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Brake Pulling, Caliper Diagnosis


Your brakes are the number one piece of safety equipment on your car. Nothing is more important to your ability to safely drive down the road than are the brakes that stop you. In the forums, user Gwen6527 listed a problem with her brakes on her 1992 Saab 900S. She described it as:

" is pulling to the left (not in the steering wheel but the whole body shifts to the left when I brake. Nothing wrong with steering when driving, only braking. I have had all the brakes checked, blead, calibers checked and lubed. I have 47000 miles on this car and no mechanic seems to know what is wrong with it."

She may not believe it's the brakes, but it's the brakes. Forum mechanic Big Block 409 said as much and posted a video showing how to fix "brake creep" when a car pulls during braking.

You can see the video from the link above, which shows how a clogged brake line can cause the issue and how to repair it. If your problem isn't a clogged brake line, start looking at the caliper instead.

Calipers and How They Work

Most modern vehicles utilizing disc brakes have what's called a "floating caliper." Some may use a "fixed caliper" which is only slightly different in terms of how it operates to apply pressure to the disc.

A floating caliper sits atop the brake rotor (disc), straddling it. The caliper holds two brake pads, one on either side of the disc. Behind one of those pads is a piston which presses the pad forward. When the pad meets the disc, friction begins and the floating caliper then "clamps" onto the disc as the other side of the caliper is pressed against. The caliper is made to move a little in order to facilitate this clamping, hence the "floating caliper" name.

A fixed caliper works much the same way, but has pistons on both sides of the rotor disc, pressing from both directions to create the same stop. Because fixed calipers are more expensive to build and install, most vehicles use a floating caliper. You will see fixed calipers on many heavier applications such as pickup trucks and large SUVs, though.

In either case, the same things can go wrong with a floating or a fixed caliper.

Diagnosing Caliper Problems

The most common problem is a compromised piston seal or worn bushings.

A compromised piston seal can result in the caliper failing to clamp onto the disc or in the caliper squirting brake fluid onto the brake pad, lubricating the pad against the rotor and causing its friction to be reduced, destroying efficiency in the stop.

Similarly, a worn bushing can cause the caliper to separate slightly when under pressure, resulting in brake fluid loss and a loss of pressure to the piston, preventing the brakes from clamping.

Both of these problems should tell the mechanic what the problem is through tell-tale leaking. Another issue could be uneven brake wear due to rust or sticking. Both of these are usually due to worn or rusty slides or bushings.

Repair Options

There are two basic options for repair when the caliper has gone bad. One is to rebuild it and the other is to replace it. Most mechanics will likely find replacing it to be the lower-cost option on most vehicles. Rebuilding a caliper requires knowledge and time. Sometimes, if the issue is as simple as worn or rusty slides or bushings, replacing just those parts is a relatively easy fix. Worn pistons or bad seals, however, require more finesse to replace as the mechanic will need to not only take the brake caliper entirely apart, but also to thoroughly clean, inspect, and replace parts inside it. If you aren't sure what to look for to ensure that a caliper is in working order, either find an expert who does know or just replace the caliper.

Again, remember, your brakes are your car's primary safety feature.