Thread keeps breaking while sewing - Brother Sewing Machines

There can be a few reasons for this. I will forgo asking if you threaded the machine correctly.
1) Check to see if there is a bunch of lint in the shuttle. Open the bobin compartment, take the bobin and all the innards out and blow it out or otherwise clean it. Reassemble.
2) Make SURE the thread is not twisted on the spool. For a check, use brand new thread in both the bobin and the parent thread. If you are one to not want to set up filling a bobbin using the winding facilities of the machine and instead would rather wind it by hand going around and around the bobbin, you have just found your probolem. Winding thread on a bobbin this way puts one twist for every revolution you go around. With a pre-twist on the thread, the looping procedure the machine does will be sabatoged because the loop around the shuttle will not behave properly and the loop will not be pulled over the shuttle. The machine will not work. Wind the bobbin using the machine.
3) (Obvious) make sure the needle is installed correctly. The flat is towards the set screw. (Try a new needle. The tip might be bent over, and it acts as a "pick".)
4) I'm going to go ahead and say it: Thread the machine properly. There are details, none of which can be neglected. I can't tell you how many times I've made a simple mistake in threading - and did the mistake again and again!
5) Last resort - have the machine serviced. It might be out of time. Have them oil it while they're at it.
Good luck.

If you have a manual look for checking the tension. Or it may be it is threaded wrong.