GMR-H and GMR40-H Disc Brake Caliper - Hydraulically Applied, Spring Released
After extended {one million operations or three years) use, the pivot pins should be withdrawn, cleaned,
replaced and regreased, or replaced if badly worn.
In order not to damage the 0-ring seals on the pins, use the following procedure. Remove the top circlip,
push pin down until the lower circlip and ‘0’-ring can be removed, then withdraw the pin upwards. To
refit, reverse this procedure.
THRUSTER
3.4 Clean the push rod as required, and inspect hydraulic connections and hoses.
3.5 In the event of leakage or malfunction of the thruster, the following parts can be inspected and replaced if
necessary, using the procedures described below:
Pushrod (3)
Sleeve (5)
Bush (11)
Wiper Seal (12)
Piston Seal (13)
O-Rings (14, 15)
Thruster Servicing
3.6 Disconnect the hydraulic supply and remove thruster from caliper. Gently unscrew the four cap screws (18) and
remove the end cap (2). The piston (4) may be extracted from the cylinder body (1) by pressing on the protruding
end of the pushrod (3). The pushrod (3), sleeve (5) and spring (6) may all be removed by futher movement through
the cylinder.
Clean and examine all parts. The suface of the pushrod should be smooth and freef from serious souring or bruising.
If the pushrod is known to be damaged, replace it.
Leakages of fluid past the piston seal or the end cap may be caused by damage to the seals, or to the seal grooves
in the piston.
3.7 The wiper seal (12) serves both to retain grease and to exclude dirt. The section of the pushrod which
moves through the wiper seal should be cleaned with a very slight lubricant film.
The wiper seal is of all rubber construction and is easily replaced without tools.
3.8 The bush (11), which is pressed into the front cap, has a number of shallow circular indentations in its
surface, which retain grease. The limit of acceptable wear on the bush is 0.2mm, approximately half the
depth of the indentations in a new bush.
A worn bush can be withdrawn (after removal of the wiper seal which may be re-used unless damaged)
using a suitable extractor. The new bush, should be pressed in until flush with the base of the wiper seal
recess.
3.9 The piston seal (13) which has two parts, (a P.T.F.E. sealing ring and an O-ring) may be removed using a small
screwdriver or similar tool. Take care not to damage the groove. Once removed the seal should not be re-used.
When fitting a new piston seal, the P.T.F.E. ring must be carefully deformed without sharp bends to allow insertion
into the internal groove, then expanded into a circle again. The piston can be used as a tool for reshaping the ring.
3.10 Re-assembly of the thruster is the reverse of dismantling. The pushrod thread, the bush and the sleeve should
be lightly greased to ease assembly and the piston oiled with hydraulic fluid.
The sleeve (5) should be screwed on to the pushrod until it bottoms on the pushrod shoulder, then the pushrod
assembly and compression spring inserted into the cylinder followed by the piston. The end cap may be located
on the piston and the securing screws (18) engaged in the cylinder but not tightened. The anti-rotation roll pin (10)
acts as a stop unless the pin and sleeve slot are in line. Therefore the pushrod should be rotated by a spanner applied
to the flats at the same time as gentle pressure is applied end cap (2). When the anti-rotation pin (10) is engaged
in the slot, the end cap screws (18) should be tightened to a torque of 30Nm. Refit the thruster to the caliper,
and adjust pushrod stroke. Check for leaks and correct operation.
