10. Nivomat suspension unit: general

  1. Nivomat suspension, developed in conjunction with the manufacturers, BOGE, requires no adjustment or maintenance and is self-adjusting to provide the same ride height, ground clearance, suspension travel and performance for all loads up to the maximum permissible and at all speeds. Spring preload (or its equivalent) and damping action are adjusted automatically to be relatively soft during low-speed solo use and become progressively harder as the need arises.
  2. The unit functions as follows (refer to the accompanying illustration): the pump rod is resiliently mounted to the top of the unit, the piston rod being attached to the bottom. As the suspension moves, the relative movement of these two components causes oil to be sucked from the low-pressure chamber via passages to the pump intake valve, from where it is forced through the pump check valve into the high-pressure chamber. This pressurises the gas, which is kept separate by a rubber diaphragm, increases the pressure in the unit's working parts and increases the spring preload to raise the machine to a pre-determined ride height. When this has been reached, a valve opens to allow the oil to flow through the unit back to the low-pressure chamber. Damping action is provided by the pumping action itself, in addition to the spring-loaded damper valves. Note that if the load limit is exceeded, a safety valve prevents excessive pressure from building up; this means that the full ride height will not be reached.
  3. 3 It is important to remember that the ride height and suspension travel will not reach their full values until the unit has pumped itself up. Therefore if the first few mi les of a journey are on a completely smooth road, the rear suspension may not be ready to take a sudden bumps. Also if the load is suddenly altered, ie the rider takes all his weight on his legs when stopped at a traffic light, if a pillion passenger mounts or dismounts, or if luggage is added or removed, the rear suspension will take a little while to adjust itself to the new requirements. This is not a fault, merely a function of the system's design and should not cause problems once the rider is familiar with it.
  4. To test the unit, place a load on the rear of the machine, sufficient to noticeably compress the suspension, then with the machine stationary but on its wheels press down on its rear end (20 to 25 strokes of approximately 15-20 mm (1/2-3/4 in). The unit should be seen to pump itself up to the normal ride height.
  5. Warning: do not attempt to dismantle the unit or to alter its performance. Do not touch the two screws in the unit body. If any fault is suspected in the rear suspension performance take the machine to a BMW dealer for attention. Note that a light film of oil on the damper piston rod does not necessarily indicate a fault, although any serious oil leakage will obviously warrant instant attention by a BMW dealer.

End of Section

Fig. 8.3 Nivomat suspension unit

1 Low pressure chamber
2 Ride height contra / passage
3 Damper spring loaded valves
4 Rubber diaphragm
5 Rebound spring
6 Pump intake valve
7 Ho/low pump rad
8 Pump check valve
9 Damper piston
10 Gas (high pressure)
11 High pressure chamber
12 Piston rad