Prepare Safely and Evaluate Rotor Condition
- Establish stable support and verify safe brake access.
- Inspect rotor condition, thickness, and mounting hardware.
- Apply rotor-specific limits while controlling hose and dust hazards.
- Shop jack and adequately rated jack stands — Lift and support the trailer at locations permitted by the vehicle manufacturer; do not use the axle or suspension.
- Lug wrench or socket set — Remove the wheel after the trailer is safely supported.
- Rotor micrometer — Measure rotor thickness at locations directed by the applicable inspection procedure and assess thickness variation.
- Inspection light — Illuminate rotor surfaces and mounting hardware to identify damage and apparent distortion.
- Caliper hanger — Support a moved caliper without placing its weight on the hydraulic hose.
- Brake-dust HEPA vacuum — Collect lining dust using equipment intended for brake dust and the applicable dust-control procedure, rather than dispersing it.
Begin disc-brake service with the trailer supported according to the vehicle manufacturer's instructions on adequately rated jack stands. The source prohibits using the axle or suspension to lift or support the trailer. Wheel removal exposes the brake, but does not by itself make hydraulic work safe.
Disable or disconnect brake actuation as directed by the applicable procedure. Verify that the hydraulic system has no pressure and that the hub and rotor rotate freely before proceeding. When a caliper is moved aside, it must not hang from the hydraulic hose.
Rotor inspection covers grooves, flaking, cracks, heat checking, thickness variation, and insufficient remaining thickness. Inspect mounting hardware for straightness as well. Replace components as required by the applicable recommendations rather than judging serviceability from appearance alone.
Thickness limits are application-specific. Dexter lists a minimum rotor thickness of 1.03 inches for its covered 6K, 7K, and 8K rotors and 0.85 inches for its covered 3.5K rotor; values vary by maker. During pad work, also control brake dust: older linings may contain asbestos, so avoid dry brushing, compressed-air cleaning, and machining, filing, or grinding the linings.
How It Works
Safe access requires mechanical and hydraulic control
Support the trailer according to the vehicle manufacturer's instructions using adequately rated jack stands, never the axle or suspension. Removing the wheel exposes the brake but does not disable actuation or release hydraulic pressure; follow the applicable procedure to disable actuation and verify an unpressurized system before proceeding. Confirm free hub and rotor rotation, and support any moved caliper independently of its hose.
Rotor condition requires measurement and inspection
Inspect for grooves, flaking, cracks, heat checking, thickness variation, insufficient remaining thickness, and mounting-hardware distortion. Friction generates heat, and uneven wear or thermal damage can compromise braking even when the rotor looks usable at a glance. Dexter lists minimum thicknesses of 1.03 in for its covered 6K, 7K, and 8K rotors and 0.85 in for its covered 3.5K rotor; identify the application before selecting a limit.
Protect hoses and contain lining dust
A hanging caliper loads the hydraulic hose and its connections, potentially damaging the hose even when damage is not immediately visible. Older linings may contain asbestos, so avoid dry brushing, compressed-air cleaning, and machining, filing, or grinding the linings. Use an appropriate brake-dust control procedure rather than spreading dust through the work area.
Step-by-Step Procedure
0/7 doneDexter rotor limits for the listed applications; values vary by maker
| 6K, 7K, and 8K rotor minimum thickness | 1.03 in |
| 3.5K rotor minimum thickness | 0.85 in |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Trailer support depends on the axle or suspension. | Stop work and compare the lifting and support arrangement with the vehicle manufacturer's instructions. | Use adequately rated jack stands and manufacturer-approved support locations; the source prohibits axle or suspension lifting and support. | An unsuitable support arrangement creates a collapse or movement hazard during service. Basis: LDServiceOnline |
| Hub and rotor do not rotate freely before disassembly. | Verify that actuation is disabled and confirm that the hydraulic system is unpressurized using the applicable procedure. Investigate continued resistance before proceeding. | Verify no hydraulic pressure and free hub and rotor rotation before disassembly. | Residual brake application or mechanical resistance may be present; resistance alone does not identify the cause. Basis: LDServiceOnline |
| Rotor is worn or thickness readings vary. | Identify the rotor application, measure thickness according to its inspection procedure, and compare findings with the applicable recommendations. | Dexter covered 6K, 7K, and 8K rotors: minimum 1.03 in. Dexter covered 3.5K rotor: minimum 0.85 in. Values vary by maker. | Wear may leave insufficient thickness or produce thickness variation; a limit for another rotor application cannot establish serviceability. Basis: LDServiceOnline |
| Rotor shows grooves, flaking, cracks, or heat checking, or mounting hardware appears bent. | Inspect exposed surfaces and mounting-hardware straightness; evaluate findings against the applicable replacement recommendations. | Inspect both rotor condition and hardware straightness; appearance alone does not establish serviceability. | Surface deterioration, thermal damage, or hardware distortion may require replacement even when remaining thickness is acceptable. Basis: LDServiceOnline |
At the Bay: Diagnose the Case
CASE 1 / 4
Trailer support depends on the axle or suspension.
- Test
- Compare
- Correct
Select the next check
Basis: LDServiceOnline. A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Treating wheel removal as proof that hydraulic work is safe.
- ✕ Using the axle or suspension to lift or support the trailer.
- ✕ Applying a Dexter thickness limit without identifying the rotor application.
- ✕ Hanging a caliper from its hose or dispersing lining dust with compressed air.
Quick Check
Practice only — not scored.
Plan the Service Sequence
Planning practice only. Follow the applicable manufacturer's instructions, employer safety program and qualified supervision on real equipment.
Plan the first action. Compare the service steps with the bay mistakes.
Hands-on: Test Bench Practice
Symptom: Healthy trailer. Learn what good readings look like.
Tap a point to place the red probe.
Good system: ~12.6 V at pins, 3.2 Ω across a 12×2-inch magnet (unplugged), 3.0 A per magnet at 12 V full gain, and at least 10.5 V at the magnet — the chart values from the axle manuals.
Hands-on: Shop Test Equipment
Hydraulic Pressure & Relief Gauge
0–5,000 psi gauge on the pump pressure port, DC clamp meter, battery voltmeter
🛠 Equip your bay for this test →Symptom: Routine check before a customer pickup.
Spec limits used
- 3,200 psi — Primary relief (factory preset) (KTI Hydraulics Troubleshooting Manual 2019)
- 1,500 psi — Secondary relief, circuit 111 (KTI Hydraulics Troubleshooting Manual 2019)
- below 9 V — Low-voltage alarm (KTI remote)
- illustrative only — Motor current & voltage drop (General shop practice)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Source: LDServiceOnline — 34-51