Thread: How to build an early hotrod frame

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Very well done, you should consider sending to some of the magazines. All of the new comers in this sport need to understand how all these options work so they can make good affordable decisions on there projects. Some of the magazine articles just don't explain in simply enough.

Yeah Brian, great stuff!!!! How much an hour would you charge a computer illiterate like me to teach me how to do all that way kewl designing and illustrating on a computer?????

Madddog---I use it 8 hours a day, 5 days a week. thats what I do---I am a design engineer. Thats where I get the money so I can afford my hobby!!!
www.rupnowdesign.com

Thanks for the thread.

the front transverse spring with a suicide perch ( did I say that right ? ) is exactly what I am considering for the '36 chevy master sedan. Wish I had a printer, this thread is going to be invaluable!

Brian, without a doubt.... YOUR THE MAN!!! Great work sir! Even though I know a bit about all of what you posted, it still gave me some great idea's on what I want to do with a 20's or 30's build that I have been planning in my head and putting together on the computer over the past 5 months or so. If i quit buying all these other hot rods and parts that I don't really NEED then I can build what I REALLY want and not just something that I can deal with for now.
I'd love to see your RPU in PERSON one day because you put great work and detail into everything you do and you know a ton about this kind of stuff. I wish I worked or knew someone like you around here to learn from and that wouldn't mind me watching or helping him every day HAHA.

One day old post---Forum was down yesterday---
Well guys and ladies---I'm just finishing up a great Christmas day. All our kids were home from far cities, my 2 year old granddaughter, and even my ancient mother (86 and still going strong). Much turkey was eaten, rum and egg-nog flowed like water, and Jeez, it was great, and will I ever be glad when life returns to normal!!!
Thank you all for the positive responses to my post----I do have a ton of things yet to share, and will continue this thread for as long as is necessary. Merry Christmas!!!! ---Brian

I have been asked to expound a bit on underslung suspensions. They are really an oddity in the hotrod world, and though some people have run them with success, I do not recomend them. In this type of front suspension, the parallel leaf springs (not transverse) are mounted above the frame rail and the front axle is also mounted above the frame rail. This type of front suspension gives the car an extremely low center of gravity, and an extremely low roll center. It gained favour with some of the champion road racing cars that were built in the late twenties and early to mid thirties, because it enhanced their ability to corner very rapidly during winding road races, without rolling the car over. Underslung suspensions have a certain "eye appeal" because of the fact that they are so "different" in appearance, but have never gained real popularity. They are inherently unsafe, because in the event of a broken main leaf on either front spring, the entire chassis will immediately lay down on the road, and it becomes impossible to steer the car to a safe stop. One of my earliest hotrods, that I built in 1965 had this type of front suspension in it, when I bought it as somebody elses semi finished project. Sadly, like many young hotrodders, at 21 years old my ambitions far outstripped my "know how" and finances, and the car was never completed.---it was stripped, parted out, and disappeared forever.

That definetely IS different. I can see where your comming from with the whole safety thing on it though... I guess that as long as you watch pot holes and keep an eye on it once in a while then it's fine.

This will be the last post in the front suspension series. I have covered all of the mainstream and some of the not so mainstream methods of suspending the front and rear axles. I know that there are a world of folks out there who will jump on me for not including front suspension systems, such as the Mustang 2, Corvair, various front frame clips, etcetera, but I'm not going to go there. I have not used these systems, and to claim any knowledge of them would put me in the same position as I see a lot of here on the forum---giving advice on things I know absolutely nothing about, and have never personally worked on---ENOUGH SAID---
Today we will talk about quarter elliptic suspensions. Imagine, if you will, taking a common parallel leaf spring as used on the early Chev cars, and cutting it almost in half. You leave enough on the "cut-off" end (about 3") so that the spring can be clamped in the center, with about 5 to 6" of flat area in the center. Then, you build a bracket on the outside of the frame rail, and engineer a clamp to hold the spring-pack in place, with the "springy end" of the spring extending out to where the axle would normally be located. (I have even seen one enterprising rodder who mounted the spring inside his frame tubes, and let the "springy end" stick out thru the open end of the frametube). This is a system that probably works very well, and is best suited to very light cars. Unless you are a chassis builder who likes to 'wow" the crowd with your "technical innovation capability", I do not recomend it. Not because it doesn't work well. Simply because it throws another level of complexity into a subject which already has many layers of technical complexity in place. I would say this type of suspension is best suited to people who have already built a few "standard fare" chassis and are ready to move on to a larger challenge.

Okay---that about covers all the suspensions that I am in any way qualified to talk about. This post is first and foremost about building an early hotrod frame, but its kinda like the chicken/egg thing--I have to talk about the suspension before I can really get to the frame stuff. We've talked a bit about the things that will affect the length of the frame from front to rear in the very beginning---length of body from center of rear wheelwell to firewall, length required from firewall to inside of radiator to fit a small block Chev engine, and inside of radiator relative to center of front axle. As you can see by all the different suspensions, the type of suspension you use will greatly effect the length of the frame. The easiest one and the most popular one as well, is the frame/chassis where the center of the front axle is also the center of the front spring, which is also the center of the front crossmember, and a rear suspension where the rear crossmember sets directly above the rear axle. We will be doing a bit of solid modelling and a bit of Autocad with dimensions. I am going to base my drawings, etcetera on a 30-31 model A Ford roadster. This works well, because the frame/chassis was the same for the roadster, coupe, two door sedan, 4 door coach, and roadster pickup. If you have some other breed of car or engine, don't worry---I will explain how we arrive at certain dimensions, and you can use the same rules to develop the frame dimensions for your particular combination.

Originally Posted by Ken Thurm

Very well done, you should consider sending to some of the magazines. All of the new comers in this sport need to understand how all these options work so they can make good affordable decisions on there projects. Some of the magazine articles just don't explain in simply enough.

An excellent thread....very informative, very explicit.
I realise that this involves a tremendous amount of work on your part, and it is appreciated.
BUT....not appreciated by a wide enough audience. Ken Thurm has raised a valid point here, this (even as it stands) has the potential to become a definetive "Bible" for many more people than will see it on CHR. This is because not only are you knowledgable, you're getting input from other intelligent/practical people. (And I emphasise the word practical.)
When this has evolved to its conclusion I think you should seriously consider publishing, or, at the very least, submitting it to various Hot Rod magazines, so as it can be utilised by a far wider audience.

johnboy

I have spent the afternoon modelling a model A ford roadster body. This model was created using info. from an internet website, so I really can't confirm the accuracy. At any rate, it will serve the purpose for what I'm doing here. I have saved both the model and the drawing as .jpg files so that I can post them on the forum. The drawing is typical of what you can expect to see as I continue this saga.---Brian

I haven't quit on you. I've been building the necessary models, based on the frame used on my roadster pickup, to continue with this thread.---Brian

Is it starting to look interesting yet???

I have had a few questions relating to "how do I calculate the angles for cutting my frame for a frame kick-up". Sometimes I forget that the whole world is not into geometry!!!! I have made 2 drawings based on a 45 degree frame kick-up and on a 60 degree frame kick up, both using 4" x 2" x 1/8" wall rectangular tubing, which is what I recomend for frame building. You will notice on the assembly of the 60 degree frame kick-up, that the rise is 16" while the horizontal distance will be 9 1/4". I didn't put any horizontal dimension on the dtawing with the 45 degree kickup, because on the 45 degree layout, the horizontal distance will always be equal to the vertical distance, so it would be 16" in that case.---Brian