At 09:22 AM 7/11/98 -0500, Becky Mahoney wrote:
>While out driving my 'B' .... I have been hearing a thumping noise coming
from the front left side. .... when I turn the rotor it turns freely most
of the way, then gets tighter, and then loose again. Apparently a warped
rotor....
Yep.
>If this is the case, do I need to replace or can it be turned???
It can be turned as long as it's not thinner than the minimum spec.
>When you measure the rotor, where do you measure?? Is it just the
thickness of the rotor...front to back?? What should it be?
Use a micrometer or vernier (or dial) caliper to measure the thickness of
the flat (and hopefully shiney) part of the disk. if it has scratches or
grooves in it, try to measure to the bottom of the grooves, because that's
where the surface will be after it is shaved down enough to be clean again.
Compare your measurement with the specified minimum thickness. If it
looks like it will thinner than the spec after cutting, it's time for a new
rotor.
You could also measure the run out on the disk, the deviation from
flatness. If you have a dial indicator, set it up aginst the side of the
disk while it's still mounted on the car and turn the disk by hand through
at least one full rotation. The variation of the indicator will show you
how distorted the disk is. When considering the thickness of the disk,
also subtract the amount of run out, as that amount will also have to be
cut away to get the disk to clean up.
And as a matter of cost, local parts stores should have pads and shoes for
your MG at very reasonable prices (maybe half of Moss list), and many of
these stores will turn your rotors and drums for free when you by the pads
or shoes. In fact they prefer to turn the rotors and drums for you, as
they will often also extend a lifetime warrantee on the pads and shoes. It
pays to check around, and ask about the warrantee and free turning.
>Could this be making the noise? I did notice that when I press on the
brakes, the noise seems to get louder.
Don't be surprised if turning the rotors does not bannish the noise. A
clunking sound indicates something loose. A warpped rotor by itself can
cause a little vibration and/or shaking of the steering wheel while
driving, and you may feel a pulsation in the pedal when you apply the
brakes. But any of that should not make noises in an otherwise healthy
car. In fact, if there is a little looseness in the caliper, pads, rotors
or wheel bearings, the noise may actually go away when you apply the brakes.
So while you're under there doing the brake work, check also for any loose
parts. Start by checking and/or tightening all the fasteners in the front
suspension, especially the bolts where the lower a-arm mount bolts to the
frame. Put the car up on jack stands with the stands under the frame of
the car. Then position a floor jack under the a-arm, directly under the
coil spring, and lift it a little, just enough to move the upper arm off of
the rubber bumper. This will unload the tension from all of the suspension
joints (excepd the inner a-arm pivots).
Get someone to help look while you wiggle the parts, or vise versa. Hold
the tire at top and/or bottom and shake the daylights out of it. Look for
any motion at the top or bottom of the kingpin, or in the bearing hub, or
at the points where the trunnions bolt to the top and bottom a-arms. Hold
the tire at the left and right and shake it some more. Look for any motion
in the tie rod ends (inner and outer). Turn the steering wheel back and
forth a little. Look for free play in the wheel (motion at the steering
wheel without motion at the tires) that would indicate wear or excess
clearance in the steering rack. Any worn parts should be replaced.
Also inspect the condition of the rubber bushings at the inner ends of the
lower a-arm. The original soft rubber bushings there are pretty much
guaranteed to deterioriate in a few years and need replacement. The
bushings from a MGB-GT-V8 are good replacement parts that may last forever.
You could also use polyurethane bushings that are easier to install and
may also last forever. The GT-V8 bushings will give you a little firmer
ride, but you may not notice the difference. The urethane bushings will
give you a firmer ride, and you probably will notice the difference. I
personally prefer the better steering response provided by the firmer
bushings, and you can learn to appreciate the firmer ride that comes with
the better handling.
Safety faster,
Barney Gaylord
1958 MGA with an attitude
|