Coil Spring Data Confusing
Thread Starter
Le Mans Master
Joined: Apr 1999
Posts: 6,134
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From: Raleigh North Carolina
Coil Spring Data Confusing
I have a 1970 LS5 with clearly tagged HV 3931826 front coil springs. The GM Heritage web site 1970 spring data (p.109) is missing the HV tag as is the 1971 pdf. I found the HV spring data in the 1972 pdf p.109. It says the free length is 12.08 inches. My 95,000 mile 43 year old 10 coil spring is clearly 15 inches free length. Why would there be a discrepency?
Burning Brakes
Joined: Dec 2010
Posts: 848
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From: CA
The October, 1972 Parts and Accessories Manual (P&A 30B) shows the 3931826 as being used from 1968 to 1971 on all big blocks with A/C.
Because they're worn out. Coil springs become longer as they wear.
Ed
Why would there be a discrepency?
Ed
Burning Brakes
Joined: Dec 2010
Posts: 848
Likes: 60
From: CA
Positive. It's the opposite of what you would think (get shorter with age), but as they wear, they get longer. I'm only referring to the unsprung (free length) height, not the "installed" height. They sag with age when they're installed in the car.
I'm not an engineer (although I play one on TV), so I can't give you the specifics of "why", but maybe I can get John Hinckley or Jim Shea to comment.
Ed
I'm not an engineer (although I play one on TV), so I can't give you the specifics of "why", but maybe I can get John Hinckley or Jim Shea to comment.
Ed
Last edited by restoman1; Mar 4, 2013 at 11:57 AM.
Le Mans Master
Joined: Jan 2006
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From: Butler Pa
Safety Car
Joined: Aug 2000
Posts: 3,711
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From: San Antonio TX
It's true. A coil spring is more likely to get longer, rather than shorter with age. You see the spring get shorter when it goes into a plastic transformation in the spring material. In other words, it goes flat. You can understand this easily when you see a spring that has been heated with a gas ax to lower the ride height. Most worn springs suffer from loss of elasticity meaning they don't hold design tension so they sag when loaded and extend when free.
Thread Starter
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Thanks. That's good. My wife will be very happy to hear this. I now have an explanation.
