Checking vacuum control on automatic transmission

AR27.18-P-1200G

Checking vacuum control on automatic transmission

26.11.97

Checking



The vacuum control valve controls the vacuum for the modulating pressure control. The vacuum control valve controls a vacuum of approx. 0.4 bar at idle speed and a vacuum of 0 bar at wide open throttle.

The vacuum control must be checked when the engine is at operating temperature and with the idle speed adjusted.

Primarily the vacuum control must be checked in the event of the following complaints:

-Harsh and late part-load upshifts.

-Slipping shifts.

Only when it is certain that the vacuum control is working perfectly, locate and eliminate complaints about the automatic transmission in the usual way.

1

Adjust throttle control

2

Check all vacuum lines for porous points or cracks.

3

Check condition of transparent pressurizing filter (2) by visual inspection (e.g. contamination) and replace, if necessary.



Checking

 Restrictor

4

Remove restrictor (4) and check for blockage.

 Harsh shifts may be caused by a defective restrictor.

5

Clean or replace restrictor if necessary.



Checking

 Vacuum pump

6

Connect tester to the restrictor (4) of vacuum line (B) to the vacuum pump.



*201589132100

Danger!

Risk of accident due to the vehicle starting off automatically when engine is running. Risk of injury due to bruising or burns when intervening while starting the engine or when the engine is running.

Secure vehicle to prevent it from starting off automatically.

Wear close-fitting, tight clothing.

Do not touch hot or rotating parts

AS00.00-Z-0005-01A

7

Start engine.

 At idle speed the vacuum displayed must be a constant 0.7-0.8 bar after approx. 1 minute.

8

Switch off engine

 The vacuum displayed should drop a maximum of 0.1 bar per minute. If there are deviations from the specified value, check vacuum lines and vacuum pump.



Checking

 Damper

9

Pull off vacuum line (D).

10

Pull off damper (5), check for blockage and replace if necessary.

 The installed direction of the damper is not specified, it works in both directions.



Checking

 Vacuum control valve

11

Pull off vacuum line (D)

12

Connect tester to damper (5)



*201589132100

Danger!

Risk of accident due to the vehicle starting off automatically when engine is running. Risk of injury due to bruising or burns when intervening while starting the engine or when the engine is running.

Secure vehicle to prevent it from starting off automatically.

Wear close-fitting, tight clothing.

Do not touch hot or rotating parts

AS00.00-Z-0005-01A

13

Start engine.

 The vacuum displayed must be 0.35-0.4 bar and be developed within 10 seconds after starting the engine.

 If the specified vacuum is not achieved, the vacuum control components must be checked.

14

Switch off engine and immediately press the accelerator to the "wide open throttle" position.

 The vacuum must be reduced completely when the full-load position stop is reached.

 If the vacuum is not reduced to 0 bar in the "wide open throttle" position, the vacuum control valve must be replaced. 

Remove and install vacuum control valve.

AR27.18-P-6056G

 Vacuum unit

15

Pull vacuum line (D) off damper (5)

16

Connect tester to vacuum line.



*201589132100

17

Using the pump lever on the tester, pump to 0.8 bar vacuum.

 The vacuum of 0.8 bar must remain constant.

 If the vacuum does not remain constant the vacuum lines and connections must be checked for leaks and the vacuum unit on the automatic transmission must be replaced if necessary. 

Remove and install vacuum unit.

AR27.10-P-0260G