How To Rebuild a Muncie 4-Speed Transmission
Learning how to rebuild a Muncie 4-speed transmission is a great way to restore your classic car back to like-new condition. You might need to perform this job if your gears are worn or chipped, or if the synchros are shot and require replacement. Some of these transmissions have a magnet on the inside to collect metal shavings. If you check this magnet and find large pieces or some shavings stuck to it, this could indicate a bad bearing or a lot of miles.
Disassembly Of The Transmission
Start the process by removing the front bearing retainer. To lock the main shaft in place for the removal of the input retaining nut, shift the main shaft into second and fourth gear. Next, remove the roll pin from the housing. This allows you to pry the selector shaft out of the way.
Now you can pull off the tail housing. Use a puller to remove the speedo drive gear from the shaft. After that, pull off the reverse main gear. Make sure to engage fourth gear before you remove the main shaft assembly from the case.
Tap the input shaft loose using a soft hammer. Take out the reverse idler and then tap out the input bearing. Next, press out the counter shaft. This could be done with a hammer, but using a press makes the job a whole lot easier. Finally, unload the main shaft by removing all the retaining clips, gears, and synchros that can be slid off.
Press the main shaft out of the third gear assembly. The rear main shaft support bearing is held in place with a snap ring. Spread this snap ring and tap the bearing loose to free it.
Cleaning And Rebuild Kit Preparation
Clean all the parts thoroughly so they are ready for reassembly. You can use a rebuild kit from Summit Racing for this job. This specific kit comes with all the gaskets, needle bearings, clips, bearings, seals, and synchros. During reassembly, make sure to use plenty of heavy grease. This grease prevents damage on your first ride out of the shop.
Rebuilding The Main Shaft
Begin by installing the new snap ring and bearing into the rear main shaft retainer. Drop on the third gear and the new synchro ring. Tap the synchro hub onto its spline. You must press the fourth gear sleeve back into place.
Slide on the second gear and its synchro, then tap the hub into place. A snap ring holds this entire assembly together. The synchro hubs each have three notches for the clutch keys. Put some grease in these notches to hold the clutch keys in place during assembly.
Slide the selector sleeves over the synchro hubs once the clutch keys are installed. Fourth gear is the last part on the stack. Install the retaining plate and secure it with another snap ring to keep everything together.
Assembling The Shafts And Case
Put the input shaft bearing assembly together piece by piece. Install one roller bearing at a time, then slide the assembly inside the shaft. Next, assemble the counter shaft assembly. Insert the spacer, then install the needle bearings. Take your time with these small pieces. Use grease to hold them in place so you do not leave any out.
Now you can start filling the transmission case. Start by installing the gear set, the thrust washer, and the counter shaft. Roll the reverse gear into place and slide in a new thrust washer. Tap the new input support bearing into the case, then slide in the input shaft.
Install the main gear assembly. The reverse gear shaft falls into place next. Follow this by installing the reverse selector gear and the speedo drive gear.
Final Case Assembly And Installation
Slide the tail housing into place. It is held by six bolts that you must torque to specs. Slide the reverse gear selector back into its spot and secure it with a new roll pin.
Install the output shaft seal and the speedo assembly. Both of these parts go on pretty easily. Apply some Loctite to the input nut to keep it from loosening up. Engage second and fourth gear before you tighten this nut down. Finally, torque the side cover down to complete the build.
Rebuilding a 4-speed transmission from a different manufacturer will be pretty similar. However, if you work on a more modern five-speed or six-speed transmission, you will need some specialty tools. Always do your homework before cracking one of those open.
