jcb JS300 Service Manual page 935

Allowable ram creep rates
Boom
Dipper
Bucket
Basic Checks (after determining that the ram creep is
outside of the allowable tolerance.)
!M
WARNING
Take care when disconnecting hydraulic hoses and
fittings as the oil will be HOT.
TRANS-1-2
Ram seal bypass
If the ram creep is in only one direction of the ram then it is
unlikely to be caused by failed ram seals, if however the
creep is excessive in both directions of the ram stroke then
it is possible that the seals have failed.
Check for seal bypass using the following procedure:
1 Place a load in the bucket of the machine.
2 Lower the attachment to the ground and vent all
hydraulic pressure.
3 Blank off the port on the ram, which will be supporting
the attachment.
4 Remove the hose from the other port on the ram,
blank the hose and leave the port on the ram open to
atmosphere.
5 Raise the attachment off the ground
6 After initial movement, note the movement of the ram
over a 10 minute period.
After the initial movement of the ram when first raised from
the ground, a continual movement of the ram or
continuous trickle of oil from the open port of the ram would
indicate that the ram seals require further inspection.
Basic Checks (after determining that the ram creep is
outside of the allowable tolerance.)
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Port relief valve (ARV) failure
If the port relief valve itself had failed, if contamination was
30mm
stuck on the valve seat or if the valve seat itself was
60mm
damaged then this would allow oil to constantly bypass to
tank causing ram creep.
20mm
A visual check can be made by removing the port relief
valve and checking the condition of the valve seat and the
seat in the valve casing, any damage of either of these two
items would require rectification or replacement.
To check for failed port relief valve, loosen the adjuster
locknut and wind the adjuster of the port relief valve fully in,
until it locks the relief section. Re-check the ram rate, any
change in the creep rate would
investigation of the port relief is required. If there is no
change in the creep rate the cause may be the ARV seat
in the valve block.
Quick hitch/Auxiliary circuits
It is common practice to take oil from the excavator service
to operate quick hitch and auxiliary circuits. If the excavator
service which is suffering from excessive ram creep has
any other services connected to it then the best policy is to
disconnect the quick hitch and auxiliary circuit and test
again the creep rate.
9813/5100-1
Section E - Hydraulics
Hydraulic System Fault Finding
Ram Creep Tests - All Services
indicate that further
E-274