Synchros - Single Gear

Replace a single synchronizer assembly in the Tremec T56 6-speed manual transmission of the 2008 Dodge Viper, requiring transmission removal, disassembly, synchro replacement, and reinstallation.

Warnings

Tools required

Parts

• Synchronizer assembly for affected gear × 1 — Use OEM specification - T56 gear-specific
• Transmission gasket set × 1 — Includes main case gasket and extension housing gasket
• Transmission front seal × 1 — Input shaft seal
• Shift rail detent springs and balls × 1 — Replace if worn during inspection
• Shift fork pad inserts × 1 — Inspect and replace if worn beyond spec
• Transmission RTV sealant × 1 — Mopar or equivalent anaerobic gasket maker

Fluids

• Pennzoil Synchromesh 75W-90 — 4.2 qt

Preparation

1. Disconnect negative battery cable and secure away from terminal
2. Raise vehicle on lift or support securely on jack stands at all four corners, ensuring adequate clearance for transmission removal
3. Remove rear wheels to access exhaust routing
4. Allow exhaust system to cool completely if vehicle has been recently operated
5. Place drain pan under transmission and drain gear oil completely from drain plug
6. Mark driveshaft-to-differential flange orientation with paint or punch marks for reinstallation alignment
7. Prepare clean workspace with parts trays for organizing transmission components during disassembly

Procedure

1. 1

   Remove driveshaft
   Remove the four bolts securing driveshaft to rear differential companion flange. Support driveshaft center and slide rearward to disengage from transmission output shaft. Cap transmission extension housing opening with plastic bag and tape to prevent fluid leakage and contamination.
2. 2

   Disconnect exhaust system
   Disconnect exhaust system at mid-pipe connection points to provide clearance for transmission removal. Remove exhaust hangers as needed to lower exhaust away from transmission. The Viper exhaust requires disconnection at the appropriate flange/collector points to allow sufficient drop clearance for transmission removal.
3. 3

   Disconnect shift linkage and electrical connections
   Disconnect shift linkage at transmission shift tower by removing the linkage pin or retaining clip. Disconnect reverse light switch electrical connector and any transmission-mounted speed/output-shaft sensor connectors from the transmission case (verify which sensors are present on this application). Disconnect clutch hydraulic line from slave cylinder at transmission bellhousing by removing the hydraulic line fitting.
4. 4

   Support engine and remove transmission crossmember
   Position a jack with block of wood under engine oil pan to support engine weight. Remove transmission crossmember mounting bolts at frame rails and remove crossmember. Allow transmission to lower slightly while maintaining engine support.
5. 5

   Remove transmission-to-bellhousing bolts and extract transmission
   Position transmission jack under transmission with securing chains or straps. Remove the bellhousing-to-transmission bolts around perimeter of bellhousing. Carefully slide transmission rearward on jack, ensuring input shaft clears clutch disc and pilot bearing. The transmission is heavy and awkward - use controlled movements and verify clearance of all surrounding components during extraction.
6. 6

   Clean transmission exterior and remove extension housing
   Clean exterior of transmission thoroughly with solvent to prevent contamination during internal work. Remove extension housing bolts and carefully separate extension housing from rear of transmission case using soft mallet taps if needed. Remove output shaft rear bearing snap ring if present. Inspect extension housing bushing and seal for wear. Note: Clean transmission exterior and remove rear/tail extension housing
7. 7

   Remove tail housing and shift tower assembly
   Remove shift tower/isolator assembly bolts and lift the shift tower with shift rails from the top of the transmission case. Keep shift rail detent springs and balls captured - these are under spring pressure. Lay shift tower assembly aside and inspect for wear. Keep shift rail detent springs and balls captured - these are under spring pressure. Lay shift tower assembly aside and inspect for wear.
8. 8

   Split transmission case
   Remove the front bearing retainer and any bearing race retention. The T56 uses an integral (non-split) main case; the geartrain is removed through the rear of the case after the extension housing is off. Withdraw the mainshaft/countershaft geartrain rearward as an assembly. Document the orientation and position of all components before further disassembly. Document the orientation and position of all components before further disassembly.
9. 9

   Remove counter gear and mainshaft assembly
   Withdraw the mainshaft/countershaft geartrain assembly rearward out of the case as a unit. The mainshaft assembly includes all gears, synchronizers, and the mainshaft. Identify the gear position of the failed synchronizer on the mainshaft. Identify the gear position of the failed synchronizer on the mainshaft. The T56 mainshaft gear/synchro arrangement varies by application - verify the exact position of the target gear against the 2008 Viper service manual before disassembly.
10. 10

    Disassemble mainshaft to access target synchronizer
    Secure mainshaft in soft-jaw vise or V-blocks. Work from the end nearest the target synchronizer. Remove snap rings retaining each gear and synchronizer assembly in sequence. Use snap ring pliers and work carefully to avoid damaging snap ring grooves. Slide gears and synchronizers off mainshaft in order, keeping components organized by position. For the target synchronizer, remove the retaining snap ring, slide synchronizer hub and sleeve assembly off shaft, and remove synchronizer insert springs and keys. Remove blocking rings from both sides of synchro assembly.
11. 11

    Inspect components and measure clearances
    Inspect blocking ring-to-gear cone engagement by installing blocking ring on gear cone and measuring clearance with feeler gauge. Specification is typically 0.050 inch minimum clearance - if original gear is below specification, replace gear as well. Inspect shift fork pad wear where it contacts synchronizer sleeve groove. Measure shift fork-to-sleeve clearance - should not exceed 0.030 inch. Inspect mainshaft splines and gear bore splines for wear or damage. Check synchronizer sleeve-to-hub engagement for wear on teeth.
12. 12

    Install new synchronizer assembly
    Install new blocking rings on both sides of gear cone. Assemble new synchronizer hub onto mainshaft with correct orientation (mark on hub typically faces one direction for proper shift engagement). Install synchronizer insert keys into hub slots and install insert springs - springs must be oriented opposite directions with gaps offset. Install synchronizer sleeve over hub, ensuring alignment marks (if present) match hub orientation. Verify smooth operation of sleeve on hub with keys properly engaged.
13. 13

    Reassemble mainshaft gear stack
    Reinstall gears and synchronizers onto mainshaft in reverse order of removal. Install each snap ring in its groove and verify complete seating by checking that snap ring gap does not align with ring locator pin hole. Measure each gear endplay with dial indicator after snap ring installation - typical spec is 0.003 to 0.010 inch per gear. Record measurements. Install all gears and synchros up to the input shaft bearing area.
14. 14

    Reinstall mainshaft assembly into case
    Clean case halves thoroughly and inspect bearing bores for damage. Install mainshaft assembly into appropriate case half, seating all bearings into their bores. Install counter gear assembly, ensuring bearing races are properly seated. Verify all shift fork positions align with their respective synchronizer sleeve grooves. Check that reverse idler gear is properly positioned if applicable to the disassembly depth performed.
15. 15

    Mate transmission case halves and install shift tower
    Apply thin bead of anaerobic gasket maker to the front bearing retainer and extension housing mating surfaces per Mopar specifications (or install new gaskets per kit instructions). Reinstall the geartrain into the case and reinstall the front bearing retainer, ensuring all dowel pins engage properly and no gears bind. Install front bearing retainer and extension housing bolts in a cross pattern and tighten gradually and evenly to specification. Install shift tower assembly, ensuring shift rail detent balls and springs are installed in their bores before lowering tower into position. Install shift tower bolts. Install the rear extension housing with new gasket or sealant, ensuring the output shaft bearing is properly seated.
16. 16

    Install new front seal and reinstall transmission
    Install new input shaft seal into the front bearing retainer using a seal driver. Apply thin film of transmission fluid to seal lip. Position transmission on transmission jack and align with engine. Guide input shaft into clutch disc splines - use clutch alignment tool if needed to center disc. Push transmission forward until bellhousing meets engine block. Install bellhousing-to-engine bolts and tighten to the factory-specified torque per the 2008 Viper service manual. Install transmission crossmember and remove engine support jack.
17. 17

    Reconnect all external components
    Reconnect clutch hydraulic line to slave cylinder and bleed clutch system. Reconnect shift linkage to shift tower and verify proper pin or clip engagement. Reconnect reverse light switch and vehicle speed sensor electrical connectors. Reconnect exhaust system at mid-pipe flanges using new gaskets if needed. Install driveshaft, aligning marks made during removal, and torque flange bolts to specification.
18. 18

    Fill transmission and perform initial checks
    Fill transmission with the factory-specified quantity of the correct manual transmission fluid per the 2008 Viper service manual (verify exact fluid specification and capacity). Fluid should reach bottom of fill plug hole. Install fill plug. Fluid should reach bottom of fill plug hole. Install fill plug. Reconnect negative battery cable. Start engine and verify no fluid leaks from transmission, extension housing, or shift tower. With engine at idle and clutch depressed, shift through all gears to verify synchronizer operation and proper shift engagement.

Reassembly

1. Reassembly is detailed within the procedure steps above, following reverse order of disassembly with critical torque specifications and measurement verification at each stage
2. Ensure all snap rings are fully seated in their grooves with no gap aligned to locator pins
3. Verify smooth shifting through all gears during bench test of shift tower before final case assembly
4. Use new gaskets or fresh anaerobic sealant on all case mating surfaces - do not reuse old gaskets

Verification

• With vehicle on ground and engine running, verify smooth engagement into all gears without grinding, particularly the gear whose synchronizer was replaced
• Test shift effort - should be consistent across all gears with no excessive force required
• Perform test drive including acceleration and deceleration shifts through the repaired gear range under varying loads
• Verify no whining, grinding, or jumping out of gear under load
• Check for fluid leaks at all transmission sealing surfaces after test drive
• Recheck fluid level after test drive and top off if needed - allow transmission to cool before checking level

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