For almost every rebuild Cook says a small-parts kit is a necessity. It includes new snap rings, shims, and most important, new needle bearings.  When rebuilding the Muncie,...  When rebuilding the Muncie, check the shafts for wear. Here, the center shaft is pitted from use and should be replaced. If it isn't, it will damage the needle bearings, quickly wear the main gear and cause broken teeth.  Before beginning assembly,...  Before beginning assembly, Cook drills and taps a hole in a boss in the bottom of the case for a drain plug.  This is the input shaft. It...  This is the input shaft. It uses a set of needle bearings that are held in place by a cage. Cook inserts the bearings into the cage first, using heavy grease to hold them in place, and then he installs the completed assembly into position.  There are four rows of 20...  There are four rows of 20 needle bearings each inside the main cluster, and there is no cage to help hold them in place. Cook uses lithium grease to hold the bearings against the ID of the cluster, a small screwdriver to aid in positioning the bearings, and truckloads of patience.  Cook drives the inner race...  Cook drives the inner race onto the main shaft. This race is what First gear rides on, but it is still necessary even with First removed, because it also locates the mid-plate bearing.  This is the mid-plate with...  This is the mid-plate with the bearing installed. However, it isn't the stock bearing. Cook has located a heavier-duty bearing and uses it instead. It features more balls inside the bearing and provides smoother operation and more protection for the shaft.  This is the stock hook slider...  This is the stock hook slider that the shifter forks move to determine what gear is used. Notice how the teeth inside the slider are straight cuts. Cook says this is a problem with the Muncie because the teeth will allow the transmission to pop out of gear unexpectedly.  In all of his racing rebuilds,...  In all of his racing rebuilds, Cook uses a hook slider like this. On this aftermarket piece, there is an angle cut on the sides of all the teeth which locks the gear in place when the car is accelerating. No more popping out of gear.  Cook gently taps the slider...  Cook gently taps the slider into position.  Here, the gear cluster is...  Here, the gear cluster is laid into position in the bottom of the case. There are three different gear ratios that were used in the Muncie, but they are generally put into two groups. The wider ratio 2.52:2.56 First gear is identified by either two ring grooves on the input shaft or the absence of any ring grooves. The close ratio 2.20 ratio cluster is what you want. It has one ring groove on the input shaft. Although you won't use First, the 2.20 cluster has a lower Third gear (1.28 versus 1.46 or 1.48) which is preferable for restarts.  Instead of gaskets, Cook uses...  Instead of gaskets, Cook uses silicone sealer on his rebuilds. He says that getting rid of the gaskets cuts out a couple thousandths of spacing, and on an older transmission that can help tighten back up the clearances.  Without First and Second gears,...  Without First and Second gears, it is possible to install the input shaft onto the main shaft and install both into the case at the same time.  The shafts slide into position...  The shafts slide into position in the case from the rear until the mid-plate is tight against the case.  The reverse gears take a lot...  The reverse gears take a lot of abuse because there is no synchronizer ring, and inexperienced drivers will often grind the gears trying to get into reverse. But reverse is rarely used in a racecar and a smart driver can baby the gears. Buying new gears can significantly increase the cost of the transmission, so Cook says he regularly reconditions the reverse gears by carefully resharpening the front of the teeth with a small grinder.  Once the reverse gears are...  Once the reverse gears are positioned in the tail housing, it is ready to be bolted into place.  After installing the output...  After installing the output seal, Cook fabricates two tabs that are held in place with a hose clamp. If something causes the yoke of the drive shaft to bang into the tail housing of the transmission the tabs will keep the seal from coming out, while the hose clamp will also prevent the cast housing from cracking.  On the left is an input bearing...  On the left is an input bearing for a Muncie. Cook says this bearing costs approximately $80 to replace. On the right is the same bearing for a T10. It is approximately 1/3 the price but is too wide and won't fit a Muncie. Cook, however, fabricates his own spacers to make the T10 bearing work in a Muncie. In addition to being significantly cheaper, the bearing also features rubber shielding that protects the bearing from grit while also preventing leaks.  The front bearing is a press...  The front bearing is a press fit. If you try to tap it in with a hammer you stand the chance of damaging the soft synchronizer gears. Instead, Cook uses an air chisel and the bearing literally drops into place.  Finally, the front cover is...  Finally, the front cover is bolted up.  To work in a two-speed setup,...  To work in a two-speed setup, the stock shifter mechanism must be modified slightly. First, the rod connecting to the First/Second shifter mechanism must be removed. Then, you need to tack weld the First/Second lever to the Third/Fourth lever in the location pointed to here. Without doing this, the shifter won't be able to get the transmission into reverse. Jim Cook Racing Transmissions
704/786-6979
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