Synchros - Single Gear

Replace a single synchronizer assembly in the Tremec T56 6-speed manual transmission, requiring full transmission removal, disassembly, synchro replacement, and reassembly with proper clearance checks.

Warnings

Tools required

Parts

• Synchronizer assembly (specify gear) × 1 — Use OEM specification for affected gear
• Transmission case gasket × 1 — Tremec T56 case gasket
• Transmission pan gasket × 1 — Use OEM specification
• Shift fork pad set (if worn) × 1 — Tremec T56 shift fork pads
• Transmission output seal × 1 — Replace during disassembly
• Input shaft bearing retainer O-ring × 1 — Use OEM specification
• Rear shift tower gasket × 1 — Use OEM specification
• RTV silicone sealant (Mopar specified) × 1 — Use OEM specification

Fluids

• 75W-90 synthetic GL-4 manual transmission fluid — 4 qt

Preparation

1. Park vehicle on level concrete surface and engage parking brake.
2. Disconnect negative battery terminal to prevent starter engagement.
3. Raise vehicle and support securely on jack stands at manufacturer lift points (front subframe and rear differential mounts).
4. Remove complete exhaust system from headers back to allow transmission clearance.
5. Remove driveshaft: mark yoke-to-flange orientation, remove 4 flange bolts, support shaft and slide rearward from transmission output.
6. Drain transmission fluid into collection pan via drain plug on transmission pan.
7. Remove clutch hydraulic line from slave cylinder at bellhousing (cap line to prevent fluid loss).
8. Disconnect reverse light switch connector and vehicle speed sensor connector from transmission case.
9. Remove shift tower assembly from top of transmission (4 bolts); leave shifter cables/linkage attached and support assembly clear of work area.

Procedure

1. 1

   Remove transmission from vehicle
   Position transmission jack under transmission pan and secure with safety chain. Remove bellhousing-to-engine mounting bolts (access upper bolts from engine bay). Remove transmission crossmember mounting bolts and lower crossmember. Verify all electrical connections and mechanical linkages are disconnected. Slide transmission rearward approximately 2 inches to disengage input shaft from clutch disc, then lower transmission while supporting rear of engine with floor jack under oil pan (use wood block to protect pan). Maneuver transmission clear of vehicle.
2. 2

   Remove external components and drain residual fluid
   With transmission on workbench, remove any remaining external switches, sensors, and the slave cylinder if still attached. Drain any residual fluid via drain plug. Inspect drain plug magnet for metal debris (shavings indicate wear pattern). Inspect for metal debris (shavings indicate wear pattern). Remove bellhousing bolts and separate bellhousing from main case. Remove rear housing extension bolts and extension housing, tapping gently with dead-blow hammer if stuck. Remove the vehicle speed sensor and output shaft seal.
3. 3

   Split transmission case
   Remove the front bearing retainer bolts and retainer, then remove the shift isolator plate/cover bolts. The T56 main case is accessed by removing end retainers and withdrawing the gear train from the case rather than splitting horizontal halves. Verify exact bolt counts against the factory service manual for the 2005 Viper T56. With the front and rear retainers/covers removed, withdraw the countershaft and mainshaft assemblies from the case in the sequence specified by the factory service manual, supporting the gear stacks during removal. Do not attempt to split the case into halves.
4. 4

   Document and remove shift rail assembly
   Photograph shift fork positions and gate plate orientation for reassembly reference. Remove shift rail detent springs and balls (3 detent assemblies, use magnetic pickup to retrieve balls). Remove shift rail retaining pin or bolt from rear of case. Slide shift rails rearward while supporting shift forks. Remove shift forks from their respective synchronizer sleeves, noting which fork operates which gear.
5. 5

   Remove counter shaft and gear cluster
   Remove counter shaft rear bearing snap ring using external snap ring pliers. Install bearing puller on counter shaft rear bearing and extract bearing. Lift counter shaft assembly (with integral gears) straight up from case. Place counter shaft on clean workspace. Inspect counter shaft bearings and gear teeth for wear, pitting, or scoring.
6. 6

   Remove main shaft assembly
   Remove main shaft rear bearing snap ring. If removing 3rd/4th synchro: remove input shaft from front of case, then withdraw main shaft from rear of case as single assembly. If removing 5th/6th or 1st/2nd synchro: remove main shaft rear bearing using bearing puller, then withdraw main shaft assembly. Support gear stack during removal to prevent gears from sliding off shaft.
7. 7

   Disassemble gear stack to access target synchronizer
   With main shaft on workbench, photograph gear orientation and order. Remove snap rings retaining gears in sequence working from the end closest to target synchronizer. For 3rd/4th gear synchro: remove 4th gear, thrust washer, 3rd/4th synchro assembly, and 3rd gear. For 1st/2nd synchro: remove 1st gear, thrust washer, 1st/2nd synchro assembly, and 2nd gear. For 5th/6th synchro: remove 5th gear, thrust washer, 5th/6th synchro assembly, and 6th gear. Use snap ring pliers and light tapping with dead-blow hammer if gears are tight on splines.
8. 8

   Disassemble and inspect synchronizer assembly
   Mark synchro hub and sleeve alignment with scribe or paint before disassembly. Compress synchro springs and slide sleeve off hub while capturing detent balls or spring assemblies (typically 3 balls or 2 springs depending on design). Remove blocking rings from both sides of synchro hub. Inspect hub splines for wear, sleeve internal splines for excessive play, blocking ring friction surface for glazing or wear beyond 0.020 inch, and springs for loss of tension. Measure blocking ring-to-gear cone clearance on mating gear: should be 0.030-0.050 inch; replace if less than 0.020 inch.
9. 9

   Install new synchronizer assembly
   Lubricate new synchro hub splines and gear cone surfaces with transmission assembly lube. Install new blocking rings on synchro hub with chamfered edge toward gear cone. Align sleeve-to-hub marks (or install with stamped side outward if new). Insert detent balls or spring assemblies in hub notches, compress with finger pressure, and slide sleeve over hub ensuring detents engage properly. Verify sleeve slides smoothly on hub with 5-10 pounds resistance and locks at both engagement positions. Install synchro assembly onto main shaft in correct orientation with blocking rings positioned toward mating gears.
10. 10

    Reassemble gear stack with clearance checks
    Reinstall gears onto main shaft in reverse order of removal, referencing photographs. Install thrust washers with bronze side toward gear faces. Install snap rings ensuring they seat fully in grooves. Check gear endplay with feeler gauge: 3rd/4th gears should have 0.004-0.012 inch endplay, 1st/2nd gears 0.006-0.018 inch endplay. Check synchro blocking ring-to-gear cone clearance with feeler gauge by inserting between ring and cone while pressing ring onto cone: minimum 0.020 inch required. If clearances are out of specification, verify correct thrust washer thickness and snap ring seating.
11. 11

    Install main shaft assembly into case
    Apply thin coat of assembly lube to main shaft bearings and gear teeth. Install main shaft into lower case half, seating rear bearing fully into case bore. If input shaft was removed, install input shaft into front of case and engage with main shaft pilot bearing. Install main shaft rear bearing snap ring. Verify main shaft rotates freely without binding. Check main shaft endplay with dial indicator: should be 0.001-0.005 inch; if excessive, check snap ring seating and bearing installation.
12. 12

    Install counter shaft assembly
    Apply assembly lube to counter shaft bearings and gear teeth. Lower counter shaft assembly into case, aligning rear bearing with case bore. Tap rear bearing into case using bearing driver or large socket until fully seated. Install counter shaft rear bearing snap ring. Check counter shaft endplay with dial indicator: should be 0.001-0.005 inch. Verify counter shaft gears mesh properly with main shaft gears and rotate without binding.
13. 13

    Install shift rail assembly and fork adjustment
    Apply light coat of oil to shift rails. Install shift forks onto their respective synchro sleeves, verifying correct fork-to-gear assignment per documentation. Insert shift rails from rear of case through shift forks, aligning detent notches. Install shift rail detent balls and springs, tightening retainers to specification if threaded. Install shift rail retaining pin or bolt. Check shift fork pad-to-synchro sleeve clearance with feeler gauge: should be 0.005-0.020 inch; replace fork pads if clearance exceeds 0.030 inch. Verify each gear engages fully and shift rails move through complete travel without binding.
14. 14

    Reassemble transmission case
    Clean all case parting surfaces thoroughly with solvent and lint-free cloth. Apply thin bead of RTV silicone to lower case parting surface (or install new gasket if equipped). Verify all shift rails are in neutral position. Carefully lower upper case half onto lower case, aligning dowel pins. Install case bolts hand-tight in star pattern, then torque in three stages (30%, 60%, 100%) working in criss-cross pattern to prevent case warping. Final torque per specification. Verify shafts rotate freely after case assembly.
15. 15

    Install external components and seals
    Install new output shaft seal using seal driver, ensuring seal lip faces inward. Install extension housing with new gasket, torquing bolts in criss-cross pattern. Install the vehicle speed sensor and any associated drive components per factory specification (the 2005 Viper uses an electronic speed sensor, not a mechanical speedometer drive gear). Install bellhousing with new O-ring on input bearing retainer, torquing bolts in star pattern. Install new transmission pan gasket and pan, torquing bolts in criss-cross pattern. Install shift tower with new gasket. Reconnect reverse light switch and speed sensor connectors.
16. 16

    Install transmission into vehicle
    Apply light coat of high-temperature grease to input shaft splines and clutch release bearing contact surface. Position transmission on transmission jack and raise into position. Align input shaft with clutch disc splines (may require slight rotation of output shaft to align splines). Slide transmission forward until bellhousing contacts engine block. Install bellhousing-to-engine bolts, starting upper bolts from engine bay. Torque mounting bolts to specification. Install transmission crossmember and torque mounting bolts. Remove transmission jack.
17. 17

    Reconnect driveline and fill transmission
    Install driveshaft, aligning marks made during removal. Torque flange bolts in star pattern. Reconnect clutch hydraulic line to slave cylinder and bleed system if air entered. Reconnect reverse light and speed sensor connectors. Install exhaust system with new gaskets. Fill transmission with the factory-specified fluid per the 2005 Viper service manual (verify exact type and capacity; the T56 typically uses a specific synthetic ATF-type manual transmission fluid rather than 75W-90 gear oil) until fluid reaches the bottom of the fill hole. Install fill plug with new crush washer if equipped and torque to specification. Install fill plug with new crush washer if equipped and torque to specification.

Reassembly

1. All snap rings must be fully seated in their grooves with no gaps visible.
2. All case bolts must be torqued in proper sequence to prevent case warping and fluid leaks.
3. Shift rails must move through full travel smoothly with positive detent engagement in each gear position.
4. Counter shaft and main shaft must rotate freely without binding after case assembly.
5. All electrical connectors must click audibly when fully seated.

Verification

• With engine off and clutch depressed, verify transmission shifts smoothly through all gears with no grinding or resistance.
• Start engine and verify reverse lights illuminate when reverse gear is selected.
• Test drive vehicle through all gears, verifying smooth engagement with no gear clash, pop-out, or grinding. Check particularly that repaired gear engages cleanly under light and heavy throttle.
• After 20 miles of operation, recheck transmission fluid level with vehicle level and engine off. Top off if needed.
• After 50 miles, inspect transmission case and pan for fluid leaks. Retorque pan bolts if seepage is observed.
• Monitor for unusual noise, vibration, or shift quality issues over first 500 miles of operation.

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