Older briggs and stratton MTD problem shifting between drive and rever

Older briggs and stratton MTD problem shifting between drive and rever

Hi, i just bought a riding mower i think it was made somewhere around 1990. i have completly clean the carburetor and bought a new battery the engine works good now but i have a problem shifting gear in the middle only got to go in reverse once and in drive and now its stuck there. Here's the model #142-849H515, i removed the cover in the middle and the lever to the transmission/transaxle is connected.