2HorsePower

Is there an "at home" way to determine what spring rate you have, on or off the car? The data for C4s on the CAC chart and carfiche for spring rates has some discrepancies, so looking up the spring codes does not give a consistent answer. Besides that, the front spring on my early C4, code BMA, simply does not exist on the charts. (It is not the OEM spring and was purchased second-hand by my car's previous owner to be as stiff as possible for autox, and it's stiff enough to break up kidney stones)

Slalom4me

I agree that BMA does not appear on the common spring charts in
circulation.

You might want to check with members scooter18155 and BlackRocket.
They both assert that the BMA spring is from the front of an '84.

BlackRocket had one for sale

scooter18155 posted at least two times that he knew the BMA to be
the non-Z51 spring.

http://forums.corvetteforum.com/show...p?p=1561195589

http://forums.corvetteforum.com/show...p?p=1560827820

Z-07 freak has often posted about spring rates, codes and the
deficiencies of some of the charts. Perhaps he will join in on this
thread to discuss the BMA front spring.

.

Slalom4me

Oops. My previous post did nothing to answer the primary question.

My vote is that it is necessary to fixture an uninstalled spring or to
gain clear access to one end of an installed spring in order to compress
one side by a measured distance and then record the indicated load
exerted by the spring.

A conversion factor is N/mm * 5.71 = lbs/in. Taking the rates attributed
to '84s in the popular charts, you might expect to see something similar
with the mystery BMA spring.

FE1: 63.5 N/mm (362.6 lb/in)
Z51: 102.0 N/mm (582.4 lb/in)

FWIW, Before I updated to an aftermarket rear spring, I considered testing
the new spring prior to installation with the intention of using the same
test procedure on the OEM spring once the swap had taken place. The
following thread has some discussion from that time.

Insitu Spring Rate Measurement

Talks with local shops was not fruitful. Although I considered fabricating
a test fixture, ultimately I installed the aftermarket spring and set the
OEM spring aside.

DRM &/or VB&P may have some advice thay are willing to offer on the
subject of testing if you get in touch with them.

.