T56 Won’t Go Into Gear: Clutch Release or Transmission?
The same complaint can come from the clutch hydraulics or from inside the transmission. The diagnostic job is to separate them.
Key symptom split
If selection is substantially easier with the engine off than running, incomplete clutch release moves high on the list. Verify it rather than immediately opening the transmission.
Hydraulic/release branch
- Master cylinder condition and fluid level.
- Hydraulic line damage/leakage.
- Concentric slave cylinder / release bearing operation.
- Pressure plate, disc and release geometry.
Transmission branch
Once the clutch is proven to fully release, investigate shifter/linkage and internal transmission causes appropriate to the actual gear/speed/load complaint.
High-RPM complaint
A car that shifts normally at low RPM but resists a high-RPM shift still needs the release system proven under the complaint condition. Aftermarket clutch geometry, hydraulic capacity and internal transmission condition can overlap.
DO NOT CALL IT SYNCHROS YET
The factory symptom strategy itself routes “unable to select gears” through the concentric slave/release system as well as internal transmission causes. Prove the split.