Problems with the Brother sewing machine workhorses are almost invariably related to the needle or thread. The machines themselves give years of service. However, jammed and tangled thread, thread tension, repeatedly breaking thread and broken needles are all problems related to these machines and you can easily troubleshoot them.
Choose the correct sized thread and needle for the fabric in question. Re-thread the machine by passing the thread through the needle bar. Hold the thread with both hands and fully pass it through the hook.
Set the tension to basic thread tension, or less, because the upper thread tension could be too tight. Badly adjusted tension will pucker the fabric and could break the thread.
Make sure the spool of thread is installed correctly. Check the correct size case is being used for the size of spool. The thread should be winding clockwise when the spool is inserted in the shuttle case. The thread should be held towards the back of the spool. Holding the shuttle case with the thread slot facing you, drop the spool into the case, direct the thread to the slot and pull it around. You'll know when it's correct because the thread won't some out too quickly. You can adjust tension with the screws on the side of the case, too.
Check to make sure you are using the correct combination of needle size, thread size and fabric. Denim, for example, needs a size 16 needle and 40 to 50 heavy duty threads. The thread will break if this is wrong. Eventually, the needle will also break. Remember that heavy-duty threads are for the top stitch only. Use all-purpose in the shuttle.
Check the bobbin is threaded properly in the shuttle hook. Re-thread it if the lower thread keeps breaking.
Replace a bent or damaged needle to avoid breaking needles. Make sure the needle is correctly inserted, the flat side faces the back on Brother machines.
For tangled threads, remove the needle plate and cut any tangled threads with scissors. Don't turn the pulley by force. Remove any loose threads or lint in the shuttle race. Let the feed dogs move the fabric, don't pull it.