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6/30/22, 12:45 PM
Article
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(Back Office Only) - Engine Brake Vibration When
In High Setting - 13L Engine With Variable
Geometry Turbo ( VGT ) - US17 And Newer
Emissions (Common Rail Fuel System)
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Internal Content
Overview
Engine brake vibration in its most noticeable form can be caused by
several things. Possibilities include failed Exhaust Brake Rockers that
don't engage the engine brake cam lobes as required, the Engine
Brake Solenoid not functioning correctly, or a Turbocharger that is
failing. Note that the Intake Throttle Valve (ITV) is not utilized for
engine braking and should not be suspected unless its position shows
to be below 90% (78 degrees) during engine brake activation.
One recent case was confirmed to have been the Exhaust Brake
Rocker Arms. However, several of the recent complaints do not
appear to have a root cause.
In these cases, the complaint seems to be based on the perception of
a light vibration during engine braking on high setting that exceeds
what the owner/operator perceives as acceptable. For this reason, in
cases where it is more perception than vibration, someone with
experience should test drive the truck to verify that an issue exists.
In cases of actual excessive vibration such as failed exhaust brake
rockers, the vibration is commonly felt throughout the cab, and will
likely be accompanied by the dash shaking and/or rattling.
If a chassis with a manual transmission is experiencing shaking or
vibration through the shifter only, Hagerstown product engineering
may need to measure the vibration profile at the driver's seat base
and review the data to ensure it is within the acceptable limit.
Procedure
Vibration complaints will need to be assessed on a case-by-case basis
at the discretion of the dealer's District Service Manager (DSM),
Uptime Center staff (Dealer Technical Support) and Service
Engineering (Reliability).
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- The first assessment should be done by the DSM
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The first assessment should be done by the DSM.
Article
- If the DSM cannot detect excessive vibration and if possible, request
that another driver operate the truck under the same conditions in
which the complaint is occurring.
• This can be a staff member or driver at the servicing dealer.
• The driver should not be told that (s)he is checking for
vibration. An assessment of general performance during
engine braking with the switch on high setting should be
requested.
- Have the rocker shaft oil pressure monitored during the test drive.
• Pressure with the engine brake inactive should be 14.5 psi
+1.4/-0.7 psi (100 kPa +10/-5 kPa)
• Pressure with the engine brake active should be
approximately 29 psi (200 kPa)
- If there is high certainty that the vibration is abnormal:
• The power (slave) pistons in the exhaust rockers should be
inspected to confirm they are not backing out or loose.
• The slave piston rides on the exhaust valve bridge as shown
above (Number 14), and is the only part of the rocker that can
be removed.
• NOTE: In cases where rocker arms are replaced, it may be
found that the part number of the rocker arm in Impact is
22418147. This number is now blocked in Parts Compass and
cannot be ordered. When ordering, part number 21406640
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is correct.
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