Uneven wear on brake pads is most easily identified by a difference in the thickness of the lining between the left and right wheels on the same axle. This is usually accompanied by a squeal or grind coming from only one side of the vehicle, as well as vibrations in the steering wheel or brake pedal. This indicates a mechanical problem with the braking system, rather than normal wear and tear, and requires the car to be checked before the braking distance increases.
In short
- A difference in pad thickness on either side of the same axle is the most reliable sign of uneven wear.
- A seized caliper or piston is the most common mechanical cause of the problem.
- A warped disc and fitting errors also lead to uneven pad contact.
- The seasonal tyre change is a natural opportunity to check the condition of the brake pads whilst you’re at it.
Contents
1. What does it mean if the brake pads are different thicknesses on either side of the axle?
2. What symptoms in the car indicate uneven brake pad wear?
3. Why is a seized caliper usually the cause of uneven wear?
4. How does a warped disc affect the performance of the brake pads?
5. How do errors during brake pad fitting lead to uneven wear?
6. How long can you drive with unevenly worn brake pads?
7. Why is it worth checking the brake pads when you change your tyres for the season?
What does a difference in pad thickness on either side of the axle mean?
A difference in pad lining thickness between the left and right wheels on the same axle means that one of the pads is pressing against the disc harder or for a longer period than the other. A set of brake pads fitted to a single axle comprises four friction pads – two in each caliper – and in a properly functioning system, they should wear at a similar rate. If one of them is noticeably thinner, this is a sign that something in the system on that side is not working as it should, rather than a random occurrence.
A quick glance through the wheel rim allows you to assess only whether the lining is still present at all; it does not, however, reveal the extent of the difference between the sides. An accurate comparison of thickness requires removing the wheel and measuring both pads with a calliper or comparing them visually side by side. A mechanic removing the wheel will spot this difference straight away, which is why regular checks whilst other work is being carried out at the garage can help identify the problem before the pad is worn down to the metal.
What symptoms in the car indicate uneven brake pad wear?
Uneven brake pad wear is rarely limited to a difference in thickness alone and is usually noticeable whilst driving as well. The driver most often notices a squeal or grinding noise coming exclusively from one side of the vehicle, vibrations in the steering wheel or brake pedal, and a noticeably longer stopping distance. In more extreme cases, the car may pull to one side whilst braking, which is particularly dangerous during emergency braking.
- A squeal or grinding noise coming from only one side of the vehicle: a sign that the brake pads on that side are closer to their minimum thickness than those on the other side.
- Vibrations in the steering wheel or brake pedal: most often caused by a warped disc or uneven pad contact.
- Increased braking distance: reduced contact area between the pad and the disc on the side where the lining is already thin.
- The vehicle pulling to one side when braking: a difference in braking force between the left and right wheels on the same axle.
Why is a seized brake caliper most often the cause of uneven wear?
A seized brake caliper – or, more specifically, a piston or guide pins that do not retract freely when the brake pedal is released – is the most common mechanical cause of uneven pad wear. The caliper is the component of the system in which the brake pad is mounted, along with the piston that presses it against the disc during braking. When the piston seizes up, the brake pad remains partially pressed against the disc even after the driver releases the pedal, and rubs against it throughout the journey, not just when braking.
Such constant contact causes the brake lining on the side with the seized component to wear down much faster than on the side where the component is functioning properly, which explains the difference in thickness described earlier. In extreme cases, constant friction leads to the pad and disc overheating, and can even cause the wheel to lock whilst driving. A similar effect is caused by a rusty or dry caliper guide, which prevents the caliper from moving evenly relative to the disc.
How does a warped disc affect the performance of the brake pads?
Even a slight warping of the brake disc causes the pad to apply pressure more strongly at one point and less strongly at another during a single wheel rotation, which over time accelerates its uneven wear. This phenomenon is most noticeable when braking from higher speeds, and it is then that the characteristic vibration of the brake pedal is easiest to feel. Disc warping can be caused by overheating during heavy use, hitting a kerb, or natural wear and tear after many thousands of kilometres.
If the warping is minor and there is sufficient material thickness, the disc can sometimes be machined; however, in practice, it is often safer and more effective to replace it with a new one, especially in older vehicles where the remaining material depth is already limited. A warped disc replaced without checking the cause of the problem with the brake pads usually does not fully resolve the issue, as a new pad pressed against the same defective surface will start to wear unevenly again.
How do errors during pad fitting lead to uneven wear?
Some cases of uneven wear are not due to a fault, but to the very way in which the pads were previously fitted. A lack of grease on the metal guide plates, failing to clean the hub before fitting a new disc, or poorly fitted, cheap replacements can cause the pad to perform differently from the very first day. That is why, before replacing the brake pads, we carry out a full computer-assisted diagnostic check of the braking system, rather than simply inspecting the condition of the brake linings.
After fitting new, fully genuine components, we carry out a series of tests to confirm that the brakes are working correctly on both sides of the axle, and not just on one. Such a check after replacement allows us to spot any fitting errors straight away, before the customer leaves the workshop, rather than only after a few weeks’ use. This is precisely why, during routine technical inspections, brake pads and discs are checked first, regardless of what other problem the car in question is brought in for.
How long can you drive with unevenly worn brake pads?
If your brake pads are clearly worn unevenly, you shouldn’t delay a visit to the garage any longer than until the next convenient appointment; and if there are severe symptoms, such as the car pulling to one side when braking or a metallic grinding noise, it’s better to limit driving to the absolute minimum. Vibrations that can be felt as soon as you lightly press the pedal usually indicate a more serious problem than vibrations that only occur when braking hard from a higher speed. This difference helps you assess whether the issue is urgent or whether you can still safely drive to a garage as normal.
Delaying action usually results in faster wear of the disc on the side that is working harder, and sometimes also damage to the caliper, which previously would simply have needed cleaning and lubrication. The cost of such neglect increases with every thousand kilometres driven, as replacing the brake pads then also involves replacing the disc or repairing the caliper. Regular, early checks therefore remain a cheaper and safer solution than waiting until the problem becomes audible to the naked ear.
Why is it worth checking the brake pads during a seasonal tyre change?
A seasonal tyre change is a natural opportunity to check the condition of the pads and discs whilst you’re at it, as the wheel is already off and accessing the braking system requires no extra work. That is why, at our garage, brake pads and discs are checked first during every service, regardless of whether the customer has come in specifically for a tyre change or for another service. Combining these two tasks in a single visit saves the driver time and allows us to spot uneven pad wear before it has a chance to develop.
In this way, we serve both private customers and companies with delivery vehicle fleets, for whom regular servicing is particularly important given their high annual mileage. The journey to the workshop is shortest from the Bemowo and Ursus districts, but customers from other parts of Warsaw, including Ochota, Włochy and Mokotów, also regularly make use of this combined service. A few minutes’ extra checking whilst having tyres fitted can save considerably more time and hassle than a separate visit once uneven brake pad wear makes itself felt in the form of squeaking or vibrations.
Summary
- Different pad thicknesses on either side of the axle, and squeaking or vibrations on only one side of the vehicle, are the most reliable signs of uneven wear.
- The most common causes are a seized caliper, a warped disc and errors made during the previous fitting of the pads.
- The seasonal tyre change is a good opportunity to check the condition of the entire braking system whilst you’re at it.
- The sooner a problem is taken to a garage, the less work is usually required to fix it.