Hopefully, this is the correct info needed:
Mod# 13AM772G755 Engine # 0606082D68504 Trans # 618-04381 SN# 2B197Q1 1496 7 spd manual transmission
OK Bill.
Thank you they are the numbers we need & you will also be needing from now on.
Now you have told us your are looking at repairing mowers, it is teach a man fish time.
So get on line & go to parts tree or Jacks Small Engines.
There are other sites but I find these to be the best.
They both subscribe to a third party ( ARD ) they hosts all the parts diagrams for nearly everything.
Assuming you are at parts tree, in the model number section start typing in the model number ( the one that start with 13).
As you do that a drop down will appear to show variations and usually you will see your full number there so click on it.
That will bring up a page with folder icons down the left side, naming what section of the mower they have the diagram for.
Hint, Left click to bring up that diagram in a new tab which will make it easier to go back & forth because some parts are not where you think they should be.
Your broken spring ( from another post ) is a perfect example.
It is in the Drive Diagram ( I think ) either part # 22 or # 23.
If either of these is broken then the mower won't go.
22 helps control the rod # 2 which controls the rod # 27 down the bottom of the diagram.
Now from the "Transmission" diagram you will see the shift fork # 20
The rod pushes or pulls the fork which moved the dog # 16 into either one of the 2 crown wheels selecting either forward or reverse.
So if the rod can not move the fork you are not going anywhere
This is one possibility
The other is the broken spring is part # 23 back in the drive diagram.
That spring pulls against the idler pulley # 62 which tensions the drive belt.
So same story.
If that belt is loose, the pulleys don't turn and you are still going nowhere.
So easy check first, is the belt tight ?
If it feels a bit loose the start the mower using jumper leads so you can see the pulleys.
If the big one is not turning then you have found a problem. there might be others.
The drive on these tractors is called "Vari Drive" and it works by having 2 belts on either end of the same pulley
The middle of the pulley can move up or down so the effective diameter of the top & bottom changes which changes the speed.
It is exactly the same principle as a stepped pulley system used on lathes & pedistal drills except the pulleys change size rather than the belt moving form one pair to the other.
MTD put out a manual which is a free download called the "Must have manual of outdoor equipment" in 4 volumes which covers everything they made prior to 2000.
Your mower is in book 2
There is also a "professional Shop manual for 700 series tractors which also covers the vari drive but not as completely as the must have.
It is also a free download.
You will also need to know how to decode MTD model numbers as they make a lot of mowers under different brands
13= lawn tractor
A = how it got sold ( not important )
M = Engine handy to know
7 = frame size ( ie 700 series tractor )
7 = transmission (vari speed with 7 speed notches)
2 = styling number ( colour & shape of hood etc ) not important to you
G = deck type & size, very important ,42" side discharge.
775 = customer code , no idea but not important for repairs.
Getting back to your mower,
Note that the spring # 23 in the drive diagram has the letter B at one end.
Then the frame drawing also ha the letter B at a hole
This tells you that the spring # 23 goes from the tensioning arm # 53 to the frame at B.
Some times they lie a little as the diagram looks like the spring is on the end of the bolt that mounts the pulley.
All the ones I have seen the spring has it's own little hole in the arm, which get torn through by the spring so if that is your spring expect to replace the arm as well or at least weld it.