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27 Sep 2018

NEWS & INSIGHTSChecking Your Trailer’s Undergear

Tyres are the only contact between your trailer and the road surface. Road safety legislation requires that all tyres must have at least 1mm of thread depth over the entire width of the tyre. If you consider having your tyres retreated at a later stage, the tread depth must be at least 2mm for the tyre casing to be accepted.

Examine the wear pattern of your tyres regularly, as this could provide important clues of the following possible problems. Tyre wear on the inside only is usually caused by overloading. Tyre wear on the outside only may indicate that wheels are running out of track and that the axle needs to be re-aligned. If only the centre of the tread is worn, the tyres have been operated while over-inflated. Where wear is on the inside and outside of the tyre then under-inflation is the cause. Check the tyre pressure regularly and maintain within manufactures specification.

In many cases trailers are not used frequently. Age of tyres used should not exceed 5 years and you will find that tyre companies will not honour claims involving tyres that are more than 5 years old. Tyres deteriorate from standing for long periods and being exposed to the elements. When parking your trailer for a long period, mount it on stands to preserve the tyres. The wheels may even be removed and stowed under cover if necessary.

Never fix radial and cross ply tyres on the same trailer. This principal also applies to textile radial and steel radial tyres. Do not overload your trailer’s tyres as a burst tyre may result in an accident. Check the tyre carrying capacity with your tyre dealer.

Wheels have the nasty habit of working loose. When checking your wheel rims for signs of distortion, ensure at the same time that all the nuts or wheel bolts are secured and tight. It is advisable to use a torque wrench for this purpose. Tightening should be in a sequence of opposite nuts or bolts first. Final tightening should be on the ground.

Axles mainly found currently are either suspended by leaf springs in the case of standard beam axles, or the rubber suspended axle system. The latter operates on a torsion bar concept using rubber elements encased in a square tube. Rubber suspended axles have become increasingly popular due to the low loading height of the trailer and the ease with which they are mounted onto trailers.

Maintenance of axles is mostly concerned with the maintenance of the roller bearings. You should perform a maintenance inspection every 6 months or 5,000km. A suggested way of doing your inspection is as follows;

Jack up the trailer and remove the wheels. Remove the grease cap. Remove the split pin and castle nut (and washer if present). Pull the hub assembly off the spindle. Remove the seal, inner- and outer bearing from the hub. Wash the bearing races and inside of the hub thoroughly with thinners or other grease solvent. Carefully inspect both the bearing races and the bearing shells inside the hub for signs of wear and overheating by noticing a blue colour on rollers and bearing surfaces. If bearings should be replaced, see “replacement of bearings” below. Smear both the bearing shells in the hub with a generous layer of wheel-bearing grease (lithium soap based grease is recommended). Also rub a generous portion of grease carefully into each bearing race. Replace the bearing races into the bearing shells in the hub. Fit a new seal. Slide the hub assembly back over the spindle. Fit the washer (if present) and screw the castle nut down tight, then loosen slightly until the hub can be easily rotated by hand. Turn the castle nut to the closest position for the split pin to be fitted. There should be no more than 0.1mm end float (“rocking”) in the hub and the hub must be easily turned by hand. Fit the split pin and bend the legs open around the outside of the castle nut. Replace grease cap into the hub by tapping it lightly with a hammer until properly seated. Replace the wheels and ensure that the wheel nuts or bolts are properly tightened. Check them again after you have covered about 10km.

If the bearings showed signs of wear or overheating during your inspection you can replace them as follows. Remember both bearings must be replaced, even if only one appears to be damaged. Each bearing is to be replaced as a unit i.e. bearing shell and race.

Follow the steps above required. Remove both bearing shells from the hub by using a suitable punch and hammer to carefully knock them out. Take care not to damage the hub bearing housings (machined surfaces in hub.) Wash inside of hub thoroughly with grease solvent. Fit the new bearing shells so that the tapered faces point toward the outside of the hub. Use a press or else a pipe and hammer. The pipe should have an outside diameter slightly less than the diameter of the bearing housing. Tap carefully to prevent the bearing shell from cocking in the hub. Follow the rest of the steps above the assemble your axle.

Perform a regular external inspection of the hubs by looking for leaking or defective seals, missing grease caps or broken and missing wheel nuts or bolts. If your trailer’s axle is exposed to fresh or salt water, or it operates under particularly severe conditions, the maintenance inspection must be performed more frequently. Do not exceed the rate load of the trailer’s axle. Remember that the load carried by the axle is the load on the trailer plus the mass of the trailer itself. Doing so may result in damage of the axle and or the bearings.

All trailers with a gross vehicle mass exceeding 750kg must be equipped with brakes. Adjusting your trailer’s brakes can be annoying, but the following procedure may help to ease the frustrations. The method here is applicable to overrun trailer brakes. If the axle is fitted with auto-reverse brakes, it is important that during adjustment the wheels/ hubs be rotated as if the trailer were going forward. The later Burquip braked axles have easily accessible adjustment nuts on the rear of the brake mechanism back plate. Some manufacturer’s brakes, especially in the case of caravan axles, are adjusted by means of an internal ratchet mounted opposite a hole in the back plate. This ratchet is turned using a screwdriver to click it over. In both cases, the method of brake adjustment is as follows;

Jack up the trailer and place on stands making sure all wheels are free of rotate. Loosen all cables from the braking rod. Starting from one side, rotate the wheel to the front of the trailer and tighten the brakes at the brake adjustment point until the drum is locked. Loosen the brakes until the wheel can be easily rotated by hand. Reconnect all brake cables to the rod. Pull up the hand brake and check the braking of each wheel. Adjust if necessary until the brakes are evenly applied to each wheel.

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