This posting is one in a series. If you have not yet read the earlier postings in the series, you’ll need to, as this posting won’t make much sense without having done so! Just do a search using the word “SLURP”.
In my last posting, I described how Red’s new “billet” Pitman arm was custom made for him by a talented local machinist and fellow rodder, Mitch Goss.
In this posting, I am excited to tell you that the mono composite leafsprings that we have been anticipating and prototyping for weeks are now ready! And, they are pretty cool in their appearance and incredible in their impact.
Here’s the story:
Mark Nielson at Flex-a-Form has been working with me to develop a set of composite springs specifically designed for the AD trucks. Conceptually, these are similar to the composite mono springs used for many years on Corvettes and on other GM vehicles. These, according to Mark, will lower the front end relative to the rear, will eliminate both breakage and noise, and will ride much nicer. In addition, we had already verified that they will reduce the weight of the four springs by a LOT (no peeking now at the numbers later in this posting)! We gain back a few pounds by adding traction control bars, which Mark told me emphatically we will definitely need with the 400 plus horsepower 6.0 liter pushing an under 3000 pound vehicle whose weight is biased very heavily towards the front! (Severe wheel hop can be expected without the traction bars).
Flex-a-Form has made its reputation building STRONG composite leaf springs that don’t break for racers, so I know they know what they are doing, and Mark is keen on entering a whole new market segment. The huge weight loss, drop in ride height, reliability, and superior performance, should all be pretty interesting to hotrodders in general and AD truck owners in particular, especially the ones who like me want to respectfully improve their trucks without gutting all the original parts and features.
Mark has been remarkably patient. He has had to work with sketchy information (TRY to find engineering drawings for AD leafsprings and the HOODED factory mounts they must fit into!). I sent him copies of the service manual pages, but then I had to also crawl around under Red taking careful measurements, which, after disassembly, proved to be insufficient to give Mark all he needed for a perfect fit the first time. After we discovered the subtle fit issues (like the hoods on the fixed spring end mounts, and factory hand grinding on the fixed end only of the leafsprings), he patiently HANDMADE a second, better fitting set of metal spring ends. These appear to be the ticket!
Here is some background and a few photos:
One reason that it has taken us so long to get these springs to where we want them to be, is that Mark had to work without engineering drawings (couldn’t get any for a 1955 1st Edition Chevy truck – surprise., surprise). So, we ran into a couple of surprises the first couple of prototype iterations. One surprise was that the factory spring mounts on the frame (for the fixed ends of the springs) are “hooded” in a manner that requires the spring end to be shaped in a way that clears the hood. Without the special shape, the spring interferes with the hood on th factory mount. Here are two photos that hopefully show this well enough for folks to understand:
The hooded mount:
A photo comparing the special shape of the factory conventional steel spring to that of Mark’s first prototype:
Note how svelt Mark’s spring looks compared to the clunky (and rusty) factory spring.
A second problem was that the factory hand ground the fixed (only) ends of the springs in order to fit into the factory frame mounts (no word on why they had unmatched springs and mountsd, but this is the way GM did it at the time). This photo shows how much the end of the spring was ground by the GM factory to fit (the width of the remainder of the factory spring in this photo is exactly the same width as Mark’s composite spring):
That ground end started out at exactly the same width as the remainder of the factory spring, before a GM worker ground it to fit inside the hooded mount! I can’t believe this was part of the factory design, but it evidently was. Naturally, the grinding did not become apparent until AFTER Mark had built the first set of prototype springs, and we took off the factory springs for the first time . . .
After we all patiently worked our way through these glitches, Mark fabricated final version new metal ends for the composite springs, that addressed all the weird features, and worked!
Here, Randy is installing the brand new bushing set into the composite spring:
Here is the new shackle spindle being installed into the frame spring shackle mount (the old spindles were worn):
Here is the first rear composite spring being installed:
Here is the first rear composite spring completely installed, but without the traction bar mounted yet:
You can see the traction bar on the floor underneath the spring. As an illustration of the weight reduction, the traction bar weighs as much as the entire new composite spring!
Here’s a photo of the completed front end springs:
Note the serious degree of lowering achieved!
Here are the awesome before versus after statistics:
First, we got a sensational weight reduction:
Total weight of the 4 metal factory leaf springs before the swap: 133 pounds
Total weight of 4 composite leaf springs after the swap: 25 pounds
Net weight reduction: 108 pounds
Note that leaf springs count as being “half” unsprung weight, since they do move with the wheels and axle, but the ends are fixed. Can you imagine the impacts of taking 100 pounds off of a set of components that count as ½ unsprung weight?
To help you understand the IMPACT of this weight reduction, let me point out that the entire front axle assembly, which includes all steering and brake components - everything except springs and wheel/tire assemblies, is 130 pounds., So with the wheels and factory springs, the total weight was 130 (axle assy) + 54.4 x 2 (wheels & tires) + 54 (factory springs) = 293 pounds. We just knocked about 44 pounds off that, or 15% off that. Engineers would kill for that kind of weight reduction in a suspension.
At the rear axle, the axle assembly without wheels and springs weighs 192 pounds, so the entire assembly with wheels, tires, and springs weighed 380 pounds. We just took 64 pounds off that, or 17%. Now, we are going to add back 12 pounds via our traction bars, but we are getting some very specific functional benefit in doing that.
Next, I had told Mark I was hoping he could lower the truck a bit, but lower it more at the front than at the rear, since Red’s natural ride height before the swap was very slightly “taildragger”. Mark delivered! The following numbers are approximate because the before and after ride heights were measured without the body in place yet - only the chassis, engine, and tranny. Now the body components would add the same weight to the “before” as to the “after”, but will not affect ride height EXACTLY the same, because Mark DID soften the spring rate a bit (I don’t plan to haul many heavy loads in the cargo bay!). What this means is that if anything, the degree of lowering will be greater than what you see in the interim numbers below.
Ride height at rear of frame before the swap (chassis, engine, & tranny): 24 inches
Ride height at rear of frame after the swap (chassis, engine, & tranny): 21 ¼ inches
Ride height reduction at rear: 2 ¾ inches
Ride height at FRONT of frame before the swap (chassis, engine, & tranny): 18 inches
Ride height at FRONT of frame after the swap (chassis, engine, & tranny): 14 inches
Ride height reduction at front: 4 inches
The ride height reduction at the front was greater partially because the factory springs on the front of the truck are mounted ABOVE the front axle, and Mark’s mono springs are considerably thinner in vertical cross-section than the factory stacked metal ones are. The reduction in spring thickness translates directly into ride height reduction in addition to any reduction achieved by shallower arch shape.
At the rear of the truck, the springs are mounted BELOW the axle, so there the thickness of the spring has no bearing on ride height.
Besides the above weight reductions and ride height reductions, appearance is also GREATLY improved. Just compare the appearance of Mark’s sleek composite springs to that of the thick, rusty steel factory springs. No contest.
I cannot comment on ride quality or noise yet, since Red is not yet drivable (as you can see from the photos . . .). But since Mark has delivered on everything else, my hopes are pretty high.
I don’t want to quote cost here, as these springs were a prototyping effort on Mark’s part, and he has undoubtedly learned lots about what went better than anticipated, what was harder, and what a fair price should be. I myself spent a LOT on multiple installs and removals, on measurements, and on multiple trial fits and reworks and the shipping associated with them.
But, that is all behind us now, and I will say that Mark’s hi-tech composite springs are NOT unreasonably costly, and when you consider the dramatic weight reduction and its multiple effects on vehicle dynamics, the ride height reduction, the appearance gains, and the obvious benefits of a component that cannot rust and that apparently will not break like a metal spring eventually does, the case for this technology is pretty compelling – and I say that before even experiencing the ride benefits that Mark assures me will be very evident once Red is roadworthy again.
Speaking of Red’s roadworthiness, David Horner told me recently that the media blaster, whose queue we had waited in for literally weeks, had begun the blasting and expected to finish “in a day or two”. David also told me that the media blaster had told him that paint layering had been thicker than we had thought, and that the process had uncovered (literally) more forensic information. Both David and I are on pins and needles waiting to see what was uncovered. That’ll have to wait until the next posting . . .
In the meantime, those of you planning a project that involves suspension mods might keep Mark at Flex-a-Form in mind. I know I am VERY satisfied. I can provide contact information to anyone who needs it.
Jim G
Linear Mode
