Skylark/GS Suspension Springs

by George Nenadovich and Dave Knutsen


Here are the spring numbers for GS455 w/ac.

They are Duralast springs from AutoZone. I have used these
many times and never had a problem 

Front  FCS5398S    Rear  RCS5385S 

The are not "in-stock" items and will have to be ordered.
I "believe" the fronts are $85-95 and rears are $50-60.

You can also try other auto parts stores such as NAPA, Kragen, Pep Boys, etc.

You can also contact:

Eaton Detroit Spring

1555 Michigan Ave
Detroit, MI 48216


Web Page

Manufacutures leaf and coil springs for GM cars. 

Dave Knutsen supplied the following info:

The 5385 spring is the stock replacement rear spring for a 67 to 72 Skylark. Here are the dimensions from the Moog catalog.
Free Height: 12.61"
Rate: 166 lbs.
Load: 602 lbs.
Load Height: 9.00"
Wire Dia.: .580"
Spring I.D. 5.530"

It is designed to replace the factory spring, you shouldn't have any issues with it falling out. If I'm not mistaken I think this is the exact spring the GSCA was/is selling as their "GS" spring.
The front spring George listed is for the standard 68 -72 Skylark. Here are those specs:
Free Height: 16.127"
Rate: 362 lbs.
Load: 1678 lbs.
Load Height: 11.50"
Wire Dia.: .650"
Spring I.D.: 3.625"

Here is another spring that is listed for the 71 GS455 as the replacement spring, which is substantially beefier. #5536
Free Height: 15.063"
Rate: 488 lbs.
Load: 1984 lbs.
Load Height: 11.00"
Wire Dia.: .690"
Spring I.D.: 3.625"

I don't know about this spring, as I've never tried it, but the Load #'s look too high. The front of a big block GS doesn't weigh that much more than a standard Skylark with a 350. Which would mean we don't have enough weight on the front of the car to push the spring down to it Load Height, so it might raise the car too much. But that's what the book calls for............??
Below is listed another front spring that looks like it might be a better fit.
Free Height: 15.615"
Rate: 454 lbs.
Load: 1642 lbs.
Load Height: 12.00"
Wire Dia.: .690"
Spring I.D.: 3.625"
The load on this spring is more in tune with the spring George listed and with just a little more Load our GS' might have it would probably push the spring down a little more than listed. It has more rate than the other spring at 454 lbs. so it would be more stable.
Just some more info.

Here is a chart:


The GM # 405929 crosses over to the 5398 spring.
The GM # 402084 crosses over to the 5536 spring.

When considering springs you need to look at the load number also. Since
the weight of the car remains constant you can adjust height with the
springs rated load and the free height. Multiplying the rated load (in
inch/pounds) by how far the spring compresses (in inches) you'll come up
with a load number in pounds.
If one spring has a difference of 5" between the free height and installed
height and another has a difference of 4", with the same load applied to
both (say 2,000 lbs) then the spring that compessed only 4" is the heavier
duty spring as the other spring compressed 5" with that same load. Make
sense? At this point its kind of a close guesstimate as to which spring
will do exactly what you want, since the Load numbers vary so much. But I'd
stick with something close to rated load of 362 lbs. like the 5398, softer
springs will affect the handling. That 5450 spring almost looks pretty
good, but will give a firmer ride, load numbers are close though.

Spring number Load Ht. Free Ht. Diff.  Load   Rate
5398           11.5"    16.12"  4.62"  1678    362
5386           11.0"    17.08"  6.08"  2043    336
5388           11.0"    16.23"  5.23"  1900    363
5536           12.0"    15.06"  3.06"  1984    488
5450           12.0"    15.61"  3.61"  1642    454
5394           11.0"    16.61"  5.61"  1896    337
5390           11.0"    16.08"  5.08"  1952    336
5382           11.0"    16.72"  5.72"  2066    360
5380           11.25"   16.55"  5.30"  1686    318

Hopefully the above chart came through alright so you can compare these