Occasionally you will need to make small adjustments to the height of your mower deck. This usually happens when grass cutting settings fall outside the range of motion that is allowed by the deck height lever within its factory settings.
There are a number of places to start looking when choosing to adjust the deck height on your tractor and you need to learn exactly how yours is regulated before you start adjusting things. Before you start wrenching on things always check to be sure some spring, bolt, or some other mechanical thing has not failed which is causing the mower deck to tilt or sag. Also checking the blades to see if they are bent can save you a lot of time and aggravation.
Typically the first height adjustment that I will check is the height of the wheels that are usually mounted on either side of the back corners of the mower deck, or there may even be one on each corner of the mower deck. These are typically forgotten when the mower is first set up and they are set too low to even do anything for you.
They allow the deck to ride smoothly across varying terrains and still give a relatively flat cut. If it is like many of the decks that I have worked on they have never been moved down from the highest position that they were in at the factory. These should roll a lot when you are at the lowest settings and touch ground only a little when you are at the highest levels even then they will touch only when you are running across uneven ground.
Adjusting these wheels usually calls for you to remove them from the deck using sockets and wrenches and moving them up or down one hole at a time followed by a test cut would be the smartest approach to resetting your mower deck cutting height.
Some tractors only have one height adjustment and it is done with a threaded linkage rod that is directly attached to the lifting lever handle underneath the fender where this lever is situated.
Some will have a clip or pin holding them onto another bolt that connects the whole affair to the tractor frame and removing this clip lets you pop the end of this rod out and then you can turn it clockwise or counterclockwise depending on whether you need the deck to go up or down.
These may be a matched set with one on each side of the mower. If this is the case making an adjustment to one side calls for the same exact adjustment on the other. Once you think the adjustments are where you need them it would be wise to fire up the tractor and make a test pass at a few different height settings to see the result of your adjustments. I would always start out cutting high and slowly lower the deck to where you would normally use it.
Most of the larger garden tractors will have trailing arms to support the deck like I mentioned above and will also include a set of leading arms in the front of the deck which will adjust the height of the front edge of your deck. Many are fixed at one setting and you can only raise or lower this end by moving the mounting pin up or down in one of the fixed holes that are drilled into a mounting plate on the tractor frame.
There are a few models where the front edge can be raised or lowered using one single centered adjusting rod with a set of locking nuts to prevent the vibrations from changing your deck height. These are really easy to work with because you can see the results of your adjustment as you are turning these nuts.
A very important thing to check out if your mower is cutting strange patterns in the grass would be to look and see if you simply have a bent blade. Depending on your model the blades can be fairly inexpensive and replacing them may improve the quality of your cutting since sharper blades do a more efficient job which in turn makes the job go faster as well. Many times I have found that the mower deck height is fine but the blades are bent or there is some tensioner spring broken or missing.
Last thing is if you are uncertain about how this adjustment is to be done you should be able to find the manual for almost any garden tractor on-line. Knowing the model number of the tractor and the cutting width always helps quite a bit. Worst case you can visit the store that sells that brand and ask for some advice on how to make these adjustments. If you feel that something major is wrong that could cause an unsafe situation like a broken pulley or worse, then it is wise to have a professional look at it before you proceed. There are some serious safety hazards with regard to any rotating equipment which contains sharp blades so it is better to be safe than sorry!