Brake Pad Squeal and other noises update


Why does brake squeal happen on different cars at different times, with different brake pad material, but not consistently across the range of make/model or brake pad brand?

Over the years we have all been well drilled that brake noise is directly linked to pad movement in the caliper. There are many possible causes for this including;- brake rotor surface roughness (regardless new or machined rotors), flexing of the caliper, caliper requiring overhaul, shock absorbers and bushes worn in front end, alloy mounting brackets expanding/contracting in heating and cooling cycles and the development of more rigid materials in the manufacture of pads.

Disc brake quiet, copper paste, various other sprays and shims have been produced to try and rectify this problem. In the past 20 years caliper designers, not pad manufacturers, have been changing the designs and material callipers and their brackets are made off, how pads are located in calipers. The only reason these changes are being continually advanced is to stop brake pad movement within the caliper body.

A bit of history-

  • Thirty (30) years ago calipers were designed, so the pad manufacturers had wire spring or clip set-ups on the pad, to absorb vibration or movement.
  • Twenty (20) years ago designs were changed so the bracket located around weird shaped “ears” or “lugs” of the pad, rather than just square lugs that slide, as the pad wore down.
  • In the last 10 years, caliper designers have taken this one step further by adding spring steel locating shims or clips to their bracket design, these for the most part aren’t manufactured by or sold with the replacement pad (regardless of the brand).

The spring tension that these locating shims or clips originally had, has been reduced or even eliminated over time thru use, heat cycles and general wear and tear.

In fitting replacement pads regardless of whether brake discs have been removed and machined, replaced with new brake rotors or even left as they are, the locating shims /clips need to be re-tensioned to enable them to do their job of stopping the brake pad from moving in the caliper.

There are two ways of doing this, removing the caliper body or removing the caliper body and bracket. Just as important as pushing the piston back, regreasing slides or cleaning muck away from where the pad slides, servicing the spring steel locating shims/clips by re-tensioning same is a must.

In the life of the worn out pads being replaced (well bedded in and cured over time) these spring steel locating shims/clips have been heated up and cooled down thousands of times over as many as 2-4 years, so when removing the old pads these clips usually stay in the bracket stuck in place (bedded or bent in the shape of the bracket) offering no tension.

These spring steel locating shims/clips were designed to take up the gap between the locating ears or lugs and the bracket guides thru the use of tension, to limit pad movement.

The three main scenarios of brake noise being;-

  • Light pedal application over the longer distance.
  • Short abrupt braking, causing the transfer of weight, to the front wheels.
  • “Graunch” or metal on metal sound, over the last 2-5 metres of braking.

In all three cases it has become more common in recent years, due to brake pad material  moving away from carbon or organic fibre content (which absorbed a lot of friction and therefore noise) to more metallic based products (due to legislation & technology to handle faster cars and higher temperatures being reached) that brake noise is on the increase.

In the first two symptoms of brake noise above, by bending/replacing the spring/clip tension you will reduce pad movement hence eliminating friction noise.

  • There are many different types of these spring steel locating shims/clips, but if you take the time to understand how each of these are designed to work and fiddle around with correcting them (re-tensioning) back to how they would have been originally, then your professionalism and thoroughness will show dividends.

In the third symptom, it is the pad which hasn’t reached it’s optimum working temperature to work efficiently, or indeed if the drivers driving style, type of car and pad compound chosen is not a suitable match (If one or two of these were different, the outcome would also be quite different).

Because pad manufacturers are moving to more and more semi metal, full metal and ceramic based materials to deal with faster cars and customer safety expectations, caliper maintenance (slides, clips, shims, piston overhaul) is an area that is requiring greater importance. Most of the focus has been on the bedding in of brake pad material to the brake discs (which is still very important) but as explained above, re-tensioning of the spring steel shims/clips, will also ensure a professional job is achieved and customer satisfaction is assured.