Synchros - Single Gear

Replace synchronizers for a single gear in the Borg-Warner T56 6-speed manual transmission, requiring transmission removal, disassembly, synchro replacement, and reassembly with proper preload settings.

Warnings

Tools required

Parts

• Synchronizer assembly for affected gear × 1 — Use OEM specification - varies by gear position
• Synchronizer blocking ring for affected gear × 1 — Use OEM specification
• Transmission gasket kit (case halves, shifter covers) × 1 — T56 overhaul gasket kit
• Transmission drain plug washer × 1 — Use OEM specification
• Transmission fill plug washer × 1 — Use OEM specification
• Clutch friction disc (if contaminated) × 1 — 11-inch twin-disc
• Clutch pressure plate (if contaminated) × 1 — 11-inch twin-disc

Fluids

• Mopar MS-9224 or 75W-90 GL-4 manual transmission fluid — 5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable
3. Allow exhaust system and transmission to cool completely (minimum 2 hours if recently driven)
4. Raise vehicle on lift or support securely on jack stands at all four corners - vehicle must be level
5. Remove rear wheels to access exhaust and transmission mounting points
6. Place drain pan under transmission drain plug

Procedure

1. 1

   Drain transmission fluid
   Locate the transmission drain plug on the bottom of the T56 case. Remove the drain plug and allow fluid to drain completely into drain pan (approximately 4 quarts will drain). Inspect drained fluid for metal particles or clutch material contamination, which may indicate additional damage. Remove the fill plug on the driver side of the transmission case to allow complete drainage and venting. Install new washers on both drain and fill plugs and reinstall drain plug only at this time.
   Torque spec

   Drain Plug34 Nm (25 lb-ft)
2. 2

   Remove exhaust system components
   Disconnect the exhaust system at the collector flanges behind the catalytic converters. The Viper uses a dual exhaust system with collectors that bolt to the transmission tunnel support. Remove the exhaust hangers and support the exhaust system, then lower it away from the transmission tunnel to provide clearance for transmission removal. You may need to remove the complete exhaust system depending on lift setup.
3. 3

   Disconnect driveshaft
   Mark the driveshaft-to-differential flange orientation with paint or scribe marks to ensure proper phasing on reinstallation. Remove the 4 bolts securing the driveshaft universal joint to the rear differential companion flange. Support the driveshaft and slide it rearward to disengage the slip yoke from the transmission output shaft. Cap the transmission tailhousing with a plug or plastic bag to prevent fluid leakage and contamination.
4. 4

   Disconnect shift linkage and electrical connections
   Disconnect the shift linkage at the transmission. The 1992 Viper uses a direct mechanical shifter with a ball-and-socket connection at the transmission shifter tower. Remove the retaining clip and lift the shift lever off the transmission shifter stub. Disconnect the reverse light switch electrical connector on the driver side of the transmission case. Disconnect the speed sensor connector on the tailhousing (if equipped).
5. 5

   Support engine and remove transmission crossmember
   Place a jack with a block of wood under the engine oil pan to support engine weight. Position the jack to avoid crushing the oil pan - use a wide wooden beam to distribute load. Position transmission jack under the transmission with the saddle centered on the transmission case. Secure transmission to jack with a strap or chain. Remove the transmission mount-to-crossmember fasteners, then remove the crossmember-to-frame bolts. Lower and remove the crossmember.
6. 6

   Remove transmission-to-bellhousing bolts and separate transmission
   Remove the transmission-to-bellhousing mounting bolts. The T56 transmission uses 6 mounting bolts securing it to the aluminum bellhousing. Carefully slide the transmission rearward on the transmission jack, ensuring the input shaft disengages from the clutch splines without binding. The transmission will need to move approximately 2-3 inches rearward before clearing the bellhousing dowel pins. Once clear, lower the transmission on the jack and move it away from the vehicle.
   Torque spec

   Mounting Bolts61 Nm (45 lb-ft)
7. 7

   Clean transmission exterior and inspect clutch
   With transmission removed, thoroughly clean the transmission case exterior with solvent and inspect for cracks or damage. Inspect the clutch friction disc and pressure plate for contamination, glazing, or wear. If the clutch shows oil contamination or the friction material is compromised, replace the clutch assembly before proceeding. Inspect the input shaft for wear, damage, or runout. Place the transmission on a sturdy workbench with soft protection under the case.
8. 8

   Remove transmission tailhousing and output shaft assembly
   Remove the bolts securing the tailhousing to the transmission case. There are 8 bolts around the perimeter of the tailhousing. Carefully tap the tailhousing with a soft mallet to break the gasket seal, then slide it rearward off the output shaft. Remove the output shaft assembly by pulling it straight out of the case - it may require light tapping with a soft mallet on the shaft end. Set the output shaft assembly aside on a clean work surface. Remove and discard the tailhousing gasket.
9. 9

   Remove shifter cover assemblies
   Remove the front and rear shifter cover plates from the top of the transmission case. The front cover has 8 bolts and the rear cover has 6 bolts. Lift the covers straight up - they contain the shift rail detent assemblies and springs which are under light spring pressure. Keep track of all detent balls, springs, and components as they are removed. Remove and discard the cover gaskets.
   Torque spec

   Cover Screws11 Nm (8 lb-ft)
10. 10

    Remove shift forks and rails
    With the covers removed, the shift rails are now accessible. Remove the shift rail retaining pins or roll pins that secure each shift fork to its rail. Note the orientation and position of each fork - the 1-2, 3-4, and 5-6 forks are similar but not identical. Slide each shift rail out of the case, removing the corresponding shift fork. Place each fork with its rail and label them clearly (1-2, 3-4, 5-6, Reverse) to prevent mixing during reassembly.
11. 11

    Split transmission case halves
    Remove the case half bolts - the T56 uses 16 bolts securing the main case halves together. Note the different bolt lengths and positions. Carefully tap around the case seam with a soft mallet to break the gasket seal. Do not pry between the machined case surfaces. Once the seal is broken, lift the top case half straight up and away. The gear clusters will remain in the lower case half. Remove and discard the case gasket.
12. 12

    Remove gear clusters and locate affected synchronizer
    With the case open, identify the gear position requiring synchronizer replacement. The mainshaft (input shaft side) carries the driven gears and their synchronizers in this order from front to rear: 3-4 synchro assembly, 3rd gear, 4th gear, 5-6 synchro assembly, 5th gear, 6th gear. The mainshaft also carries the 1-2 synchro assembly, 1st gear, and 2nd gear toward the rear of the shaft; the countershaft is a fixed cluster gear with no synchronizers. Remove the mainshaft and countershaft assemblies from the lower case half by lifting straight up. Place on clean work surface.
13. 13

    Disassemble shaft to access synchronizer
    To access the affected synchronizer, disassemble the shaft carefully. Remove the snap rings securing the gear and synchronizer assembly in position using snap ring pliers. Note that some snap rings are under bearing preload tension. Slide the gears and synchronizer assembly off the shaft in order, marking or photographing each component's position and orientation. The synchronizer assembly consists of a sliding sleeve, hub, blocking ring, and spring-loaded keys or inserts. Lay out all components in removal order.
14. 14

    Remove and inspect synchronizer assembly
    Remove the synchronizer sliding sleeve from the hub by sliding it off (note the directional marks or chamfers). Remove the synchronizer keys/inserts and springs from the hub - there are typically 3 keys with 2 springs arranged in opposite directions. Remove the brass or carbon-fiber blocking ring from the gear cone. Inspect the blocking ring engagement teeth for wear, rounding, or damage. Inspect the gear cone surface for scoring, heat discoloration, or wear. Measure the blocking ring-to-gear cone clearance with a feeler gauge and compare to the factory-specified new and wear-limit values (verify exact specifications against factory service documentation). Inspect the synchronizer hub and sleeve for wear on the engagement teeth.
15. 15

    Assemble new synchronizer
    Install the new synchronizer hub onto the shaft in the correct orientation (chamfered side typically faces the gear). Install the new blocking ring onto the gear cone - ensure it rotates freely and seats properly on the cone taper. Place the synchronizer keys/inserts into the hub slots. Install the two springs, ensuring they are arranged in opposite directions with the spring ends engaging different keys. The springs provide outward pressure on the keys. Slide the synchronizer sleeve over the hub, aligning the sleeve teeth with the hub teeth. Ensure the sleeve slides smoothly over the hub with moderate resistance from the springs. Verify the blocking ring-to-gear cone clearance is within specification using feeler gauges.
16. 16

    Reassemble shaft with new synchronizer
    Reinstall all gears, spacers, and the new synchronizer assembly onto the shaft in the reverse order of removal. Ensure all components are oriented correctly using your photos or marks from disassembly. Install the retaining snap rings, ensuring they are fully seated in their grooves. Check that the synchronizer sleeve moves freely along the hub and that the blocking ring can rotate independently. Measure shaft endplay using a dial indicator - total endplay should be 0.003-0.010 inches. Record this measurement.
17. 17

    Check bearing preload and endplay
    Install the mainshaft and countershaft assemblies back into the lower case half. Install the bearing retainers and measure the bearing preload using a dial indicator and spring scale, or by measuring endplay with shims. The T56 uses tapered roller bearings that require specific preload set via selective shims. Set the mainshaft and countershaft bearing preload to the factory-specified values (verify exact preload/shim specifications against factory service documentation). Adjust preload by selecting appropriate shims or bearing spacers. This is critical - incorrect preload causes bearing failure.
18. 18

    Install new case gasket and assemble case halves
    Clean both case mating surfaces thoroughly with solvent and inspect for damage. Install a new case gasket on the lower case half, using a light coating of gasket sealant or transmission assembly lube to hold it in position. Carefully lower the upper case half onto the lower half, aligning the case dowel pins. Ensure no gears or components are pinched by the case seam. Install all case bolts in their correct positions (note different lengths). Tighten the case bolts in a criss-cross pattern starting from the center and working outward, in stages to the factory-specified final torque (verify exact value against factory service documentation).
    Torque spec

    Mounting Bolts61 Nm (45 lb-ft)
19. 19

    Install shift rails, forks, and detent assemblies
    Install each shift rail into its bore in the transmission case, sliding it through from the appropriate end. Install the corresponding shift fork onto the rail, positioning it in the synchronizer sleeve groove. Align the fork-to-rail retaining pin holes and install new roll pins, tapping them flush. Verify each fork moves smoothly through its full travel range. Install the detent balls, springs, and plugs into their bores in the case. Install new shifter cover gaskets and the shifter covers, tightening the cover bolts in a criss-cross pattern.
    Torque spec

    Cover Screws11 Nm (8 lb-ft)
20. 20

    Install output shaft and tailhousing
    Lubricate the output shaft bearings and seals with fresh transmission fluid. Carefully slide the output shaft assembly into the rear of the transmission case, aligning the splines with the mainshaft. Tap gently with a soft mallet if needed to seat the bearing. Install a new tailhousing gasket, then slide the tailhousing onto the output shaft and case. Install the 8 tailhousing bolts and tighten in a criss-cross pattern.
    Torque spec

    Mounting Bolts61 Nm (45 lb-ft)
21. 21

    Perform transmission function test
    With the transmission fully assembled, manually shift through all gears to verify proper synchronizer engagement. Rotate the input shaft by hand while shifting - you should feel smooth, positive engagement in each gear with no grinding or excessive resistance. The repaired gear should engage smoothly with firm detent feel. Check for proper shift fork alignment and verify that the transmission returns to neutral properly. If any binding or abnormal resistance is felt, disassemble and inspect for assembly errors.
22. 22

    Install transmission into vehicle
    Apply a light coat of high-temperature grease to the input shaft splines. Position the transmission on the transmission jack and raise it into position under the vehicle. Align the input shaft with the clutch disc splines and bellhousing dowel pins. Slide the transmission forward - it should engage the clutch splines and seat against the bellhousing with moderate hand pressure. If excessive force is required, lower the transmission and check alignment. Install the 6 transmission-to-bellhousing mounting bolts and tighten in a criss-cross pattern.
    Torque spec

    Mounting Bolts61 Nm (45 lb-ft)
23. 23

    Install crossmember and remove supports
    Raise the transmission jack slightly to align the transmission mount with the crossmember position. Install the crossmember and loosely install the crossmember-to-frame bolts. Install the transmission mount-to-crossmember fasteners. Tighten the crossmember-to-frame bolts first, then tighten the mount-to-crossmember fasteners. Remove the transmission jack and engine support jack.
    Torque spec

    Mounting Bolts61 Nm (45 lb-ft)
24. 24

    Reconnect driveshaft and shift linkage
    Lubricate the transmission output shaft splines with fresh transmission fluid. Slide the driveshaft forward, engaging the slip yoke with the output shaft. Align the driveshaft-to-differential flange using the marks made during removal. Install the 4 universal joint bolts and tighten in a criss-cross pattern. Reconnect the shift linkage at the transmission shifter, installing the retaining clip. Reconnect the reverse light switch and speed sensor electrical connectors.
25. 25

    Install exhaust system
    Raise the exhaust system into position and connect it at the collector flanges. Install new gaskets if the originals are damaged. Install all exhaust hangers and ensure proper clearance around the transmission tunnel, driveshaft, and chassis components. Tighten all exhaust fasteners.
26. 26

    Fill transmission and check operation
    Remove the transmission fill plug. Using a fluid pump or squeeze bottle, add the manufacturer-specified T56 transmission fluid (verify correct spec for the 1992 Viper against factory documentation) through the fill hole until fluid begins to drip from the fill hole. This indicates proper fluid level (approximately 4 quarts). Install a new washer on the fill plug and install the plug. Reconnect the negative battery cable. Start the engine (clutch pedal depressed) and verify no leaks. With the engine running and clutch pedal depressed, shift through all gears slowly, pausing 2-3 seconds in each gear. Shut off engine.
    Torque spec

    Fill Plug34 Nm (25 lb-ft)
27. 27

    Road test and final verification
    Install rear wheels and lower vehicle. Perform a road test, carefully testing the repaired gear under various load conditions. Verify smooth engagement without grinding or gear clash. Test upshifts and downshifts into the repaired gear at various speeds and loads. Check for proper synchronization - the gear should engage smoothly at appropriate engine/vehicle speed matching. Verify no abnormal noises from the transmission. After road test, recheck transmission fluid level (with vehicle level and transmission at operating temperature) and inspect for leaks at all connection points.

Reassembly

1. Reassembly is detailed in the procedural steps above, as this job requires complete transmission disassembly and reassembly
2. Critical: All bearing preload specifications must be verified with dial indicator and torque measurements
3. Use new gaskets for all case joints, covers, and tailhousing
4. Install new washers on drain and fill plugs
5. Lubricate all bearings, synchronizer cones, and shaft splines with fresh transmission fluid during assembly
6. Apply medium-strength thread locker to case bolts if specified by manufacturer
7. Ensure all shift forks are properly engaged in synchronizer sleeve grooves before final assembly
8. Verify proper gear timing and alignment before closing case halves
9. Tighten all critical fasteners in specified criss-cross patterns and torque sequences

Verification

• Verify smooth, grind-free engagement of the repaired gear during road test under various load conditions
• Confirm no transmission fluid leaks at case seams, covers, tailhousing, or drain/fill plugs
• Verify proper transmission fluid level with vehicle on level surface and transmission at operating temperature
• Confirm no abnormal noises (whining, grinding, rattling) from transmission in any gear
• Test synchronizer function by attempting to engage the repaired gear at inappropriate speeds - proper synchronization should prevent engagement until speed matching occurs
• Verify smooth shifting into and out of all gears, not just the repaired gear
• Check for proper clutch operation and complete disengagement
• Confirm shift linkage operates smoothly with proper gate definition
• Verify no driveline vibration that could indicate improper driveshaft phasing

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