Its 2004, How about 21st Century Engineering in your car line?

Today I am going to address suspension systems.

In the beginning there was the solid axle. Still used on some big rig
trucks. Very durable but rough riding.

Knee action independent suspension came along, popularized after WWII. A
refined version can be seen in the '82 Mercedes Benz. Upper and lower
control arms in sort of a parallelogram geometry. Spring acts on lower
control arm. There is a robust steering knuckle and spindle for the wheel
mount. Very effective for its day. A knee action suspension can
frequently hold its alignment for the life of the car. You will note the
M.B. uses very refined forged arms instead of the usual pressed steel found
on the American cars.

McPherson struts came next, with huge savings to the manufacturers not
passed along to the consumers. Its an all-in-one assembly of spring and
damper and sort of resembles the struts used on aircraft, from which I
assume the design was adapted for cars. Since this design is predominately
in use today, I will delve into its serious deficiencies:

1. It will not hold alignment. Mere friction is used at the two lower
bolts, one an adjusting cam and the other a clamp bolt to hold the camber
adjustment fixed. A good bump or light curb hit can and will move the
camber angle, requiring a new alignment job. In contrast, the knee action
used a micrometer screw or shims to affect adjustment, both very robust.
Also, in the knee action system, caster could be adjusted; caster is fixed
in McPherson suspensions.

2. As the wheel undulates over bumps, the McPherson strut will alternately
compress and extend and as it does so, the camber of the wheel is in
constant change from its nominal zero degrees from vertical. This produces
a constant scrubbing action on the tire. You can demonstate this by simply
jouncing up and down on the front end or even better, jacking up and then
lowering your front end. Observe the wheel take on a pronounced positive
camber as your jack up and then as you apply extra weight (simulating
rebound), it will assume a pronounced negative camber. With camber in a
constant state of flux from neutral (where it should stay), to positive to
negative, the tires wear out about double the rate they would if a constant
zero camber could be maintained. Knee action is guilty of the same fault.
Only a true aircraft strut maintains a zero in all spring deflections or
compressions. Such a strut requires a scissors link and is more complex,
of course, but the extra expense is indicated in $30,000 cars, if not in
$8000 cars.

You will note that year-to-year model changes no longer involve complete
body style changes as in the 50's. Even in those days, the running gear
remained largely unchanged, at least in principle; it was style that
changed significantly from year-to-year. Even today, with the style
changes taking several years, the running gear is carried over as long as
the factory can possibly can get away with. Suspension systems are at
least 50 years out of date. Now you know why radial tires should provide
at least 100,000 miles of service but don't. Now you know why your wheels
are always out of alignment. Its the McPherson strut.

 

Why???

 

Give it up, he's high on Cheetos,

Ted

 

The cars I've had over the last 15 years have held alignment much MUCH better
(and longer) than anything I owned in the 60's and 70's. I don't know what
you're talking about.

 

Don't feel bad, he doesn't know what he's talking about either. At least
you have the ability to see it. Sadly , he doesn't.


Tom Heintz "Mopar Maniac"

 

Funny. Just had alignment checked on my '00 Intrepid and caster IS
adjustable from 2 to 4 degrees positive, with ideal at 3. Requires
replacement of the original strut clevis to knuckle attachment bolts
with undersized bolts.

 

The undersized bolts are to allow camber adjustment.

There is no published procedure on a 2000 Intrepid for caster
adjustment. There is a specified range as cited above.

 

Will double check with shop. They said it's possible.

 

I've never had anything hold alignment BETTER than a torsion-bar
Chrysler from the 60s/70s (NOT the F/M/J transverse T-bar setup, but the
A/B/C/E/R body longitudinal setup). But my '93 has held alignment AS
WELL as the old cars.

However, if you read some of the trade magazines there are quite a few
modern cars that are problem children when it comes to alignments.
Limited range of camber adjustment, NO provision for camber adjustment,
etc. etc. Moog and other companies are making good money on 'problem
solver' kits that have offset cam bolts that allow you to add adjustment
capability to these cars.

 

No doubt that it's possible by shifting the sub-frame forward or
back, but caster is not going to change by replacing with the
previously mentioned strut to knuckle bolts.

 

Actually, the car comes from the factory with one eccentric bolt and one
non-eccentric bolt holding the knuckle to the strut, and they replace
the non-eccentric bolt with an eccentric bolt to double the range of
adjustment of the camber.

As you point out in your next post, there is some adjustment of caster
on the LH vehicles by shifting the engine cradle as allowed by the 4
bolt to hole clearances (but shops don't know about this, or don't admit
to knowing). This fix is in fact documented in TSB #02-16-99 and a
repair procedure referenced in that TSB.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")