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 only be administered after a failure occurs. The decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS0602" as the Part Number and "7755" as the Group Number. Use "96" as the Warranty Claim Description Code and use " Z" as the SIMS Description Code.
NOTE: This Program does not allow for any labor to remove and install the belts and idlers. Since the idlers must be removed to install the drain plugs, it is recommended that the idlers be inspected while implementing the January 25, 1992 Service Letter - PI1186 and the January 26, 1992 Service Letter - PS3574.
NOTE: This Revised Service Letter replaces the March 29, 1992 Service Letter. Changes have been made to the Termination Date and Service Claim Allowances.
Termination Date
January 31, 1994Problem
The fatigue life of the 1R0868 Idler may not be as long as desired on certain Challenger 65 and Challenger 75 Tractors.
Fatigue failures can progress to the point of causing air loss and idler flats. Operation with an under inflated or flat idler can cause the track to come off and/or result in severe belt damage.
Fatigue failures can cause air loss by either of two mechanisms. The second is probably a progression of the first.
1. A ruptured internal sidewall allows separated or broken cords to chafe the tube.
2. An internal failure through the sidewall allows the tube to extrude into a hole through the sidewall, resulting in a pinch type tube failure. Cracks in the external sidewall will first be visible in the idler bead area, usually on the guide block side.
Affected Product
Model & Identification Number
Ch 65 (7YC1-2500)
Ch 75 (4CJ1-500)
Parts Needed
Action Required
The illustration shows the area of the idlers that will first experience a fatigue failure. Check the guide block side of the idlers. Look for slight diametral bulging of the three ridges molded into the sidewall near the bead area. Also, look for signs of sidewall bubbles near the bead area. It takes a good light and two repositioning of the tractor to make this inspection with the idlers in place. This fatigue type failure may occur before any air is lost from the tube.
Replace idlers showing signs of fatigue failure. At the same time, inspect the guide block sides of the idlers on the other side of the tractor for signs of possible fatigue failure. If such signs are present, replace the idlers showing the symptoms. This does not cover punctures, abuse, or failures due to under-inflation.
NOTE: Any time an inflated idler runs with a flat or substantially underinflated idler on the same side it is overloaded and should be seriously considered for replacement. Replacement may be necessary depending on its hours of service and the length of time operated while overloaded.
Service Claim Allowances
Parts Disposition
Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.