Rear Knuckle 55-SJ13 for HM123: Wear Signs and Replacement
By BEZGAR | Published: 2026-11-01
Category: Product Reviews
Learn how to spot a worn rear knuckle on your HM123, confirm it's the real cause of wobble, and replace it with the correct 55-SJ13 part.
Quick answer
If your HM123 has rear-end wobble, uneven tire wear, or a loose hub that won't tighten, a worn rear knuckle is a likely cause. Replace it only after confirming play at the knuckle itself; the genuine BEZGAR 55-SJ13 rear knuckle is a direct-fit part for the HM123.
Why the rear knuckle wears and what it affects
The rear knuckle (also called a rear hub carrier) holds the rear axle and wheel in place. On the HM123, it takes a lot of punishment from landings, curbs, and rough surfaces. Over time, the plastic can develop play around the hinge pins or axle bore, which lets the rear wheel move out of alignment.
That movement shows up as wobble, poor straight-line stability, and uneven tire wear. Because the rear knuckle is a structural part, even a small amount of play can change how the car handles. Catching it early prevents secondary damage to the axle or suspension arms.
When the problem is not the knuckle
A worn rear knuckle is not the only source of rear-end wobble. A bent axle, worn bearings, a loose wheel nut, or a damaged suspension arm can produce similar symptoms. Before ordering a replacement, check those parts too. If the wobble disappears when you hold the knuckle still, the knuckle is the culprit; if play remains elsewhere, replace that part first.
Diagnose your rear knuckle: symptom, cause, action, stop point
- Symptom: rear wheel wobbles or feels loose: With the car off, lift the rear and try to rock the wheel side-to-side. If you see movement at the knuckle where it meets the suspension arm, the knuckle is worn. If the wheel itself is tight but the whole hub moves, suspect the knuckle or its mounting points.
- Likely cause: worn plastic or elongated holes: The HM123 rear knuckle is plastic; repeated impacts can ovalize the hinge-pin holes or wear the axle bore. Compare a new 55-SJ13 knuckle side-by-side if you have one. If the old knuckle has visible cracks or enlarged holes, replacement is the right fix.
- Corrective action: replace with the 55-SJ13 rear knuckle: Remove the rear wheel, disconnect the suspension arm and axle, then swap in the new knuckle. Reuse the original hardware unless it is damaged. Tighten screws snugly, then check for free movement. After reassembly, spin the wheel and check for binding before you run the car.
- Stop point: when to stop or choose another option: If the new knuckle still has play, the problem is likely in the suspension arm, axle, or bearings—not the knuckle. If the knuckle is cracked but the car is otherwise fine, you can replace just the knuckle; if multiple rear parts are worn, consider a full rear-end refresh. Do not replace the knuckle if the wobble comes from a loose wheel nut or a bent axle; fix that first.
Product facts
- Rear Knuckle(55-SJ13) for HM123: This is an original BEZGAR replacement spare part with part number 55-SJ13, designed to be 100% applicable for the HM123 RC car model. Using the correct part number ensures a factory fit, so you avoid the misalignment and extra wear that can come from a generic or incorrect knuckle.
Rear Knuckle(55-SJ13) for HM123
