Dealing with Brake Squeal
by Brian Brown
Brake squeal is caused by the brake pads vibrating when light to moderate brake pressure is applied. Heavy braking usually stops squeal because the extra pressure dampens the vibration. If heavy braking doesn't stop the squealing, it's a sign of a significant problem. Squealing under light braking isn't a safety concern, it's just annoying.

When squealing occurs, it's usually the leading edge of the brake pad that is in contact with the rotor, causing a twisting force on the pad that makes the trailing edge want to lift away from the rotor.

PREVENTIVE MEASURES WHEN INSTALLING NEW PADS:

PADS: Pad compound is a big factor with squeal resistance:

(I still have the stock pads in my ti. The following comments are from experiences with other cars.)

The factory pads have pretty good squeal resistance, good fade resistance, and are pretty easy on the rotors. They do have pretty messy dust.

Some popular aftermarket pads, the Repco/PBR/Axxis Deluxes, have excellent squeal resistance, good fade resistance (but not as good as stock), are easy on the rotors, and have relatively clean dust. A good choice for average street driving.

The Repco/PBR/Axxis Metal Masters have good squeal resistance, much better than stock fade resistance, moderate dust, but are harder on the rotors. These work well for harder street driving.

Track pads are beyond the scope of this post (it's probably best to use a separate set of track pads anyway). Some of these can be used on the street (if they operate OK when cold) and can be kept reasonably quiet if proper precautions are taken. If improved fade resistance is needed, it would probably help to replace the front rotors with the vented versions from the 328 (and with the matching calipers). M3 brakes (maybe even those nice european M3 floating rotor versions) would have even better fade resistance, but would require larger wheels. Rear vented brakes are probably much less of a benefit for the ti (unless the ASC + T can be reprogrammed to actuate the brakes at higher speeds without cutting back the engine so much :} - anyway I'd better get back on topic).

There may be some other suitable aftermarket pads as well. NAPA premium pads are pretty good (somewhere between the Deluxes and Metal Masters in their characteristics). Stay away from economy pads. I've seen junk pads available for all sorts of cars, even expensive performance ones. These are often seen as the cheap option at national auto parts chains. A couple of hard stops and they're smoking. These don't save any money anyway because they don't last very long at all.

I probably should also comment about Friction Tech pads. These are being promoted a bit for BMW's. They have OK fade resistance, but are exceptionally prone to squeal. I tried one set, and it took every trick in the book to quiet them down. I have heard of similar experiences from others.

When installing new pads, make sure that they fit with just a tiny little bit of clearance in the frame. Hold the backing plate next to the pad that is being replaced. If the new pad has significantly more clearance (so that it will fit looser), I would probably send it back. If it fit's too tight, a little bit off the edges of the backing plate with a file can help (particularly if the tightness is due to a sharp edge left from the stamping process). Again, use the old pads for a comparison of the outline.

ROTORS: If there was previously any pulsing of the brakes, the rotors should be replaced. Even if they are machined, the warpage will probably return.

If the rotors aren't worn too thin, and there are no significant groves, I usually leave them alone and replace the pads. I do clean them up though. Eastwood sells a ~1.5" diameter 3M Scotch Brite disk that's backed with velcro. They have a mandrel that can be mounted in a hand drill to hold these disks. Used wet with brake cleaner, this does an excellent job of cleaning and polishing the rotors. (This is also excellent for preparing gasket surfaces on engines).

Rotors are reasonably inexpensive to replace on these cars (especially the solid ones). Because of this, and also because I've had pretty good luck with rotors wearing evenly, I usually don't get rotors machined. I just replace them when it's time. Make sure to completely clean off the protective coating before installation.

If a rotor is grooved, but still has enough thickness and isn't warped, then machining can be a good option.

Most shops machine rotors on a brake lathe. This leaves an annealed surface that new brake pads can have difficulty seating against. A much better option is to take the rotors to a machine shop that has a machine for regrinding flywheels. This is a rotary surface grinder. It leaves the surface with a nice open - pore cross hatch pattern that will allow brake pads to seat much better. This is the same surface finish that new rotors have. It's surprising, but in my experience it doesn't cost any more to have this done than to have the rotors turned on a regular brake lathe.

CALIPERS: The main thing is to make sure they slide freely on the guide pins, and that the piston moves smoothly when pressed back in. If not, fix the problem. If the pins need to be regreased, completely clean out all traces of the old grease before applying the new. This will prevent compatibility problems. Also make sure that none of the rubber parts are torn. If the pistons are sticky in the calipers, rebuild kits are available. Unless the piston has rusted up, these kits are only a fraction of the cost of a caliper.

CLEANLINESS: Try to keep everything as clean as possible. Use brake cleaner to spray down dust before disassembly. Don't stir up dry dust. Make sure the pads and rotor surfaces are very clean before reassembly.

Side note: I like to use Nitriol rubber gloves when working on cars. These are similar to latex surgical gloves but are much more durable, both in terms of tear resistance and solvent resistance (carburetor cleaner will soften them up pretty quick, but they resist just about everything else). These allow a good feel for handling parts, while protecting your hands. A side benefit is that they can be quickly wiped clean with alcohol, so that you don't contaminate clean parts right after handling dirty parts. You can't keep recleaning bare hands like this.

Laboratory supply and farm supply places usually carry these. I've been surprised that I've never seen them offered by an automotive place (usually just the junky latex ones). I use the 4mil thickness for most things, but 6mil and 8mil are also useful to have around.

BREAK-IN: For street pads, take it easy on them for the first fifty miles or so, especially with reused rotors. This gives them time to seat without glazing over. Track pads are different in that they require some hard stops to seat and temperature cycle them.

TROUBLESHOOTING SQUEAL:

If new pads are squealing and the above precautions were taken, try the following:

Remove the pads. If they are glazed over (from braking too hard before they were seated), wet sand the surfaces with brake cleaner (so you don't generate dust). Take a file and bevel the leading edge of the pad about an eighth of an inch. (This prevents the leading edge from digging in quite so hard, so that the trailing edge won't be driven away so hard by pad rotation.

I usually don't find it necessary to supplement the anti-squeal springs. If the brakes still squeal, NAPA sells anti-squeal shims with an adhesive backing that stick to the back side of the brake pads. These work much better than the spray or brush on anti-squeal coatings that I've tried. I've usually only needed to use these when running combination track/street pads.

If pads develop squeal after a long period of use:

Try braking hard a few times. This might be successful in breaking through any glazing that's occurred or clearing away dirt.

If that doesn't work: Remove the pads. If the trailing edge of the pad is thinner than the leading edge, replace the pads (something else is probably sticking). Check to make sure the caliper is sliding freely on the pins. Clean the rotor. Wet sand the pads and bevel the leading edge.

Hopefully that will take care of the problem.

Regards, Brian Brown


http://www.318ti.org/notebook/brake_squeal/
September 17, 1999