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Jim Grant's Tech Tips
93
Nissan Sentra, Unrepairable Brakes
Q: I own a '93 Nissan Sentra (purchased new),
with 112,000 miles on it. At 90,000 miles, having had NO problems with
my brakes, I had the front disc brake pads replaced due to normal wear.
Beginning Of Problems! Every few thousand miles since, I have had the
pads or the calipers replaced or the rotors turned down or replaced. It
has developed a pulsation, almost imperceptible at first, which grows
steadily worse, to the point where the car actually shakes when slowing
to a stop. The pulsation is always in the left front wheel and, upon inspection,
the pad(s) on that wheel are excessively worn and must be replaced along
with the caliper, and/or the rotor turned down or replaced.
Although after the initial charges for the original repair, my cost has
been nil, I would like to extricate myself from these regular trips to
the repair shop and get the job done right once and for all. Am I being
unreasonable, or have you ever encountered a situation like this? In trying
to apply logic to the problem, it seems as though either the parts are
defective or the installation is not being done correctly. The large number
of parts seems to rule out the former, and I am reluctant to suggest the
latter. On the other hand, could there be a non-brake part causing the
problem,-a suspension part perhaps?
A:
Why would the front brakes on one side of the
car wear faster than the other? There are three possible causes for your
brake problem.
1. The brake pads and/or caliper are sticking, not moving freely. The
possibility of the brake calipers sticking and not moving freely after
so many repair attempts is unlikely, but I wouldn't rule it out. Another
problem area is the holder for the brake pads which is called a torque
member. Rust and corrosion can cause the brake pads to bind in the holder,
not releasing completely, accelerating brake pad wear.
2. The brake is being held on, brake pressure not being released. It takes
only a small amount of residual brake pressure to hold the front brake
on slightly. The result is rapid pad wear and rotor problems. This can
be caused by a bad brake hose that is degrading internally, blocking the
return of brake fluid after the pedal is released or a misadjusted or
failing master cylinder.
3. The opposing brake is not working, due to misadjustment, air in the
system or a mechanical problem. If I'm not mistaken, your Nissan uses
a split diagonal braking system. This means that the left front and right
rear wheel are one part of the hydraulic system, while the right front
and left rear are the other part of the system. Air, misadjustment or
mechanical problems in a hydraulic system for the left rear and/or right
front will cause accelerated brake wear on the left front.
Just focusing on the left front brake could be misleading. Have the garage
check the braking system completely, all four wheels.
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