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Spring "Tune-Up" Tech

 
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av8
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PostPosted: Wed, May 30 2007, 9:04 am    Post subject: Spring "Tune-Up" Tech Reply with quote

SPRING TUNE-UP

Coil springs are essentially unknown in Vern Tardel’s Prune Orchard where I spend the bulk of my old-car time and where leaf springs rule. As a consequence, there’s a lot of leaf-spring massaging carried out there to fine-tune spring packs, and to make them presentable in the process.

With a large cache of original Ford springs to work from, plus a steady supply of aftermarket pieces harvested from old street rods in for a makeover, we’re never short of good “makings.”

For good progressive spring action, leaves must move smoothly on top of one another, and that’s just not going to happen with most old spring packs I see that are damaged because of a lack of periodic lubrication. The most common damage feature is the groove worn into the top of a leaf by the end of the leaf above it. Under hard jounce (compression) the groove restricts the movement of the leaf on top and can make spring action harsh.

First step, then, is to dress the top of worn springs to remove the notch and create a uniformly smooth sliding surface. I do this on a large belt sander fitted with a quality butt-joint 80-grit belt. I’m partial to Norton belts but there are other good ones available.

Next, I radius the ends of the springs, both to make them pretty and to make them a bit more “progressive” in their resistance. The bottom of the ends are than progressively chamfered so no sharp edge on the end of the leaf comes in contact with the leaf below it.

Finally, just for grins, I chamfer the top of the ends of the leaf 45 degrees for appearance sake. You can get really anal here and do a neat blend of the chamfer, just so long as the customer is willing to pay for your time – or it’s your own spring.

This is a typical spring pack from some old hot rod. The main leaf was missing, and the task was to tune up these leaves to be used with a new main with reversed eyes. The lower two leaves are nearly equal in length and would act much like a single thick leaf. You can see where leaves have dug into one another and where they’ve been trimmed and “dressed” rather haphazardly. Tuning up a spring pack like this used to take a couple of hours. (Just click on the tags to see the images.)

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/256208813.jpg [/img]


I made a couple of simple fixtures that reduced the work to one-half and as little as one-quarter the time with uniform and repeatable results. The first fixture is a scribe template that permits me to really bear down with scribe and lay an easily seen mark on the hard spring. This fixture has two radiuses, one for the front leaf and another for the wider rear leaf. This is the underside . . .

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/256208822.jpg [/img]

. . . and this is the top with a leaf in position to be scribed. Each end of a leaf must be scribed top and bottom because the leaf has to be turned over half way through radiussing; this template ensures that the scribes are on the same location both top and bottom.

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587455.jpg [/img]


This fixture bolts to the table of a large belt sander and performs three functions. It sits close to the belt (about 1/32 inch) so the belt doesn’t “suck” in a leaf that is having its top dressed to remove wear notches. A 90-degree material rest on the right permits quick uniform radiussing of the ends of the leaves. And the two opposing 45-degree rests permit quick uniform chamfering of the top of the leaf.

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587474.jpg [/img]


Wear notching can be seen on the top of this partially dressed leaf. It will be completely eliminated.

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/256208826.jpg [/img]


The scribed ends of the leaves are first radiused. This task takes less than a minute for both ends.

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587482.jpg [/img]


The tops are then chamfered, first on one half of the radius . . .

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587496.jpg [/img]

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587501.jpg [/img]


. . . and then the other.

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587513.jpg [/img]

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587518.jpg [/img]


Finally, the lower edge of each spring leaf is given a blended radius so it will slide easily on the leaf below it. No fixture is used for this step; it’s largely a matter of feel and appearance.

That hashed up spring pack seen at the start of this thread was massaged into this nice-looking and serviceable collection of leaves with well under an hour of work using the two fixtures.

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/150587526.jpg [/img]

[img] http://pic20.picturetrail.com/VOL64/2013751/3941350/256208823.jpg [/img]


Like it or not, leaf springs require lubrication, or some synthetic slipperiness such as Teflon-like buttons or sheets, to operate satisfactorily. High-load greases work very well, although they get messy looking on open-wheel cars. It was common practice on leaf-spring dirt cars in the past to wrap well-lubricated springs with tape. This is not only practical, but it’s also a neat old-timey touch. And it’s a lot more durable and neater today with products like 2-inch-wide 3M moisture-barrier tape than it was in the past when frictions tape was about all there was.

Mike
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jusjunk
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PostPosted: Wed, May 30 2007, 9:24 am    Post subject: Reply with quote

Nice tech post Mike. Ive got a brand new posies superslide non painted spring that i need to clean up. If it was chrome it would have been cleaned up and had a radius on the ends so im gonna do it myself.
Dave Wink

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Mac
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PostPosted: Wed, May 30 2007, 11:14 am    Post subject: Re: Spring "Tune-Up" Tech Reply with quote

Nicely detailed tech.
My `54 Jag sedan came with laced on leather "gaiters" covering the leaf springs to retain grease.
I must confess I've wacked that out from under the car in favor of an air bag sprung T-Bird IRS. Embarassed
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Mikej
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PostPosted: Wed, May 30 2007, 2:43 pm    Post subject: Reply with quote

Nice tech article. Simple fixtures to make the job easier. Thanks for taking the time to post all the pictures...........
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