Beware Of Rustjacking
If brake linings and shoes look like those in this photo, you have a severe brake rustjacking problem. Rust has formed on the brake shoe under the lining, eaten away part of the shoe table so the lining no longer has flat, firm support. Lining rivets work loose so lining can move which leads to cracking and even pulling loose from the shoe.
Chemicals spread on road surfaces to control snow and ice melt or mix with slush and rain and are sprayed all over a vehicle's undercarriage. The liquid works its way into brakes from the backing plate area and can attack shoes and linings. If dust shields are not used, road spray quickly gets on all brake parts. If brakes are applied frequently, there's sufficient heat buildup to dry them out which helps. Wet brakes on trailers which are then parked tend to be more susceptible.
Calcium chloride and magnesium chloride are the two most commonly used highway chemicals. Calcium chloride attracts and absorbs water from the air which also adds to the problem. States that use the anti-icing procedure of spreading chemicals on bare highways in anticipation of winter storms make matters worse. Rustjacking is worst in so-called "rustbelt" states which use large quantities of road chemicals in the winter but it can also happen in summer driving on dirt roads which may be treated with chemicals to lay down dust. Fleets operating in "rustbelt" areas report that frequent undercarriage washing helps to reduce the problem.
Dana and ArvinMeritor brake engineers report that it takes three or more years before brake rustjacking shows up. Routine under-vehicle inspections should include a check of lining edges (visible without dust shields) for cracking.
While rustjacking may show up on original brake linings, fleets report the worst cases seem to be on replacement linings on which the reliner has chemically removed the OE coating during the cleaning process, then dipped or sprayed the shoes with paints or coatings which are not chemical resistant. Rustjacking is reported more often when the reliner does not use all the rivet holes. This allows road splash to work through to the shoe table and form rust.
A TMC task force will be producing a White Paper covering this whole subject early in 2003. Right now you can get an in-depth understanding of vehicle rust and corrosion issues including brake rustjacking in HDT, September 2001 issue's award-winning article "Killer Chemicals."
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