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by “C'Dale Rider” — contributed by “swalve”
Bob Sheaves wrote: Spring rate is governed by several parameters:
1. Wire shape in cross-section (a way to vary rate is to draw a wire with a varying diameter or cross-section contour.)
2. Wire material - alloy components. (Self-explanatory)
3. Wire mandrel (the inside of a coil is wrapped when plastic around a round -generally- bar to set the centerline of the spring at a specific diameter, if round, or on a specific parabola -in the case of a "barrel" mandrel)
4. Length of the wire (a coil spring works exactly like a straight torsion bar- the rate is derived from the twist, internally to the material grain) for a given installed height in the package.
5. Number of turns of the wire for a given height and a given cross section profile. (Self explanatory.)
All of these items affect the spring rate.
At this point, you may ask, "Why should I care?" Because misunderstanding what a spring is affects understanding of what a spring does and how to identify a rate.
On Chrysler minivans at least, Monroe specifies three part numbers for the full range of vans Chrysler made. Dealers have well over 25 part numbers for the same vans.
There was a vast difference in fitment for my brother (a mechanic, ASE certified in almost all car systems, over 25 years experience). He got the appropriate Monroe Sensa-Tracs for a Town & Country minivan and they fit terribly; it took forever to get them in, and they rode horribly, so the customer was not satisfied.
A replacement set of Monroes were put in (on the assumption that the first set was "bad") and there was no improvement. On a whim, John ordered a set from the Chrysler dealer. They fit properly and the ride was dramatically better.
The dealer items seem to last over 60,000 in normal use; while aftermarket manufacturers provide lifetime warranties, lifetime is a relative thing; most cars are presumably traded or sold before the new struts and shocks wear out significantly enough to warrant replacing. Interestingly, the struts cost little at the jobber end, which makes one wonder exactly how much Monroe really has in each one; the replacement cost is likely built into the original price.
The dealer's stock of struts are specific to model, options, engines, etc. and valved differently for each. Monroe, to control costs, whittled down the rather large range of struts Chrysler specs to three units and hoped they fit well and generally satisfy the drivers. Many times, though, the dealer struts can be had at the same price as the Monroes.
Not knocking Bilsteins, KYBs, or Konis here ... they're for a different set of expectations and give different results.
Matt Hoffman wrote: My sister told me her 2002 Sebring sedan sounded like something “gave” in the back, with a loud bang noise, and then a loud rattle in the rear. I pulled the dust cap off, and found that the top of the shock was loose - I could move it with my hand. The shock looks like a strut, but just has one bolt at the bottom. I saw Internet claims that Chrysler used aluminum mounts which corrode, and changed them after the 2002 model year.
The problem: on a 1989 Dynasty, the driver's side had a mysterious rattle/bump. The problem appeared to be the shock absorber mount. On a 1991 Spirit R/T, the same problem arose from both sides when the stock shock absorbers were replaced with KYBs. In both cases, the problem appeared to be the shock absorber bolt.
I've suffered from rattling rear shocks on my '89 Acclaim. The problem started when I replaced the factory shocks with NAPA shocks. Suddenly, I had a rattle that actually sounded like something larger, like the exhaust system banging around on larger bumps. ... It seems like the upper shock mounting hole was slightly larger than the factory bolt. I eventually shrunk some heat-shrink wire insulation over the bolt and pounded the bolt in place - no more rattle. Many quiet miles later, I again replaced the shocks, this time with Monroe Gas-Matics. AARGH, the rattle was back. I'm wondering if there's some kind of metric vs. SAE fastener incompatibility issue at work here.
I've found that although the motor (2.5T) is all metric, the body and chassis seem to randomly mix fastener standards. I'm going to try the nearest larger metric and SAE bolt sizes and see if that works.
I ended up taking the old shock and pressed the metal piece out of the bushing. I then took it to the store and matched it up with the metric bolt.
If you have already gotten rid of the old shocks, I would pull off the new shocks and take on of those to the store.
It took me a while to figure out that the little bump/tap noise was from the bolts.
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