Testing Oil Pump and Level Control Unit

TESTING PRESSURE OIL PUMP AND LEVEL CONTROL UNIT ON REAR AXLE (MODEL 124 WITH LEVEL CONTROL ON REAR AXLE





Oil filter in oil reservoir (2):
remove, install and check for cleanliness (items 1 and 2).

Oil reservoir (2):
check oil level, top up if required (item 3).

Connecting rod (7) on level control unit (3):
remove, install. Renew self-locking bolts and nuts, 10 Nm (items 4 and 20).

Oil drain hose:
put on, remove at oil drain plug (3p) on level control unit (3) (item 5).

Oil drain plug (3p):
open slowly and release pressure. Collect oil in a clean container. Unscrew oil drain plug (items 6 and 7).

Pressure tester (038):
connect to level control unit with test hose (038g) (item 8). Model 124 (Illustration A).

Engine:
start, stop.

Lever (3a) on level control unit:
position on "fill" (item 10).

Pressure tester (038):
The pointer on the pressure tester 126 589 14 21 00 must display a pressure of at least 133 bar (item 10).

Lever (3a) on level control unit:
position on "emptying" (item 12).

Pressure tester (038):
read off basic pressure. Minimum value 30 + 6 bar (items 13 and 14).

Oil drain hose:
install, remove at the bleed screw on pressure tester (item 15).

Bleed screw on pressure tester (038):
open slowly and release pressure, whilst catching the oil in a clean container (item 16).

Pressure tester (038):
disconnect at level control unit (3) (item 17).

Oil drain plug (3p):
screw into the level control unit (3), 14 Nm.

Pressure oil system:
fill.

Oil level in oil reservoir (2):
check and if necessary add hydraulic oil 000 989 91 03 using funnel 126 589 12 63 00 (item 21).

Test values
Pressure relief valve (level control unit) 133-153 bar
Basic pressure Minimum value 30 + 6 bar





Note: The following parts of the pressure tester are required for testing: Pressure tester (038) with connector and union nut with sealing ring, test hose (038g) and bleed screws.

Testing





1 Disconnect return line (T). Unscrew union nut (2i) and remove oil filter (2h).

2 Check for clean oil filter and install. Connect return line (T).

Note:
If the oil filter is contaminated, the results of this testing will be inaccurate.





3 Check oil level in oil reservoir, replenish if required.

Note:
In ready-to-drive condition the oil level is between the "min" and "max" marks when the engine is off.

Model 124





4 Unscrew self-locking nut (7a) and detach linkage (7).





5 Plug oil drain hose (061) on the oil drain plug (3p) on level control unit.

6 Open oil drain plug (3p) slowly and reduce pressure. Collect oil in a clean container.

7 Unscrew oil drain plug (3p) on level control unit.

8 Connect pressure tester (038) to level control unit (3) with test hose (038g).

Due to high pressure, testing should be performed for short durations of time in order to protect the pressure oil pump as well as the spring struts and their rebound stops.

The pressure relief valve in the level control unit is designed for max. permissible rear axle load. If the vehicle is overloaded, the opening of the pressure relief valve may be indicated by hissing and knocking noises during driving.





Note:
If the desired value is not attained on vehicles with ASD, perform ASD pressure testing on the hydraulic system.

9 Start engine and allow to idle.





10 Set level control unit lever in "fill" position while watching the display on the pressure gauge.

Set value: min. 133 bar.

Note:
The minimum values are sufficient in evaluating the pressure oil pump and the pressure relief valve in the level control unit (refer to table on test values).

11 Turn off engine.

12 To check basic pressure after performing the tests in accordance with item 8, set level control unit lever to "emptying".

13 Read basic pressure on pressure gauge. Test value 30 + 6 bar.

14 After a stabilization period of approx. 5 minutes, read off basic pressure again and leave pressure tester connected for approx. 4 hours. After a stabilization period or after the second reading, the basic pressure should no longer drop. The same applies for a longer test period, e.g. overnight.

A drop in basic pressure may lead to rumbling noises on rear axle while driving under partial load.

Note:
To prevent measuring errors due to possible cooling of hydraulic oil, the hydraulic oil should not be hot prior to testing. Slight heating, e.g. following a short test drive, will not produce inaccurate measurements.





15 Install oil drain hose (061) on bleed screw.

16 Slowly open bleed screw (038n) and release pressure. Collect oil in a clean container.

17 Disconnect pressure tester. Screw oil drain plug into the level control unit, 14 Nm.





18 Pour collected oil through funnel with filter (060) into oil reservoir (2).

Note:
Re-use clean oil only.

19 Fill pressure oil system. Procedures

Model 124





20 Attach connecting rod (7) in level control unit lever and tighten new self-locking nut (7a), 10 Nm.

Model 124 in bore "b"





21 Check oil level in oil reservoir (2) when the engine is off and correct if required. In an operational system the oil level in ready-to-drive condition should be between the marks "max" and "min". When the vehicle is laden, the oil level will then be below the "min" mark (no longer visible on dipstick).