Bosch table saw model 4000

[dray]

I recently had the tail bearing on the armature go bad. Because it had basically fried the seat where the bearing sits, I replaced the bearing, the rubber cup, the motor housing, and also got new brushes. When I finished and turned the saw on, it ran smoothly. I didn't use it right away but came back to it a few hours later to find that when I turned it on it quickly ramped up to warp speed. I immediately turned it off and came back to this forum. I read that either the speed control or the field (or both) would be the problem. I really can't see where something like the speed control could just "go bad" during the course of a few hours. Since I am rather new to this kind of repair, perhaps there is a kind soul out there to either help or put me out of my misery!

[cmoorejack]

Hey dray;
First off..congrats on your initial repair. To the best of my knowledge the speed control is designed to keep the speed constant under load and to help with start up load..the saw can't really run any faster then it is designed because of the size of wire and the number of times it is wound to maintain the speed and load..so.. you still may have a field problem or maybe you brush's started to seat in causing the rpm's to increase but the saw really can't go any faster then it is designed to go..[if the speed control does have some issues it would be just a minor difference in the rpms and not a warp speed situation..Anyhoo, that's been my experience with this saw..
hope this helps..?
cmoorejack

[dray]

Jack,
I finally got a chance to install a new field and- Voila! it seems to be OK! Of course I'm going to cross my fingers every time I turn it on (at least for a while). Thanks for some good advice!!
Don