>tomorrow, next month or next year but it will fail. It will often fail
>at it time of most stress, when it is running down the highway in a
>straight line(ever hear of centrifugal force,it keeps us from falling
>into the sun).
The forces exerted on a cv joint going in a straight line, even at high speed,
are nominal.
Take a car going down the road at say 70 mph. A wheel and tire assembly are
roughly 22 inches in
diameter. This means the tire and axle assembly rotates about 919 times per
mile, and about 1069 rpm.
A typical cv joint is about three inches in diameter at the ball cage. Using
this we get a radius arm
of 1.5 inches. Call it two inches to make it even worse. And lets call each
steel ball about 1/4 lb.
That's quite high, but lets err on the side of high numbers.
Rotational acceleration is v^2/r. Where v is the angular velocity and r is the
radius arm. The
rotational path is four inches in diameter, going about it at 1069 rpm, giving
us a rotational velocity
of 225 inches/second. Divide that by the radieus and we get 112.5 inches per
second squared.
112.5in/s^2 if you like math symbols.
Force is mass times acceleration. Pretty basic. Multipy that mass (not the
weight, 1/4 lb, but the
mass) by the acceleration and you get .87 inch pounds of force. Not terribly
high in anyones book, even
a "real mechanics" book. And that's an oversized cv joint with artificially
heavy balls. In actuality,
the numbers would be lower.
When you contrast this against the tons of force exerted on a cv joint
accelerating a car from a
standstill into a sharp turn, it's obvious that straight line driving is not
where the serious forces
are.
> Belive me I have repaired many vehicles that have had
>this misfortune. The damage from the flailing half shaft at 70mph is
>incredible. Two examples: My own 78 Spit tossed the right joint
>outboard. The damage required replacing every thing related to the
>suspension including the seal and shaft at the differential.
That's quite interesting. For I had a VW that loved to throw it's half shafts
off constantly. I became
quite proficient at reattaching them in under a minute. Things would get a bit
beat up, but no great
damage. Perhaps there are other factors you are not mentioning that would
result in such severe damage
to your particular vehicle.
> MORALE: ck those joints regularly.
Of course. But just as there is no need to instantly throw away an engine
because the dipstick read low
there is no reason to tow a vehicle in to have a half shaft replaced the
instant it clicks.
>Hope we can all be as lucky as our friend Nolan,
Indeed, if you've had the problems you've described, you could use a little
luck.
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