Jim Grant's Tech Tips
97 Jeep
Grand Cherokee, Brake Problems
Q: We have a ‘97 Grand Cherokee with 55k
miles. It just had the 4th set of brakes put on including the original
set. The rotors and pads were replaced each time. That equals a new set
approximately every 14k miles. It is driven in very mild conditions around
town with no heavy braking. It always has the same problem. The brakes
feel like they engage and disengage as you come to a stop. It gives a
slow pulsing sensation.
The first
evaluation always offered is warped rotors. The problem is that immediately
after a brake job you still can feel this problem. It’s milder at first
and then becomes more pronounced as time goes on. I also know it has nothing
to do with the rear brakes because if you use the hand brake to stop you
don’t get the symptom.
The second
theory is some type of ABS malfunction.This
has been completely dismissed by the dealer.
Any idea
what the problem could be??
A: How
about checking the hub that the brake rotors are mounted on? Just the
day of answering your letter we a had a Mercury Crown Vic in the shop
that had a brake pulsation complaint. Diagnosis indicated that the front
brake rotors were the problem. From what we were told, they had been a
problem for sometime. As often as possible we’ll machine the brake rotors
on the vehicle. When the equipment was installed on the vehicle to machine
the rotors there was a problem. The computer, yes we used computerized
equipment to perform this task, was at a loss. It could not calibrate
itself properly, meaning it needed help from a carbon based life form
(humans). Inspection found that the hub that the brake rotor set on was
off by .003" of an inch. Now .003" of an inch is just about 2 hairs stacked.
That’s not much you may say. But, in the world of brakes that adds up
to a lot when you carry that line out another 4 to 5". My point is that
no matter how many brake rotors are installed on this vehicle the brakes
will always end up pulsating,, which could very well be the problem with
your vehicle. They just have to look deeper. As for the Crown Vic, there
is no silicone based form (computer) that can problem solve the way the
carbon forms do.
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