SCANIA 3136620 PNEUMATIC HYDRAULIC CLUTCH BOOSTER

The Pneumatic-Hydraulic Clutch Booster (Scania OEM 3136620) is the clutch servo assembly for Scania 4-series, P, G, R, and T-series heavy commercial vehicles. It is a combined pneumatic and hydraulic servo unit that amplifies the driver’s clutch pedal hydraulic pressure using the truck’s compressed air system, dramatically reducing the pedal effort required to disengage the large-diameter dry clutch fitted to heavy diesel commercial vehicles. The booster body bore is Ø125 mm. The unit is filled with and operates on mineral oil (not DOT brake fluid — this distinction is critical for service). The Scania OEM number 3136620 is an early part number that was succeeded by 1784480 and subsequently by 1927825; all three numbers describe the same Ø125 mm clutch servo unit and are interchangeable across the applicable Scania platform.

Heavy commercial vehicles with large-diameter multi-plate or single-plate dry clutches require considerably more force to disengage the clutch than a passenger car pedal can reliably provide. Scania’s solution on the 4-series, P, G, R, and T-series platforms is a tandem pneumo-hydraulic servo: when the driver presses the clutch pedal, hydraulic pressure generated by the clutch master cylinder travels through the fluid line to the servo body inlet. Inside the servo, this hydraulic signal pressure triggers the pneumatic section, which draws regulated compressed air from the vehicle’s air reservoir and uses air pressure against a piston to generate the high output force required to push the clutch fork and disengage the large clutch plate from the flywheel. The hydraulic and pneumatic sections act in proportion — greater pedal pressure generates greater air-assist, giving the driver consistent pedal feel across the full travel.

The result is a power-assisted clutch that requires no more pedal effort than a typical passenger car despite the vastly higher clutch clamping force required by the truck’s engine torque output. When the servo fails — whether from internal seal degradation, air supply problems, or hydraulic circuit contamination — the driver must operate the clutch against the full mechanical spring load, which is physically extremely difficult and typically causes the driver to report the clutch as “locked” or “immovable.”

Clutch booster/servo assemblies are classified under HS 8708.93 as parts of transmission systems. Always verify the exact 8- or 10-digit subheading with your customs broker for the destination market. The unit is supplied dry — mineral oil is not included and must be added during installation and bleeding.

The supersession chain 3136620 → 1523399 → 1784480 → 1927825 confirms fitment across multiple production generations. Always confirm by chassis number for any specific vehicle before ordering in bulk.

Difficulty: Advanced — commercial vehicle workshop with depressurisation procedure required. The clutch booster is connected to the vehicle’s main air system. The air system must be fully depressurised before disconnecting any pneumatic lines — never disconnect pressurised air lines. The hydraulic circuit must also be drained before disconnecting the hydraulic lines. Estimated workshop time: 1.5–3 hours.

1. 1
   Depressurise the air system and drain the clutch hydraulic circuit. Exhaust all air reservoirs. Place a drain container under the hydraulic line connection at the servo. Crack the hydraulic union open slightly to allow fluid to drain before full disconnection. Cap the hydraulic line immediately after removal to prevent contamination.
2. 2
   Disconnect the air supply line, hydraulic inlet line, and push rod from the clutch fork. Note the orientation of the servo body relative to the mounting bracket — photograph before removal. Label or tag each connection for reassembly. The push rod connection to the clutch fork may be secured by a clevis pin and split pin — remove and retain the split pin.
3. 3
   Remove the servo mounting bolts and withdraw the old unit. The servo weighs approximately 13 kg — support its weight during removal to avoid dropping or damaging the adjacent hydraulic and air lines.
4. 4
   Compare the new 3136620 servo with the original. Confirm bore size (Ø125 mm), hydraulic port thread, air connection thread, push rod length, and mounting bolt pattern match the original before installation. If the replacement is supplied dry, confirm the internal fluid chambers are clean before fitting.
5. 5
   Install the new servo in the reverse of removal. Reconnect the push rod to the clutch fork with a new split pin — never reuse a removed split pin. Reconnect the hydraulic line and air supply line. Tighten all hydraulic fittings to the torque specified in the Scania service documentation.
6. 6
   Fill the hydraulic system with the correct grade of mineral oil and bleed the clutch hydraulic circuit. Use only mineral oil — confirm the fluid type from the reservoir cap. Bleed progressively from the servo bleed nipple until all air is purged and pedal feel is firm. Build air pressure in the system and verify the clutch operates correctly through its full travel before returning the vehicle to service.