I want to change the carbon brushes, what type are the screws that hold thd the brush casing to the motor?

Carbon brushes are delicate and easily damaged so good access is highly desirable and good visibility is needed for fiddling with springs, screws, terminals.

In addition, by the time carbon brushes are worn out, especially if the motor is an enclosed type, a great deal of highly conductive carbon dust has been generated that if left inside can rob a motor of efficiency. It is therefore better to remove the dust.

Sometimes a motor should be dismantled and washed, sometimes a cleaning aerosol can be used but mostly the best way is to use compressed air in the open air while wearing a dust mask or holding a breath.

If the motor must be removed for that, then it must be removed...

yes u need to change the brush

first of all check the drive belt is loose or not. Drive beit connect with the motor and roller of the treadmill. its not possible to see the drive belt out side. you can only see it if you remove the motor cover. if its loose the try to tighten it. if its not the problem then the treadmill motor have some problem. Either the motor is faulty or the carbon brush is faulty. There is 2 carbon brush inside the motor which is replaceable, its used to take the voltage to the rotary part (armature) of the motor. If the contact with the rotary part and carbon brush is poor the this type of problem can occur. tyr to change the brush. Here i have added a video which demonstrate how to change the carbon brush of the treadmill motor. It not the exact model you have. but almost all treadmills have the same type of motor. even after replacing the carbon brush the treadmill shows the same problem then you have to charge the motor with a new one .
http://electro-medical.blogspot.com/

Fitness repairs

I am assuming that you are discussing a motor from a Swiss made older model Bernina machine using a phase controller such as the type 290 or YC-420. The motor description will say SEG 884...? If so, the motor brush holder's black plastic tab can be bent up (lifted up) to remove the old brush and bent back down to hold the brush in position.
Note: The tabs can only be bent 3 times before they break off.....

Generator replacement brush notice:
1, from the model and material needs and the original brush.
2.It is best to grind the new brush to the Radian size of the old brush.
3. pay attention to adjust the brush grip pressure.
4. the carbon brush size should be equal, not too big or too small. The carbon brush is not subject to force in the process of placement.
5. pay attention to the carbon brush and armature to have obvious contact, do not push the carbon brush in.


Generator brush replacement method:
1, the first with a special wrench loose brush braid fastening screws, loose fastening screws should not be loosened excessive, to prevent screw loosening and falling off.

2, take off the carbon brush braid, the carbon brush and the pressure-equalizing spring at the same time. When installing a carbon brush, put the brush into the brush grip.
3, then press the equalizing spring.
4.Use special wrench to fasten the brush and braid to fasten the screw. When fastening the screw, it is not necessary to exert too much force to prevent the screw from being damaged.
5. Check that the brush moves freely in the brush grip, and the spring can be pressed in the center of the brush.

Looking at your manual pdf, it appears that your machine has an internal motor. On the end of the machine with the hand wheel there are a few screws that removes a panel. Remove that and you should be able to access the motor area. The brushes are typically riding in a port and held in place with 2 screw in type caps and a spring. One on top and one on bottom (though that can by side to side too.) remove the caps and catch the spring and brush as it comes out.

Hope that helps. Here is the PDF in case you need it.
http://www.singerco.com/uploads/download/648_328.pdf

Make sure you unplug your machine before accessing anything.

Have you checked the carbon brushes within the motor, chances are they are worn. you will need to remove your motor to get to the 2 carbon brushes.these will be in a plastic casing, held in place by 2 screws. There is just 1 wire going to each brush. When brush is removed, the carbon should be at least 20mm long. If not replace with new

This could be the motor brushes worn, depending on make of machine, as some motors work with capacitor. Most likly cause is the brushes. To get to them you may need to remove the motor, and you will find 2 plastic casings on motor, each will have 1 wire going to it. remove the 2 screws holding the casing and you will find a black carbon bush. they should be no less than about half inch long, and should slide in and out of casing,or sleeve.

hi Many universal motor malfunctions are caused by wearing down of the carbon brushes, the soft blocks of carbon that complete the electrical contact to the motor's commutator. When these brushes become worn, the motor will spark, and electrical contact may be incomplete.try this
Step 1: To sight-check the carbon brushes, remove the screws that hold the brushes and brush springs into the brush holders at the sides of the commutator. The screws will pop out of the screw holes; turn the motor over to tap out the brushes. The ends of the brushes should be curved to fit the commutator; if they're worn down, new brushes are needed.
Step 2: To check carbon brushes with a continuity tester, remove the motor lead wires from the circuit. Tag the wires as you disconnect them so that you'll be able to reconnect them properly. Hook the tester clip to one motor lead and touch the probe to the other lead; the tester should light or buzz. Slowly rotate the motor shaft, keeping the tester in position. If the tester doesn't light or buzz, or if it flickers or stutters when you turn the motor shaft, the brushes should be replaced. If the springs behind the brushes are damaged, they should be replaced as well.

Step 3: Replace worn carbon brushes and damaged springs with new ones made specifically for the motor. The model information (number and make) is stamped on a metal plate fastened to the motor, or embossed on the metal housing of the motor. If you can't find the model information, take the worn brushes and springs with you to an appliance-parts store to make sure you get the right kind. Insert the new springs and brushes in the brush holders, replace the brush assemblies, and secure the new brushes with the mounting screws that held the old brushes.

u can sometimes tip the washer backwards and with a torch u should be able to see the carbon brushes and the 2 star screws which hold them in undue these screws and the carbon brushes will pop out very easily for u to change them m8