Tuesday, January 15, 2013

Fixing an old Singer 'carbon pile' foot control

Tonight I was working on a Singer 758 sewing machine. This machine looks to have been used very heavily. I adjusted and oiled it, then noticed the foot control was one of those that is either on or off, no variable speed in between. The machine has two speeds but having variable speed control would still be nice to have, so I ventured into the depths of the foot control.

The ubiquitous Singer clamshell controller...

To open one of these, you need to skewer the rubber backing, then unscrew the screw that is behind the rubber backing. Feel around on the bottom of the controller until you find an indentation. That is where the screw is. I just poked the screwdriver through the rubber to get to the screw.

Unscrew the screw, then open up the clamshell, like so.

Next, vacuum out the decades worth of lint and spider remnants. You can see a carbon pile resistor (long white thing). The way this works is when the long copper strip is pressed in the center by a protrusion on the top cover (shiny spot on the copper strip), the strip bends or bows down. The first thing this does is the top strip contacts another copper strip just under it. The underside strip supplies power to the top strip. Bow the top strip down further and it tilts the left-hand side of the copper strip inward. You'll see a carbon button attached to the copper piece on the left. This button presses against the carbon pile resistor.

The harder the contact point pushes against the stack of carbon, the less resistance that the carbon pile has, which is what provides speed control of the motor. At the extreme end of travel, when the pedal is pressed all the way, the bowed copper strip contacts another copper strip that bypasses the carbon pile resistor and gives full power to the sewing machine motor.

On my controller, there was a gap between the carbon contact and the carbon pile. When the pedal was pressed all the way, the contact point had not even started contacting the resistor, which is why my controller provided no variability. What I did was remove the contact point on the right side of the carbon pile. It is an L-shaped brass piece. I then elongated the screw hole so I could have some adjustment left to right. This next photo shows the elongated screw slot in the brass bracket.

I reinstalled the bracket and slid it to the left as far as it would go, then tightened the screw. This took out all the slack between the left-side carbon contact, the carbon pile, and the brass bracket on the right. One other thing I did was to take a pair of needle-nose pliers and carefully rotate the carbon button 180 degrees. This presented a new surface of the button to press on the carbon resistor (the old location was looking a bit worn and rounded).

Now you just need to close up the controller and screw the cover screw back in. I don't know how there got to be such a gap between the various parts, if it was just heavy usage over the years or if some part is missing. In any case, I now have a functioning motor controller. And it didn't cost me a cent to fix.


  1. I replaced the gears in a Singer 758 I purchased from craigslist. It was the first time I took apart a sewing machine. My local repair guy helped me with the timing. I also replaced the worn out rubber feed dogs with a metal set.

    Do you like your Singer 758?

  2. The "newer" Singers are OK machines but just don't seem to be built as well as the older machines in my opinion. I buy them only if they are a great deal anymore. If I sewed more (or at all?), I might get interested in one, and very well may in the future. Thanks for the comment.

  3. Agreed. The best Touch & Sews (in my humble opinion) are the early ones with metal gears. I have a 600, 603e.

    I recently purchased a 626 with metal gears. I'd been on the hunt for one for a long time. I greased & oiled it, added a new bobbin, needle and thread and it sews perfectly.

  4. Thank you SO MUCH for this post! I am a resident advisor in an MIT sorority, and found a Singer 626 in the basement, with little carbon pieces falling out of the foot controller. Thanks to your blogpost, we realized what was happening and opened it up. Turns out the carbon pile resistor had gotten loose and all the carbon pieces fell out. We put the pieces back in, and replaced the broken and lost pieces with bits of steel wool. It works almost perfectly now!!! Maybe a slight loss of variability, but compared to not working at all before, this is a GIANT improvement. Hooray and thank you!!!!!

    1. Glad it helped you out. I'm all for keeping these old machines alive.

  5. Hi. Than for the help. I am trying to fix my wife's controller. It looks exactly like the one you show (but it is a 4X) and has two screws. One, comes off easily, another does not come off despite the effort (just turns...). Any suggestions?

    part: 619494-079

    1. Sorry I don't have any good ideas for the stubborn screw. Maybe try using needle nose pliers to pull the screw while turning? Or hit up a thrift store and pick up a replacement controller for a few bucks? Best of luck.

  6. great tutorial - machine had/has got one speed - slow - ok up until a few days ago so followed the above and motor still runs slow - i understand the bit about making the final contact and bypassing the carbon pile and have done that with the top off the foot pedal - carefully i might add as its live in there and again the motor runs slow so i guess the problem is in the machine rather than the foot pedal - shame - but it looks like a new machine

  7. bought a heavy singer g105 zigzag (it has plastic gear though) and this foot controller separately at carboot sale for about £3 each. machine ran after a few times then it just ran by itself without pressing the controller, then a strong smell of smoke. open it up and found a cracked capacitor, an old notorious riva 0.1uf 100nf x, and I guess a diode, across the live and neutral copper strip. thought of changing the capacitor and diode but the machine seems to be running well without them.

  8. THANKS FOR POSTING THIS. I got a Touch and Sew off of freecycle and with a little attention ($50) got it running. Then, suddenly it stopped and all these little carbon circles came out of the foot pedal. I thought kids were playing around and stuck those into it. When i opened the pedal as you said, I saw a few more and threw them away. Then I read Grace's comment and realized what a carbon pile was. When i showed my husband and told him that I was going to use steel wool as Grace, he told me to buy a new one which I am finding for $12 when i google it. I think he is afraid i am going to burn the house down. In any case, it will be fixed and back in use. (still tempted to try the steel wool........:)

  9. Thanks for showing how to open up this type of pedal. I kept looking at it and wondering how to get the pieces apart. Of course, a hidden screw! What were they thinking at Singer in the 60's?

  10. Hi, any idea where I can get a carbon pile resistor?

  11. hi! I want to buy a lot of old Janome foot controller!
    can you help me!
    contact for me by gmail: tung.nt210793@gmail.com
    thank you so much!!!

  12. I was about to buy an old controller but
    it might well have been even worse. I
    have the -004 model. It has a an adjusting
    screw on the right end which I turned clockwise
    and tested. The control is now incredibly
    precise at the slow and fast speeds Thanks
    for giving me the idea