Checking vacuum control on automatic transmission

AR27.18-D-1200A

Checking vacuum control on automatic transmission

3.4.96

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

AR30.10-D-1010C

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.

 A defective restrictor may be the cause of harsh shifts.

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 vehicle starting off automatically when engine is running. Risk of injury due to being trapped and burns when intervening during the starting operation 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 may drop by a maximum of 0.1 bar per minute. In the event of 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 vehicle starting off automatically when engine is running. Risk of injury due to being trapped and burns when intervening during the starting operation 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 0.35‑0.4bar and be developed within 10seconds after starting the engine.

 If the specified vacuum is not achieved, the components of the vacuum control 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. 

Removing and installing vacuum control valve.

AR27.18-D-6056A



Checking

Vacuum unit

15

Disconnect vacuum line (D) at damper (5).

16

Connect tester to the 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. 

Removing and installing vacuum unit.

AR27.10-D-0260A