"Good
grief! Now I'm in for it,"
groaned Joe Clark, as he glanced out of the window of the tiny office of the
Model Garage. A small sedan was
just pulling up in front of the establishment, to the accompaniment of a
most unpleasant chattering noise.
Gus Wilson, his partner and the mechanic of the firm, was out on a
job with the service car, so Joe tossed aside his pencil and went out to see
what he could do for the tall, angular woman who was climbing out of the
sedan.
"Howdy, Miss Simpkins. Some, little trouble we can fix for you
today?" Joe saluted her with a
hopeful smile.
"Where's Mr. Wilson?" the customer snapped, glaring at Joe. "I want
to give him a piece of my mind!
You swindlers relined the brakes on this car only three months ago, and now
see how it acts? What kind of
brake lining did you use - pasteboard?
Every time I put my foot on the brake, the car starts to shake and
chatter. It's making me a
nervous wreck. I want it fixed
right now, and don't expect to pay for your time, either!"
"We'll do that gladly, Miss Simpkins," Joe agreed, hastily.
"We guarantee all work.
Probably a bit of grease has worked into the linings; something like that.
I'll see to it right away."
Joe cast a despairing look down the road to see if by any chance Gus
was returning. As there was no
sign of the service car, he went inside for a kit of tools.
"Just my luck to have that eagle-eyed old hen on my neck the minute
Gus gets out of sight," he grumbled disgustedly, as he grabbed the tool kit
and a small can into which he could draw some gasoline to wash out the
grease he suspected was causing the trouble.
He had Miss Simpkins start and stop in from of the garage a couple of
times. Each time she put on the
brake, a most alarming noise broke out and continued almost until the car
had reached a complete stop.
"Now I'll have a look at those brakes," he said, wheeling the garage
jack under the front axle and lifting both wheels off the ground.
There seemed to be no doubt that the chattering noise was coming from
the front end of the car.
Miss Simpkins promptly climbed out and came around to watch the job.
This didn't improve matters for Joe. A bit clumsy with tools at best,
the little bookkeeper found all his fingers turning to thumbs under this
distinctly hostile scrutiny.
However, he kept at it until both front wheels and the hubs were off.
No trace of grease appeared on the brake facing of either wheel.
"There! I
just knew it would turn out you were wrong, "Miss Simpkins observed
triumphantly. "Anybody should
know that slippery grease couldn't make anything stick and chatter."
As science teacher in the local high school, Miss Simpkins prided
herself on her mechanical knowledge.
Joe admitted his error and proceeded to stall along with a minute
examination of the brake surface while he racked his brain trying to figure
out what could really be the matter.
He was just at the point of admitting he was stumped when, to his
intense relief, he heard the familiar rattle of the old service car, and Gus
drove up.
There was a twinkle in the veteran auto mechanic's eye as he took in
the situation. He promptly came
to his partner's rescue.
"Having trouble with that brake job we did for you, Miss Simpkins?"
he asked with a smile. "I
see Joe is well along with it," He turned to his partner with a wink, "Mr.
Thomas wants you to call him at once.
I'll finish this."
Joe took the hint and headed for the office, after explaining to Gus
what the symptoms were.
"Chattering brakes are not very common these days, Miss Simpkins,"
Gus remarked, as he tested for play in one of the brake connections.
"Grease can do it, sometimes.
A greasy brake shoe may act like a rubber heel on wet pavement.
The best holds all right till it starts to slip, but once it starts,
the water forms a cushion under it and you slide like you would on ice.
If the brake-drums surface happens to be a little uneven, a greasy
brake facing may slip and catch again and start to vibration.
Of course the usual effect of grease in a brake is just to make it
not hold at all."
"That may be so," Miss Simpkins admitted.
"In fact, I can see how it would work like that under certain
conditions if grease got in the brakes, but there isn't a speck of grease on
these brakes. Anybody can see
that."
"So that can't be the trouble in this case," Gus smiled, "But if you
look closely, you can see something is wrong. Can you spot it?"
The science teacher adjusted her spectacles and peered closely at
first one brake facing and then the other.
"the only thing I notice, is that one is a lot shinier than the
other. Is that what you mean?"
"Yes, that's it," replied Gus, "When a brake facing gets that
particular kind of a shine on it, we call it glazed, and it doesn't hold
nearly as well."
"I can understand that," said Miss Simpkins, interestedly.
"Science teaches that friction depends on the kind of surface as well
as on the pressure, and a shiny surface should slip more easily than a rough
one. But how did that make the
brakes chatter, and what causes the glazing?"
"I'm pretty sure it had nothing to do with the chatter in this case,"
Gus replied, "As to what causes brake linings to glaze, it's one of those
troubles nobody is any too sure about.
They do it now and then for no reason that you can see.
"One thing is sure," Gus continued, as he remounted the wheel, "and
that is, when you have adjusted all the brakes as that they're as tight as
you can get 'em but still are free when there is no pressure on the brake
pedal, and yet one brake doesn't hold when you put on the brakes, take a
look at the brake lining. It's
almost sure to be either grease or glazing - unless, of course, the lining
is worn out."
"Why couldn't there be something the matter with the levers that work
the brakes?" the teacher asked ,her grouch forgotten is the search for more
knowledge.
"Suppose they're hydraulic brakes?" Gus countered.
"You know that fluid pressure must be the same in all connected parts
of the system unless something has actually jammed in one of the brakes -
and that's mighty unlikely."
"But this car hasn't hydraulic brakes," Miss Simpkins objected,
"Surely, with all those levers, one might get out of adjustment and pull
harder on one brake than on another, mightn't it?"
"The equalizers prevent that," said Gus, looking up from the front of
the car, where he was tightening some bolts.
"When you push down the brake pedal, the force is applied to the
middle of a bar, and the brakes are hooked to the ends so the pull on all
the brakes is bound to be the same.
So, no matter whether it's hydraulic or mechanical brakes, if one
wheel doesn't do any work when you stop, always look first for the trouble
in the brake itself. As a matter
of fact, you hardly ever get brakes so they're exactly the same on both
sides of the car no matter how even the pressure maybe.
"There's sure to be little difference in the surfaces of the brake
linings or the drums."
"Wouldn't it be possible to fix things so you could adjust the
relative pull applied to each brake to suit its own peculiarities?"
Miss Simpkins suggested.
"Gosh!" Gus laughed as he shifted his wrench to the other hand.
"That would be a sure-enough headache for the brake-service man.
Besides, there'd be no use in doing anything like that.
As brakes wear, they keep changing.
One day, they'll be perfect.
A few days later, say, after a long trip, you'll find that one rear
brake is a bit stronger than the other.
In a week or so, you may find that the strong brake has shifted to
the other side for no reason at all."
"What are you going to do about that glazing-- put in new material?"
Miss Simpkins asked, as Gus finished with the other wheel and fished a
hacksaw out of the tool kit.
"No, I'll just roughen it like this," explained Gus, scraping the
fine teeth of the hacksaw blade back and forth across the face of the brake,
and gradually working around until he had removed all the shiny glaze.
"Won't it become glazed again very shortly?" Miss Simpkins asked,
dubiously.
"It won't happen to this brake any quicker than to the others, now
that I've put it in shape," Gus replied as he tossed the hacksaw back in the
kit and started to remount the wheel.
"But what about that awful chattering?
Can't you do anything to get rid of it?"
"Oh, that! Sure,
it's fixed already. Didn't you
see me tighten up the bolts that hold the front axle to the springs?"
"But what does the axle have to do with it?" the teacher in
astonishment, peering curiously at the bolts he had mentioned.
"A whole lot, in this case," Gus grinned.
"Whenever you get chattering or vibration in any piece of machinery,
there's three things to look for.
The first is motion - and there's plenty of that in an automobile.
The second is friction or strain, and that's where brakes shine.
The third is looseness that'll give the friction and motion a chance
to turn into vibration. Those
loose axle bolts were right where the strain of the brake and the motion of
the wheel could get together and make the whole works jitter back and forth
to beat the band."
Gus finished assembling the wheel and Miss Simpkins climbed into the
car to test the brakes again.
"As a science teacher, I should have known it was something like
that," she muttered to herself, as she vigorously jammed down the pedal.
The chattering was gone.
END
