How do you know a leaf spring is bad?

[Skip Fix]

So other than obvious sagging how do you know when to replace a leaf spring? Factory 30 year old 75K miles but no sagging, rate in relation to chassis setup is good.

You hear about guys whose spring break but they look OK. Or get a spring shop to copy the rate for some new ones.

[David Pozzi]

If they are not sagging or corroded, then age hasn't affected them. Cracks are more related to how much abuse or miles they accumulate. 75K miles isn't a lot if the applied stress is normal.

[Skip Fix]

Thanks David. One set going back on the '78 has 75 K and has actually been off the car for 20 years with the drag Tri City Launcher (Mopar Super Stocker copies) on it,making the shift back to street/cornering. Although free standing on the garage floor one is 1/2-3/4" taller.

[Rod]

Thanks David. One set going back on the '78 has 75 K and has actually been off the car for 20 years with the drag Tri City Launcher (Mopar Super Stocker copies) on it,making the shift back to street/cornering. Although free standing on the garage floor one is 1/2-3/4" taller.

theres no performance advantage in the stock springs? so it will not corner with any performance, spring rates on stockers were made for comfort

[Skip Fix]

Front springs are not stock ,solid A arm bushings, sway bars and shocks(Guldstrand valved Bilsteins) have been swapped around to fit the handling with the rear springs. With sticky tires it cornered better than my friends Corvette(with him driving), and he generally won the Vette class at our autocrosses so a decent driver and car-road races a Prepared Mazda. In fact just the next bigger rear sway bar would pick up an inside REAR wheel in tight autocross turns, and even angled driveways.

So I have a package that worked pretty good together with the factory Trans Am rear springs, since the car is going back street/cornering as I have a new dedicated drag car. My current drag springs work great for that but the rate is about as stiff as a dump truck.

I'd actually prefer a rear spring with teh second leaf a little longer to prevent wrap up but close to factory rate(could live with a little stiffer) to still fit the handling I've dialed in. Since few of the aftermarket folks like Hotchkis will tell you rate(Landrum does) and even getting rates listed for factory springs-other than buying several,taking them all to a spring shop that can measure leafs it is a guess-other than having customs ones done-a possible option.

Then you get into all the debate on spring bushings-poly binds and pops(I think the "stock" Hotchkis are poly), rubber too soft, Delrin good for shackles but even too stiff from front eye, front eye a spherical but on a street/track car too much.

[rustomatic]

If they're not broken, it's only a matter of where your ride height goes. Bushings and shocks will take care of the rest, based on your ride/handling preferences. Far too many old, yet perfectly good springs have been thrown out in favor of a new set that provided absolutely no improvement (except maybe for pretty paint). If you have no locating device, your bushings should be as solid as you can stand, front and rear, with uber-beefy shackles or sliders. This will make the rear end's movements (or lack thereof) far more predictable (when it's dry, anyway)...