Low speed sometimes doesn't engage or speeds up after short period of use.
How stable is your line voltage? The SCR phase control used for speed control is more sensitive to line voltage changes at low speeds than at high speeds. Brushes should be changed when they are worn down to about 1/2 of their original length. Much more than this and they don't have enough tension to properly contact the commutator ring. Check with power off when the tool is cold and slowly turn the chuck by hand to feel the resistance. Run it a while and let the bearings warm up. Turn off power and turn by hand again. If it feels looser when warm (which would cause it to speed up at slow speeds), the tool might need to be disassembled and bearings oiled. I use Dexron automatic transmission fluid to lube most motors. Wipe down any excess.
SOURCE: How to replace brushes?
On either side of the switch is a black disk with a notch small enough for a small screwdriver. Unscrew it and take it off to expose the spring. Gently pull the spring out and the brush should be attached. If you encounter resistance, then you may disconnect the spring from the brush. If this happens then push the spring back in and hope you catch the brush; if this does not work, then get creative or take the whole thing apart to get to it. After that, just put the new brushes in and recap.
SOURCE: have a multip speed dremel 350
clean the slots that hold the brushes, sometimes they get cloged and the springs do not push the brushes all the way to the armeture.
SOURCE: Variable Speed Does Not Work - Model 395
It probably can be replaced. For info on this tool call 1-800-437-3635 (Dremel) and speak with customer service about a replacement part. Hope this helps
SOURCE: need new variable speed switch for dremel 395 type 1
Someone else recently asked the same question and got the following solution;
http://www.fixya.com/support/t1515699-variable_speed_switch_dremel_395_get
SOURCE: Cordless Dremel variable speed stuck on maximum
Hi, There are several dealers in London who can help you solve your problem. The following link is has a list of those dealers with addresses and phone numbers:
http://www.dremeleurope.com/dremel/dealerlocator/index.cfm?lang=en-GB
Good Luck to you, this should Fixya!
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