Ok, todays challenge is to help me understand how the following broken coil spring situation may have happended. 

First, a picture is worth a thousand words.  1969 510 rear springs. 

First two are left and right springs “pieces” on the floor after extraction. Third is the left rear as I saw it initially. 

 

First clue is the vehicle mileage

50.000 miles.

Second clue is the condition of spring pockets. Both are filled with very hard packed, very dry mud. I had to literally excavate the mud by chipping and digging with pointy tools to extract the broken ring segments.

Third is a usage history. 1969-1980 used by a rural north BC dwelling mother of three. Car was then parked after a low speed front end accident. The car was moved around very sporadically over the remainder of its life.  

There is no admitted history of extreme driving, though you can just imagine. No other part of the car suggests any General Lee type stunts. 

Forth is the definite lack of rust in the spring pocket metal or surrounding area. Not like the springs were immersed in water for forty years nor is the spring material shows more than minor rust damage.

Edited September 30, 20213 yr by zKars

Sp the question is, under what conditions would the springs break into so many pieces?

The first break is above the packed mud. The remainder were all buried in the terra-very-firma

My guess is a big bump.  Poor quality heat treating on the spring steel.

My first thought was general lee.

Dirt road, 3 kids in the car. Jump, coil bind, bad springs....

They kept driving it after the first break! The spring kept self deteriating. Wouldn’t want to install a new spring when you still have 2/3 of a spring left! Those 510’s are tough little bitches!!!!👍

Edited September 30, 20213 yr by Diseazd

I think the packed mud is a clue that the car spent time on a dirt road.  The mud likely packed between the coils as well as below them and caused coil bind when subjected to full jounce travel over the rough dirt road.  The owner likely overloaded the car often with kids and stuff in the trunk making the situation worse.  Once a coil broke, the car would sit lower and when not repaired, the next weakest spot failed from being subjected to unusual forces from the spring position.  The rust might be minor, but it did likely factor in a bit.

I'm inclined to agree with Jeff G 78.  If the mud packed at the bottom of the spring, then the free portion would be carrying the entire load at that corner and it would eventually cause flex fatigue.  I'll bet the second break came soon after the first one.  Poor little spring.

Here are my original 510 front springs,

 

21 minutes ago, grannyknot said:

Here are my original 510 front springs,

Wow, those look terrible.  Did they forget to use spring steel?

They look like they've lost their temper.  Maybe they've been modified with a low temperature flame (propane, MAPP), and got to their annealing temp for a while.

4 hours ago, grannyknot said:

Here are my original 510 front springs,

 

Maybe they were designed like that. Variable rate progressives.

The lower coils bind on big bumps. You know... Like when you let it down off the jack.