29 in/lb servo dynamics brushed DC servo motor, brake will not release when power is applied. Motor data plate indicates 24vdc 44in/lb holding capability. Brake terminals at the motor measure 74 Ohms and an ammeter in series reads 0.346A when 24vdc is applied. I can override the spindle brake (without voltage applied) with torque of 39 in/lbs and that does not decrease at all with power applied and is smooth and consistent so I don't think I've dropped a magnet and it is not jammed. This is an older servo but was working prior to being put into storage, I'm doing a CNC control retrofit. There is almost no info on the net about disassembly of brushed DC servos other than (possibly overstated by repair facilities?) that its not possible other than by a qualified shop because of demagetization, etc. I would just like to take the end bell off to access the brake and make sure it is not just packed with carbon dust, brake dust or delaminated/swollen brake pad material. The encoder would need to come off (easy) and there is a 7v/1000 rpm tach just under the end cover, then probably the brake, which I can't see but may be at either end of the armature. I have a complete machine shop here and have taken apart and repaired many induction and universal motors but need more information to proceed. This motor was used vertically with pulley end down. any tips?

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    \$\begingroup\$ How about a couple of paragraph breaks (2 x <Enter>) to break up the wall of text? Please make sure that you capitalise brand names, etc., to make them clear and 'V' for volt. Hit the edit link. \$\endgroup\$
    – Transistor
    May 29, 2020 at 18:56
  • \$\begingroup\$ The brake may be polarized - did you try it wired opposite? \$\endgroup\$
    – rdtsc
    May 29, 2020 at 19:48
  • \$\begingroup\$ When you have to shoot, shoot ...don't talk. Take it apart, it's just a motor.. \$\endgroup\$ May 29, 2020 at 21:18

1 Answer 1


You need to mark the end bell and frame before removing the end bell to make sure it is aligned the same way when reassembling.

If this is a permanent-magnet motor, the rotor will be drawn to collide with the stator magnets as soon as it can move once the end bell is no longer holding the bearing in place. You need to work out a way to keep that from being a hard collision.

If you are going to remove the rotor, the brushes need to be moved away from the commutator. You may need to insert some kind of spacer material in the air gap so the rotor won't be held against the stator magnets.

  • \$\begingroup\$ I just got some information that indicates the brake is behind the front flange, which reinforces the theory that debris may have accumulated at that end because thats the way it has been oriented. My goal then is to leave the rotor in place while removing the front end flange from the brake and shaft/bearing assy so I can vacuum then blow off any accumulated debris that may be preventing the brake from retracting. not quite sure how I can hold the rotor centered in place while pulling the front flange, but I'm hoping I can get it out enough to at least see if there is stuff in there somehow \$\endgroup\$
    – tomj
    May 31, 2020 at 0:54
  • \$\begingroup\$ I thought about trying reverse voltage to the brake but the wires are color coded black and red and I'm afraid I'll ruin the coil if I do that? \$\endgroup\$
    – tomj
    May 31, 2020 at 0:57
  • \$\begingroup\$ As soon as the front flange is disengaged from the housing, the rotor is going to be be pulled to the stator. You will need to either be able to keep it from hitting too hard or have some means to block it from moving. By "front" do you mean drive end or non driver end? \$\endgroup\$
    – user80875
    May 31, 2020 at 3:00
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    \$\begingroup\$ OK so after much thought I clamped the rear of the motor body in a lathe 3 jaw chuck as it was only 4" OD, chucked a dead center smaller than the motor shaft in the tailstock and moved it up to hold the motor shaft centered. I then was able to easily slide off the motor front flange but had to remove the front bearing from the armature. \$\endgroup\$
    – tomj
    Jun 3, 2020 at 0:15
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    \$\begingroup\$ ... to access the brake. To do this I took a small bearing separator and put a small section of rod in where the clamp bolts usually are (so it would fit) and tucked it behind the bearing, then a SECOND, larger bearing separator on the end of the shaft between the shaft and the dead center. I was able to run bolts thru the large one into the small one and pull the bearing. Everything was then slid up the thin dead center to allow access to the brake. I was able to clean that, verify operation and use the bolts in the front flange to reseat the front bearing. All is well now. \$\endgroup\$
    – tomj
    Jun 3, 2020 at 0:23

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