Usage:
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 "PS8051" 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: Some of the Affected Product fall into more than one group. All applicable portions of this Program are to be completed at the same time for the wheel being reworked. Although it is not required, it is recommended that both wheels be reworked at the same time.
NOTE: This Revised Service Letter replaces the February 10, 1994 (Revised March 1994) Service Letter. A change has been made to the Termination Date.
Termination Date
February 29, 1996Problem
The rear wheels and associated parts can be updated to improve their service life on certain 793 and 793B Trucks.
Group 1 - The rear wheel bearings may rotate on the spindle causing wear to the spindle and to mating parts.
Group 2 - The bearing preload may be incorrectly set on the first and/or on the second reduction planetaries.
Group 3 - The axle orbiting may occur on some applications causing AETA housing wear.
Affected Product
Model & Identification Number
Group 1 - Bearing Retention
793 (3SJ1-56)
793B (1HL1-43)
Group 2
First Reduction
793 (3SJ1-56)
793B (1HL1-56)
Second Reduction
793 ( 3SJ1-56)
793B (1HL1-58)
Group 3 - Axle Orbiting
793 ( 3SJ1-56)
793B (1HL1-58)
Parts Needed
NOTE: Quantities listed are for one wheel. It is suggested that both wheels be reworked at the same time.
Group 1
Group 2
First Reduction Parts
NOTE: If 1st reduction planetary has been previously rebuilt (3SJ1-56 and 1HL1-65) this section is not required.
Second Reduction Parts
NOTE: If 2nd reduction planetary has been previously rebuilt (3SJ1-56 and 1HL1-58) this section is not required.
- 4 - 7I5534 Shaft (3SJ1-43 and 1HL1-15 only)
- 8 - 8E7926 Cone/Bearing
- 8 - 8E7927 Cup/Bearing
- 2 - 8X0566 Shim Pack
- 8 - 8E7926 Cone/Bearing
Group 3 - Axle Orbiting
Action Required
See the attached procedure.
Service Claim Allowances
Parts Disposition
Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.
Attach.
- (1-Rework Procedure)
Rework Procedure
NOTE: All quantities are for one wheel. It is suggested that both wheels be done at the same time but is not required.
NOTE: Refer to Guideline For Reusable Parts And Salvage Operations SEBF8187 "Standardized Parts Marking Procedures" before beginning this rework procedure.
Group 1 Rear Wheel Bearings
NOTE: Refer to the December 6, 1993 Service Magazine article "Procedure to Adjust Rear Wheel Bearings Has Been Changed."
1. If necessary, due to wear on the outer bearing journal of the spindle, machine spindles for undersize bearings. The correct diameter for 793 Trucks is 409.545 ± 0.038 mm (16.1238 ± .0015").
2. Machine grooves in the spindle for the dowels. Groove dimensions and locations are shown in Illustrations 1 and 2.
Illustration 1
Illustration 2
3. Use a 106-9612 Retaining Pin in both inner and outer grooves in the spindle.
4. Use the following wheel bearing cup and cone part numbers when rebuilding the wheel:
5. If cone part numbers other than the above are to be used, modify the slots in the inner and outer bearing cones as shown in Illustration 3.
Illustration 3 - Modify The slots In The Inner And Outer Bearing Cones
Illustration 4
Group 2 - Bearing Preload
NOTE: Refer to the December 6, 1993 Service Magazine article "New Procedure to Adjust Final Drive Planet Bearings"
1. Disassemble the 1st and 2nd reduction planetaries and remove all planetary bearings. (1st Reduction = Inner Planetary, 2nd Reduction = Outer Planetary)
2. First reduction planetaries that are covered by this program are from 3SJ1-56 and 1HL1-65.
The first reduction 8X8412 Planet Shaft can be pressed out and must be machined to the small O.D. dimensions of the 7I5540 Planet Shaft or replaced by the 7I5540 Shaft. See the Service Magazine article. The planet shaft, first reduction, must have the small O.D. equal to 77.839 ± 0.012 mm to achieve the correct bearing preload with this procedure.
Small O.D. = 77.839 ± 0.012 mm (The small O.D. is the only dimensional difference between the 8X8412 and 7I5540 Planet Shaft.
The 8X8412 Planet Shaft was used in 3SJ1-43 and 1HL1-14. The 7I5540 Planet Shaft, which has a looser fit than the 8X8412 Shaft, was effective with 3SJ44-up and 1HL15-up. It can be measured and reused if it is within the the tolerance specified above.
3. Use the following procedure to rebuild the first reduction planetary.
NOTE: This procedure differs from the Service Manual Power Train Spec. & D & A.
NOTE: When replacing the bearing cups in the planetary gears, it is recommended the cups be pressed together to make sure they are completely seated and that there is no gap between the cup and 8W3074 Ring.
1) Assemble the planet gear, ring and two new bearing assemblies. Apply some oil to the bearings and assemble these parts into the inner carrier.
2) Install 1U5812 Plate (test), 1U5813 Shaft (test) and two bolts.
3) Tighten retainer bolts to 40 ± 5 N·m (30 ± 4 lb. ft.) and rotate the gear two complete revolutions. (Rotating the gear the designated number of turns is critical to bearing seating.) Loosen the bolts. Tighten the bolts to 20 ± 5 N·m and rotate the gear 2 revolutions.
4) Tighten the bolts to 34 ± 3 N·m and rotate gear 2 revolutions.
5) Repeat Step 4 as required until no bolt rotation is observed while tightening the bolts.
6) Use a depth micrometer and measure gap between 1U5812 Test Retainer Plate and the 1U5813 Test Planet Shaft. Select Shims from the 8X6910 Shim-Pack equal to the gap plus 0.323 + 0.000 - 0.030 mm (0.0127 + 0.000 - 0.0012").
7) Remove the 1U5812 Plate (test) and 1U5813 Shaft (test).
8) Be sure the 8X8412 Shaft (machined to the 7I5540 dimensions or if necessary replaced by 7I5540 Shaft) and the 1U5813 Shaft are the exact same length from the shoulder that contacts the bearing to the end of the shaft where the shims are placed. If there is a difference in lengths, add or subtract the correct amount of shims from the amount already determined in Step 4.
EXAMPLE: 8X8412 Shaft (7I5540 New Shaft) is 0.05 mm (0.002") shorter than the 1U5813 Shaft (test). Add 0.05 mm (0.002") to the thickness 0f shims determined in Step 4.
9) Using a press, install 8X8412 Shaft (7I5540) through carrier and bearings. Use a maximum force of 40 Tons to install the shaft.
10) Install shims (measured in Steps 6 and 8) and 8W3088 Retainer Plate. Install bolts with 4C9506 or 4C9507 Retaining Compound. Tighten them to a torque of 135 ± 15 N·m (100 ± 11 lb ft).
11) If no gap exists between retainer plate and carrier, press shaft into the bore until there is a slight gap.
12) Tighten retainer plate bolts again to 135 ± 15 N·m (100 ± 11 lb ft). Using a mild steel drift, drive retainer plate towards carrier to close the gap. Be sure gear rotates with slight resistance when rotated by hand.
13) Tighten the retainer bolts to the correct torque again 135 ± 15 N·m (100 ± 11 lb ft).
4. The second reduction 8X0565 Planet Shaft will have to be lanced (burned) out of the carriers in 3SJ1-43 and 1HL1-14 to avoid damage to the 8X0603 Carrier Bores. The 7I5534 Planet Shaft (looser fit than 8X0565 Shaft) was effective with 3SJ44-up and 1HL15-up. It can be measured and reused if within the tolerance specified.
- Overall Length = 222.8 ± 0.5 mm
- Length to Shoulder = 181.82 ± 0.05 mm
- Large O.D. = 131.012 = ± 0.012 mm
- Small O.D. = 101.651 ± 0.012 mm
- Length to Shoulder = 181.82 ± 0.05 mm
Second reduction planetaries covered by this program are 3SJ1-56 and 1HL1-58.
5. Use the following procedure to rebuild the second reduction planetary.
NOTE: This procedure differs from the Service Manual Power Train Spec. & D & A
NOTE: When replacing the bearing cups in the planetary gears, it is recommended the cups be pressed together to make sure they are completely seated and that there is no gap between the cup and 8W3074 Ring.
1) Assemble the gear ring and two new bearing assemblies. Apply some oil to the bearings and assemble these parts into the outer carrier.
2) Install 4C9923 Plate (test), 4C9924 Shaft (test) and two bolts.
3) Tighten retainer bolts to 40 ± 5 N·m (30 ± 4 lb ft) and rotate gear two revolutions. (Rotating the gear the designated number of turns is critical to bearing seating.) Loosen the bolts, then tighten the bolts 20 ± 5 N·m (15 ± 4 lb ft) and rotate the gear two complete revolutions.
4) Tighten the bolts to a torque of 34 ± 3 N·m (25 ± 4 lb ft) and rotate gear 2 complete revolutions.
5) Repeat Step 4 until no bolt rotation is observed at (re)tightening.
6) Use a depth micrometer and measure gap between 4C9923 Test Retainer Plate and the 4C9924 Test Planet Shaft. Select shims from the 8X0566 Shim Pack equal to the gap plus 0.356 + 0.000 - 0.030 mm (0.0140 + 0.000 - 0.0012").
7) Remove the 4C9923 Plate (test) and 4C9924 Shaft (test).
8) Be sure the 7I5534 Planet Shaft and the 4C9924 Test Shaft are the exact same length from the shoulder that contacts the bearing to the end of the shaft where the shims are placed. If there is a difference in lengths, add or subtract the correct amount of shims from the amount already determined in Step 4
Example: 7I5534 Shaft (production) is 0.05 mm (0.002") shorter than the 4C9924 Shaft (test). Add 0.05 mm (0.002") to the thickness of shims determined in Step 4.
9) Using a press, install 7I5534 Planet Shaft through carrier and bearings. Use a maximum force of 40 tons to install shaft.
10) Install shims (measured in Steps 6 and 8) and 8X0567 Retainer Plate. Install bolts with 4C9506 or 4C9507 Retaining Compound. Tighten them to a torque of 255 ± 15 N·m (190 ± 11 lb ft).
11) If no gap exists between 8X0567 Retainer Plate and 8X0603 Carrier, press shaft into the bore until there is a slight gap.
12) Tighten the bolts again to 255 ± 15 N·m (190 ± 11 lb ft). Using a mild steel drift, drive retainer plate towards carrier to close the gap. Be sure gear rotates with slight resistance when rotated by hand.
13) Tighten the retainer bolts again to a torque of 255 ± 15 N·m (190 ± 11 lb ft).
Group 3 - Axle Orbiting May Occur Causing AETA Housing Wear
1. Effective with 1HL58, a guide and bearing arrangement was installed in the final drive to eliminate AETA housing wear. Remove the current 6G8580 Guide from the inboard end of the 8X1067 Axle Housing on 3SJ1-56 and 1HL1-58 and replace with the following parts:
2. Check 1T0284 Socket Head Bolt torque on the 8W8743 Clamp (7I5093, 3 Lobe Clamp on 1HL49-up) on the 8X0496 (RH) and 8X0497 (LH) Axle Shaft in the 8X0250 Axle And Mounting Group. If the torque is below 30 ± 4 N·m (22 ± 3 lb ft), remove bolt and do the following: