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Street Race Truck More... The Toolbox

Using a High Arc Spring Suspension on a Model A Roadster

9/16/2016

Speedway Motors employee Tim M. takes his creativity up a notch with this installment by incorporating a Model A rear crossmember and a high arc spring into his '29 roadster build. See what Tim goes through to restore the spring and gets it ready to fit on the car.

I’ve always wanted to build an early 50’s style Model A hot rod on a pinched deuce frame incorporating a model A rear cross member and high arch stock spring. I was lucky to find a deal on such a frame that had already been started, but the first owner installed a triangulated four bar rear for a more modern street rod. While they work great, a 4-bar suspension just wouldn’t fit the mid-50’s era build I was aiming for so I decided to remove it. I cut out the 4-bar and replace it with stock parts a builder might have used back in 55. Why use a high arch Model A Ford spring in a 32 frame you may ask? This answer is simple. Forever guys have been doing this to clear a quick change rear end. When I scrounge up enough money for my quick change this rear suspension will not only be period correct; it will also clear the extended case of the quick change but sit just high enough to show it off nicely.

In this article I will document the work done to my rusty 100 year old Model A spring to bring it back to life. I will talk about some important information to keep in mind regarding old springs while also showing some handy items available to make using an old spring easy.

I tracked down my Model A spring in an old junk yard back home in South Dakota. The spring was resting in a pile of other parts not far from an original dilapidated Model A frame. I knew I needed a good high arch spring and the rear cross member on the frame looked good so I brought them both home. In thinking about what the roads around America looked like in 1928 it quickly became apparent why so many frames cracked, and also why so many of the original springs took a beating. If you are scrounging original parts like me keep this in mind, and make sure items are free of stress cracks and heavy rust. Most original A springs will be rusty to some degree, but watch for heavy pitting on the flat surfaces between the leaves where moisture would sit.

Cleaning up my old spring was going to take time and patience! If you want to fast forward to another area of your project you could take the easy route here, and simply purchase Speedway Motors replacement high arch spring. Part number 91043102 fits both Model T and Model A, and is hot rod ready! I would recommend that route if time is of the essence!

I have time, am a glutton for punishment, and like the romance of using 100 year old parts when I can so the decision was made to dive into my old spring head-first and fix it up.

The first order of business for me was pulling the spring apart to inspect the individual leafs. It is important to note that even with the spring out of the car, the leaves are bound by the centering bolt and there is a substantial amount of potential energy stored. You must clamp your spring before removing this bolt. Some Model A guys talk about these rear springs flying apart with enough force to seriously hurt you so be very careful! I of course didn’t do any reading ahead of time and cut my bolt head off to get the spring apart. I was surprised when it came unglued, and needless to say I wish I would have been more careful! Next time I will clamp the spring, remove the bolt, and release the pressure slowly! Having survived the bolt head flying across my garage like a bullet, I looked over each leaf to make sure the rust wasn’t an issue.

Most of what I saw was surface rust with only a few deep pits. You will want to give your spring a good look here, and if the rust is too bad go back and order the new Speedway high arch spring. I took each leaf out into the yard with a flapper wheel mounted to a Makita grinder and began cleaning them up. The flapper wheel worked great, but you might have a wire wheel, or sand blaster to do the same work.

Everything you read about using model A springs in a hot rod will talk about removing leafs to soften the ride. How many leaves depends upon if you have a roadster or sedan spring as Ford did put stouter springs in heavier cars. Model A pickups came with a 12 leaf rear spring, sedans and coupes came with 10 or 8 leaf springs, and the roadsters typically had 7. My car will be extremely light being a roadster with only a small fuel tank and battery riding in the trunk. The first order of business is to either remove leaves, or cut them down to minimize their effect. I decided to cut down the top 4 leaves to about 16 inches and leave them in the stack to act as a spacer. I need my car raised up in the rear, so I will be leaving these “spacer leaves” on the top. To lower the car you can move these to the bottom of the stack. I am going to run 6 leaves at stock length with the top four as a spacer.

Cutting the unused “spacer” springs required a nice carbide cutting wheel on my chop saw but the old Henry Steel will eventually yield. What I like about using the flapper wheel to clean up each leaf is it really took care of two tasks at once. The high speed flapper wheel cleaned off the rust, but also ground and chamfered the ends of each spring leaf.

This step is very important because in doing this you help the leaves glide over each other without digging in. Back in ‘28 the boys in the Ford factory didn’t have time to do this but it makes a world of difference when it comes to reducing noise and wear on the spring. I also pressed out the original spring eye bushings, and replaced them with new plastic bushings from Speedway Motors. Part number 91033323-1 will work perfect, and give you some extras for your shackles.

Once the leaves were clean of rust and old paint I cleaned each one with lacquer thinner, then primed and painted them. Many modern springs have nylon buttons that ride in between the leaves to reduce friction and noise. Over the years hot rodders have tried different things to lubricate springs to reduce noise and wear. Grease works well, but it attracts dust and dirt so wrapping the spring is a necessity. Spring wrappings are either made out of leather, tin, or some other material that seals them from the elements. I have seen electrical tape used which keeps things sealed, but it can also bind the spring and keep it from moving properly. I wanted to try something to reduce friction with my spring, so decided to try plastic spring liner. This comes in various widths for different springs. I stopped by the Speedway parts counter and ordered one roll of 2 ¼ inch liner, part number 91033038. One roll will take care of one spring. The material is very thin at just 1/16” thick, and is very easy to cut and trim with scissors.

The material has a raised edge to keep it centered on each leaf. When fully assembled it blends in well. I decided to take a razor blade and trim off the edge of the spring liner on the rearward facing side of the spring. This makes it invisible to anyone looking at the car from behind.

A new nut and bolt finished things up! Here you can see the spring restored and ready for the car. I have one additional leaf ready if I need to stiffen up the ride but will start with this arrangement. The next steps for me will be finishing the welds on the rear Model A cross member, and build a spring spreader for installation and removal of the leaf spring.

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