Stitches are not connecting top to bottom

you probably wont find it listed anywhere as it is from experience and changes with different material thickness and needle size
SO how to set tension
thread the machine and adjust the tension until you feel a drag on the thread
now thread the needle and sew a piece of scrap material
if the thread bunches up underneath then increase the thread tension until it sews properly
if the bottom thread is pulled to the top or the thread keeps breaking loosen ti off a bit
when the stitch is being properly formed , both bottom and top threads should meet at the center of the two materials being sewn

try changing the needle
try rethreading the top thread
do you have a manual for the sewing machine ?

Check the bobbin tension and that the thread is tight around the bobbin. Make sure that the bobbin is in the right way around - the bobbin thread should double back on itself coming out of the bobbin holder.

Pull both bottom and top thread to the back of the machine for about 10 cm or 4 inches out before you start stitching. Hold them loosly. Put fabric under the foot (the whole foot, don't start at the raw edge), make sure foot is down (to ensure tension). Start with the needle in the top position.
Your needle is likely to become unthreaded when the needle goes down and back up. But not if you hold the thread (and enough of it). Happy sewing.

Well is your machine skipping stitches? "Not looping" does that mean not creating a stitch? To adjust your bottom stitch you usually adjust the top tension regulator. I can try to help you more in detail check out my forums http://www.sewingmachineryrepair.com/forums/index.php

according to the diagram in the manual, the upper thread tension is set by the wheel/knob on top and just to the right of the thread take up lever and thread guide. If you don't have a manual, go to www.brother-usa.com they have a downloadable manual for your machine.

Hi, general rule of thumb:: loops on the top, problem on the bottom.. Loops on the bottom, problem is on the top.. When threading your machine, stop just before you thread your needle, put the presser foot down. Try pulling the thread. If it pulls easily, the thread is not thru the tension wheel right. If it pulls hard, you got it right.

you have your thread tension too tight that's why it is pulling the bottom stitch all the way through it looks good from the bottom but not good on top. Its pulled the stitch all the way through the material.
I had my own upholstery shop 18 yrs and tension gets you every time.Just loosen the top tension.

It sounds like your tensions are out of adjustment. Your upper tension should be between 3-5 and make sure the tension in your bobbin case is not too tight as well. Pull the thread through the bobbin case and make sure it comes out with a small amount of resistance. If no resistance, tighten the tension just a bit, if too much resistance, loosen it just a small bit at a time.

The top of the machine is not threaded correctly. First raise the presserfot then rethread the machine. Bottom looping is usually caused by a lack of top tension. There could allso be a bur on the hook.