I have a 42 in riding mower and i need to know what could be causing it to mow grass uneven leaving a high streak in the middle of a cut?

jack the tractor (using a tractor jack) or remove the deck, measure the blade tips against each other where they meet in the center of the deck and see if they are the same tip to tip. Bearing wear, a bent deck or blade can make them cut at different heights in the center.

sounds like you have a lose blade ,pulley or belt.

Look under the mower deck. If you can't see well and work on it, you may have to remove the mower deck and flip it over on the ground. Grass and mud buildup in the decj could cause a blade to pinch grass, 'scalping' the lawn. Clean it all out. Dull blades cause cut grass to look torn and brown. Remove and sharpen. Bent blade will cause uneven cut. Replace it. Good luck! Please rate if you found this helpful, thanks!

Are your blades upside down? Mower deck level?Proper air pressure all 4 tires?Correct blades for the diameter of cut? Deck bent? Deck hangers bent?

Your forward speed may be too fast for the mower blades to cut every blade of grass. It may be new, but check the deck to see if there are any dents pushing the quill assemblies up making the deck cut uneven. Or it may have the wrong blades on it.
I have seen this problem in the past with a Gravely mower. The person was trying to cut grass to fast. He sold the unit and the new onwer did not noticed any the problems the old owner described.

I have seen dull blades, blades not installed right and an un-level deck cause that.

Hope this helps.

is blade need sharping and are you doing this when the grass is wet ore raining

check your front tire air pressures

yes its repairable & yes it can bend the spendle but most likely the blades is it one that does it or both blades or the center or the sides of deck is bent by stepping on the deck let me know if i can further help thanks wade

THE answer that FINALLY worked for me. Torque the bolt that holds on the blade to the recommended torque specified in your owners manual (for my Exmark this torque is 120 ft-lbs). When I first used the torque wrench, i was quite surprised by the amount of addional force I needed to apply to reach 120 ft-lbs Exmark blades have a round blade hole with a washer and therefore, relies only on friction provided by torquing bolt to the proper torque to prevent slippage so that the blade rotates at the same speed as the spindle. When slippage between the blade and spindle occurs, blade tip speed slows leaving uncut grass.
Note: this solution will NOT work for mowers with a blade and spindle design which uses a positive means (e.g., a star shaped hole on the blade) that assures the blade rotates at the same speed as the spindle with no slippage.