1995/05/29 Caterpillar

Challenger 65, 65B (7YC),
Challenger 65C (2ZJ),
Challenger 70C (2YL),
Challenger 75 (4CJ),
Challenger 75C (4KK),
Challenger 85C (9TK) Agricultural Tractors

Reference: Service Magazine; November 28, 1994; Page 5; "New Front Axle Shims Make Adjustment Easier".

Challenger Agricultural Tractors can experience guideblock scuffing. Guideblock scuffing can result from four situations:

1. Break-In Conditions If belts are broken-in in very wet conditions and/or dry but clean (lacking dust) conditions, the rubber will scuff as it "breaks in" to the driver and idlers. Break-In scuffing can last up to 400 hours. The guideblocks will appear moderately to severely worn on the surface. Some material may be removed. Although scuffing affects the appearance early, the overall life of the guideblock should not be affected. Unless scuffing is associated with high guideblock temperatures, no action should be needed. The guideblock surface will eventually "heal over" and round at the edges of the damaged area. No reshimming should be necessary.

If scuffing continues past 400 hours or is associated with high temperatures, one of the following conditions may be present.

2. Factory Misalignment Occasionally, new machines will not be aligned properly from the factory. Follow the alignment procedure described later in this article.

3. Bent Front Axle If belt alignment was initially correct from the factory, but suddenly becomes out of alignment and exhibits severe guideblock scuffing to the outside of one or both belts, a bent front axle may be the cause. The misalignment can also cause high temperatures of guideblock surfaces and possible guideblock loss. Scuffing caused by a bent front axle will always be to the outside. Scuffing may be on guideblocks of only one belt or on the guideblocks of both belts.

To verify an axle is bent, remove both front idlers and spindles. Measure between the front axle spindle mounting faces. A difference significantly greater than 0.5 mm (.02 in) indicates a bent front axle. Replace the axle. See Illustration 1.

Illustration 1. Measure axle width between outer faces at these locations (B).

The following measures can be taken to reduce the likelihood of front axle bending.

* Use as few front counterweights (if equipped) as possible. Remove the counterweights when not needed.

* Maintain midwheel air bag pressure at 551-620 kPa (80-90 psi) to allow the midwheels to take more vertical loading. Be sure that the machine's center of gravity is at or behind the midbeam.

* Be sure that debris guards are installed inside the undercarriage. Avoid conditions that load up the undercarriage components with mud and debris. If a machine becomes stuck in the mud, use caution when retrieving it. Do not pull machine from the front. Instead, unload the undercarriage of as much debris as possible and slowly pull the machine from the rear. Avoid "snow plowing" mud with the undercarriage and front axle.

4. Replacing Worn or Damaged Belts If a belt is changed and exhibits scuffing while the previous belt was aligned correctly, the cause may be related to a belt characteristic referred to as "ply steer." "Ply steer belts" required substantially different shims on left and right sides of the machines. Belts manufactured after mid-1993 have been modified in construction to reduce the need for different shims. "Ply steer" belts are now serviced by "neutral steer" belts. When a "ply steer" belt is replaced by a "neutral steer" belt, reshimming is usually necessary. To ascertain whether a machine has "ply steer" or "neutral steer" belts, See chart E. See Chart D for the proper shims. When "neutral steer" belts are combined with a "ply steer" belt, use the "neutral steer" shim angle for the side with the "neutral steer" belt. Use the "ply steer angle" for the side with the "ply steer" belt.

Alignment Procedure

NOTE: The machine should not be operated for at least 5 hours prior to temperature measurement. Residual heat on the rubber surfaces could give erroneous temperature readings.

1. Drive the machine for 15 to 18 minutes at maximum speed on a paved, level surface. Make as few turns as possible. The undercarriage must be dry for proper results.

Illustration 2. Measure temperatures at these locations (A).

2. As quickly as possible, record the maximum temperature of the inboard and outboard idler sidewalls. See the illustration for the correct location for taking the temperatures. The temperatures should be measured within 2 minutes after stopping the machine. Scan the rubber sidewalls with an infrared thermometer in the idler portion not obscured by the belt. It is not necessary to scan the entire circumference of the idler to find the maximum temperature.

3. If the temperature difference between the inboard and outboard idlers is 22.1°C (40°F) or more, see Charts A and B below for the shimming requirements. If the temperature difference is less than 22.1°C (40°F) then alignment is generally not a problem. Operation of the tractor may continue with regular observation of the guideblocks.

NOTE: Charts A and B indicate how much the angle should be changed. These charts are a general guideline and are not absolute. Shimming requirements vary depending on the machine tolerances.

4. Determine the previous shim angle by removing the existing shim and determining the shim's angle using Chart C.

5. If shimming is required, the new shim angle can be determined by using the formula: New Angle = previous shim angle ± angle from Charts A and B. By using one or two shims shown in Chart C, increase or decrease the total shim angle by the amount indicated in Charts A and B.

EXAMPLE: A Challenger 75 has guideblock scuffing to the outside on the right belt. The temperature differential is 33.3° C (60° F). The machine is currently equipped with a 8R-3601 shim.

SOLUTION: Because the belt is on the right side and the outer idler is hottest, the shim angle should be increased by .33° as shown in Chart B. Because the machine is already equipped with an 8R-3601 Shim (0.275°), the total new angle will be : 0.275°+.33°=0.605°.

The new angle can be approximated by either of the following: Remove the 8R-3601 Shim and install a 111-1560 Shim (0.63°); or add a 4E-5059 Shim to the existing 8R-3601 Shim to get a new angle of .585°.