Pilot Valve Stem Seal May Leak In The Cab Of Certain 994 Wheel Loaders Caterpillar

Pilot Valve Stem Seal May Leak In The Cab Of Certain 994 Wheel Loaders

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Caterpillar: Confidential Yellow

NOTE: The information supplied in this service letter may not be valid after the termination date of this program. Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.

NOTE: This Program can be administered either before or after a failure. In either case the decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS8453" as the Part Number and "7755" as the Group Number. If administered before failure, use "56" as the Warranty Claim Description Code and use "T" as the SIMS Description Code. If administered after failure, use "96" as the Warranty Claim Description Code and use "Z" as the SIMS Description Code.

NOTE: This Revised Service Letter replaces the October 7, 1995 Service Letter. Changes have been made to the Termination Date, Affected Product, Parts Needed and Action Required.

Termination Date

December 31, 1996

Problem

Pilot valve stem seal may leak in the cab of certain 994 Wheel Loaders for the following reasons:

1. Pilot relief valve contamination.

2. Excess supply pressure to the pilot valve from the lift cylinder due to a pressure reducing valve sticking.

3. High drain line pressure due to a small drain line.

4. Low pressure seals were used.

Affected Product
Model & Identification Number

994 (9YF6-13, 9YF15, 9YF18-35, 9YF37-38, 9YF40-46, 9YF48, 9YF50-53, 9YF55-68, 9YF70-71, 9YF73, 9YF74-86, 9YF90-95, 9YF97, 9YF99-105, 9YF107-108, 9YF111-112, 9YF114, 9YF116-135, 9YF137, 9YF139)

Parts Needed

2 - 2D7689 Clamp - Hose

2 - 7D7233 Clip

1 - 6E5444 Valve Group

4 - 3J1907 Seal - O- Ring

2 - 9J3893 Housing - Seal

2 - 2K8199 Seal - O- Ring

1 - 3K0360 Seal - O- Ring

11 - 5K9090 Seal - O- Ring

1 - 2M9780 Seal - O- Ring

3 - 7M8485 Seal - O -Ring

6 - 3S7252 Sleeve

491 - 8S9355 Hose - Hydraulic

12 - 6V8397 Seal - O- Ring

4 - 6V8398 Seal - O- Ring

2 - 6V8635 Connector

1 - 6V8714 Connector

2 - 6V8724 Elbow

1 - 6V8781 Tee - Face Seat

1 - 6V8936 Reducer Assembly

1 - 6V8984 Elbow - 90 Degree

2 - 6V8998 Union - Face

3 - 6V9172 Nut - Bulkhead

1 - 6V9829 Cap Assembly

1 - 6V9836 Tee - Swivel

1 - 6V9844 Tee - Swivel

1 - 6V9850 Elbow - Swivel

1 - 6V9854 Elbow - Swivel

5 - 6V9957 Coupling Assembly

1 - 6V9958 Coupling Assembly

1 - 9X8259 Washer

1 - 1180018 Valve Group

1 - 1195988 Valve Group

1 - 1196220 Elbow - 90 degree

1 - 1197268 Hose Assembly

1 - 1197275 Tube Assembly

1 - 1197276 Block

2 - 1350349 Tube Assembly

1 - 1352755 Tube Assembly

1 - 1353301 Tube Assembly

1 - 1353302 Tube Assembly

1 - 1353303 Tube Assembly

Action Required

See attached Rework Procedure

Service Claim Allowances

NOTE: This is a 10-hour job.

Parts Disposition

Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.

NOTE: A 1180018 Valve Group should be ordered only for machines with serial numbers 9YF6-118.

Attach.

(1-Rework Procedure)

Rework Procedure

NOTE: A 1180018 Valve Group should be ordered only for machines with serial numbers 9YF6-118.

1. Install a vacuum transducer in the hydraulic tank breather port or drain the oil from the tank. Make up the required hose assemblies.

2. Remove the original 6E3078 Selector Valve Group near the center of the machine and all lines connected to it. Install the 1195988 Selector Valve Group in its place and reinstall the tee on top and the drain lines connected to it. See Illustration 1.

3. Remove check valve, fitting, tee and all tube assemblies and fittings connected to the tee on the left end of the pilot relief valve block.

4. Remove the plugs from the three remaining ports in the 1195988 Valve.

5. Install the tube assemblies, tees, adapters, reducer assembly, check valve group, elbow and seals as shown in Illustration 1.

6. Remove the pilot valve return lines, fittings and tube assembly completely from the pilot valve to the tank. remove the 8X1537 Block and install the new 1197276 Return Line Block. See Illustrations 2 - 5.

7. Enlarge the holes through the support plates for the drain lines and tube to 40 mm diameter. See Illustrations 2, 3 and 5.

8. Install the new bulkhead fittings in the 40 mm diameter holes and install the lines, tube assembly, tee, connector and fittings. Use the 6V9829 Cap Assembly to block the extra opening in the tee. See Illustrations 2, 3, 4, and 5.

9. Disconnect the pilot valve links from the valve stems and remove the support bolts from the pilot valve allowing it to drop down. See Illustration 5.

10. Remove the top stem seal covers and seals from the pilot valve. Install the new 1350349 Seals in the new 9J3893 Covers using quick cure primer and locktite to secure the seals. Using new 2K8199 Seals, carefully install the covers and seals over the stems.

11. Bolt the pilot valve in place and reconnect the linkage.

12. On machine serial numbers from 9YF6-118, replace the pilot system relief valve with the new 1180018 Valve Group.

Illustration 1