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Potential Causes for Excess Heat Build-Up in Hubs/Drum

Question:

One of the four self-adjusting electric brakes on our 5th wheel trailer seems to be over-adjusting. I say this because the tire pressure monitoring system shows that one wheel is overheating and causing the pressure to rise. This eventually returns to normal until the cycle repeats. Wat is the cause and is there an easy fix?

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Expert Reply:

Properly-adjusted trailer drum brakes should apply enough drum pressure to put some noticeable drag on the hub as you rotate the wheel by hand. You should hear and feel drag but still be able to rotate the tire.

Self-adjusting brakes require an initial manual setting, after which they will automatically TIGHTEN as needed but they will NOT automatically loosen if the initial setting was too tight. Odds are your one brake was simply set too tight at the start. You can use a brake spoon tool like # W80630 to back off the pressure so that brake can then self-adjust up to the proper drum tension.

I would be surprised that the tire pressure monitoring system would actually detect a tire pressure increase caused by heat from the hub/drum. That heat would first have to travel through the hub material to the wheel material and then to the tire.

Keep in mind tires always heat up as you drive. How much of a pressure increase are you finding? 10-degrees Fahrenheit ambient temperate change will raise or lower a tire's pressure by about a pound. This will occur even if the trailer is still.

Drums can also heat up if there is insufficient bearing grease in the hubs or if the castle nut that secures the hub is too tight. A too-tight castle nut will cause the hub/drum to heat up by putting too much pressure on the bearings which generates excess heat. A bent spindle can also cause tire heat/pressure to rise.

Chances are good you just need to manually reduce the pressure on the one brake assembly.

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