Casing

The main gearbox housing holds shafts, gears and roller bearings in their specified positions, contains the transmission oil and provides mounting points for components including the clutch housing and driveline. A damaged housing is therefore more than a source of leaks: a distorted bearing seat or misaligned mating face can cause further damage to the gears and seals. This category includes main casings, front and rear covers, and clutch housings.

Housings vary by gearbox series, gear ratio configuration and equipment, such as a PTO (Power Take-Off). MAN TGL and TGM vehicles may be fitted with ZF Ecolite or Ecomid gearboxes, while TGS and TGX vehicles may have ZF Ecosplit, AS-Tronic or TraXon gearboxes. Mercedes Atego, Actros and Arocs vehicles also have different transmission variants. Mercedes Atego vehicles may be fitted with G 90-6 gearboxes, while Actros and Arocs vehicles may have Mercedes PowerShift 3 gearboxes. Castings that look alike do not necessarily have the same bearing bores, bolt patterns, sensor openings or lubrication and cooling connections.

Also check how the housing mates with the engine and driveline. A version for a MAN D08 may require different connection dimensions from a configuration built around a D26; the same principle applies, for example, to Mercedes OM 936 and OM 471 engines. For trucks, buses and vans, the correct part must always be identified using the chassis number, together with the transmission code and part number. Selecting a part by model name alone or by visual comparison is never sufficient.

Typical signs of damage include cracks around mounting points or bolt holes, damaged threads, leaks at mating faces and oil seals, and worn roller bearing seats. Causes range from vibration and overloading to a damaged propshaft, incorrect installation or operation with insufficient transmission oil. A leak that returns after an oil seal has been replaced may point to a misaligned shaft, a blocked breather or a distorted housing rather than a fault with the seal itself.

Start diagnosis by cleaning the area and locating the leak. Then check the oil level according to the manufacturer’s procedure and inspect the drained transmission oil for metal particles. Inspect the housing visually and, if a hairline crack is suspected, use a suitable dye penetrant test. Check mating faces for flatness with a straightedge and feeler gauge, measure bearing bores with a dial bore gauge and compare the readings with factory tolerances. Where relevant, measure shaft runout and end float with a dial indicator. This helps distinguish housing damage from wear to shafts, roller bearings or seals.

Replace a housing if cracks, distorted mating faces or bearing seats outside tolerance prevent a reliable fit. Thread or bearing seat repairs are appropriate only when carried out using an approved method and followed by dimensional checks. During installation, clean all oil passages and mating faces, renew the specified seals, and use only the specified sealants and tightening torques. Set bearing preload and end float to the transmission specifications; a new casting does not automatically retain the previous adjustment settings. After filling with the correct transmission oil, check for leaks and abnormal noise. Technical support with identification can help prevent the installation of a housing that fits but differs internally.