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 Caterpillar

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.

***** 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