I assume you mean the hex shaft. There are no illustrations or written instruction for the replacement of the hex shaft. I am including the illustrated instructions for replacing the friction wheel. These will provide you with teardown instructions to the hex shaft (see images below). I am also including a link to the ownersâ€™ manual for this model number, please click here;
If you require further assistance please resubmit your question with more details. I will be looking forward to helping you again in the near future.