Carbon brushes are the wear item on any brush-type vacuum motor. They are also the cheapest part in it. This is a matched set of two replacement carbon brushes for Ametek Lamb 120V motors - the motors used throughout central vacuum systems, carpet extractors and commercial vacuum equipment. Replacing them on time is the difference between a low-cost bench repair and buying a new motor.
Built for
- A motor that has stopped or lost power. Worn brushes lose contact with the commutator, and the motor either runs weak or will not start at all.
- Preventive maintenance. Service shops swap brushes on a schedule specifically so the carbon never wears down far enough to let the brush wire score the commutator.
- Central vacuum service. A very common call, and one of the few repairs where a homeowner with basic mechanical skill can do the work themselves.
- Extractor and equipment fleets. Keeping a pair on the shelf means a machine comes back into service the same day.
How to tell your brushes are done
A new brush measures roughly three-quarters of an inch. Industry guidance is to replace at or before three-sixteenths of an inch remaining. Symptoms that arrive before you get a chance to measure include weak or absent suction, a motor that will not start, and visible sparking at the commutator. A small blue spark at the brush is normal on a universal motor. A large blue spark that rings the whole commutator is not - that is a machine telling you it is past due.
The reason the timing matters: once the carbon is gone, the brush wire itself rides on the commutator and cuts into it. At that point brushes alone will no longer fix the motor, and the repair becomes a motor replacement.
Brushes or a new motor?
Pull the brushes and look at the armature. If the commutator surface is smooth and the bearings run quiet and true, new brushes will bring the motor back and typically give you several hundred more hours of service. If the commutator is pitted or grooved, or the bearings are loud or have play in them, replace the motor - brushes will not save it. Typical service life for these motors runs somewhere in the range of 800 to 1200 hours in total.
Always replace as a pair
Both brushes wear together and both should be changed together. Replacing one side leaves an unmatched pair with different spring pressure and different seating, which loads the commutator unevenly and shortens the life of the new brush.
Specifications
- Type: carbon motor brushes, sold as a set of two
- Part number: 833392-61
- Cross-references: 33392-11, 3339211, 3339261
- Voltage: 120V motors
- Brand: Ametek Lamb
Ametek part 33392-17, also listed as 833392-67, is shown by several suppliers as the current replacement for 33392-11 with an orange winged holder. If your motor documentation calls for either number, send it to us and we will confirm which set you need.
Frequently asked questions
When should I replace my carbon brushes?
A new brush is about three-quarters of an inch long. Replace at or before three-sixteenths of an inch remaining, before the carbon wears down far enough for the brush wire to contact the commutator.
What are the symptoms of worn brushes?
Weak or no suction, a motor that will not start, and heavy sparking at the commutator. A small blue spark is normal on this type of motor. A large spark that rings the commutator means the brushes are past due.
Does part 33392-17 work in place of 33392-11?
Several suppliers list 33392-17, also shown as 833392-67, as the current replacement for 33392-11. Send us your motor number and we will confirm which set fits.
Should I replace the brushes or the whole motor?
Inspect the armature. If the commutator is smooth and the bearings are quiet, brushes will restore the motor. If the commutator is pitted or the bearings are worn or noisy, replace the motor.
How long will new brushes last?
Industry guidance suggests roughly four hundred additional hours after a fully worn set is replaced, with total motor life commonly in the eight hundred to twelve hundred hour range.
Do I have to replace both brushes at once?
Yes. Brushes wear as a pair. Replacing only one side gives you mismatched spring pressure and seating, which loads the commutator unevenly.
Discount Cleaning Products is an authorized dealer for the vacuum and floor care brands we carry, with US-based support from people who work on this equipment every day. If you are not certain this part matches your machine, send us your model number and serial plate details and we will confirm the fit before you order.
