Field Power Hop on MFWD Tractors
Date: MARCH, 1994
NOTE: This bulletin replaces F-011-X dated May 1991.
COMPLAINT OR SYMPTOM:
Tractor jumps or bounces during field operation and creates a very uncomfortable ride and loss of traction. Operator may need to shift to a lower gear, reduce throttle or raise implement to continue operation.
Under certain soil conditions or operating conditions, tractor may experience "power hop." Some of those conditions are:
- Dry to very dry soil; loose soil over hard pan
- Pull-type implements in heavy draft conditions
- Implement not adjusted properly
- Improper drawbar position
To control "power hop," without changing implement depth or tractor ground speed, it is necessary to stiffen front tires by increasing tire inflation and/or adding liquid weight, and soften rear tires by reducing inflation and/or removing liquid weight. Generally, the tractor must be equipped with duals or triples on the rear axle.
Use the following procedures:
- Check for proper ballast as recommended in the operator's manual; see ballasting recommendations for tractor weight split, total working weight and wheel slip.
- Check for proper adjustment of implement hitch and tractor drawbar position. (See appropriate manuals to adjust implement or drawbar position.)
IMPORTANT: Adjust inflation in front and rear tires at same time. Check tire inflation, when cold, at least once per week.
Adjust front and rear tire inflation as follows:
- Increase front tire inflation to 28 psi for 2 "star" tires and 34 psi for 3 "star" tires. Set inflation pressure in all rear tires to the minimum value to carry the axle load. (See Tables.)
- If "power hop" is still present, increase front tire inflation to 30 psi for 2 "star" tires and 36 psi for 3 "star" tires. Leave rear tire inflation as set in 3A.
IMPORTANT: Never operate radial rear tractor tires with inflation less than 12 psi singles, or 6 psi duals/triples.
- If "power hop" is still present after following recommended tire inflation guidelines, install liquid weight in front tires to 75% fill (valve-stem level). Inflate front tires to 30 psi for 2 "star" tires and 36 psi for 3 "star" tires. Remove front cast weight, if needed to stay within ballast recommendation and/or tire carrying capacity. Leave rear tire inflation as set previously in Step 3A.
- If "power hop" is still present and the above recommendations have been implemented, it is most likely due to liquid weight in the rear tires. Select either 5A or 5B below. 5A is preferred because it is more effective and does not place additional restrictions on use of loaders and other front mounted equipment.
- If there is liquid weight in rear tires, reduce liquid weight in rear tires to 38% or less on all rear tires (4 o'clock valve position). Inflate rear tires to the minimum value to carry the axle load. Note: Cast rear weights are preferred over liquid weight.
- Increase liquid weight in front tires to 90% fill and inflate front tires to 30 psi for 2 "star" tires and 36 psi for 3 "star" tires. Leave rear inflation as set previously in 5A.
IMPORTANT: To operate the tractor with a loader, heavy spray tanks, front mounted implements, or other attachments which could cause high front tire loading, front liquid weight must be limited to 75% fill.
IMPORTANT: Tire inflation pressures and ballasting may need to be changed when operating conditions change. For example, when tractor is being used with hitch-mounted implements, rear tire inflation will need to be increased from the above recommended levels for pull-types implements.