I have an operator's manual for an MTD Model Series 760-770 Lawn Tractor. This Manual seems to indicate two different part numbers for the spindles on a 46" deck. One spindle is a Double Pulley, part number 618-04134B. The other two spindles are single pulley, part number 618-0240A.
However 760-770 is a series number. So this does not necessarily match your machine. The first question is what year is your Lawn Tractor? Following is a discussion of MTD serial numbers from 1997 till now. Pre 1997 is a different discussion.
The second question is what is your actual Model Number?
Locating Your Model and Serial Numbers
The model and serial numbers are essential to find correct MTD® genuine factory replacement part numbers for your outdoor power equipment. Once you know these numbers, you can use either the illustrated parts look-up tool or the operator's manual download to easily search for the correct part numbers needed.
What should my model and serial number look like?
MTD's current (1997 and later) model and serial numbers are generally 11 characters in length. A character could be a number, dash or a letter. If 0 represented all numbers and/or dashes and X represented all letters, the model and serial numbers should appear as follows: 00XX000X000.
These are made of both letters and numbers, and typically look like this: 11AA111A111.