PSP FOR INSTALLING NEW BRAKE PISTON SEALS ON CERTAIN 950F, 966F AND 970F WHEEL LOADERS - COSA LETTER NO. 4 - PS0781 - MAI LED COSA - REVISED 02/95
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 AVSpare product analyst.
HEBE1423-02 AUGUST 23, 1994 (Revised FEBRUARY 1995) COSA LETTER No. 4 PRODUCT SUPPORT PROGRAM FOR INSTALLING NEW BRAKE PISTON SEALS ON CERTAIN 950F, 966F AND 970F WHEEL LOADERS 4250 PS0781 NOTE: This program can only be administrated after a failure occurs. The decision whether to apply the program is made by the dealer. When reporting the repair, use "PS0781" as the Part Number, "7755" as the Group Number Causing Failure, and "96" as the Warranty Claim Description Code. NOTE: Apply the program PS0778 of August 24, 1994 - COSA Letter No. 5 at the same time only if necessary. NOTE: This Revised Service Letter replaces the August 23, 1994 Service Letter revised December 1994. Changes have been made to Rework Procedure (Annex B, item 2).
August 31, 1995
On certain 950F, 966F, and 970F Wheel Loaders axle oil can transfer to the brake system and overfill the brake oil reservoir. See procedure in Annex A for problem identification.
Model Identification Number 950F 6YG1-up 5PJ1-up 6LJ1-up 950FII 8TK1-628 5SL1-29 966F 3XJ1-up 6FJ1-up 966FII 9YJ1-737 970F 9JK1-259
PER AXLE ***** For 950F and 950FII ***** 2 - 1173270 Seal As 2 - 8R9207 Seal 1 - 1U8846 Gasket Maker ***** For 966F, 966FII and 970F ***** 2 - 1173271 Seal As 2 - 8R9809 Seal 1 - 1U8846 Gasket Maker
***** Parts Stock ***** Remove all 8R8811 and 8R9810 Seal Assemblies from parts stock. ***** Affected Product ***** Install new brake piston seals. See rework procedure in Annex B.
Service Claim Allowances
***** Parts Stock ***** Submit one claim for all 8R8811 and 8R9810 Seal Assemblies removed from parts stock. ***** Affected Product ***** Product AVSpare Dealer Suggested Customer Suggested smu/age Parts Labor Hrs Parts Labor Hrs Parts Labor Hrs whichever (D/N) (Cost) (C/L) (Sell) comes first 0-6000 100% * 0 0 0 0 0-48 mo. * AVSpare will participate as follows: - 10 labor hours to repair the front axle, - 12 labor hours to repair the rear axle.
Handle the parts in accordance with your Warranty Bulletin on warranty parts handling. Attachment 1-Problem Identification Procedure 1-Rework Procedure ANNEX A
IDENTIFIAVSION PROCEDURE Axle oil transfer to brake system must be clearly identified before repair. This transfer is usually caused by a twisted backup ring in the two piece seal assembly. The backup ring can become twisted during the installation process if the inside diameter of the ring is too small, or if the piston is not pressed evenly into the bore of the axle center housing. The oil transfer can occur on one or both axles of a machine. To identify which axle is transferring oil, follow the procedure below: 1. Adjust the oil level in the brake oil reservoirs to 30 mm from the top edge of the can. On machines equipped with only one single brake oil reservoir (950FII, 966FII and 970F) it may be necessary to temporarily install a second 9U4540 Reservoir and connect each reservoir separately to a corresponding brake master cylinder. 2. Watch for any change in the oil level in the reservoirs over a period of one month or 250 operation hours. The oil level must always be checked in the same conditions of oil temperature. The best way is to check the oil level when oil is cold, i.e. in the morning prior to starting the machine. This will eliminate the impact of thermal expansion. 3. An oil level increase over the period given above of 10 mm or more in the previously used larger steel brake oil reservoir (8R0859), or of 20 mm or more in the current smaller plastic reservoir (9U4540), will be sufficient evidence that axle oil is transferring into the brake system. NOTE: This Support Program covers only axle oil transfer to brake system. If the oil level in the reservoir(s) is going down, it means the brake oil is leaking somewhere. Check for any leak in the lines from the reservoir(s) to the master cylinders and from the master cylinders to the axles. Such a leak might also be due to a damaged brake piston seal. PS0781 does not cover the repair for such defects. ANNEX B
The disassembly and assembly procedure is described in the Service Manual. Additional procedures for the installation of the new brake piston seals are listed below. NOTE: The procedure listed below is for one brake. Each axle has two sets of brakes, one for each wheel, so the procedure is to be repeated for each wheel. 1. After disassembling the axle at the point where the brake can be accessed, remove the reaction plate, 3 springs, the disc, and the piston from the brake housing. Save all these components for reuse. 2. Remove the brake piston seals. Thoroughly clean the seal grooves in the center housing and the mating parts. Check seal grooves in center housing and pistons for dimensions, porosities, burrs and any machining chatter marks. Dimensions must be as follows: 950F 966F/970F --------------- --------------- 2PC seal groove OD 381.00 +/- 0.10 *417.50 +/- 0.10 1PC seal groove OD 364.00 +/- 0.10 401.50 +/- 0.10 large piston OD 371.50 +/- 0.05 408.00 +/- 0.05 small piston OD 351.70 +/- 0.05 389.20 +/- 0.05 NOTE: Dimensional non conformance to above requirements, specially larger seal groove OD and smaller piston OD will require replacing the center housing or the piston. Chatter marks on the bottom face of the seal grooves that can be felt when going over with a pencil or similar pointed object will require replacing the axle center housing. Make a separate claim to justify replacement of a center housing or a piston. 3. Install new seals into the brake housing, with the following precautions. NOTE: Do not leave the seal assembly package open. NOTE: Before installing the seals into the center housing, check the fit of the backup ring. If the backup ring is too tight, it will not slide loosely over the piston like it should. In this case it should be discarded and another backup ring used. NOTE: Install the seals into the center housing dry, and then lightly coat the entire assembly with petroleum jelly. See the illustration for the correct installation of the seal and backup ring. 4. Turn the center housing with the piston bore facing up, and install the piston evenly into the bore. Be sure to install the piston with a steady, even stroke. Misalignment and/or a jerky motion (such as pounding) can cause the seal to become damaged. For best results, use three screw-push blocks to press the piston into the bore evenly. 5. Install the friction disc over the dowel pins in the brake housing. 6. Install the 3 springs over the dowel pins in the brake housing. 7. Install the reaction plate into the brake housing. 8. Assemble the axle following the procedure in the Service Manual. NOTE: Seal the axle housing with 1U8846 Gasket Maker. 9. In order to verify the brake pistons are actuating and retracting correctly, attach an air nozzle to the brake oil feed holes after the axle has been completely assembled. Remove the inspection port plug and allow a short burst of compressed air to flow into the assembly. The piston must retract at least 0.5 mm. 10. Install the necessary fittings on the brake feed holes to allow an air pressure gauge rated at 0 to 2000 kPa (0 to 290 psi) to be used. Pressurize the brake assembly with approximately 690 kPa (100 psi) of air pressure. Turn off the air pressure. The pressure drop on the gauge should not exceed 100 kPa (15 psi) in one minute; if there is a greater drop than this, the seal and/or backup ring may be damaged and the axle assembly will need to be disassembled. 11. Fill the axle with oil as specified in the Operation and Maintenance Manual. BRAKE SEAL DAMAGE SEQUENCE RESULTING FROM INCORRECTLY INSTALLED BACKUP RING INSTALLATION SEQUENCE OF CORRECTLY ASSEMBLED SEAL NOTE: Chamfer-side of ring is facing the seal