Fluctuating motor speeds

[74simon]

I have a couple of machines that have a disconcerting habit of having motors that will suddenly change pitch (sounding like they're slowing down or being strained), even though the motor bearings seem fine and no undue strain is being put on the motor. I suspect that both machines are the kind that hadn't seen much if any use for years, until I got my mitts on them. I'm never sure whether to keep them running in the hope that they smooth out, or whether they need attention lest they burn out or worse! although I'm more worried about injury happening to me than to the machine...

 

[hoovercelebrity]

My guess...

Is that the carbon brushes in the motor are worn out... That's usually what it is if a machine speeds up and slows down on its own.

What kind(s) of machines are they?

~Fred

 

[74simon]

Thanks Fred,

One is a Hoover Junior 1354A. I've just compared the free-ness of the drive pulley with my smoothest Junior, and it seems very stiff in comparison, although it does turn evenly, and there's no wobble from worn motor bearings.

The other is a Hoover 652 which has been in storage for a couple of months. Again, there's no bearing wobble on the agitator drive shaft, but this time the motor turns freely. However, when I spin it by hand, there's a distinct clicking/rattling sound, almost like a stick being dragged along a picket fence or something. So I guess that that is dodgy carbons on that one. I've had this sound on this type of machine before, but as I'm not clued up on motor repair i've never known quite what to do about it!

 

[centralvacman]

check the comutator ,armature& fields

worn brushes,weak springs,brushes sticking in the holders
open or shorting of armature can cause that.along with loose field coil assembly causing dragging on armature will cause erratic operation,one or 2 severly burned comm bars usually an open armature wire,