Tuesday, January 22, 2013

770G and 772G Off-Highway Truck (OEM) Hydraulic and Braking System: Service Brake Discs - Check


Rear Brakes


WARNING: 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.

Note: This procedure should be performed at the initial delivery in order 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 new benchmark for the piston travel. Record the measurements in the Testing and Adjusting, "Worksheets" story which is located in the back of this book.
Table 1
Required Tools    
Part Number    Description    Required Amount    
5P-9726    Gauge Plug    2    
1U-7425    Brake Wear Gauge    2    
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 labeled with a "P". The purge valve for the service brake is labeled with an "S".
Make sure that the transmission is in PARK.
Note: Do not activate the service brakes or the retarder while the 5P-9726 Gauge Plug is installed.

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

  1. Install the 5P-9726 Gauge Plug .
    Brake wear gauge
    (1) Service brake piston
    (2) Pin
    (3) Gauge plug
    (4) Brake wear gauge
    (A) Distance with the parking brake disengaged
    (B) Distance of stroke(C) Distance with the parking brake engaged


    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.


  1. Push pin (2) until pin (2) contacts service brake piston (1), as shown above.

  1. 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.

  1. Remove brake wear gauge (4) from gauge plug (3). Measure distance (C). Distance (C) 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, if this is a more convenient method.

  1. Pull pin (2) away from piston (1) and against plug (3). This precaution will ensure that pin (2) does not break when piston (1) is retracted.

  1. Start the engine. Operate the engine at high idle so that cooling oil is sent to the service brake piston.

  1. Move the transmission to the PARK position. Doing so releases the parking brakes. Brake cooling oil flow and pressure ensure that the parking brake piston is completely released.

  1. Again, push in pin (2) until pin (2) contacts service brake piston (1) .

  1. With one hand, hold brake wear gauge (4) over gauge plug (3). Push down on the plunger until the plunger touches pin (2) in gauge plug (3) .

  1. 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, if this is a more convenient method.

  1. Subtract measurement (A) from measurement (C). Distance (B) is the total movement of the brake piston. This measurement represents the stacked height of the brake discs.Note: Refer to Tables 2 and 3 in order to determine the percentage of brake wear. Refer to Guideline for Reusable Parts and Salvage Operations, SEBF8095, "Service Brakes for Off-Highway Trucks" in order to determine the service intervals.
    Table 2
    Table For Determining The Wear Of Brake Disc Pack    
    Percent of Brake Wear    Rear Brake Piston Travel    
    0 percent    
    7.4 mm (0.29 inch)    
    10 percent    
    8.1 mm (0.32 inch)    
    20 percent    
    8.9 mm (0.35 inch)    
    30 percent    
    9.7 mm (0.38 inch)    
    40 percent    
    10.4 mm (0.41 inch)    
    50 percent    
    10.9 mm (0.43 inch)    
    60 percent    
    11.7 mm (0.46 inch)    
    70 percent    
    12.4 mm (0.49 inch)    
    75 percent    
    12.8 mm (0.50 inch)    
    80 percent    
    13.2 mm (0.52 inch)    
    90 percent    
    14.0 mm (0.55 inch)    
    100 percent    
    14.7 mm (0.58 inch)    

    Note: The brake assembly should be rebuilt when wear reaches 75 percent of the baseline value. Refer to the Testing and Adjusting, "Worksheets" story which is located in the back of this book.
    Table 3
    Table For Determining The Wear Of Brake Disc Pack    
    Percent of Brake Wear    Front Brake Piston Travel    
    0 percent    
    3.4 mm (0.13 inch)    
    20 percent    
    4.6 mm (0.18 inch)    
    40 percent    
    5.8 mm (0.23 inch)    
    60 percent    
    7.1 mm (0.28 inch)    
    75 percent    
    7.4 mm (0.29 inch)    
    80 percent    
    8.3 mm (0.33 inch)    
    100 percent    
    9.5 mm (0.37 inch)    

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

  1. Remove gauge plug (3). Install the plug.

  1. Repeat Steps 1 through 13 for the other side.

    WARNING: 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.
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  1. Make sure that you purge 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. (Material that has flaked off.) Check for shallow oil grooves.
Table 4
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)    

Table 5
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)    
( 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" story which is 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 usable life of the brake after the rebuild.



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770G and 772G Off-Highway Truck (OEM) Hydraulic and Braking System: Service Brake Discs - Check Rating: 4.5 Diposkan Oleh: Unknown

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