Twiflex GMR-S User manual

170 Mounting Hole CRS
To Edge of Disc
87 17
Disc Centre Line
ø 610 Min. Disc Diameter
110
ø 254
44
150
300
19345
Air Inlet
6 1/2
Brake Disc
254 (GMR)
38/40 (GMR40)
212 (GMR)
223 (GMR40)
170 Mounting Hole CRS
270 New Pads
300 Fully Worn Pads
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Braking Torque kNm
Air Pressure - bar
Minimum Pressure for Full Retraction 8·4 bar
Maximum Pressure 9 bar
7
6
0
1
2
3
4
5
40
24 (GMR)
GMR-S and GMR40-S Disc Brake Caliper - Spring Applied, Air Released
DB4603
The ratings shown on the above graph are based on fully bedded and conditioned brake pads. For bedding in
and conditioning procedures see Publication M1060.
Braking Force is defined as the Tangential Force acting on the brake disc at the Effective Disc Radius.
Braking Torque (Nm) = Braking Force (N) x Effective Disc Radius (m)
where Effective Disc Radius = Actual Disc Radius- 0.06
Note:
The caliper may be assembled as
drawn (right hand assembly) or with
arms and thruster oppositely handed.
Nominal dimensions given.
For specific dimensions please
contact Twiflex.
For GMR Mk 2 caliper details see DB 3604

27
3
1
35
Max
Stroke
15 11 28 14 292
18
19
20
26
25
311013212316
12
6
5
4
9
7
30
222417
8
76 Fully Retracted
156 Fully Extended
209
GMR-S and GMR40-S Disc Brake Caliper - Spring Applied, Air Released
Thruster Type - S
Maximum Displacement Volume 1.3 l.
Item Component Part No. Qty.
1 Front Cap 1
2 Rear Cap 1
3 Thrust Collar 1
4 Stud 1
5 M16 Nut 2
6 M16 Spring Washer 2
7 Wiper Seal 600242 1
8 Pushrod 1
9 Rod Seal 600243 1
10 Sleeve 1
11 Spring Plate 1
12 ‘O’ Ring 600138 1
13 ‘O’ Ring 600224 1
14 Circlip 1
15 Diaphragm 7200776 1
16 Support Plate 1
Item Component Part No. Qty.
17 Spring Ring 1
18 Main Spring 1
19 Centre Spring 1
20 Inner Spring 1
21 M8x 35 Bolt 12
22 M8 Nut 12
23 G 1/8 Plug 1
24 G 1/8 Washer 1
25 Redcap 1
26 Retraction Screw 1
27 G 1/2 Redcap 1
28 Label 1
29 Helicoil Insert 1
30 Bush 1800372 1
31 Bush 1800374 1
Parts List

GMR-S and GMR40-S Disc Brake Caliper - Spring Applied, Air Released
The GMR-S and GMR40--S calipers are available in various ratings, as shown on the performance charts.
Part numbers are given below.
These are typical performance figures for bedded and conditioned brake pads having a friction coefficient of 0.4 when used
with standard Twiflex discs an appropriate ‘service factor’ should be applied when designing the braking system and in the
case of brakes used for holding duties or in wet conditions this should be not less than 2.0.
Marinised versions of the calipers, and thrusters with nodular cast iron castings (instead of aluminium alloy) are available to
special order.
A monitoring unit is also available (Part No. 7700212) which is fitted to the back of the thruster. The unit incorporates two
microswitches, of which one indicates full retraction of the pushrod (i.e. brake off) and the other indicates the need for
adjustment due to pad wear.
Thruster Thruster Thruster Max. Braking Retraction Air Caliper Part No.
Type Part No. Weight Kg Force kN Pressure Bar GMR GMR40
S 8.4 7200777 12·2 19·5 4·8 6780971 6781006
S 11 7200807 13·2 25 6·0 6780971 6781006
S 12-9 7200806 14 30 7·0 6780971 6781006
S 15-6 7200805 15 36 8·4 6780971 6781006
Installation, Operation and Maintenance
1. Installation
1.1 The caliper must be mounted on a suitably rigid support, upon which braking forces of up to 36kN will be imposed.
1.2 The caliper should be positioned symmetrically with respect to the disc, as shown on the drawing.
1.3 Three fixing bolts are required, M16 grade 8.8. The bolts should be tightened to a torque of 150Nm.
1.4 If the caliper is to be mounted on an inclined surface, the caliper should be fitted with adjustable stop screw
and bias springs, included in the inclined mounting kit (Part Number 6700458, drawing number A11074).
1.5 Calipers are normally supplied assembled ‘right-handed’, as shown on the drawing, unless otherwise specified.
1.6 The thruster is normally supplied separately from the caliper, and with the retraction screw fitted to hold it in the ‘off’
position (see section 2.2) until it has been fitted on the caliper arm. Nuts and washers for this purpose are supplied
and should be tightened to 45Nm torque. Thrusters are normally fitted with the air inlet uppermost.
1.7 The air inlet connection on the thruster is tapped G 1/2 (1/2” BSP). The air supply should be connected via a
length of flexible tubing to accommodate the movement during operation. A quick exhaust valve may be
fitted if very rapid brake operation is required.
1.8 Control of brake operation is effected by a 3 port, 2 position valve with open exhaust. Standard ‘Twiflex’
controllers, with electrical, pneumatic or hydraulic signalling are available if required.
1.9 The air supply used should be dry and oil free if possible; operation of the thruster at full stroke requires
approximately 1.3 litres of compressed air.
2. Operation
2.1 The brake is applied by the thruster springs and released pneumatically. The required supply pressure
varies with the caliper rating and is given on the performance charts. Variable braking torque can be
achieved by regulating the air pressure as shown on the charts.
2.2 To enable the brake to be released in the event of air supply failure, a retraction screw is supplied (M16 x
130, Part number 5350249). This is inserted into the rear of the thruster and screws directly into the end of
the pushrod; adequate access to the back of the thruster is required. The retraction screw is also used as
the safety screw during maintenance.
2.3 THE RETRACTION SCREW SHOULD BE REMOVED COMPLETELY WHEN THE BRAKE IS IN SERVICE, and
the red plastic cap supplied fitted in the hole. (The brake should be off i.e. pressurised, when removing the
retraction screw).
2.4 THE THRUSTER STROKE SHOULD BE MAINTAINED AT ABOUT 20mm BY UNSCREWING THE PUSHROD.
To adjust, the brake must be off (i.e. air pressure on). Pull the caliper arm away from the pushrod and turn
the rod as required; one turn gives 2mm adjustment. Releasethe caliper arm, ensuring that the flats on the
push rod are engaged in the slot in the caliper arm. (A 17mm A/F spanner will fit the flats on the pushrod).

GMR-S and GMR40-S Disc Brake Caliper - Spring Applied, Air Released
N.B. Keep fingers clear of the space between push rod and caliper arm at all times.
If an inclined mounting kit is fitted, the stop screw should be re-adjusted to maintain equal pad clearance
on either side of the disc.
2.5 Pad wear can be monitored by observing the gap between the lugs on the pads pressure plates and the
machined surfaces on the caliper frame, when the brake is applied. Pads must be replaced {see 3.2)
before the gap is reduced to zero. The maximum allowable wear on a pad is 10mm).
3. Maintenance
CALIPER
3.1 Ensure that the brake pad and disc remain tree from oil and grease. Clean the disc as require. If the pads
become contaminated they should be replaced. Carry out any periodic statutory testing that is required,
or otherwise check for satisfactory performance.
3.2 Pad replacement is carried out from the rear of the caliper; DO NOT release the spring clips which attach
the pressure plates to the caliper arms. With the brake off (retraction screw may be fitted as a safety
screw) remove the caliper return springs and the keep plates. If an inclined mounting kit is fitted, remove
this also. Withdraw the pads to the rear and lift out. (The hole in the end of the pad retaining plates is
provided to assist in withdrawing the pads). Fit the new pads (part number 7080080), ensuring that the
slotted retaining plate is located around the keep disc on the pressure plate; the pads should slide freely
into position. Replace remaining parts. Re-adjust the push rod, as in (2.4), and the stop screw if fitted.
3.3 The surface of the caliper arm on which the thruster pushrod bears should be kept well greased. The
knuckle joints between the caliper arms and the pressure plates should be cleaned occasionally, and a
small amount of grease applied; the joints may be levered apart slightly against the pressure of the
spring clip. Occasionally, or if caliper is not operating freely, inject a small amount of grease via grease·
nipples to lubricate the pivot pins, then rotate pins to distribute the grease. Any grease exuding past the
‘0’-rings should be wiped off. The pins may be turned by gripping the knurled end at the top of the
caliper.
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. If the air supply is wet, the drain plug (23) should be removed at intervals
to release any accumulated water.
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, without decompressing the spring pack:-
Diaphragm (15)
Rod Seal (9)
Bush (30)
Wiper Seal (7)
Push rod (8)
3.5 Replacement of any other component, i.e. 0-rings (12), (13), bush (31) and springs requires the spring
pack to be decompressed. This is not covered in these instructions, and should only be carried out by
Twiflex or their agents. If the pushrod is known to be damaged, replace it first, as in 3.11. Otherwise
proceed as below.
WARNING:- DO NOT ATIEMPT TO DECOMPRESS THE SPRINGS BY UNSCREWING THE RETRACTION SCREW.
Thruster Servicing
3.6 With the brake ott, insert retraction screw and screw it fully in; finger tight is sufficient. (If thruster will not
retract, the brake should be released using the retraction screw, which should be well lubricated).
Disconnect the air supply and remove thruster from caliper.
Adjust the retraction screw to allow a thruster stroke of approximately 32mm (i.e. just under full stroke).
This adjustment allows the diaphragm to assume its natural shape, which eases re-assembly. The use of
a temporary air supply will be found convenient, as it avoids having to turn the retraction screw under
load.
Withdraw the bolts (21), and remove the front cap (1), spring ring (17), support plate (16) and diaphragm
(15). The diaphragm should be free from splits of cracks, but some wear from the edge of the spring plate
(11) is acceptable if the fabric reinforcement is not damaged.

GMR-S and GMR40-S Disc Brake Caliper - Spring Applied, Air Released
3.7 Leakage of air past the rod seal may be caused by damage to the seal or to the pushrod. The surface of
the pushrod must be smooth and free from scoring or bruising. Note that the pushrod cannot be removed
whilst the thruster is dismantled. (For removal and replacement of the push rod see 3.11 below).
The rod seal (which has two parts, the P.T.F.E. sealing ring and an 0-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 seal, the P.T.F.E. ring must be compressed, which requires the use of a fitting tool; see
drawing A21123. Note that the stepped side of the ring is the pressure side.
3.8 The wiper seal (7) 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.
3.9 The bush (30), 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 bearing.
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.
3.10 Re-assembly of the thruster is the reverse of dismantling. Seals should be lightly greased to ease
assembly; the grease reservoir groove in the front cap and the bush indentations should be filled with
grease.
Ensure that the beaded edge of the diaphragm locates correctly in the grooves, and tighten the bolts
progressively until flanges are in contact all round.
After re-assembly, pressurise the thruster and check for leaks. Using the retraction screw to maintain
full retraction, refit the thruster to the caliper. (After removing the retraction screw replace the red
plastic cap in the hole).
Push rod removal/replacement Re-Lubrication of Thruster
3.11 With the thruster removed from the caliper (as in 3.6), remove the retraction screw, so that the thruster
operates through its full stroke, and the spring load is supported on the front cap. Remove the thrust
collar (3) from the rear cap (2). This is a light press fit.
Unscrew the pushrod until it can be withdrawn through the rear of the thruster. Clean and examine the
push rod, replace if damaged. Clean other parts.
Re-lubricate the front cap bearing, the internal thread of the sleeve (10), the rear cap bore adjacent to
the end of the sleeve, and the threads (internal and external) of the push rod, with grease.
Re-fit the pushrod into the thruster and replace the thrust collar (if it is loose, use a low-strength grade of
‘Loctite’ to retain it). Pressurise the thruster, check for leaks and fit the retraction screw. Re-fit the
thruster to the caliper. (After removing the retraction screw, replace the red plastic cap into the hole).
4. Recommended Lubricants
4.1 Caliper: Medium grease containing Molybdenum disulphide.
e.g. Castrol LMM
Shell Alvania 2 + MoS2
4.2 Thruster: Medium lithium based grease with rust inhibitors
e.g. Duckham’s Keenomax L2
Castrol AP 2
Shell Alvania R2
5. Spares
5.1 A spare set of brake pads, a diaphragm and a set of seals should be kept in a cool, dry, dark place
where there is no chance of contamination.
5.2 For caliper spares see Data Sheet DB 3604.
5.3 Spare components for air-line equipment, including the filters and the controller should be kept in
readiness, as appropriate.
6. Service
Address all enquiries regarding this equipment to your Twiflex agent or direct to Twiflex.

GMR-S and GMR40-S Disc Brake Caliper - Spring Applied, Air Released
Minimum Pressure for Full Retraction 7 bar
Maximum Pressure 9 bar
Minimum Pressure for Full Retraction 6 bar
Maximum Pressure 7 bar
Minimum Pressure for Full Retraction 4·8 bar
Maximum Pressure 7 bar
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
0 2 4 6 8 10 12 14 16 18 20 22 24 26
Braking Torque kNm
Air Pressure - bar
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
Braking Torque kNm
Air Pressure - bar
0 2 4 6 8 10 12 14 16 18 20 22
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
Braking Torque kNm
1 kNm = 736·6 lbf-ft 1 bar = 14·5 psi
Air Pressure - bar
0 2 4 6 8 10 12 14 16 18
7
6
0
1
2
3
4
5
6
5
0
1
2
3
4
5
0
1
2
3
4
Brake performance at 30 kN braking force
Brake performance at 25 kN braking force
Minimum Pressure for Full Retraction 7 bar
Maximum Pressure 9 bar
Minimum Pressure for Full Retraction 6 bar
Maximum Pressure 7 bar
Minimum Pressure for Full Retraction 4·8 bar
Maximum Pressure 7 bar
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
0 2 4 6 8 10 12 14 16 18 20 22 24 26
Braking Torque kNm
Air Pressure - bar
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
Braking Torque kNm
Air Pressure - bar
0 2 4 6 8 10 12 14 16 18 20 22
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
Braking Torque kNm
1 kNm = 736·6 lbf-ft 1 bar = 14·5 psi
Air Pressure - bar
0 2 4 6 8 10 12 14 16 18
7
6
0
1
2
3
4
5
6
5
0
1
2
3
4
5
0
1
2
3
4
Brake performance at 19.5 kN braking force
Minimum Pressure for Full Retraction 7 bar
Maximum Pressure 9 bar
Minimum Pressure for Full Retraction 6 bar
Maximum Pressure 7 bar
Minimum Pressure for Full Retraction 4·8 bar
Maximum Pressure 7 bar
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
0 2 4 6 8 10 12 14 16 18 20 22 24 26
Braking Torque kNm
Air Pressure - bar
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
Braking Torque kNm
Air Pressure - bar
0 2 4 6 8 10 12 14 16 18 20 22
Disc Diameter mm 610 760 915 1065 1220 1370 1525 1830
Braking Torque kNm
1 kNm = 736·6 lbf-ft 1 bar = 14·5 psi
Air Pressure - bar
0 2 4 6 8 10 12 14 16 18
7
6
0
1
2
3
4
5
6
5
0
1
2
3
4
5
0
1
2
3
4
DB4603 5/19
www.twiflex.com
9 Briar Road, Twickenham
Middlesex TW2 6RB - England
[phone] Issue 05