Motors and carbon brushes

What It Is

Spring-loaded graphite blocks that ride on the motor's commutator. Nearly all central vacuum power units use Ametek Lamb universal motors (MD: 'Lamb Ametek motors are used in nearly all central vacuum brands'). Brushes are sold in pairs matched to the motor family; common Ametek Lamb part numbers include 2311480, 333261 and 33326-1 (and 850228 as an equivalent).

What It Does

Conduct current to the spinning armature. They wear by design and are listed as consumables excluded from warranty (Vacuflo warranty excludes 'motor brushes').

Symptoms

• Large sparks that wrap around the commutator (a slight blue spark is normal) - MD motor troubleshooting.
• Motor runs 10-15 minutes then cuts out, or runs only after tapping the unit (can also be a failing motor).
• Unit's circuit protector/mini-breaker keeps tripping after a short run - Vacuflo manual: 'the motor brushes may be worn out'.
• Motor clicks (relay) but does not run, with worn brushes no longer touching the commutator.
• Burning shellac smell = windings cooking, which is a motor problem not a brush problem.

Specs

New Length

about 3/4 in of carbon

Replace At

when worn to about 3/8 in (MD)

Motor Hours Rule

MD flowchart: motors under about 800 hours may be saved by replacing brushes

Replace Brushes Or Motor

With power off, push on the armature shaft. Any play other than spinning = bearings gone, replace the motor. Solid shaft = brushes can be replaced. If the commutator is scored, blackened and rough, replace the motor; new brushes will not seat.

How To Replace

Unplug the unit, remove the motor cover, note the brush holder style (screw-in cap or clip-in holder with a lead wire), slide out the old brush, compare shape and dimensions before fitting the new one, reconnect the lead (some aftermarket brushes require soldering the lead to the holder), run the motor unloaded briefly to seat.

Compatibility Checks

• Match the Ametek Lamb motor number stamped on the motor label to the brush part number; dimensions (e.g., 6.3 x 11 x 33 mm for 2311480-type) and lead/terminal style must match.
• Aftermarket brushes vary in carbon grade; a motor near the end of its life may not be worth re-brushing.

Common Mistakes

• Replacing brushes on a motor with worn bearings or a damaged commutator.
• Leaving the unit running with no hose attached (no airflow = overheating).
• Mixing up brush orientation / not seating the spring.

When To Replace

At about 3/8 in remaining, at the first heavy-sparking or intermittent-running episode, or proactively around several hundred hours of use on an otherwise healthy motor.