Have a old Sears Zero turn Model ZT 7000. when I moved levers forward the mower will violently jerk left or right and then even spin in circles. when I try to correct it it will throw the drive belt.

Question edited for clarity, full 'make model (what it is)'.
Question moved from Cars and Trucks.

Some ideas here

https://www.google.com/search?q=Husqvarna+rz46i+drive+slipping

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Zero turn mowers in general require the following.

1. PTO off.
2. Steering levers to neutral position.
3. Parking brake engaged.

A good habit to learn is; When a zero turn won't crank, cycle all the start engine interlocks. Move park lever off/on, steering levers out/in, PTO on/off.

And a simple basic electrical check is; With key in run position (engine not running), you should hear the electric clutch engage/disengage when PTO switch moved ON/OFF.

Whoever told you to use 5w30 oil was wrong! 20w50 is correct for the transmissions, as evidenced below:

http://www.searspartsdirect.com/partsdirect/part-model/craftsman-parts/craftsman-parts/Repair-Maintenance/Questions-Answers/ZT-7000-Transmission-Fluid-Type-10727772/Model-107277720/0247/1506000/355126?modelNumber=107277720

thank you for using managemylife.com. this zt 7000, model 107.277720, has a left and right hand transmission. both of these transmissions will use 20w50 motor oil. if there are no level markings on the oil reservoirs measure from the top of the oil port to the oil level and it should be 3/4 to 1.5 inches.
hopfully this will help get the transmissions serviced. if you have any further questions or inquiries, please don't hesitate to ask. thank you for using managemylife.com.

At the bottom of the lever there should be a pinch bolt with locking nut, this will just need tightening up to increase resistance on the lever.

sounds like a safety switch problem. but maybe you can help me i have the same model do you have a lot of jerking when you start off of turn with yours?

yes,on the bottem of the handles

First check both rear tyre pressures, if ok you need to adjust the rod that runs between the left lever and the hydrostatic drive on the left rear wheel so that the short lever on the hydrostatic drive travels further when push the drive lever forward. Regards Phil

Whirlpool split air-conditioning error code EA

Same problem. The drive belt pulley tensioner spring broke. Replaced and everything worked great.

I assumed you dropped the mower deck already to access the belts? Now access sears parts.com and enter that part number. They will give you a diagram of the belt routing (#1 Belt). You will have to loosen a few belt retainers and such to put the belt back on. if reinstalling the old belt - find the tensioner to take up some slack.