Resto Series Number 6: Restoring Leaf Springs




Story and Photos by John Gunnell

One way to restore leaf springs is to “re-arch” them using the cold-setting method. Cold setting is done by bending spring steel back to its original shape while cold. There is some debate over how well cold setting works, but first let’s talk about how it’s done and what it costs. There is a Web site that talks about cold setting springs by working them manually with a big hammer. However, the best work can be done by a professional using a precisely controlled, electronically operated 50-ton (or larger) press.

First, you must remove the leaf springs from the vehicle. If you’re working with rusty original parts, you’ll want to spray everything with WD-40 and let it sit a few days. Then, get the car up in the air and make sure it’s safely supported. The old nuts and bolts will come off with an air-powered impact wrench, but try not to snap them. A spring shop may be able to find replacements, but don’t count on it if you have a rare or foreign car.

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To remove the springs, jack up the rear end and support the chassis in front of the front spring anchor. Take the weight off the axle with a small jack. Remove the nuts from the U-bolts that go through the support plates to secure the spring to the axle. Slowly and carefully lower the jack and remove the U-bolts. Remove the rear shackle pin nuts and outer shackle plate. Remove the inner plate with the shackle pins on it. Lower the rear end to the ground. Remove the pivot pin at the front spring eye. Lower the front of the spring down.

Accurate Alignment in Appleton, Wis., is one of a few shops in my area that still has the equipment to re-arch a spring by cold setting it. Each leaf is bent by a hydraulic press moving along it. The press should be at least 50-ton capacity to do a good job on car springs.

In order to work the leaves in the press, you have to take the spring pack apart. Before taking it apart, the professional will check the shop manual specs and make some measurements to help him determine the proper arch. Through sighting, measuring and other skills, a good spring man can figure almost precisely what a spring looked like when it was new. 

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After disassembly and cleaning, the re-arching process starts. The first leaf to be worked is the longest one on the bottom of the pack. It is measured to determine a reference point near the center to work from. The leaf is then worked back and forth from center, a bit at a time, under the hydraulic press.

There is a rhythm to a spring bender’s movements and just the right pressure has to be applied to the right point at the right time. If the pressure is too light, the spring steel will flex, rather than bend. If the pressure is too heavy, the spring will break. Working the leaf right to the tip is difficult and takes skill.

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Once the longest leaf is done correctly, the others are arched to conform to it. Each gets a little more arch than the last. Companies that do cold setting say that springs that bend back and forth, instead of cold setting, have “lost temper.” In this case, the only solution is making a new spring, but spring steel is no longer made in all “old car” sizes.
 
Mike Eaton at Eaton Detroit Spring, Inc., in Detroit says cold-setting steel is a temporary repair. “Spring steel never loses its temper unless it’s heated,” he said. “It’s memory that springs lose, not their temper.”

According to Eaton, the cold-setting method of re-arching springs results in a short-term fix. “Spring steel has a memory, and unless this memory is erased, the spring will eventually return to the height it was at prior to being re-arched.”

Eaton says once a spring pack is re-arched, you can take a leaf out, lay it on the floor and chalk mark both ends. “Go back in a year and the spring will be back to its flattened-out length,” he says. “Re-arching is a good quick-fix, but if you have a car worth restoring the ultimate way, re-shaping is best.”

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Eaton is one of few companies equipped to offer restorers “spring re-shaping” services. It can anneal a spring to take the memory out of it, re-shape it and re-heat treat it so that a new memory is put back in. In order to anneal a spring, it must be taken apart and visually inspected for fatigue. Each leaf is blasted clean. After being re-inspected, it is heated to 1,650 degrees Fahrenheit. Then, the leaf is placed on a pattern with the correct form and arch to re-shape that leaf.

The re-shaped leaf is quenched in special oil to cool it. This heating and quick cooling results in a leaf that is too hard or brittle to work well as a spring, so the leaf is heated again, for a set time, to 950 degrees. This process draws out some of the hardness. Once it cools, the leaf is shot-peened to relieve stress on it. The result is a spring that’s re-tempered, re-shaped and re-heat-treated.

Re-shaping a classic car spring costs more than manufacturing a new spring. The minimum charge is about $225 per spring assembly, and can be more. This doesn’t include the cost of new bushings, spring liners, clips, re-assembly and shipping. Eaton does not re-use old parts.

Not every spring can be restored by reshaping. The condition of the spring has to be considered. If there are broken leaves, or if the leaves are separating at the ends, they probably can’t be restored. Also, if there are pit marks on the flat sides of the springs, or crazing, they may not be candidates for restoration.

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In many cases, it’s best to look for reproduction parts or even used parts, but if you are restoring a valuable straight-axle Corvette to concours standards, you will want original springs made out of no-longer-available grooved spring steel. In this case, re-shaping probably makes economic sense.

There is certainly debate over whether it’s a good idea to re-arch leaf springs by cold setting. Some say it gives a stiff ride. Others argue that the spring will loose its memory and settle back to its collapsed state in a short time. But, one Web site for Jeep enthusiasts points out that heavy truck suspension shops have re-arched springs for 50 years and wouldn’t do it if it didn’t work.

Mark Broehm of Accurate Alignment agrees, in a sense, that re-arching doesn’t have as much appeal to classic-car restorers as to truckers. “Truckers are looking to save costs,” he says. “If you’re restoring an old car to drive, re-arching is probably suitable and affordable, but if you’re restoring a classic as an investment, the cost of the job that Eaton can do might well be justified.”


Mechanic Vince Sauberlich loosens the nuts and locking nuts on the bottom of one of the U-bolts that holds the rear leaf springs on an MG TF. This particular “underspung” car has the axle above the springs.

The two U-bolts hold one leaf spring on the car. The support plate bolts to the car chassis and the U-bolts go through the holes in it.

After they are removed from the car, the spring packs should be carefully disassembled. Make sure they are clamped together so they don’t fly apart.

 


This spring is being re-arched using the cold-setting method. Eaton and possibly a few other companies can re-shape springs to original specs, but this is an expensive process that requires special equipment.


 
Leaf springs are arranged in “spring packs.” They must be removed from the car before a spring can be restored by either cold setting or reshaping.


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