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What Causes a Wheel to Get Hot? (Fix it like a pro!)

Who doesn’t like hot wheels? Well, when it is caused by a dragging brake, tell when it’s a real pain in the hiney. In most cases, the fix is an easy one, and you are in the right place. I’m a mechanic, and we are about to fix this exact problem.

Vehicle wheels will naturally get hot with increased braking; excessive heavy breaking will cause them to get hot enough to smoke and glow. However, a vehicle with a single hot wheel suggests a brake fault; it’s dragging on that wheel.

In this post, you’ll learn why your vehicle’s wheel gets hot, how to diagnose it and what you can do to fix it.

Mercedes wheel with Conti tire

Index

Hot Wheel & Sticking Brakes

A hot wheel goes hand in hand with a sticking brake, also known as a dragging brake; it’s a real pain and comes with some additional symptoms, which include:

  • Vehicle pulling to one side
  • Vehicle feels sluggish
  • Vehicle hard on gas
  • Excessive brake dust on one wheel
  • Brake noise
  • Brake grabs aggressively

The easiest way to diagnose a suspected sticking brake is to jack up the hot wheel (always on a level sealed surface) and with your vehicle in N (neutral) and parking brake off, try to spin the wheel by hand. A wheel should spin freely and, at the very least, continue to spin a little after hand spinning.

If it’s hard to spin, you’ve found the most likely reason for a hot wheel – Your brakes are dragging, also known as stick.

You should know it’s best to run this test when your vehicle is hot, as brakes rarely don’t drag until they heat up. The heat, as you likely know, causes the components to expand, which commonly results in unwanted brake pad and rotor contact.

Why Do Brakes Drag?

Dragging brakes are brakes that don’t fully release after the operator presses the brakes. The reasons as to why that happens to vary by what type of brakes you have fitted on the sticking wheel. 

Passenger vehicle brakes come in two flavors, rotor and drum brake setups. Most modern cars have the rotor caliper set up, but less expensive cars typically employ rotors & calipers to the front and brake drums to the rear.

Usually, rotor & caliper brake drag is caused by a faulty caliper issue, brake pad issue,  contaminated rotor, or brake line issue.

Usually, brake drum drag is caused by an issue with the shoes, brake hardware, drums, or brake cylinder.

Diagnose the Root Cause of Brake Drag

As there are two types of brake systems, we’ll deal with them individually. First, we’ll look at the rotor type, which is fitted to the front wheels of all passenger vehicles. However, your vehicle may have drum brakes fitted to the rear, and if that’s the wheel that’s sticking, you can skip this section and jump on down to drum brakes here.

Rotor & Caliper Type

A rotor-type brake setup consists of the following components:

  • Rotor
  • Brake calipers
  • Brake pads
  • Brake lines (hard & soft)
  • Brake modulator
  • Brake master cylinder and reservoir
  • Brake equalizer
  • Brake booster 
  • Brake pedal
  • Brake fluid

Typically the first three or four items on the above list are what cause brake drag in a rotor brake setup. And of those, the most likely cause is a faulty brake caliper. That said, the other components play their part, too; very often, it’s more than a single component causing the problem but a combination of all three – Rotor, caliper, and brake pads.

Next, we’ll look at each in a little more detail, together with how to diagnose it and what you can do to fix it today. We’ll begin with the calipers, as they are likely the main contributor.

Faulty Caliper

Calipers work really hard and in a hostile environment; no surprise then, a faulty caliper is right up there on our list of possible causes. Caliper issues are always more common in salt states than in the southern dryer.

Typical caliper issues include frozen pistons and binding caliper slides. Calipers come in two main flavors – Sliding or Fixed calipers.

Fixed calipers are, as their name suggests, fixed and employ pistons on each side of the brake rotor to apply the brake pad. Fixed calipers are typically fitted to higher-end and performance vehicles. 

Most vehicles, however, are fitted with what’s known as a Floating caliper. So-called because they slide laterally on slide pins. 

The floating caliper employs one or, on larger vehicles, two pistons on the inner side of the rotor only, and because the caliper is free to slide laterally, applying the brakes forces the caliper to slide across, thereby pulling the outer pad against the rotor too.

The floating caliper, as said, may be single or twin-piston, but you’ll always recognize a floating caliper as the piston(s) will only be fitted to the inner rotor side and, of course, when grabbed, pushed, and pulled latterly you’ll feel a little give.

Since floating calipers make up the vast majority, we’ll focus on them. That said, much of the same content applies to fixed calipers.

How to diagnose – 

The process is as follows:

  • Jack up the offending wheel and remove (on level sealed surface and support vehicle with axle stand)
  • Spin wheel (tranny in N and parking brake off) to verify it is dragging (stiff to turn)
  • Using a flat long, handled screwdriver, lever the caliper piston(s) back a little by prying on the pads as per the diagram below. We don’t need much, just enough to move the pistons back and make some wiggle room for the pads.

Now go ahead and try spinning the rotor by hand. At this point, two outcomes are likely:

  1. The rotor is a lot easier to spin now. If that’s the case, it’s likely your caliper is the root cause and most likely because the caliper slides are dry or corroded or both. Removal and cleaning will fix it; we’ll cover that below.
  2. The rotor feels the same, stiff to spin. If that’s the case, your caliper, brake pads, or brake line could be at fault. We cover brake pad and brake line diagnosis below, and we’ll deal with the two common caliper faults next in this section.

How to diagnose two common caliper faults

The two main caliper faults include:

  • Caliper slides dry or corroded
  • Caliper pistons frozen

Caliper slides dry or corroded – As you know, a floating caliper must slide freely. To this end, floating calipers employ two lubricated and sealed slide pins. The problem is that although the slide pins are fitted with weather and dust-protected boot, some moisture still gets in. And eventually, unless regreased by a mechanic, that moisture promotes corrosion. 

The corrosion obviously prevents free movement, and you know the rest.

The fix: To reverse this process, we’ll need to remove the brake caliper and remove the slide pins, clean, regrease and replace rubber boots if damaged. Use silicone grease as petroleum grease will damage the rubber protection boot.

There’s another possibility here; the slide pins may be frozen solid in the caliper bracket. If that’s the case, we’ll need a replacement caliper bracket, slide pins, and boots. Unfortunately, this will require a visit to the main dealer or a used parts dealer. 

Caliper pistons are frozen – A frozen caliper means the caliper piston just won’t move back into the caliper body, no matter how much you pry on it. The most common root cause is the corroded caliper piston wall. 

bRAKE FLUID CHART

The corrosion on the wall causes the piston as it tries to slide back into the cylinder of the caliper. Pistons are under attack from moisture both on the exterior and from the moisture within the brake fluid.

Brake fluid attracts moisture and should be replaced every 3 to 4 years unless your vehicle uses silicone fluid.

Anyhow a frozen caliper needs to be replaced, we don’t repair them, and it’s best to replace both left and right calipers as pairs, making for improved braking stability.

To test for a frozen brake caliper, we’ll need to open the bleed screw. (Note when we open the bleed screw, the brakes will need to be bled afterward as the system will take on air. I’ve covered brake bleeding previously, and you can check it out here. “Spongy brakes after bleeding.”)

The caliper test process is as follows:

  • Open bleed screw
  • Pry or use channel locks to push back the piston

The fix: Two outcomes are likely:

  1. No brake fluid squirt and the piston didn’t move any. If that’s the case, your caliper is indeed faulty and needs to be replaced. Remember you’ll need to replace both left and right on the same axle and bleed the brake, or better, replace the brake fluid altogether.
  2. Fluid squirts from the bleeder, and the piston now moves back. If that’s the case, then your caliper is OK; it doesn’t need to be replaced. Instead, you have an issue with the flexible brake line, and you can jump ahead to that repair here.

Brake Pad Issue

Brake pads are at the business end of stopping your vehicle. Are they important then, you betcha they’re important, and because they are under a ton of stress, they cause a ton of issues.

Here’s a list of the more common brake pad issues:

  • Brake pads corroded or broken
  • Pads are worn out
  • Pads are too tight in the carrier
  • Pads fitted on the wrong side of the vehicle
  • Brake pads are contaminated

How to diagnose – Let’s deal with all of these in turn:

Brake carrier corroded – technically, this isn’t the brake pad, but it directly affects the pad’s operation. The brake carrier is positioned over the rotor and is fixed to the hub. The pads fit neatly into the carrier on either side of the rotor, and the caliper fits over the top. Carriers have an important function. Not only do they keep the rotor in place, but they keep the pads in place too.

Problems occur when corrosion buildup on the carrier rail prevents the pads from moving away from the rotor. This is easy to spot with the caliper and pads removed and a wire brush and some copper grease to fix the issue. 

Pads wore out – worn-out pads can bind and cause the brakes to drag. That said, the noise should be a dead giveaway that something is up.

Pads are too tight in the carrier – In some cases, new pads don’t fit correctly. I’ve worked at a dealership where we had to file the metal backing of pads, so they fit correctly, and they were OEM pads. Just saying, if you have to hammer the pads into place..then something up. 

Pads fitted on the wrong side of the vehicle – While pads may still fit on the inside or the outside of the rotor, they may be specific. Some pads are designed specifically for fitting inside or outside. Check the location is correct.

Brake pads damaged or contaminated – Contaminated pads may well jam and stick inside the carrier. Oil road salts all contribute to general brake contamination.

Contaminated Brake Rotor

So what is a contaminated brake rotor? A rotor, also known as a brake disc, is the circular disc seen behind the wheel. It’s fixed to the wheel hub and so rotates with the wheel. 

The brake caliper and pads remain fixed, and when the brakes are activated, the pads are forced against the rotor, slowing the vehicle. 

A contaminated rotor is a rotor (disc) where the surface is affected by contamination, such as corrosion (rust), road grime, oil, brake fluid, etc. 

The contamination generally causes the brakes to grab aggressively, which, when used regularly, will generate excessive heat.

How to diagnose – As many modern vehicles are fitted with spoked wheel rims, it’s generally possible to view the outer surface of the rotor without removing the wheel, but the inner side will remain hidden.

Inspect the rotor and check for hot spots (surface discoloration, such as blue tint) or any obvious difference in the surface of the rotor. 

How to fix – Not all rotor contaminants may be fixed; surface corrosion may be cleaned indeed; driving the vehicle and applying the brakes is sufficient generally to clean naturally occurring surface rust.

If, however, the corrosion is beneath the rotor surface, the rotors will need to be removed.

Stubborn surface rust may be removed with rough grit paper and brake cleaner. Note that brake pads will also need replacing as the contamination transfers to the pads. It is possible to clean the pads so long as the contamination hasn’t penetrated the material.

Brake Line Issue

A brake line may fail in such a way as to cause the brake to stick on. This condition really only happens in older cars. The background to the condition goes like this.

As your brake calipers are fixed to the suspension, they move up and down; a flexible rubber brake line is therefore needed to continue the brake fluid from the hard chassis mounted lines to the dynamic calipers.

The flexible rubber lines known as flexi lines are through kit. They are twin walled to guard against puncture impacts from road debris.

In vehicles where the brake fluid isn’t changed as regularly as it should, the old fluid causes the inner walls of the brake lines to break down.

Strips of the inner wall partially peel away and act as a valve blocking the return fluid and jamming the brake in the on position. We’ve sort of covered this test previously in the caliper test, but here it is again.

How to diagnose

  • Open bleed screw
  • Pry or use channel locks to push back the piston
  • If fluid shoots from the bleed screw, your flexi hose looks good. If, however, no fluid squirts from the bleed screw, then go ahead and remove the flexi hose from the caliper side and use channel locks to once again push the piston back. 
  • If the piston now moves back, you have a faulty flexi brake hose.
  • If the piston fails to move back, it’s a caliper issue.

How to fix – Best to replace all flexi brake hoses and fill the system with fresh brake fluid.

Brake Fluid Reservoir Too Full

While an overfull reservoir isn’t the most common cause, it is worth mentioning as I’ve experienced it a few times while chasing brakes that stick but only when they heat up.

The fluid in the reservoir has a min and max for good reason; the fluid level changes as the brake pads wear down, brakes are applied but also as the temperature of the fluid changes due to heat soak.

The fluid expands when hot, and so that expansion must be taken up somewhere. If the fluid reservoir doesn’t have the expansion space, then the next accessible space is pushing out the pistons, and that’s exactly what the hot fluid does.

That said, it would push all brakes on, not just one wheel. 

Brake Drum Type

Typically brake drum brake drag is caused by an issue with the shoes, brake hardware, drums, or brake cylinder.

Drum brakes too tight

Most drum brakes are self-adjusting and don’t need manual adjusting. That said, drum brakes still need a little Luv; they like to be inspected for correct adjustment and cleaned. Excessive brake dust buildup can cause brake hardware to bind. 

Brake cylinder issue

The brake cylinder is the business end of pushing out those brake shoes against the rotating drum. Cylinders are famous for leaking, and a leak will be obvious. (drum wet at the bottom) The leaking cylinder contaminates the drum, shoes, and brake furniture and very often causes brake drag.

Brake shoe fault

Contaminated, damaged, or worn-out shoes are all possible reasons they stick. 

Brake hardware issue

Broken hardware and springs usually break off and become trapped between the shoes and drum, causing them to stick on.

Drum issue

An out-of-round, damaged, or corroded drum will cause all kinds of crazy. This content is owned by moc.sotuaytsu

Drum removal is required to fully inspect for wear, damage, or contamination.

Hot Wheel & Worn Wheel Bearing

Excessive friction caused by a worn-out wheel bearing will cause the wheel rim to heat up. It is a much less likely cause of wheel heat but is nonetheless a possible culprit.

There are some other tell-tale signs of a worn-out bearing too, and here they are:

  • Excessive roar
  • Possible wandering steering

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