777F Off-Highway Truck Hydraulic System Caterpillar

Service Brake Discs - Check

Usage:

777F JRP

Checking the Brake Wear with Gauges

Note: This procedure should be performed at the initial delivery to establish a baseline. Also, perform this procedure again after any of the brakes are rebuilt. Rebuilding the brakes will change the piston travel. Rebuilding the brakes will create a benchmark for the piston travel. Record the measurements in the Testing and Adjusting, "Worksheets" located in the back of this book.

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Personal injury or death can result from machine movement.

Place blocks in front of and behind the wheels to make sure the machine does not move while the parking brakes are disengaged.

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Personal injury can result from hydraulic oil under pressure.
Hydraulic oil under pressure can cause injury to persons on or near the machine when the pressure is suddenly released.
At operating temperature, the hydraulic oil tank is hot and under pressure. Hot oil can cause burns.
Remove the fill plug only when the engine is stopped, and the fill plug is cool enough to touch with your bare hand.

Do not allow hot oil or components to contact skin.

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NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat^® products. Dispose of all fluids according to local regulations and mandates.

Front Brakes

Front Caliper Service Brakes

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Illustration 1	g00540364
(1) Disc (2) Caliper (3) Linings (4) Thickness of the disc (5) Thickness of the lining

Linings (3) are part of caliper (2). There are two linings (3) for each caliper (2). Disc (1) rotates between the two linings (3). This causes linings (3) to wear. The thickness (5) can be visually checked. Linings (3) must be replaced when thickness (5) is less than 3.15 mm (0.124 inch).

Disc (1) should be checked for damage or for wear. Disc (1) should be replaced when thickness (4) is less than 15.87 mm (0.625 inch).

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Illustration 2	g00645613
View of the Service Brakes (Front Caliper) (6) Pins (7) Bolts

Linings (3) are held in position by pins (6). Pins (6) are locked in position with bolts (7).

Refer to Specifications, "Service Brake (Front Caliper)" for the clearance for pins (6). When the proper clearance has been made, tighten bolt (7) to the appropriate torque.

Note: Make sure that bolt (7) fully engages the groove in pin (6) before bolt (7) is tightened.

Front Oil Cooled Service Brakes

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Table 1
Required Tools
Qty	Part Number	Description
2	8S-9191	Bolt

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Illustration 3	g02096135
View from the Inside of the Machine of the Inside of the Service Brakes (Front Oil Cooled) (8) Port (9) Purge valve for service brake

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Illustration 4	g02096136
Section A-A (8) Port (9) Purge valve for service brake

Remove the plugs from ports (8).
Install a 8S-9191 Bolt in each open port (8). Tighten the bolt finger tight, until the bolt lightly touches the spacer disc, then back off the bolt one complete turn.
Engage the service brakes.
Tighten the 8S-9191 Bolts to 27 N·m (239 lb in) while the service brakes are engaged.
Measure the distance from the top of a 8S-9191 Bolt to the spot face around port (8). Record this measurement.
Note: Use the same bolt for all the measurements.
Release the service brake.
Loosen purge screw (9).
Tighten the 8S-9191 Bolts evenly to 27 N·m (239 lb in).
Tighten purge screw (9).
Measure the distance from the top of the 8S-9191 Bolt that was used in Step 5 to the spot face around port (8). Record this measurement.

Find the difference between the measurement in Step 5 and the measurement in Step 10. The difference is the amount of wear on the brake pack. Refer to Table 2 for the percentage of wear on the brake pack.

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Table 2
Table for the Wear of Front Service Brakes (Oil Cooled)
Percent of Brake Wear for the Front Brakes	Measured Difference
0 percent	3.41 mm (0.134 inch)
20 percent	4.63 mm (0.182 inch)
40 percent	5.85 mm (0.230 inch)
60 percent	7.07 mm (0.278 inch)
75 percent	7.99 mm (0.315 inch)
80 percent	8.29 mm (0.326 inch)
100 percent	9.51 mm (0.374 inch)

Note: 25 percent of remaining service life refers to 75 percent wear of the brake assembly. The brake assembly should be rebuilt when brake wear reaches 75 percent of the baseline value. Refer to the Testing and Adjusting, "Worksheets" located in the back of this book.

Remove all test equipment.
Install the plugs in ports (8).
Purge the air from the brake lines. Refer to Testing and Adjusting, RENR8315, "Brake System Air - Purge" for instructions on purging the air from the brake lines.

Rear Brakes

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Table 3
Baseline Nominal Value for the Piston Stroke for the Rear Wheels ⁽¹⁾
3.3 mm (0.129 inch) to 9.3 mm (0.366 inch)

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⁽¹⁾	The baseline nominal value is the piston stroke that is measured through the service port. This value can float up to 6 mm (0.236 inch) due to tolerances.

Measure and record the baseline value of new and/or rebuilt brakes. The piston stroke should be between the values shown in Table 3.

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Table 4
Required Tools
Qty	Part Number	Description
1	344-9164	Brake Wear Gauge As
1	1U-7425	Brake Wear Gauge

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Illustration 5	g01261560
Rear brake housing (S) Purge valve for service brake (P) Purge valve for parking brake

Note: Identification letters are embossed on the purge valves at the top of the brake housing. The purge valve for the parking brake is marked with a "P". The purge valve for the service brake is marked with an "S".

Make sure that the transmission is in NEUTRAL.

Note: Do not activate the service brakes or the retarder while the 344-9164 Brake Wear Gauge As is installed. Activation of the service brakes or the retarder will force oil from the system through the brake wear gauge assembly.

While the engine is off and the parking brake is engaged, remove the top plug that is marked with an "S".

Install the 344-9164 Brake Wear Gauge As.

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Illustration 6	g02096538
Brake wear gauge (1) Service brake piston (2) Pin (3) Gauge plug (4) Brake wear gauge (A) Distance with the parking brake engaged (B) Distance with the parking brake disengaged (C) Distance of stroke

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NOTICE

Do not allow the brake piston to retract while the pin is installed in the plug hole. This could cause the pin to break off when the brake piston retracts. It is possible for broken pieces of the tool to fall into the brake housing and cause damage.

Push pin (2) until pin (2) contacts service brake piston (1), as shown above.
Hold brake wear gauge (4) in position on gauge plug (3). Push down on the plunger until the plunger contacts pin (2) in gauge plug (3). Available space permits the use of only one arm to perform this task.
Remove brake wear gauge (4) from gauge plug (3). Measure distance (A). Distance (A) is the measurement of the extension of the plunger beyond the tube. Record this measurement. You may also use a micrometer to take this measurement.
Pull pin (2) away from piston (1) and against plug (3). Pulling pin (2) away from piston (1) will ensure that pin (2) does not break when piston (1) is retracted.
Start the engine. Operate the engine at high idle so that cooling oil is sent to the service brake piston.
Move the parking brake lever to the OFF position. Brake cooling oil flow and pressure ensure that the parking brake piston is released.
Again, push in pin (2) until pin (2) contacts service brake piston (1).
With one hand, hold brake wear gauge (4) over gauge plug (3). Push down on the plunger until the plunger contacts with pin (2) in gauge plug (3).
Remove brake wear gauge (4) from gauge plug (3). Measure distance (B). Distance (B) is the measurement of the extension of the plunger beyond the tube. Record this measurement. You may also use a micrometer to take this measurement.

Subtract measurement (A) from measurement (B). Distance (C) is the total movement of the brake piston. This measurement represents the stacked height of the brake discs.

Note: Refer to Table 5 and Table 6 to determine the percentage of brake wear. Refer to Guideline for Reusable Parts and Salvage Operations, SEBF8095, "Service Brakes for Off-Highway Trucks" to determine the service intervals.

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Table 5
Baseline Nominal Value for the Piston Stroke for the Rear Wheels ⁽¹⁾
3.3 mm (0.129 inch) to 9.3 mm (0.366 inch)

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⁽¹⁾	The baseline nominal value is the piston stroke that is measured through the service port. This value can float up to 6 mm (0.236 inch) due to tolerances.

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Table 6
Additional Piston Stroke (Compared to the Baseline Value for the Piston Stroke from Table 5)
Percent of Brake Wear	Rear Brake Piston Travel
10 percent	0.8 mm (0.03150 inch)
20 percent	1.5 mm (0.05906 inch)
30 percent	2.3 mm (0.09055 inch)
40 percent	3.0 mm (0.1181 inch)
50 percent	3.8 mm (0.1496 inch)
60 percent	4.6 mm (0.1811 inch)
70 percent	5.3 mm (0.2087 inch)
80 percent	6.1 mm (0.2402 inch)
90 percent	6.8 mm (0.2677 inch)
100 percent	7.6 mm (0.2992 inch)

Note: Record the baseline value of the piston stroke. Compare the baseline value of the piston stroke to the measured stroke throughout the life of the brake. The brake is worn when the measured stroke is equal to the baseline value of the piston stroke plus the "100 percent" value that is shown in Table 6.

Note: The brake assembly should be rebuilt when wear reaches 75 percent. Refer to the Testing and Adjusting, "Worksheets" located in the back of this book.

Remove gauge plug (3). Install the plug.

Repeat Steps 1 through 13 for the other side.

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Personal injury or death can result from air in the oil for the brake hydraulic system.
Air in the system can prevent complete brake application and it is possible that the wheels on the machine can not be stopped.

Air must not be in the oil for the brake hydraulic system to function properly.

Make sure that you remove all air from the hydraulic brake system.

Brake Disc Wear Check And Plate Wear Check

Note: See Specifications, "Service and Parking Brake (Rear)" for new dimensions.

Friction Discs

Check for the thickness of the discs. Determine if friction material needs to be removed. (Friction material is material that has flaked off.) Check for shallow oil grooves.

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Table 7
Table For Determining The Wear Of Friction Disc
Percentage Of Disc Wear	Disc Thickness
0 percent	5.08 mm (0.200 inch)
10 percent	5.03 mm (0.198 inch)
20 percent	4.98 mm (0.196 inch)
30 percent	4.93 mm (0.194 inch)
40 percent	4.88 mm (0.192 inch)
50 percent	4.83 mm (0.190 inch)
60 percent	4.78 mm (0.188 inch)
70 percent	4.72 mm (0.186 inch)
80 percent	4.67 mm (0.184 inch)
90 percent	4.63 mm (0.182 inch)
100 percent	4.57 mm (0.180 inch)

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Table 8
Table For Determining The Wear Of The Grooves In The Friction Disc⁽¹⁾
Percentage Of Disc Wear	Disc Groove Depth
0 percent	0.64 mm (0.025 inch)
10 percent	0.62 mm (0.024 inch)
20 percent	0.60 mm (0.024 inch)
30 percent	0.59 mm (0.023 inch)
40 percent	0.57 mm (0.022 inch)
50 percent	0.55 mm (0.022 inch)
60 percent	0.53 mm (0.021 inch)
70 percent	0.51 mm (0.020 inch)
80 percent	0.50 mm (0.020 inch)
90 percent	0.48 mm (0.019 inch)
100 percent	0.46 mm (0.018 inch)

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⁽¹⁾	This measurement is based on three measurements per side and the measurements are taken at 25.4 mm (1.00 inch) from the outside of the disc.

Replace the discs if any of the following conditions exist.

The remaining brake disc life does not last until the next rebuild of a major component.
The disc has more than 20 percent of a wear difference when you compare the disc to the other discs that are in the same assembly.
10 percent or more of the friction material is flaked off or the discs have a flaking tendency. (Flaking tendency means that the friction material easily flakes off with only light force.)
Oil grooves average less than 0.46 mm (0.018 inch) in depth per side.
The brake assembly should be rebuilt when wear reaches 75 percent of the baseline value. Refer to the Testing and Adjusting, "Worksheets" located in the back of this book.

Steel Plates

Check the plate for thickness, for scored surfaces, for radial grooves, and for warpage. Replace the plates if any of the following conditions exist.

The plate thickness is less than 2.29 mm (0.090 inch).
More than 10 percent of the surface area is scored.
The plate has deep radial grooves that would act as a cutting edge on the friction material on the discs.
The plate is warped and the plate cannot be flattened with a force of 90 N (20 lb).

Damper Plate Assemblies

Always use new dampers when you repair the oil cooled multi-disc brakes. Permanent shrinkage of the damper material and deterioration of the damper material will reduce the brakes usable life after the rebuild.

Checking the Brake Wear with Permanently Mounted Brake Wear Indicators (If Equipped)

Note: Some machines are not equipped with the ports that are required to install permanently mounted brake wear indicators.

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Table 9
Required Tools for Checking the Brake Wear with Permanently Mounted Brake Wear Indicators
Qty	Part Number	Description	Wheel
2	348-8573	Brake Wear Gauge As	Rear Wheel⁽¹⁾

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⁽¹⁾	Only the rear wheels can be checked with permanently mounted brake wear indicators.

Note: This procedure should be performed at the initial delivery to establish a baseline. Also, perform this procedure again after any of the rear brakes are rebuilt. Rebuilding the brakes will change the piston travel. Performing the procedure after rebuilding the brakes will create a benchmark for the piston travel.

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Illustration 7	g02096554
Typical view of the rear brake housing (S) Purge valve for service brake (P) Purge valves for parking brake

Note: Before checking for wear, perform the Systems Operation/Testing and Adjusting, "Service Brakes and Retarder System Pressure - Test".

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Personal injury or death can result from machine movement.

Place blocks in front of and behind the wheels to make sure the machine does not move while the parking brakes are disengaged.

Show/hide table

Do not allow hot oil or components to contact skin.

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NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat^® products. Dispose of all fluids according to local regulations and mandates.

Installing and Setting the Brake Wear Indicator

While the engine is off and the parking brake is engaged, remove the top plug that has the label "S".
Install the brake wear indicator into the open port. Tighten the brake wear indicator to a torque of 140 ± 14 N·m (105 ± 10 lb ft).
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Illustration 8 g01979773

Typical view of an installed brake wear indicator
Remove cap (A) from the brake wear indicator.
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Illustration 9 g01979775

Typical view of newly installed brake discs
Apply forward pressure to indicator rod (B) so that the indicator rod contacts brake piston (C).
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Illustration 10 g01979778
Push dowel bushing (D) into the body until the end of dowel bushing (D) is flush with the notched shoulder that is on indicator rod (B).
Reinstall cap (A) that was removed in Step 3. Tighten cap (A) to a torque of 34 ± 4 N·m (300 ± 35 lb in).

Checking the Brake Wear

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Illustration 11	g01979795
Typical view of an installed brake wear indicator

While the engine is off and the parking brake is engaged, remove cap (A) from the brake wear indicator.
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Illustration 12 g01979777

Typical view of worn brake discs
Push indicator rod (B) until the indicator rod contacts brake piston (C).
Note: If the end of rod (B) is flush with dowel bushing (D), or if the end of rod (B) goes below the end of dowel bushing (D), then the brake material has exceeded the service life. If the brake material has exceeded the service life, replace the brake discs.
After the brake wear has been checked, pull back rod (B).
Reinstall cap (A) that was removed in Step 1. Tighten cap (A) to a torque of 34 ± 4 N·m (300 ± 35 lb in).