11/30/21, 2:53 PM

Article



Mack Chassis - mDRIVE Transmission - AMT Gear
Box Air Leaks







Internal Content

Complaint:
Air leak from the left or right side vent of the TECU all the time. AMT-D:
See Figures 2 and 3.
Air leak from gearbox case vent tube all the time AMT-C: see Figure 5
Cause:
AMT - C & D; One or more TECU shift valves have become stuck open
allowing the air path to the open venting solenoid. This can be an
intermittent issue. Testing and investigation has shown that exercising
the valves with TT by forcing shifts can ‘unstick’ the valves and the leak
might not return however there is a good chance that the valve will
become stuck again. TECU to control housing seals can leak causing
symptoms like described and should be checked prior to major
component replacement. A leak between ports in the TECU due to a
failed gasket like in picture below can cause erratic or undesired
shifting due to air bleeding to the wrong ports during shifting. The
seals should be pliable and have a peaked appearance. This seal is
bad due to the flattened sealing surfaces.

; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

1/8

11/30/21, 2:53 PM

Article

; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

2/8

11/30/21, 2:53 PM

Article

Repair:
Replace TECU to Control housing seals if faulty and retest
Replace TECU
Complaint:
Air leak only when shifting or certain gears are not avail during
operation or slow shifting accompanied by an air leak.
Cause:
Air leaks like these are in the shift control housing and not the TECU.
Causes of these leaks are typically screws backed out of the shift
piston covers (see figure 4) that allow the end cap to come out and
vent air to the case during a shift. This will typically only be affecting
one shifter and only when the shifter is asked to move in only one
direction. The complaint may indicate that several gears are
UI
; Live
unavailable at random times. The TECU will find these gears and will
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

3/8

11/30/21, 2:53 PM

Article

try and avoid them if possible during operation. This may not always
happen consistently but in an effort allow unit operation the TECU will
abandon certain gears. A key cycle will typically reset this learning and
the unit will have to relearn the ‘bad’ gears.
Other causes of these types of leaks are broken shift forks piston rods
and cracked internal pistons. The broken rods can be identified by
inspection after removal of the control shift housing and manipulation
of the shift forks. One of them will feel like it is ‘not attached to
anything inside’. An AMT-C with external vent tubes on the right side
of the gearbox will vent air from the vent tubes when these two
failures occur. An AMT-D is internally vented through the TECU and
will leak air from the vents on the TECU.
Warning: Do not transfer the external vent tubes from an AMT-C to
an AMT-D gearbox during a repair.
The other types of failure that can occur and cause leaks during
shifting are broken/cracked internal shift pistons. This failure will in
addition to having an air leak will be a slow shift of the failed piston.
These failures will vent through the TECU vents on all AMT versions.
Cracked pistons will vent air from the TECU vents but this is only
during shifting. Air leaks during shifting can also be caused by a
leaking countershaft brake assembly, CVU or CCA. Testing of these
components is needed prior to replacing the control housing
assembly.

Repair:
Replace shift control housing only, unless other damage is found.
Complaint:
Gearbox slow to engage a gear from Neutral or shift quality is bad.
Slow to shift between gears or harsh shifting. Air leak heard from
clutch/flywheel housing.
UI
; Live
Cause:
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

4/8

11/30/21, 2:53 PM

Article

Air leak on CCA (Clutch control Actuator) inside clutch housing.
Air leak on Countershaft brake assembly
Perform clutch release tests in TT and listen for excessive air to escape
during these tests. Some air venting is normal but long blasts of air
are not normal.
Repair:
Inspect and replace the cause of the leak. Tech tool can be used to
manipulate the clutch actuator with the gearbox in or out of chassis to
investigate this type of leak. Use 4111-08-04-01 - PWM Valves Clutch
Activation, Test (Transmission Removed) or 4111-08-03-06 - PWM
Valves Clutch Activation, Test to pressurize the clutch system to check
for leaks.
Internal AMT-D venting

The internal venting of the AMT-D is provided in the bearing
retainer plate for the rear main shaft bearing. This provides
venting and oil separation for return back to the gearbox.

; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

5/8

11/30/21, 2:53 PM

Article

AMT-D gearbox venting with bearing retainer removed. All of this
is contained behind the high range synchronizer cone in the rear
of the gearbox.

The Vent port is cast and drilled in the main case and leads into
the control housing and TECU and is vented through the ports on
the left side of the main case.

; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

6/8

11/30/21, 2:53 PM

Article

Internal ports in the control housing and the air path for gearbox
case venting.



Tags

mack

air leak

; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

7/8

11/30/21, 2:53 PM

Related links and attachments
No links or attachments available

Article

Feedback
Give feedback
to help improve the content of this article

; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD3?pyActivity=%40basec…

8/8