How do you change the transmission in a 20067 toro personal pace lawn mower

Sounds like either the gears on the wheels or ends of the trans shaft are bad, or the internals of the trans are bad. Are the parts actually new-new, or used and new to the machine, you didn't specify. What happens when you manually spin the pulley on the top of the trans in either direction?

Either the transmission is shot or the gears on the wheels that turn have been worn away;. They are plastic and do not last long nor take much abuse.

If ir starts and runs for only a few seconds it's a dirty carb/bad gas. Drain the fuel system and use FRESH gas; change out your fuel supply monthly to avoid "phase separation" issues. If it runs for several minutes and then dies it is possibly a sticking valve. Do a compression check cold and after it stalls to confirm. Hope this helps

Yes it is the transmission. A Mower shop will charge you about $225 to fix.. I order parts online and fixed mine for $90. Transmission consist of 3 gears which turns the rear wheels to self-propel.

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309

carburetor needs cleaning and rebuilding

got oil in it, or do you add oil. Left outside alot, fuel line clogged. Is the gas old. Check the blades and the exit portion of the clippings. Does it have a drive train for ease of moving. those can bog down a mower. good luck

You should post this question in the lawnmower section so the proper expert will see it..

Sounds like a piston ring or valve issue. If it is still under warranty, I'd think about a return.