I have a riding lawn tractor "Murray Model 42591X8B", 17 horses. During the last cut, the rear transaxle was lacked and stopped the engine. I replaced the motion drive belt but it didn't solve the problem. I still can start the engine but as soon as I release the pedal the engine will die (rear wheel still lacked). Can someone help me with this problem? Or tell me where can I buy the new transaxle for this tractor model? Thank you.

Try your briggs and stratton dealer, briggs now owns murray. Or you maybe able to find a used transaxle.

I had a similar thing happen to me. I opened up the transaxle to find the problem. (A _very_ messy job! And definitely not for the mechanically challenged!) It turned out to be a bearing retaining bolt in the transaxle that had broken, and the bolt head had gotten stuck in one of the gear clusters. The remaining retaining bolt was loose. I was able to replace the broken bolt w/o problem, but finding the correct torque spec for the bolts was difficult, even w/ a factory repair manual. I am very skilled mechanically, and I had troubles getting the differential back together so that the gears didn't bind. It took several iterations of assemble/disassemble to get the gear indexing right. So, anyone that is of 'better than average' mechanical skill, or less, should not attempt this repair on their own. I recommend taking it to your local lawn & garden/small engine repair shop to have it fixed. If you do decide to take on the challenge of doing the repair, I strongly suggest the following:
Buy a repair manual for the transaxle!! (Read & understand it! Ahead of time.). Be certain it matches the model of transaxle that you have. Do your homework before starting this project;
Get _Lots_ of rags and a place that you won't mind getting _covered_ in hypoid gear oil, (_really_ smelly stuff, gets everywhere);
Take _lots_ of pictures of the disassembly, especially of the differential gear indexing & spacing, and also pix of the position of any control shaft brackets _before_ opening the case, (e.g.:shift or brake brackets);
Use permatex gray/silver RTV for sealing the transaxle case for reassembly, (Careful not to use too much in certain places so as not to clog internal oil passages with squeeze-out);
Make ABSOLUTELY SURE that your work environment is CLEAN & that you get NO grit/dirt into the gears/transaxle at any time! Clean up the case _before_ you try to open it up. No grass residue, no dirt, Nothing!;
Be _careful_ separating the case halves so that you don't ruin the mating surfaces & give yourself a chronic oil leak. It may take quite a bit of persuasion to get the case apart. Be gentle.;
Check all the linkages/control shafts for binding _before_ reinstalling the transaxle into the tractor.