The safety brake handle on my Stihl MS250 chainsaw is flopping around and no longer stopping the chain. Here are the steps I worked through to repair it. In my case, the brake band was broken (#7 in figure below). Repair takes about 30 minutes. You will need a screwdriver, pliers, Torx bit T-25, paper towels, a small brush, air hose, and WD-40.
Parts diagram for MS 250 relevant to this repair. You will remove everything, except parts 16, 17, and 19.
View of the inside of the saw at the beginning of Step #6. The brake band, spring, E-clip, pivot pin, and slotted bar are clearly visible. You can also see the lower curved end of the flat spring at the 2 o'clock position off the chain sprocket; it runs beneath the upper tail of the brake band and behind the slotted bar.
Removal Order - Numbers correspond to the diagram above
1.) Sleeved screw for handle w/ Torx T-25 (12, 13)
2.) Plastic outer cover (14) and two M8 collar nuts (15)
3.) Chain and bar
4.) 2 small white plastic bumper strips (11) <-- Pry out easily
5.) 2 pan head screws (10) and plaster cover (9)
6.) Spring (8) <-- Grab tail end near coil with needle nose pliers and twist off
7.) Small E-clip (6) <-- Use a flathead screwdriver
8.) Slotted steel bar (5) <-- Pulls off easily
9.) Small black washer/spacer (4) <-- Pulls off easily
10.) Brake band (7) <-- This part was broken on my saw (OEM Part #1123-16-5400, $8.00)
11.) Wiggle out handle assembly (1, 2) off pivot pin <-- Takes patience
12.) Flat spring (3) <-- This can also get bent, broken, or put in wrong, so check it.
13.) Clean up area, clean off parts, blow clean with air hose
14.) Repair/replace broken part(s)
15.) Reassemble in reverse order
The flat spring was OK, but the brake band, in the photo above, was sheared in two. Replace with OEM Part #1123-16-5400 for about $8.00.
Helpful YouTube Videos
How to Replace a Stihl Safety Brake with Taryl, https://www.youtube.com/watch?v=RQEwciFla2s
Start watching @ minute 3:45
Stop watching @ minute 11:17
Stihl MS230, MS250 Rebuild Part 5: Chain brake, band, main spring, lever centering spring
Start watching @ minute 3:00
Stop watching @ minute 10:42
Stihl Brake Spring Fitting, https://www.youtube.com/watch?v=EIjgZchlxFY