Synchros - All

Complete transmission disassembly and replacement of all synchronizer assemblies in the G56 6-speed manual transmission, requiring transmission removal from vehicle.

Warnings

Tools required

Parts

• 1st-2nd gear synchronizer assembly × 1 — Use OEM Mopar specification
• 3rd-4th gear synchronizer assembly × 1 — Use OEM Mopar specification
• 5th-6th gear synchronizer assembly × 1 — Use OEM Mopar specification
• Reverse synchronizer assembly × 1 — Use OEM Mopar specification
• Transmission input shaft bearing × 1 — Use OEM Mopar specification
• Main drive gear bearing × 1 — Use OEM Mopar specification
• Countershaft rear bearing × 1 — Use OEM Mopar specification
• Transmission case gasket × 1 — Use OEM Mopar specification
• Transmission rear seal × 1 — Use OEM Mopar specification
• Shift fork pads (set) × 1 — Use OEM Mopar specification
• Snap ring set (various sizes) × 1 — Use OEM Mopar specification
• Transmission mounting bolts × 8 — Use OEM Mopar specification
• Transfer case adapter gasket × 1 — Use OEM Mopar specification
• Clutch hydraulic line clips × 4 — Use OEM Mopar specification
• Transmission vent hose × 1 — Use OEM Mopar specification

Fluids

• ATF+4 (manual transmission) — 8 qt

Preparation

1. Park vehicle on level surface and set parking brake
2. Disconnect both battery cables (negative first)
3. Raise vehicle on lift to comfortable working height
4. Remove skid plates and belly pans to access transmission
5. Place drain pan under transmission and drain fluid completely
6. Remove transfer case completely from transmission
7. Disconnect shift tower from transmission case
8. Disconnect backup light switch and speed sensor connectors
9. Support engine with overhead hoist or support fixture across engine bay
10. Remove driveshafts (front and rear) and cap all openings
11. Disconnect clutch hydraulic line from slave cylinder
12. Remove transmission crossmember mounting bolts
13. Support transmission securely with transmission jack
14. Remove all transmission-to-engine bell housing bolts
15. Carefully slide transmission straight back away from engine until input shaft clears clutch
16. Lower transmission and move to clean workbench with transmission holding fixture

Procedure

1. 1

   External disassembly and case separation
   Remove the shift tower assembly, detent springs, and all external components. Remove the rear extension housing and output shaft seal. Remove all case bolts in proper sequence (from outside working inward in cross pattern). Using dead blow hammer, carefully tap case halves apart. Lift front case half straight up to separate from rear case, exposing all internal components.
2. 2

   Document gear positions and remove mainshaft assembly
   Take photographs of all gear positions, noting orientation of synchronizer assemblies. Mark timing positions on all synchro hubs and sleeves with paint marker. Remove the mainshaft assembly as complete unit by lifting straight up. Place on clean work surface. Note positions of all shims and thrust washers.
3. 3

   Remove countershaft and input shaft
   Lift countershaft assembly from rear case half, noting bearing positions and any shims. Remove input shaft from front bearing bore. Use bearing puller to remove front input shaft bearing if required. Inspect all bearing races in case for damage or wear. Mark location of any shims found during disassembly.
4. 4

   Disassemble mainshaft and remove synchronizers
   Mount mainshaft in holding fixture or padded vise (clamping on shaft only, never gears). Remove rear snap ring securing 5th-6th synchro assembly. Press or carefully drive 5th-6th synchronizer off shaft, noting direction of hub. Remove 5th gear and thrust washer. Remove snap ring for 3rd-4th synchro. Press off 3rd-4th synchronizer assembly. Remove 3rd gear and synchronizer ring. Continue disassembly removing 1st-2nd synchro assembly and associated gears. Keep all components in order on clean bench.
5. 5

   Inspect all gears and shafts
   Thoroughly clean all gears, shafts, and bearing surfaces with solvent and compressed air. Inspect mainshaft and countershaft for scoring, wear, or damage. Check all gear teeth for chips, pitting, or excessive wear. Inspect synchro cone surfaces on gears for scoring or discoloration indicating overheating. Measure shaft runout with dial indicator (maximum 0.003 inch). Replace any damaged components.
6. 6

   Install new synchronizer assemblies on mainshaft
   Begin reassembly with 1st gear and 1st-2nd synchronizer. Install synchronizer ring onto gear cone, checking engagement (minimum 0.050 inch clearance required). Press new 1st-2nd synchro hub onto shaft in correct orientation per timing marks. Install snap ring. Continue with 3rd gear, new 3rd-4th synchro assembly, and snap ring. Install 5th gear components and new 5th-6th synchro assembly. Verify all snap rings are fully seated in grooves. Check that all gears rotate freely and synchro sleeves slide smoothly.
7. 7

   Install reverse synchronizer on countershaft
   Install new reverse synchronizer assembly in the correct position per factory service manual for the G56 (verify shaft location and orientation before installation). Ensure reverse idler gear engagement is correct. Install any required thrust washers or shims that were documented during disassembly. Verify reverse gear engagement and clearances.
8. 8

   Install bearings and measure preload
   Press new bearings onto input shaft and countershaft using proper bearing driver tools. Install bearing races into transmission case bores, ensuring they are fully seated. Install original shims behind bearings as starting point. Use dial indicator to check bearing preload and end play on all shafts. Adjust shim thickness as needed to achieve proper bearing preload/end play per the G56 factory service manual specifications (do not rely on generic values—verify exact spec).
9. 9

   Install shift forks and rails
   Install new shift fork pads on all shift forks. Apply light coat of 75W-85 GL-4 gear oil to shift rails. Install shift rails into case in proper sequence, positioning detent notches correctly. Install shift forks onto synchronizer sleeves, ensuring forks engage properly in grooves. Install interlock mechanisms and detent springs. Verify smooth operation of all shift rails through full travel.
10. 10

    Assemble transmission case halves
    Apply thin bead of anaerobic sealant to case mating surface (if gasket is not used) or install new case gasket. Carefully lower mainshaft assembly into rear case half, aligning with bearings and shift forks. Install countershaft assembly into position. Lower front case half onto rear case, ensuring all components align properly and shift rails enter front case bores. Do not force case halves together.
11. 11

    Secure case and install extension housing
    Install all case bolts, starting with center bolts and working outward in cross pattern. Tighten bolts gradually in three stages to allow even case compression. Rotate input shaft and shift through all gears to verify smooth operation before final tightening. Install new rear extension housing gasket and secure extension housing. Install new output shaft seal using seal driver.
12. 12

    Install external components and bench test
    Install shift tower assembly with new gasket. Reconnect detent springs and install all external sensors. With transmission on bench, manually shift through all gear positions multiple times, verifying smooth engagement and proper synchro operation in each gear. Check for any binding, grinding, or abnormal resistance. Verify reverse gear engages properly.
13. 13

    Install transmission in vehicle
    Apply thin coat of high-temperature grease to input shaft splines. Position transmission on transmission jack and raise into position, aligning input shaft with clutch disc splines using clutch alignment tool if needed. Slide transmission forward until bell housing seats against engine block. Install all transmission-to-engine bolts and tighten evenly in a cross/star pattern to the factory-specified torque per the G56 service manual. Install transmission crossmember and mounting bolts. Remove engine support fixture.
14. 14

    Reconnect all components and fill transmission
    Connect clutch hydraulic line to slave cylinder. Reconnect backup light switch and speed sensor. Install shift tower and linkage. Install front and rear driveshafts with new hardware. Install transfer case with new gasket. Install skid plates. Fill transmission with approximately 4.75 quarts of SAE 75W-85 API GL-4 synthetic manual transmission fluid through fill plug (fill to bottom of fill hole). Reconnect battery cables (positive first, then negative).

Reassembly

1. Ensure all snap rings are fully seated and visible in their grooves
2. Verify all shift forks engage properly in synchronizer sleeve grooves before closing case
3. Check that all timing marks align on synchronizer hubs and sleeves
4. Apply anaerobic sealant sparingly - excess will contaminate transmission internals
5. All bearings must be pressed on squarely using proper tools to avoid damage
6. Verify transmission shifts smoothly through all gears on bench before installation
7. Double-check that all sensors and electrical connections are secure
8. Ensure driveshaft phasing marks align during reinstallation

Verification

• Start engine and verify clutch pedal feels normal with proper engagement point
• With engine running and clutch depressed, shift through all gears verifying smooth engagement without grinding
• Test drive vehicle through all gears under light load, confirming smooth shifts
• Verify no grinding, popping out of gear, or difficulty engaging any gear
• Check for fluid leaks around case, extension housing, and all seals
• Verify backup lights function in reverse gear
• Test synchronizer operation by attempting shifts at various RPMs - should be smooth without grinding
• After 50-100 miles, recheck transmission fluid level and top off if needed
• Monitor for any unusual noises, vibrations, or shifting issues during break-in period

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