Street Rod Chassis Tech


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Copyright 1997-2002 Horton Inc.


This is the text of a tech session presented by Paul Horton
at the 2002 Syracuse Nationals

Topic: Street Rod Chassis
A discussion about street rod chassis building (1948 and older vehicles).

My name is Paul Horton. I've been able to turn our hobby into a business by designing and building street rod frames and chassis parts and by selling parts made by other street rod companies. In 1978 my wife, Dorothy, and I were the whole staff. The company grew to a staff of 12. We still manufactured our product line and also repaired street rods and we custom-built customers' projects.

At the beginning of the year 2000, the company made a successful transition out of the custom work and repair business back to manufacturing a standard line of frames for Model "A" to 34 Fords and parts for a broader range of street rods, as well as continuing to serve as a dealer for major American manufacturers. I say a successful transition because some of our old staff carried on in the custom work field with their own businesses and we now count them among our customers. We designed and built the basic frame for last year's Syracuse Nats give-away '32 Ford coupe, built by Tucci Engineering and we have built the basic frame for next year's '32 roadster give-away. Dave Tucci (Tucci Engineering) is in charge of the overall project.

KISS: Keep It Simple & Safe
During this session I'll outline my ideas on simple street rod chassis design. Our company has used the acronym "KISS" in our catalogue and promotional material. KISS has various meanings in different contexts. We used "Keep It Simple and Safe". This has always been my philosophy, although there have been times when I fell off the wagon. There are lots of workable ways to build your street rod. Probably most of you are here because of the creativity that street rodding encourages and accepts. I hope this session feeds your imagination.

Frame cross sections

Most frames are 1 of several cross sections (with variations):
Channel: e.g. Ford "T" thru' 1940.
"Top hat": e.g. Chev 1937-48.
Box section: e.g. Ford 1942-1948.

Early Ford frames (up to 1932) were channels with straight crossmembers. (The '32 had a "K" that made it slightly stronger.) They had little torsional strength. (The whole frame could twist.)

It was known that a tube had more torsional strength than a channel, so builders began boxing early Ford frames. There are several ways to box a frame...

3 ways to box + "Step Boxing"

There are advantages to corner-to-corner and step boxing. Corner-to-corner weld penetrates 100%. Cosmetic grinding does not have to remove much weld. I feel it is easier to clean a corner-to-corner boxed frame than a step boxed frame.Step boxed frames offer a protected area for hoses and wires.
inside / outside / corner-to-corner / step box
"Top hat" Cross Section
Chev "Top hat" frames are already a box section. We find that they are susceptable to rusting along the bottom of the rail. Our front end kits, and those of some other companies, include plates to weld to the frame to spread the stress load over a larger area.
33-48 Ford cross section
The suspension needs a firm foundation to work properly. The strength and rigidity of the frame has a great impact on the ride "feel" of the car.

In 1933, Ford strengthened their frames by adding a second channel inside the main rail, and by incorporating an "X" center section. After 1940, Ford reversed the inside channel, effectively boxing their frames.

33 - 40 / 41 - 48
Boxing strengthens the side rails, but the center section provides torsional strength or resistance to twisting. The frame is the foundation for the vehicle. If the frame twists, the body has to absorb and resist the movement. This can result in cracked body panels or doors that pop open. A pure "X" is the strongest center section, because the twisting force has to bend both lengths of the "X". Street rod chassis builders use channel sections or round or rectangular tubing to fabricate their center sections. The main point is to transfer the stress through the center section and use the opposite frame rail and the center section to resist the twist.

We use a triangulated tower design in our '32-34 Ford frames. This is not as strong as a pure "X", but is plenty strong enough for 400 HP. It provides space for exhaust above the lower tube. This section is easy to install at home. It is in the Syracuse Nationals frame from last year and next year's car, too.
Horton Centre Section
Model "A" Fords have fairly short and narrow rails. We have not found the twisting to be as much a problem when the rails are made using 2x4x1/8 wall HSS (Hollow Structural Section) tubing with the transmission crossmember welded in place.

Building a street rod requires a mix of 5 things: time, talent, facilities, sources, and money. This is an entry sentence to whether original rails or repro rails are "better". I feel a quality street rod can be built using either. Repro rails will save time. We find this is necessary in building frames to sell.

I don't think there is a significant difference between stamped or welded rails. The stamped rails give a more original radius at the corners. The welded rails are available boxed, saving time.

Mounts: nuts, riv-nuts, weld nuts, plates
Body, fender and running board mounts can be put in the frame in several ways: Nuts welded inside the box section, riv-nuts, weld nuts, or plates.
nut / riv-nut / weld nut / 3/8" plate

Nuts can be welded inside the frame. This has been done for decades. Usually they must be tapped because the welding distorts them.

Riv-nuts are like pop rivets with an internal thread. They are an easy way to get a quality threaded fastener into a tube section. We have found that bolts can freeze in a riv-nut, causing the riv-nut to spin. This can be very frustrating. One way to clear the bolt is to drill a hole in the head the same size as the bolt or larger.

Weld nuts are small plates with a threaded hole. They get welded on the inside of the frame. Their advantage is that they don't distort the thread.

Another way to mount the body or other parts is by welding a small 3/8" thick steel plate inside the frame. After the body, fenders, or running boards have been positioned, drill a hole where you need it and tap the required hole.