Suspension - Level Control Adjustment & Testing
REF. NO. MBNA 32/1TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: May 1991
SUBJECT:
MODEL 129
TESTING AND ADJUSTING VEHICLE LEVEL CONTROL WITH ADAPTIVE DAMPING SYSTEM (ADS)
In case of customer complaints regarding the bumper apron scratching concrete parking blocks during parking, check the adjustment of the ADS system on the 1991 Model 129. Shop adjustment of the vehicle level from the lowest allowable range to the nominal value or (within the allowed tolerances) slightly above can allow more clearance for parking blocks, curbs, etc. Raising the vehicle height can also smooth the ride slightly, since the increase provides slightly more suspension compression travel.
The following procedure should be used to check and adjust the vehicle to the nominal level.
Component Locations
General procedure for vehicle
level measurement
Check with measurement tool 201 589 00 21 00 on the front axle, and with measurement tool 201 589 01 21 00 on the rear axle (see test and adjustment specifications). The test is similar to that described in job number 40-300 (201.034). If the vehicle level lies outside tolerances, adjust.
Notes:
The vehicle level tolerance ranges between test and adjustment specifications are determined by freeplay of the leveling valve. This does not affect control precision when driving. This test and adjustment procedure must be done on a drive-on hoist, with the vehicle's weight on the wheels.
Front axle connecting link (54)
Remove nut from ball pin stud at leveling valve (6)1).
Rear axle connecting link (55)
Remove nut from ball pin stud at leveling valve (3)1).
Engine
After attaching an exhaust hose, run at idle.
Vehicle level at the front and rear axle
Using the lever of the level control valve at the front axle (6) and/or at the rear axle (3) adjust the level until the prescribed adjustment values are reached on the scales of the measurement tools (see test and adjustment specifications). Always adjust the vehicle up to the desired level from a lower position.
Leveling valve control lever
Lock the front axle (6) and the rear axle (3) in the middle position (hole, a) with a 4 mm pin.
Engine
Shut off
Test and adjustment specifications for vehicle level
Connecting links (54, 55)
Adjust to the resulting lengths and attach unloaded to the level controller lever (hole, C). Check that the connecting links can pivot through their full angular travel. Observe the ADS specifications shown.
4 mm pin
Remove from the leveling valves of the front and rear axles.
Headlamp adjustment
Check and correct if necessary.
1) if required, hold ball pin stud in place with an 8 mm open end wrench. Do not pull ball pin out of ball socket.
Special Tools
Level control at the front and rear axles
The control at the front and rear axles is a partial load-carrying suspension system. It keeps the vehicle level constant independent of the load. Thus, the steel springs also have only a partial load carrying function. Two leveling valves, one at the front and one at the rear axle, achieve the level control.
When the vehicle is loaded, the lowering of the vehicle level moves the leveling valve to filling position F by the stabilizer bar and the connecting link. When the engine is running, the hydraulic pump supplies oil through the valve unit and the leveling valves, increasing the oil quantity in the suspension elements, until the vehicle level is again adjusted correctly. When the vehicle is unloaded, the leveling valve moves to the empty position L, reducing the oil quantity in the suspension elements until the vehicle level is again adjusted correctly.