Dexter Magnets & Brake Parts
- Determine when a brake magnet requires replacement based on wear patterns and coil exposure.
- Apply the requirement for matching magnet and drum armature surfaces during service.
- Specify brake parts by size, side, and axle-set consistency to ensure even braking.
- Straightedge — Check the friction face of the magnet for uneven or abnormal wear.
- Identification labels — Mark magnets and kits by side (left/right) to ensure correct installation.
- Measuring tape — Determine brake size to ensure the correct replacement parts are ordered.
Replace a magnet if it shows uneven or abnormal wear, or if the friction face is worn to the coil. Use a straightedge across the face to check wear.
Replace magnets and drum armature surfaces together; a new magnet on a worn armature wears unevenly.
Order brake parts by brake size and side (left/right), and match kits across the axle so both sides brake evenly.
How It Works
Magnet Wear Limits
A magnet must be replaced if it shows abnormal or uneven wear. A critical failure point is reached when the friction face is worn down to the coil. A straightedge is the primary tool used across the face to verify these wear conditions.
Surface Compatibility
Magnets and drum armature surfaces function as a matched pair. Installing a new magnet against a worn armature surface leads to uneven wear. Therefore, these components should be replaced together to maintain system integrity.
Component Matching
Brake performance depends on symmetry across the axle. Parts must be ordered according to the specific brake size and side (left or right). Kits must be matched across the entire axle to ensure both sides provide even braking force.
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Magnet face shows the internal coil. | Visually inspect the friction face for depth of wear. | Replace if worn to the coil. | Normal service life exhaustion or excessive friction. Basis: Dexter Axle Operation, Maintenance & Service Manual (600-8000) |
| New magnet shows immediate uneven wear patterns. | Inspect the drum armature surface that contacts the magnet. | Replace magnets and drum armature surfaces together. | New magnet was installed on a worn or non-resurfaced armature. Basis: Dexter Axle Operation, Maintenance & Service Manual (600-8000) |
| Trailer pulls to one side during braking. | Verify that brake kits and parts are identical on both sides of the axle. | Match kits across the axle so both sides brake evenly. | Mismatched brake parts or kits between the left and right sides. Basis: Dexter Axle Operation, Maintenance & Service Manual (600-8000) |
| Magnet face is not flat when checked with a straightedge. | Place a straightedge across the magnet friction face. | Replace if it shows uneven or abnormal wear. | Mechanical misalignment or irregular armature contact. Basis: Dexter Axle Operation, Maintenance & Service Manual (600-8000) |
At the Bay: Diagnose the Case
CASE 1 / 4
Magnet face shows the internal coil.
- Test
- Compare
- Correct
Select the next check
Basis: Dexter Axle Operation, Maintenance & Service Manual (600-8000). A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Replacing a magnet without inspecting the drum armature surface.
- ✕ Installing a right-side brake kit on the left side of the axle.
- ✕ Reusing a magnet that has wear reaching the internal coil.
- ✕ Mixing different brake kit brands or types across the same axle.
- ✕ Failing to use a straightedge to verify magnet face flatness.
Quick Check
Practice only — not scored.
Hands-on: Shop Test Equipment
Dial Indicator — Bearing End Play
Magnetic-base dial indicator (0.001 in) on the hub face, spindle nut adjustment
🛠 Equip your bay for this test →Symptom: Bearing service — set end play after repack.
Spec limits used
- 0.001–0.010 in — Allowable end play, double-nut wheel end (Dexter 9-15K service manual, p.64)
- 0.008 in — Nev-R-Lube 50 mm max axial end play (Dexter 059-831-00)
- illustrative only — Face runout limit (General shop practice)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Source: Dexter Axle Operation, Maintenance & Service Manual (600-8000)