Synchros - All

Complete replacement of all synchronizer assemblies in the NV4500 or NV5600 manual transmission, requiring full transmission removal and disassembly.

Warnings

Tools required

Parts

• 1st/2nd gear synchronizer assembly × 1 — Use OEM or quality aftermarket (NV4500/NV5600 specific)
• 3rd/4th gear synchronizer assembly × 1 — Use OEM or quality aftermarket (NV4500/NV5600 specific)
• 5th gear synchronizer assembly × 1 — Use OEM or quality aftermarket (NV4500/NV5600 specific)
• Reverse synchronizer assembly (if equipped) × 1 — NV5600 only
• Transmission gasket and seal kit × 1 — Use OEM specification
• Input shaft bearing × 1 — Inspect and replace as needed
• Mainshaft bearings × 2 — Inspect and replace as needed
• Countershaft bearings × 2 — Inspect and replace as needed
• Pilot bearing × 1 — Use OEM specification
• Clutch release bearing × 1 — Replace while transmission is out
• Transmission drain plug washer × 1 — Use new washer
• RTV silicone gasket maker × 1 — Use Mopar or equivalent
• Assembly lube × 1 — Transmission assembly lube

Fluids

• 75W-90 synthetic gear oil — 8 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect both battery cables, negative first
3. Raise vehicle on lift or support securely on jack stands at frame rails
4. Remove skid plates and belly pan if equipped
5. Drain transmission fluid completely and reinstall drain plug with new washer
6. Remove shift tower/shifter assembly from top of transmission
7. Disconnect reverse light switch and vehicle speed sensor connectors
8. Remove driveshafts (front and rear) and mark U-joint positions for reinstallation
9. Support transfer case with jack and remove transfer case to transmission mounting bolts
10. Remove transfer case carefully and set aside
11. Disconnect clutch hydraulic line at transmission (slave cylinder)
12. Support engine with support bar or overhead hoist
13. Remove transmission crossmember mounting bolts
14. Place transmission jack under transmission with safety chain
15. Prepare clean workspace with adequate lighting for transmission disassembly

Procedure

1. 1

   Remove transmission from vehicle
   Remove all transmission mounting bolts securing bellhousing to engine. There are typically 6-8 bolts of varying lengths. Carefully slide transmission rearward on jack, ensuring input shaft clears clutch disc and pilot bearing. Guide transmission down and out from under vehicle. Transport to clean work area and mount in transmission holding fixture or secure on workbench.
2. 2

   Remove external components and shifter assembly
   Remove backup light switch and vehicle speed sensor. Remove all shift rail detent springs, balls, and plugs from case exterior (label each location). Remove shift rail covers and any remaining external components. Clean exterior thoroughly before opening case to prevent contamination.
3. 3

   Split transmission case
   Remove the top shift cover/PTO cover bolts and lift off the cover. Remove the front bearing retainer bolts and the rear adapter/extension housing bolts in proper sequence. Do not pry at sealing surfaces. Carefully separate the housing from the main case, keeping track of which components remain where. Remove old gaskets and inspect sealing surfaces for damage.
4. 4

   Remove shift forks and rails
   Remove shift forks and rails, most of which are located in the top shift cover assembly on the NV4500/NV5600. Remove any fork setscrews or roll pins using an appropriate punch, note fork engagement with the synchronizer sleeves, and keep each shift fork with its corresponding rail. Inspect shift forks for wear at synchronizer sleeve contact points and replace if wear grooves are present.
5. 5

   Remove mainshaft assembly
   Remove the rear bearing retainer/adapter. Following the NV4500/NV5600 service sequence, remove the countershaft as needed to gain clearance, then withdraw the mainshaft assembly rearward out of the case with its gears and synchronizers. Place on clean workbench. Mark gear positions and orientation before disassembly. Remove snap rings securing each gear and synchronizer assembly, working from rear to front.
6. 6

   Remove countershaft and input shaft
   Remove countershaft rear bearing retainer and snap ring. Carefully tap countershaft rearward using soft mallet on front end, then lift out. Remove input shaft from case by pulling forward through front bearing bore. Inspect all shaft surfaces for scoring, wear, or damage. Replace if damaged.
7. 7

   Disassemble synchronizer assemblies
   For each synchronizer: mark hub and sleeve alignment, slide sleeve off hub while retaining keys and springs. Remove blocking rings and inspect for wear (should have sharp teeth). Measure blocking ring to gear clearance with a feeler gauge and compare against the NV4500/NV5600 service manual specification (verify exact new and wear-limit values for your unit). Inspect synchronizer teeth on gears for wear or damage. Clean all components thoroughly with solvent.
8. 8

   Press off bearings and inspect shafts
   Using hydraulic press and proper bearing separator, remove all bearings from mainshaft, countershaft, and input shaft. Inspect bearing surfaces on all shafts for scoring, pitting, or discoloration. Measure shaft runout with a dial indicator and compare against the NV4500/NV5600 factory service limit (verify exact TIR spec for your unit). Inspect splines for damage. Replace any shaft showing excessive wear or damage.
9. 9

   Assemble new synchronizer assemblies
   Install new blocking rings on gear cones. Install synchronizer springs into hub slots (if dual springs, install in opposite directions for balance). Place keys into hub slots on top of springs. Carefully slide sleeve over hub, aligning marks made during disassembly. Ensure keys engage sleeve properly. Test sleeve slides smoothly on hub. Install blocking rings on both sides of each assembled synchronizer.
10. 10

    Press on new bearings
    Using hydraulic press and proper bearing race drivers, install new bearings on all shafts. Support shaft properly to prevent bending. Press bearings until fully seated against shoulders. Apply transmission assembly lube to all bearing surfaces. Install bearing retaining snap rings and verify proper seating in grooves.
11. 11

    Reassemble mainshaft with new synchronizers
    Apply assembly lube to mainshaft. Install gears and new synchronizer assemblies in the correct order per the service manual for your specific transmission (NV4500 5-speed and NV5600 6-speed differ). Verify each synchronizer, gear, and thrust washer position against the factory sequence before pressing/snap-ring installation. Install all retaining snap rings and ensure proper seating. Check endplay of each gear (typically 0.003-0.010 inch). Verify synchronizers engage smoothly when shifted by hand.
12. 12

    Install shafts into case
    Apply assembly lube to all bearing bores in case. Install input shaft into front case half, seating bearing fully. Install mainshaft assembly into case, ensuring rear bearing seats properly. Install countershaft, aligning gear mesh properly with mainshaft gears. Verify all gears rotate freely without binding. Install all bearing retainers and snap rings.
13. 13

    Install shift forks and rails
    Apply light coat of assembly lube to shift rails. Install each shift fork into its corresponding synchronizer sleeve groove. Slide shift rails through case bores and through fork holes. Install fork retaining pins or roll pins. Verify each rail moves smoothly through full range of travel. Install detent balls, springs, and plugs.
14. 14

    Assemble case halves
    Apply thin bead of RTV silicone to case mating surface (or install new gasket per manufacturer specs). Carefully position second case half, ensuring all shift rails and components align properly. Install case bolts and tighten in criss-cross pattern from center outward. Allow RTV to cure per manufacturer specifications before filling. Install all cover plates with new gaskets.
15. 15

    Reinstall transmission
    Mount transmission on transmission jack. Apply thin coat of high-temp grease to input shaft splines. Carefully guide transmission into position, aligning input shaft with clutch disc splines (use clutch alignment tool if needed). Push transmission forward until bellhousing seats against engine block. Install all mounting bolts and tighten in star pattern to proper torque specifications. Remove transmission jack. Install crossmember and tighten mounting bolts. Reconnect clutch hydraulic line. Install transfer case with new gasket, torquing mounting bolts properly. Install front and rear driveshafts, aligning marks made during removal. Reconnect all electrical connectors. Fill transmission to the fill plug level with the manufacturer-specified lubricant: the NV4500 requires a GL-4 gear oil (Mopar/Castrol Syntorq LT or equivalent) — do NOT use GL-5. Verify the correct spec for the NV5600 as well. Install shift tower with new gasket. Lower vehicle and reconnect battery cables.
    Torque spec

    Fill Plug34 Nm (25 lb-ft)

Reassembly

1. Torque all fasteners to specification in proper sequence
2. Fill transmission with 75W-90 synthetic gear oil until it runs out of fill plug hole
3. Bleed clutch hydraulic system after reconnecting slave cylinder
4. Verify all electrical connectors are properly seated
5. Check transfer case fluid level and top off if needed
6. Inspect for fluid leaks after initial fill

Verification

• Start engine with clutch pedal depressed and transmission in neutral
• Verify clutch pedal feel is normal with proper engagement point
• With engine idling, shift through all gears without grinding (vehicle stationary)
• Test drive vehicle and verify smooth shifting under load in all gears
• Check that synchronizers properly prevent gear clash during upshifts and downshifts
• Verify no whining, grinding, or abnormal noises in any gear
• Confirm no fluid leaks from transmission, transfer case, or driveshaft connections
• Recheck fluid levels after test drive and top off if necessary
• Verify speedometer operation (vehicle speed sensor functioning)
• Check reverse lights function properly

More procedures for this vehicle