Synchros - Single Gear

This procedure covers the removal, disassembly, and replacement of synchronizer assemblies for individual gears in the NV4500 or G56 manual transmission found in 2007 Ram 3500 vehicles with the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Synchronizer assembly for affected gear × 1 — Use OEM specification
• Transmission gasket set × 1 — Use OEM specification
• Transmission input shaft seal × 1 — Use OEM specification
• Transfer case input seal × 1 — Use OEM specification
• RTV silicone gasket maker × 1 — Mopar or equivalent
• Shift fork pads (if worn) × 1 — Use OEM specification
• Synchronizer blocking rings (as needed) × 1 — Use OEM specification

Fluids

• ATF+4 — 8 qt

Preparation

1. Park vehicle on level ground and engage parking brake
2. Disconnect negative battery cable
3. Raise vehicle on lift or support securely on jack stands at frame rails
4. Remove skid plates and belly pans for access
5. Drain transmission fluid into suitable container
6. Drain transfer case fluid into suitable container
7. Remove shift boot and shift lever assembly from inside cab
8. Support engine using support fixture or hoist to prevent movement when transmission is removed
9. Take photos of all shift linkage positions and electrical connections for reference during reassembly
10. Clean exterior of transmission and surrounding areas to prevent contamination during internal work

Procedure

1. 1

   Remove transmission from vehicle
   Disconnect electrical connectors from vehicle speed sensor, reverse light switch, and any other transmission-mounted sensors. Disconnect clutch hydraulic line at transmission. Remove driveshafts, marking their orientation to flanges. Support transmission with transmission jack. Remove crossmember bolts and lower crossmember. Remove bellhousing-to-engine bolts. Carefully slide transmission rearward off input shaft and lower from vehicle. Move to clean workspace.
2. 2

   Remove transfer case from transmission
   With transmission on bench, remove bolts securing transfer case to transmission adapter. Carefully separate transfer case from transmission output shaft, being careful not to damage seals or splines. Set transfer case aside. Remove adapter plate if necessary for access.
3. 3

   Remove transmission top cover
   With transmission positioned upright, remove all bolts securing the top cover. Carefully lift cover straight up to avoid damaging shift forks or rails. Observe and document the position of all shift forks, detent balls, springs, and rails. Remove shift rail detent balls and springs, keeping them organized by position.
4. 4

   Remove shift forks and rails
   Note the engagement position of each shift fork with its corresponding synchronizer sleeve. Remove shift fork roll pins using a punch, being careful not to damage shift rails. Slide shift rails out of case, removing shift forks as rails are withdrawn. Keep all shift forks identified by position and gear. Inspect shift fork pads for wear grooves and replace if necessary.
5. 5

   Remove front bearing retainer and input shaft
   Remove bolts securing front bearing retainer to transmission case. Carefully tap retainer with soft mallet to break seal and remove. Extract input shaft assembly from front of case, being careful not to drop loose needle bearings if present. Place input shaft in secure position with gear teeth protected.
6. 6

   Remove output shaft rear bearing and housing
   Remove bolts securing output shaft rear bearing housing to case. Use slide hammer or careful prying to remove housing. Remove rear bearing snap ring from output shaft. Use bearing puller or press to remove rear bearing from output shaft if necessary for access to gears.
7. 7

   Remove countershaft and cluster gear assembly
   Note position and orientation of countershaft. Remove countershaft snap rings or retaining devices. Support cluster gear assembly while driving countershaft out of case using brass drift. Carefully remove cluster gear assembly, being cautious of loose needle bearings and thrust washers. Keep all bearings and washers organized by position.
8. 8

   Disassemble output shaft to access target synchronizer
   With output shaft now accessible, remove snap rings securing gears and synchronizers in sequence from front to rear (or rear to front depending on which gear's synchro needs replacement). Use snap ring pliers to carefully expand and remove snap rings. Mark orientation of each synchronizer hub to shaft with punch marks. Remove synchronizer assemblies, gears, and spacers in order, keeping them organized. Continue disassembly until reaching the synchronizer assembly that requires replacement.
9. 9

   Remove and inspect faulty synchronizer assembly
   Once the target gear and synchronizer are accessible, remove the synchronizer sleeve from the hub by sliding it off. Note the position of synchronizer keys (inserts) and springs. Carefully remove keys and springs, controlling them to prevent loss. Remove blocking ring from gear cone. Inspect gear cone surface for scoring, wear, or heat discoloration. Inspect synchronizer hub splines for wear or damage. Measure blocking ring-to-gear cone clearance using feeler gauges and compare to the manufacturer's specification in the service manual (verify exact wear-limit value for the G56).
10. 10

    Install new synchronizer assembly
    Install new blocking ring onto gear cone, ensuring it moves freely. Position new synchronizer hub onto shaft in original orientation (align punch marks). Install synchronizer keys (inserts) into hub slots. Install synchronizer springs, ensuring they are positioned correctly (springs should typically be staggered 180 degrees and not share the same key). Slide synchronizer sleeve onto hub, ensuring it engages keys properly and moves smoothly. Verify sleeve moves freely in both directions and blocking ring engages properly.
11. 11

    Reassemble output shaft
    Reinstall gears, spacers, and synchronizer assemblies onto output shaft in reverse order of removal, using alignment marks made during disassembly. Install all snap rings, ensuring they are fully seated in their grooves. Check end play of each gear using dial indicator or feeler gauges to verify proper spacing and snap ring seating. Rotate each gear and verify smooth operation without binding.
12. 12

    Reinstall countershaft and cluster gear
    Install thrust washers in case with petroleum jelly to hold in place. Load cluster gear with needle bearings and install bearing retainers if equipped. Position cluster gear in case. Align countershaft bore and carefully drive countershaft into position using brass drift, ensuring it passes through cluster gear bearings properly. Install countershaft retaining devices and snap rings. Verify cluster gear rotates freely with minimal end play.
13. 13

    Install output shaft assembly and rear bearing
    Carefully lower output shaft assembly into case from rear, engaging front pilot bearing area with case. Install rear bearing onto shaft if previously removed, using press or bearing driver. Install rear bearing snap ring. Install rear bearing housing with new gasket or RTV as appropriate. Install and torque housing bolts in crossing pattern.
14. 14

    Install input shaft and front bearing retainer
    Install input shaft through front of case, engaging pilot into output shaft pilot bearing area. Ensure input shaft gear properly meshes with cluster gear. Install front bearing retainer with new gasket or RTV, aligning oil return passages. Install and torque retainer bolts in crossing pattern. Verify input shaft rotates freely.
15. 15

    Install shift forks, rails, and top cover
    Insert shift rails into case in proper positions. Install shift forks onto rails and engage fork pads into synchronizer sleeve grooves, verifying correct fork-to-gear relationship. Install shift rail roll pins. Install detent balls and springs into case bores. Verify all synchronizers can be shifted through full range of motion. Clean top cover gasket surface and install new gasket. Carefully lower top cover onto case, ensuring shift forks align properly with cover openings. Install and torque cover bolts in crossing pattern.

Reassembly

1. Install transfer case to transmission with new gasket or seal, torquing bolts in crossing pattern
2. Install new input shaft seal and transfer case input seal
3. Position transmission on transmission jack and carefully raise into position, aligning input shaft with clutch disc splines
4. Install bellhousing-to-engine bolts and torque in crossing pattern
5. Install crossmember and torque mounting bolts
6. Reconnect clutch hydraulic line
7. Install driveshafts in original orientation as marked during removal
8. Reconnect all electrical connectors to transmission-mounted sensors and switches
9. Install shift lever assembly and boot in cab
10. Reinstall skid plates and belly pans
11. Fill transmission with 8 quarts ATF+4 through fill plug until fluid reaches level of plug opening
12. Fill transfer case with 2.5 quarts ATF+4 through fill plug
13. Reconnect negative battery cable

Verification

• With engine running and clutch pedal depressed, verify transmission shifts smoothly through all gears without grinding, especially the repaired gear
• Test drive vehicle and verify smooth engagement and disengagement of all gears under light load
• Verify no grinding or difficulty engaging the specific gear that was repaired
• Test upshifts and downshifts through the repaired gear under various load conditions
• Check for fluid leaks at all transmission seals and gaskets after test drive
• Verify proper clutch pedal feel and clutch engagement point has not changed
• Recheck transmission and transfer case fluid levels after test drive and top off if necessary
• Listen for any abnormal noises from transmission during operation in all gears

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