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A Pulsing Problem

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On: Fri, Sep 2, 2011 at 10:48AM | By: Peter C Sessler

A Pulsing Problem

There are many reasons for vehicle brakes to pulsate, or move up and down (you can feel the pedal actually moving). This is often most noticeable when you have to slow down quickly from a high speed, and it can be unsettling.

As with any other repair, the first thing to do is eliminate the most obvious and easy reasons why this is happening. If your car has ABS brakes, are you sure that it isn’t that system causing the problem? If you know what the wheel speed sensors look like and see a bad connector or some other ABS-related component, it could be the source of your troubles. This is a long shot, but you never know.

Next, check to see if there are any technical service bulletins for brake problems on your particular car. This is another long shot, but again, anything is possible.

Before you start thinking it’s the brakes, check your wheel’s lug nuts. It’s possible that the lug nuts, or at least a couple of them, have been over-tightened, distorting the brake disc. You can check the torque of each lug nut with a torque wrench and if you find that there’s a 20-percent difference between any two lugs that could be your problem.

If you don’t have a torque wrench, simply remove each lug nut, clean the threads with a wire brush, lightly coat them with oil, and reinstall the lug nuts. Do this in steps—first finger tight, then in two more steps using a crisscross pattern. Again, since most people don’t own a torque wrench, tighten each lug so it’s "tight," but be careful not to overdo it. If getting some of the lug nuts off was really hard, then you can be pretty sure they were the problem source.

If that doesn’t do the trick, then you have to check the brake discs themselves. Some cars have four-wheel disc brake systems, so they can all pulsate. If you know from driving that it’s only the front ones that pulsate, then you don’t need to check the rear ones. If you’re not sure, all you have to do is to drive the car slowly in a deserted parking lot. Slowly engage the parking brake (which works only on the rear wheels) and if the car stops smoothly, then you know it’s not the rear brakes.

Sometimes, if the discs are wearing unevenly, it could mean a sticking or bad caliper piston. If the caliper doesn’t move back and forth smoothly it can cause brake chatter and pulsation. If the guide bolts look pretty cruddy, just replace them with new ones, and use silicone grease on them and the bushings they typically fit through.

However, more often than not, the problem is with the front brakes. The correct way to do this is to use a micrometer to check the disc for uneven thickness and compare these specs with what the discs are supposed to be when new. It’s amazing how a small variance of .0008 inches can be felt, but typically, anything over .0005 inches will make the brakes pulsate. There are two choices here—either have the discs cut or replace them. You’re probably better off in having them replaced. The problem is that a lot of cars these days come with discs that are a little on the thin side to begin with. If they get overheated and warp, they’re done. And if you do decide to replace the discs, you should have them checked before installation as well. Many times they’re off.

You may have noticed that prices can vary significantly from part store to part store when it comes to replacement discs, or even brake drums, for that matter. There’s a good reason for that. Often, you’ll find that the "cheapo" replacement discs are a lot thinner to begin with and that’s something you don’t want. It’s better to get discs and drums that are as thick as the original equipment parts.

Hopefully one of these solutions will solve all your pulsating problems!


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