Rick's Free Auto Repair Advice

Swollen lug nuts

Swollen lug nuts — What causes lug nuts to swell and how to remove them

What is an acorn lug nut?

An acorn style lug nut protects against water intrusion into the threads. That feature, by itself is a great idea. But there are two ways to make an acorn style lug nut: 1) weld a steel cap over the end of the lug nut prior to chrome plating the entire lug nut, OR, 2) form a thin aluminum cap over the steel lug nut.

solid versus capped acorn lug nuts

The first method is more expensive and adds weight to the vehicle. The second method is less expensive and lighter, but cause problems down the road, and that problem is referred to as swollen lug nuts.

What causes swollen lug nuts ?

Rust Jacking. As steel rusts forms, it expands outward with great force. Rust jacking develops enough force to distort the aluminum shell that was formed around the steel lug nut. At that point the 21mm socket not longer fits properly on the lug nut.

The shop is faced with using a lug nut removal socket which damages the

stripped lug nut with cap

Swollen lug nut removed by using a chisel to peel back the formed cap to the point where a regular socket will fit over the steel lug nut.

lug nut or, in extreme cases, they must use a hammer and chisel to peel off the cap.

How to prevent swollen lug nuts

There is no way to prevent capped lug nuts from rusting.

The only way to prevent lug nuts from rusting and swelling is to replace them with solid acorn lug nuts. Solid lug nuts are available online. Just make sure you buy the correct thread size and taper to fit your wheels.

How to remove swollen lug nuts

There are three ways to remove swollen lug nuts

Method 1— Buy half-sized sockets

Buy a 19.5mm or a 21.5mm socket to fit over the swollen lug nuts

half size lug nut sockets





Method 2 — Buy stripped lug nut removal sockets

stripped lug nut sockets






Method 3 — Chisel off the formed cap and use a regular socket

Use a small cold chisel and ball peen hammer and chisel off the acorn cap. Then slice down the sides of the lug nut and peel the thin metal away from the hex nut until you can fit a socket over the steel lug nut.

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Posted on by Rick Muscoplat


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