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The following excerpt from the AC B-Series Service Manual was originally for the B-112. but applies to all models with the Variable Speed Pulley drive system called a "Vari-Drive."   

NOTE:  The linked Figure 3 is quite large, even when compressed, and will print as a full page.  Be patient if you click on the hyperlinks....


The variable speed mechanism is adjusted at the factory under ''no load'' conditions. In most instances, this adjustment should provide satisfactory operation. If, however, under load or after the "break-in" period, erratic or improper operation is noted, follow the procedures outlined below to make necessary adjustments.

NOTE: All adjustments require the variable speed lever to be placed in the "High'' or the ''Low'' position. Carefully observe which position the variable speed lever should be placed in before making each adjustment. DO NOT ATTEMPT TO MOVE VARIABLE SPEED LEVER WHEN ENGINE IS NOT RUNNING OR WHEN CLUTCH PEDAL IS DEPRESSED.


1. Check bolt and locknut holding arm assembly to rocker arm. (See No. 1) (This adjustment to be made in ''High" speed position.)

2. Check for proper clearance on front belt guard. (See No. 2) (This adjustment to be made in "High'' speed position.)

3. Check for proper clearance of idler pulley belt stop. (See No. 3) (This adjustment to be made in "Low" speed position.)

4. Check for proper clearance between the nuts on clutch rod and the set collar. (See No. 4) (This adjustment to be made in the "Low'' speed position.)

5. With variable speed lever in the ''Low" speed position, the belt in the large, rear pulley should be approximately 1/8'' below the top of pulley. (See No. 5)

6. Check brake adjustment. (See No. 6). (This adjustment to be made in "Low'' speed position.)


1. Do not attempt to move variable speed lever when tractor engine is not running or when clutch pedal is depressed.

2. Insure that parking brake is fully disengaged before placing tractor in motion.

3. Occasionally check and remove foreign objects and debris from variable speed belt and pulleys.


1. To obtain the most desirable results with various attachments on the Sovereign Tractor, it is recommended the tractor engine be operated at 3/4 to full throttle setting.

2. When operating attachments such as the 10" Plow, Spring Tooth Harrow or Cultivator, which place a heavy draw-bar load on the tractor, it is preferable to operate tractor in I or II speed rather than III speed, low range.


If belt slippage is noted, check the following:

1. Check to insure the parking brake is fully disengaged.

2. Check No. 4 under Assembly Adjustments.

3. Check No. 5 under Assembly Adjustments.

4. On early production models the spring is normally in the top hole. If less spring tension is desired, move spring to next lowest hole of pivot lever assembly. Less tension can be used when mowing on level terrain and if clutch pedal is found to be uncomfortably hard for the operator to depress. (See Fig. 3) Greater belt tension is necessary to prevent variable speed belt from slipping when tractor and attachment are under heavy load. A slight chattering of the variable speed belt on the pulleys will be noticeable until the belt loses its stickiness and becomes smooth.

On later production models no further spring adjustment is necessary.


If sliding pulley halves stick, lubricate bushing on which pulley rides lightly with a few drops of oil. Excessive lubrication will tend to collect dirt and dust and tend to hamper operation. Also lubricate all clutch and brake lever pivot points and all places where pull rods or links join levers.

[Source:  Service Manual, B Series Tractors, Allis Chalmers Lawn & Garden Equipment, Part No. 9003453, February, 1976.]




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