Classic Mustangs List Archive

This read-only message was archived from a public mail list.
Mail From: Wal Marshall (email redacted)

Having just been through the process of replacing the leaf springs on my
70, I thought I would share a few points for those contemplating a similar
exercise. Although nearly all suppliers offer "stock" and "uprated" springs
I found it difficult to get any accurate data on matching tolerance, spring
set and spring rates. So I did my own measurements as follows:

1. Checking for matching set.

On receiving the new springs (locally made in NZ), I checked to make sure
they were matched. (They weren't, but the supplier offered to replace them
immediately no questions asked freight paid).

The correct way to measure them (I did it wrong at first) is to lay the
springs upside down on their eyes, side by side, and measure the height
differential.

Ideally they should match exactly, but normal factory tolerances mean there
will probably be a difference. The $64,000 question is , what is acceptable?
Local opinion is that approx 1/4 of an inch is an acceptable tolerance for
new springs. (Our local roads are more steeply cambered than in the US, so a
slight difference is actually not such a bad thing). A 1/4 inch difference
seems to correspond to a body tilt of around 3/8th inch (measured at the
outer edge of the wheel arch's), which is hardly perceptible . Obvious
leans
must correspond to spring mismatches of over 1/2 inch, (probably well over).

2. No-load Spring set.

With the springs lying on their eyes (as above) measure the height from the
garage floor to the highest point on the spring arch.
For stock (new) springs this is likely to be in the vicinity of 9 + 3/4 to10
inches. Used springs may well have settled to less than that; mine had sunk
to 9 + 1/4 inches. The new springs I fitted, which were uprated from 4 to
5 leaves, had the no load set reduced to 9 inches. The final result was that
the fitted ride height is similar to the softer stock springs, because (of
course) the stiffer springs compress less.

3. Spring rate.

I attempted to measure the spring rates of the old and new springs. I put a
weight of 25 kg /55 lbs (just because it was to hand in my garage), on each
(upside down) spring and measured the deflection. The new springs deflected
15 mm which works out (if my maths is correct) to 93 lbs per inch. The old
stock springs were about 65 lbs per inch.

After all this, its worth nothing that according to the NPD catalogue, Ford
fitted 32 different combinations of spring rate and set to the 64-73
Mustangs, so there must be quite range of "stock" figures.

Perhaps if your car is sagging, leaning or whatever, the above data might be
useful in helping decide what to do about it. Others may have some
measurements or experience to add to this?

Regards

Wal Marshall
Wellington New Zealand
70 351C 4V Fastback





------------------------------------------------------------------------
All the list info you'll ever want: antler.moose.to/~server/cm