How to replace a trailer overrun damper – guide and symptoms
The overrun damper is a central component of the trailer’s overrun brake system. It controls the movement of the drawbar when the towing vehicle brakes, ensuring that braking force is built up smoothly and evenly. A worn or faulty damper causes jerky braking and can put extra stress on the entire brake system.
How do you recognise a faulty overrun damper?
The following symptoms suggest the overrun damper needs to be replaced:
– The trailer jerks noticeably when braking
– The overrun device hits hard at the end of its travel
– The drawbar moves too quickly or without resistance
– Braking feels uneven or unpredictable
– Oil leaking from the damper
What does the overrun damper actually do?
When the towing vehicle brakes, the trailer pushes forward. The overrun damper slows this movement so that braking force is transferred gradually to the wheel brakes via the brake cables. Without a functioning damper, the movement becomes sudden and uncontrolled, leading to hard jolts and uneven braking across the wheels.
Can a trailer overrun damper be repaired?
No – an overrun damper cannot normally be repaired. Once it is worn or damaged, it must be replaced completely. Only a new damper in the correct specification will restore proper function to the overrun brake.
How to replace a trailer overrun damper – step by step
The exact procedure depends on the overrun device model, but the general process is as follows:
1. Secure the trailer. Make sure the trailer cannot roll. Use wheel chocks if necessary.
2. Relieve the overrun device. Ensure there is no tension on the drawbar before starting work.
3. Remove the old damper. Undo the mounting bolts and detach the damper from its attachment points. Note the orientation before removal.
4. Fit the new damper. Install the replacement damper in the correct position. Make sure it matches the manufacturer, model and dimensions of the original.
5. Tighten all fixings correctly. Check that all bolts and mounting points are properly secured.
6. Test the overrun brake. At low speed in a safe area, check that the brakes engage smoothly and the trailer no longer jerks.
What else should you check during replacement?
While the overrun device is accessible, inspect the mounting points and pivot bearings for wear. It is also worth checking the condition of the brake cables and brake shoes at the same time. If you are unsure about any part of the process, have the work carried out by a qualified workshop.
When should the entire overrun brake be inspected?
If the trailer continues to brake poorly or jerk after fitting a new damper, the problem likely lies elsewhere in the system. Common additional causes include stiff or stretched brake cables, worn brake shoes, or incorrect brake adjustment. In that case, the full overrun brake should be checked.
Summary
A faulty overrun damper typically causes jerky braking and uncontrolled drawbar movement. Since the damper cannot be repaired, it must be replaced with a matching part. Correct fitting and a function test afterwards are essential to ensure the trailer brakes safely.