Gearbox & Transmission Overhaul (ZF, Allison, Scania Opticruise)

Cora Amyra
4 days ago
3 min read

Transmission Overhaul for European Commercial Vehicles in Singapore

On modern European buses and trucks, the gearbox is no longer a simple manual unit: it’s an integrated system of mechatronics, retarder, PTOs and software. Improper repair can destroy clutches, cook oil and wipe out the rest of the driveline.

Scantruck specialises in automatic, AMT and manual gearbox overhauls for:

City buses and articulated buses
Prime movers and rigid trucks
Waste, municipal and distribution vehicles

Our current transmission portfolio covers Allison, ZF and Scania Opticruise units used widely in Singapore’s European CV fleets.

Allison AL306 – 6-Speed Automatic for Distribution & Municipal Trucks

The Allison AL306 is part of the Allison 3000 Series™, a 6-speed fully automatic transmission rated for GCW up to 36 tonnes and engine torque up to around 1,695 Nm, depending on variant.

Key tech points:

Hydraulic torque converter with lock-up clutch
Planetary gearsets giving 6 forward ratios (typical range ~3.49:1 in 1st to ~0.65:1 in top)
Integral retarder option for downhill braking
Electronic control module with adaptive shift strategies

Typical failure modes we see in Singapore:

Overheated ATF from stop-start, high-temperature duties (waste, distribution)
Worn converter lock-up clutch causing shudder and slip faults
Valve body contamination leading to harsh or missing shifts

Scantruck’s AL306 overhaul programme includes:

Full teardown, replacement of wear elements (clutches, steels, seals, bushings)
Reconditioning or replacement of torque converter
Cleaning and flow-testing valve bodies
Refill with approved Allison-spec fluids and resetting of TCM adaptions

ZF Ecomid 9S1110 – 9-Speed Manual Transmission

Many Volvo FE/FL and other mid-range European trucks in this region run the ZF Ecomid 9S1110 family – a 9-speed synchromesh gearbox for vehicles up to 36 tonnes GVW.

Key specifications:

9 forward speeds + 1 reverse
Maximum input torque roughly 1100 Nm
Initial oil fill around 8.8 litres and dry weight in the ~190 kg range

What this means in practice:

Correct synchroniser pack setup and clutch adjustment are critical for smooth shifting.
Abuse (skip-shifting, poor clutch use) rapidly accelerates wear of blocker rings and dog teeth.
Incomplete repairs often ignore internal detent and interlock components, leading to “mystery” jumping-out-of-gear complaints.

Our ZF 9S1110 overhaul routine covers:

Full measurement of shafts for run-out and spline wear
Replacement of synchro assemblies with OE or high-quality aftermarket kits
Bearing and seal replacement, correct preload setting
Oil selection according to ZF specification and the vehicle’s duty profile

ZF AS-Tronic 12AS2130 – 12-Speed Automated Manual

The ZF AS-Tronic 12AS 2130 is a 12-speed automated manual transmission (AMT) widely fitted to DAF, MAN and other heavy European trucks, with torque ratings in the ~2100 Nm class.

The complexity comes from:

Electro-pneumatic shifting system
Automated clutch actuator and position sensors
Integration with the engine ECU, retarder and cruise control

Scantruck’s overhaul and commissioning process includes:

Mechanical rebuild – bearings, synchros, seals and any damaged gearing.
Actuator & clutch system service – inspection/replacement of clutch actuator, position sensors and gear-select actuators.
Software calibration & learn-in – clutch biting point, gear selection maps and any OEM-specific procedures.

Scania Opticruise Gearboxes – GR875R, GRS905R, GRSO925R

In the Scania world, many buses and trucks in Singapore run Opticruise AMT gearboxes such as:

GR875R – 8-speed Opticruise with retarder, widely used in K-series buses (e.g. K360).
GRS905R / GRSO905R – 12-speed AMT with and without overdrive, common behind 12–13 L engines in P/G/R series trucks.
GRSO925R – overdrive variant used in long-haul applications with integrated retarder.

Technical points that matter:

These are split-range constant-mesh gearboxes, not simple manuals.
Opticruise relies on accurate input shaft speed, engine torque data and clutch control to execute smooth shifts.
Internal retarder units demand correct cooling and oil flow.

Scantruck’s approach:

We treat the Opticruise gearbox as an integrated driveline system – engine ECU, gearbox ECU, clutch control and retarder.
When overhauling a GR875R / GRS905R / GRSO925R, we also check:
- Clutch condition and flywheel run-out
- Gear selection cylinders and valve blocks
- Retarder performance and cooling circuit

If you run a European bus or truck fleet in Singapore and are seeing harsh shifts, slipping clutches, gearbox fault codes or overheating oil, Scantruck can support you from diagnosis to full rebuild and recommissioning.