Unimog 425
The Unimog 425 is the first series production heavy duty Unimog series, made by Daimler-Benz from 1975 to 1988 in the Mercedes-Benz Gaggenau plant, alongside the long-wheelbase model Unimog 435. It was first presented to the public on the 1974 DLG show in Frankfurt, then named Unimog U 120, indicating a power output of. However, series production models were equipped with or engines, and therefore called U 1300 and U 1500. Daimler-Benz made three types of the Unimog 425, and a total number of 3135 were built, making the 425 much rarer compared to the longer wheelbase, but otherwise similar Unimog 435, of which more than 30,000 were built. The 425 was the first Unimog to feature the "edgy cab", which is still used in the Unimog today.
Technical description
The Unimog 425 is a two-axle lorry with a downswept ladder frame and rear-wheel drive. Front-wheel drive can be manually enabled. Both axles are coil-sprung, live, portal axles, with panhard rods, torque tubes, and hydraulic shock absorbers. All four wheels have the same size; the braking system is a pneumatic, dual-circuit system with disc brakes on all wheels. A trailer braking system was available as a factory option. For powering implements, the 425 has two switchable PTO shafts, and a hydraulic rear three-point linkage. The steering is hydraulically power-assisted. Daimler-Benz offered only one engine, the turbocharged Mercedes-Benz OM 352 diesel engine.The torque is transmitted from the engine to the wheels through a dry single-disc clutch, and synchronised UG 3/40-8 gearbox. It has four gears and an additional planetary two-speed box, resulting in eight total gears. The gearbox shifts its gears pneumatically, and has a single gear leaver with a traditional H-shift pattern for all eight gears. When shifting from fourth into fifth, the main gearbox shifts from its fourth gear into its first gear, and the planetary gearbox shifts from its first into its second gear. There is no reverse gear on the UG 3/40–8 gearbox, instead, the Unimog 425 has an additional gearbox just for reversing. The reduction is only 1 : 1.03, meaning that, given a top speed of 85 km/h, the maximum reverse speed exceeds 80 km/h. Therefore, the planetary gearbox's second group can be locked to prevent drivers from reversing at very high speeds.
Daimler-Benz offered another gearbox option for agricultural customers. The agricultural extra gearbox is a planetary gearbox with three gears, regular, field, and crawler, thus resulting in 2×4×3=24 gears. Unimog 425 with the agricultural gearbox option have a pneumatic dual-clutch transmission instead of the dry single-disc clutch.
Unimog 425 types
| Type | Model name | Cab style | Wheelbase | Engine power | Number built |
| 425.121 | U 1300 | Closed cab | / | 1063 | |
| 425.131 | U 1500 T | OEM part, closed cab | 282 | ||
| 425.141 | U 1500 | Closed cab | 1790 |
Technical specifications
| U 1500 | |
| Production years | 1975–1988 |
| Mass | |
| Length | |
| Width | |
| Height | |
| Wheelbase | |
| Track width | |
| Ground clearance | |
| Turning diameter | |
| Tyres | 16–70/24″ |
| Engine type | OM 352 |
| Engine layout | Water-cooled, straight-six, diesel engine |
| Injection system | Helix-controlled direct injection with inline injection pump |
| Displacement | |
| Bore × Stroke | |
| Compression ratio | 16 : 1 |
| Rated power | at 2550 min−1 |
| Max. torque | at 1600 min−1 |
| Top speed |