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muncie m22 rock crusher restorations

guide to muncie m20, m21, and m22 four-speed transmissions

guide to muncie m20, m21, and m22 four-speed transmissions

Few things excite like the sound and feel of an old-fashioned Chevrolet muscle car and that familiar whine of a classic Muncie four-speed transmission going through the gears. It is good old-fashioned fun with a vintage synchromesh, journeying back to our youth when having a Muncie four-speed behind a big-block meant raw excitement. According to Paul Cangialosi, Muncie transmission historian, technician, and author of Muncie 4-Speed Transmissions: How to rebuild and modify, the Muncie four-speed transmission has its roots back to 1935 and the U.S. patent number 3,088,336 along with an engineer named James W. Fodrea. This patent number, according to Cangialosi, can be found cast into most Muncie four-speed main cases. Fodrea's legacy is far-reaching, extending into popular transmissions around to this day, yet most have no idea who he was.

According to Cangialosi, two companies, Borg and Beck and Warner Gear, merged in 1928 to form BorgWarner. The T-85 three-speed transmission was one result of that merger. The T-10 four-speed was an evolution of the T-85 three-speed transmission, with both of these transmissions being quite similar in appearance. If you've ever looked at a BorgWarner T-10 and a Muncie four-speed and gotten them mixed up, you are not alone because the Muncie (M20, M21, and M22) is a direct descendant of the T-10 according to Cangialosi. The Saginaw four-speed box is quite similar to both the T-10 and Muncie four-speed transmissions. However, neither compares to the Muncie in terms of strength.

That the Muncie has much in common with the T-10 is no accident. It was a matter of economics when Chevrolet needed a four-speed manual transmission for the Corvette in the mid-1950s. According to Cangialosi, GM took the basic T-10 design and beefed it up to conceive the Muncie M20 and M21 four-speed transmissions, which arrived in 1963.

GM's goal with the Muncie four-speed was to produce a better shift employing larger synchro cones. He tells us both the M20 wide-ratio and M21 close-ratio transmissions were first offered in 1963. The M22 Rock Crusher would come later to accommodate the heavy twist of Chevrolet's big-blocks in the mid-1960s.

The M20 and M21 transmissions produced from 1963-'74 are easy to identify in both wide- and close-ratio units. The M22 to come later in 1967-'74 is also a close-ratio unit, but much stronger than the M21, with a higher torque capacity.

Because the Muncie has so much in common with the T-10 and even similar Saginaw boxes, it is easy to get this guy mixed up with non-Muncie units. Although the Muncie's bloodline goes way back, this legendary gearbox entered service for the Chevrolet Division in 1963. In fact, 1963 is a standalone year because changes in this box came almost immediately for 1964, beginning with the front bearing retainer, which was aluminum for 1963 and became cast-iron in 1964. The bearing bore size was also one year only with a #6207-style input shaft bearing, according to Cangialosi.

The early production Muncie four-speed case is the small-bore unit and can be identified by the GM casting number 3831704 (see Muncie M20/M21/M22 Main Case Identification chart). The large-bore Muncie came into production in 1964-'65 and became the standard from then on through the end of production in 1974. What makes the small-bore and large-bore case Muncies different is the input shaft bearing size and first gear, which rode on the mainshaft void of a bushing for 1963. For 1964 and beyond, it rode on a bushing between it and the mainshaft.

Cangialosi explains there were two basic mainshafts produced for the M20, M21, and M22 transmissions (see Input Shaft Identification chart). From 1963-'70, the Muncie was fitted with a 27-spline mainshaft and must have the corresponding slip yoke. For 1971-'74, a larger diameter, 32-spline mainshaft was employed along with the corresponding yoke. Because this mainshaft is larger, you're also going to need larger bushings and seals. Keep this in mind when you're searching for a Muncie transmission.

What you will find in your search for the right Muncie four-speed is conflicting information from different sources. Before you here are the basics of Muncie M20, M21, and M22 four-speed transmissions. Glean the basics and use them in your research. Expect to find various combinations out there because these high-performance four-speed transmissions have been thrashed, trashed, and rebuilt through the decades. You're going to find various combinations of main cases, tailshaft housings, and side covers coupled with variations inside of each case. Pure dumb luck will lead you to a completely unmolested Muncie.

One more way to identify the Muncie is via stamped codes in the case, which indicate when the transmission was built at Muncie (see How To Read Muncie Build Date Codes chart). According to Cangialosi, the date was based on model year, not necessarily the calendar year.

Of course, restorers and rebuilders will tend to re-stamp the date code to suit a particular restoration. This can add confusion to what you've found. Muncie transmissions also tend to get performance improvements such as a gear ratio change and stronger internal parts. This is when you have to remove the side cover to see what's inside. Examine the input and output shafts to see if you've found the box you want.

And finally, if forced to choose between a Muncie or the BorgWarner T-10, it is suggested you choose the Muncie due to its brute strength. The Muncie was originally a stronger alternative to the T-10 and Super T-10 because it could take the torque. If you find an M22, you have the ultimate Muncie designed for the high torque of a big-block that will bolt to your small-block.

muncie 4 speeds - homestead

muncie 4 speeds - homestead

Muncie 4 speed transmissions were used in General Motors cars from 1963 to early 1975. These gear boxes were used when power levels exceeded the limits of the early Borg Warner T10 4 speed. It was actually based on the T-10 design and uses the same basic gear layout. The T10 made it's appearance in GM cars in 1957. From 1957 to 1963 many changes took place inside the gearbox to meet the increasing horsepower the new engines were putting out. It was replaced by the Muncie in late 1963. The Muncie 4 speed was used in production vehicles until power levels dropped in 1975. 1975 was the first year catalytic converters , smog pumps, and low horsepower were introduced. These new requirements led to the demise of the Muncie and the reintroduction of the improved T10 called the Super T10.

While General Motors was switching gearboxes around from 1963 to 1975 other companies such as Ford and AMC kept the T10 in production. So we got to see T10, and First Design Super T10 transmissions end up in these cars. It was also an opportunity for Borg Warner to design replacement Super T10's for the Muncie. These 4 speeds offered 9310 nickel gears, had a wide variety of gear ratios, and were available from any auto parts store carrying the Borg Warner parts line. A variation of this Super T10 ended up in GM cars from 1975 to 1983. Also as the 4 speed section of the 4+3 Corvette Overdrive in 1984 to 1988 Corvettes.

Well enough of this little 4 speed history. I figured I pass these facts on to you so that one day you can tell your children and just maybe all won't be lost. Lets face it today's muscle car is the Honda Civic. A majority of kids today will never feel the awesome torque of the big blocks as well as the feeling of ripping thru a few sets of gears.

Many people are always calling me or asking me at shows on how to identify Muncie 4 speeds. Not to many people actually know what type they have and most publications have done a good job of giving out wrong information. This includes performance parts books from GM as well as a multitude of poorly written "How To" articles in just about every car magazine around. One important point I'd like you to know is that most of the so called "Muncie Specialists" are in business because of me. Now with the use of my rebuild kits and knowledge you too can become a Muncie Specialist, and if your lucky a "Muncie King".

Several things are needed to identify a Muncie correctly. The first is a main case casting number. Second a count of the input shaft and output shaft splines and if any rings or grooves exist around the input shaft splines. Third are date codes and VIN numbers that help confirm that the above case and gears belong together. Tooth counts on the input shaft will help confirm a certain gear ratio, but you may not have access to this information if the transmission is still in the car or an unwilling vendor at a swap meet won't remove the cover.

Please note that there are 7 different Muncie input shafts. All 26 spline inputs came with 32 spline output shafts and all 10 spline inputs came with 27 spline output shafts. A common mistake is thinking that all "fine spline" 26 spline input shafts are M22 heavy duty types. This is not true. An M22 gearbox has a 20 degree helix angle on the gearset as opposed to a 45 degree angle. Also M22 gear sets were of a higher nickel alloy. The straighter angle was designed to produce less end loading of the gear train and less heat but created more noise, thus the nickname "rockcrusher". The higher nickel alloy allowed for more impact of the gears. Another misconception is if you have a drain plug you have an M22. Again this was only true when the first M22 boxes were created. But all 3925661 castings had drain plugs.

Serial numbers for Muncie 4 speeds always begin with the letter "P". P stands for Muncie Plant. Not for passenger car as some self proclaimed specialists may think. The letter M was used to ID the Muncie plant for the Muncie 3 speed, so P was the next logical letter. The letter O would add confusion since it resembles zero. The serial number is a date code the transmission was built for a particular year. Serial numbers from 1963 to 1966 included only the month and day. P0101 would indicate January 1st. From 1967 to 1968 the serial number got a year designator and a letter designator for the month such as P8A01, meaning January 1st 1968. One important point is that if you have a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13. This is for a 1968 production car. The T stands for December and 13 is the day. To confirm this simply look at the VIN number. It will usually begin with a 18S101350 or a 28N12950. This means the Muncie was assembled December 13, 1967 for the 1968 model year. The VIN number will usually be a low number. 1969 to 1974 Muncies got a ratio designator at the end of the serial number. An example would be P4D23B. This equates to April 23, 1974, M21 ratio.

Some input shafts produced by the aftermarket and General Motors have no identifying rings on them. The rings originally corresponded with rings or grooves on the counter gear so that the assembler matched a one or two ring input with a one or two ring cluster. When manufacturing was stopped, GM stopped making inputs with these marks, probably to save machining operations. Also 3831704 and 3851325 castings come with a 7/8" counter shaft all others come with a 1 inch counter shaft. There are some odd ball castings out there produced in 1963 to 1966 years. I've left them out since they really are not common.

The most popular question has to be that everyone thinks they have the famous "rockcrusher" M22 4 speed. This had the same gear ratios as the M21 but with a heavy duty gearset. The reason you may ask? Well it wasn't designed so that you could go drag racing on Saturday night or impress girls in front of Burger King by doing massive hole shots. It was primarily designed as a road race transmission. The straighter angle of the gearset produced less heat and less end loading of the gear train. Combined with high impact alloy gears this 4 speed really pushed the limits of it's aluminum case in drag race applications. Although the gears are not spur gears ( completely straight ) they still produced a fair amount of gear noise thus the "Rockcrusher" name. These 4 speeds sound like a blower drive. For the real gear head the best documented movie that sports a real M22 in a car is the famous movie " Two Lane Black Top ". You can really hear this gear box howl in the background as James Taylor and Dennis Wilson talk shop in a 55 Chevy. Later on we get to see the same car with new paint in the classic film "American Graffiti" with Harrison Ford at the helm. Since they used a dummy car for inside dialog shots you miss the flavor of the M22 in that flick.

The dead 2.20 first gear ratio which is the same in the M21 is not that good for off the line acceleration. You would need at least a 4.56 rear end gear to compensate for the dead first gear. That was OK when gas was cheap in 1967 and you did not mind pulling 3000 RPM at 50 MPH while going to work. Times and requirements have changed making both the M21 and M22 the closest ratio production 4 speeds ever produced but also not practical for today's driving habits unless road racing is your thing. Today's examples of the new car gear set ups are Mustang GT's with a 3.35 1st gear and 3.08 rear. New Camaros with a 2.68 1st gear, 3.73 rear gear and .59 overdrive. ZR1's with a 2.68 1st gear, 3.54 rear gear and a .59 overdrive. Get the picture? If you want to learn about this stuff DOWNLOAD our RPM Calculator software for windows its free.

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