How to build an early hotrod frame

Thanks Brian, I am in the process of building my frame for my Model A truck.and I was a little stumped with what I was doing.

 

Brian
Thanks for the great information. I have just started a Model T coupe project and have a ton to learn. This thread has helped me immensily.

 

That is some of the best info I have seen, thanks and keep it comin..

 

Great post on frame and suspensions.

 

In a perfect world, yes, it should be exactly centered in the frame. However, this old world ain't perfect. For 1/8 of an inch, leave it as is, and don't tell a soul!!! You won't notice any difference in the finished car. For 3/8" I would say definitly change it. For 1/8" it isn't going to effect anything.---Brian

 

The info you have provided is top notch. Thank you very much. G

 

The following link will get you to a complete post I did in March of 2009 on how to build engine mounts for a small block Chev V8.---Brian
http://www.jalopyjournal.com/forum/showthread.php?t=339822

 

Brian, I want to thank you personally and thank you for the many, many others you have helped with this thread. We must all never forget that every time someone is injured or causes injury in a poory built or modified vehicle, we all come one step closer to be legislated out of our hot rods. If you could please find time to go over a area of frame building, that I feel is often overlooked or misunderstood, and a area that I am currently needing the correct information. They both have to do with rake of the frame, while setting up of the front cross member and also the relationship of the angle of the tailshaft and the pinion angle to the frame. I understand pinion angle and angle of engine/tranny to one another, you dont have to explain that. My question is, if my finished vehicle will have a 3 degree rake, lower in the front/ than rear, is it correct to have frame level while mocking up engine mounts to give a 2-3 degree tilt down in rear and then have pinion angle up 2-3 degrees in front?{ the pinion angle of course will be adjusted with the 4 link }. Because isn't it true the angle of the engine tilted down in back, is in relationship to the "frame", and "rear pinion" and not the "ground"? Or do I need to tilt the engine down in back 6 degrees to account for the 3 degrees of down rake in the frame . For the front cross member to have the 10 degrees positive camber, should I also have the frame level and provide the 10 degrees or simulate the 3 degrees down rake of the frame and weld the crossmember at 13 degrees positive caster, to achieve the end result of the 10 degrees positive caster at the spindle? If I was not clear on anything, please give me the opportunity to clarify. Thank you in advance for the priceless help and information to all who are listening, you sir are a blessing to us all!!

 

You will get as many opinions on all of this as there are fleas on a dog, but here is how I go about it. First I build the frame rails with front and rear crossmembers in place, and I do install the front crossmember tilted back at the top by 6 degrees in relationship to the top of the frame itself. This is to establish positive caster on the front axle, eventually. I get the front spring and axle under the car, along with whatever rims and front tires I will be running. On the back end, I get the rear axle in place, along with whatever spring type I am using. I generally use coil springs in the rear, and since the weight in the rear of most model A's is very similar to many other 4 cylinder front engined cars, I generally grab a pair of coils out of the wrecking yard, and I try damn hard to measure the spring while in the donor car to see how much it was compressed when in place. I use bayonet style shock absorbers thru the coils(thats the standard type that have been used since the 1950's up untill McPherson struts started coming "stock" on all cars). Since Iknow approximately what the compressed height of the spring will be, I use a couple of threaded 1/2" rods in place of the rear shocks, and this lets me adjust the ride height in the rear to where I want it to ride when the body is in place. (you have to tighten nuts on each end of the threade rods to compress the springs to that ride height you measured from the donor car when the springs were in compression) I don't worry too much about how far the front spring is going to compress, because a stock model A front spring pack will only compress about 1 1/4" with the weight of a small block chev engine on it.
This rearend mock up with the threaded rods gives me an approximate idea of where the rear radius rods will attach to the frame---I will just tack them to a temporary bracket to keep the rearend from wanting to roll for now. The front bones I generally attach about 1 1/2" below the frame rail just about in line with where the cowl is going to start. (This is kind of a moving target, but thats a good reference point to start from. Now, I have my frame up on wheels and tires, and I can see if I want a bit more or less rake, although its not time to do anything about it yet.
I like my cars to have about 3 to 5 degrees of rake on the frame---thats what looks right to me.
Now I install the motor. Pick the motor and tranny up on the hoist, dangle it inside the frame, center it between the framerails, perform whatever your favourite magic math is to establish the engine position fore and aft (this is dictated by where your radiator is going to set and the required clearance from the rear side of the radiator to the end of the waterpump nose.) Figure out how high you want the engine to set in the frame (see my attached link about building small block chev motor mounts--some good engine positioning measurements there) then bolt a couple of temporary braces from the front of the engine down to the frame and tack them to the frame. Pull off the carburetor, and put a qood quality level on the top of the intake manifold where the carb sets, and start lowering the engine hoist untill the level indicates that the top of the carb base is level. When this position is reached, the tailstock of your tranny will be facing downhill at an approximate angle of 3 degrees, because that angle is aleady built into the engine/transmission package. Now your engine is fully located---front to back, side to side, heightwise, and at the correct angle. Now build your mounts based on this position, the car won't squat any lower on the rear suspension because it is held at whatever height you set the threaded rods to in the rear. It may squat a bit in the front, but only by about 1 1/4" which isn't going to matter.
Now you can dial in the exact position that you want your rear wishbones to be in, and adjust the nose of the pinion so it is facing about 3 degrees UP to be parallel to the tranny output shaft. (which will be pointing 3 degrees DOWN)--It doesn't have to be dead nuts in line with it---only parallel to it.
Now this is where things get a bit tricky---stand back and eyeball your frame from the side, with the engine properly mounted in place, the rear crossmember built to hold up the transmission, and the front spring compressed by the weight of the engine. If you like it (and I like a 3 to 5 degree rake) then your lucky. If however you don't like it---if there is no rake at all, or the rake is running in the wrong direction--Then you have to figure out if you are going to have to change the amount of "kick" in the rear of your frame, or change the position on your frame where your springs attach. Now is the time to fix this aspect of your final ride "aspect". If you don't correct this now, then you're screwed!!!
Now to dial in the front axle---remember that we installed the front crossmember in the framerails with a 6 degree positive lean back at the top. In a perfect world, if your frame and ride height ended up perfectly level, then your spring and axle and consequently your kingpins would all lean back at that magic 6 degree number that we all aim for with beam axled cars. However---remember also that we like our frame to be on a 3 to 5 degree rake, which kind of negates that 6 degree lean back on the crossmember.---Don't despair--there is enough flexibility in the shackle bushings that we can use the adjusters on the front hairpins or 4 bars to set that kingpin angleto 6 degrees anyways. If you are running a set of bones, then you will have to cut and pie notch them up close to the axle to bend them into a position where the ends which attach to the frame are about 1 1/2" below the frame rail at the cowl--then weld up the pie notch.
If you screwed up at the front end and the front is too low, you can build a spacer up to 1 1/4" thick to place between the top of the front spring pack and the crossmember to lift the front end up a little, or you can get a front mainleaf with the eyes "unreversed"--that will raise the front end another inch. Other than that amount of adjustment, you will have to get a different front axle with a different amount of "drop" built into it. If you are running a suicide front end, then you can monkey with the height of the suicide bracket on the frame.

 

Brian, thank you very much. I seem to be on the right track, and although this info is after the fact, I thought I would share with you that I am building a 28 Model A TUDOR sedan, w/ a 55 Dodge {Super? all of 270}Red-Ram Hemi, the frame was started by previous owner, 3 x 2 x .187". I will be bracing the rails with a K type of structure. I have a 4 inch drop tube axle up front with spring over, and 36" long hair pins I had built, that are fully adjustable at both ends with adjustable bushing rod ends into bat wings, {bat wings from a 4 bar set up- not the plates welded to the axel kind}, at the axle end. The spring I built with reverse eye bottom and 8 leaves for wieght of the baby hemi, and standard shackles. The front cross member is the Speedway, 2" drop 28-31 universal one. Front tires are 26" diam., and rears will be 29" diam. Frame has a small 6" kick in the rear, with the uprights at 45 degrees. I will build it using cross steering and the 525 box, just a little larger and stronger than the Vega, and yes a panhard bar also. The rear is fully adjustable ladder/link bars, 36" long also, and yes a panhard mounted drivers side frame end. I will try an establish the 3-5 degree rake as you suggested, should provide the stance I am looking for. I still have time yet for the mounting of ladder links and I will take your advice on the, "just wider than the driveshaft theory", for the front mounting points. Coil overs on rear for springing. I am hoping to post more pictures of the build, but with my disability's, sometimes its very hard. I hope some other members have appreciated this thread as much as I have, and everything you have shared with me and the other members regarding this specific info on my ride, is greatly appreciated. Thank you, Brian. I am sending you a whole lot O' Florida sunshine!!!

 

I have never had a problem with bending an axle tube when welding a bracket onto one side only , but then again, all the rearends that I have ever used were from donor cars that had a zillion miles on them already, and had a lot of wear on them. This meant that probably if the axle tube did bend a bit, there was enough slop in all the clearances that a slight bend would go unnoticed. However, if you are concerned, then make your brackets like this 3D model I just created. Make it a full 360 degree bracket, then split it as shown to get it over the axle tube, then tack it back together. Position it correctly, then weld all the way around a full 360 degrees in short "bursts" alternating from side to side as you weld. The thing that causes axle tubes to bend is a lot of welding and concentrated heat on one side of the tube only. With a bracket like this, the heat is equalized all the way around the tube, so bending will be kept to an absolute minimum.---Brian

 

Awsome thread !! need input on 1933 IH truck build,chop & drop.

 

My Question:

When a shop sets your vehicle's alignment, they take several ride height measurements and compensate the camber/caster angles accordingly. I am just curious why we don't have to take rake into consideration when setting camber on this type of suspension?[/quote]

For starters, we're talking caster here---not camber. Camber is something else. Camber is pre-established by the way your axle was built, and the way your spindles were built. In theory, when the full weight of the car is on the suspension, a line drawn through the centerline of the tire should intersect the ground at the same point that a line drawn thru the centerline of the kingpin would intersect the ground.--Now---on to caster--That magic 6 degree figure is a "theoretical number". It gives us something to aim for. By setting the crossmember at 6 degrees to the frame, thats a starting point. Then, after your vehicle is "up on its legs" with all the weight on the suspension, with engine in and body on, you can use the adjustments on the end of 4 bars or hair pins to adjust the final kingpin angle. There is enough "give" in the shackle bushings that you can tweak the axle 1 or 2 degrees either way to get closer to that 6 degree figure regardless of your "rake" without putting the spring into a bind.--If you are "Old School" and running split bones, then you have to heat them and bend them to dial in the caster angle. When you are building a frame, you really have no idea what final rake angle the finished car is going to set at, and you have to start somewhere to get the frame built. That 6 degree angle is a "starting point".---Brian

 

I guess I should have just posted my question...

I asked:

I am just curious why we don't have to take rake into consideration when setting camber on this type of suspension?

I meant to say:

I am just curious why we don't have to take rake into consideration when setting CASTER on this type of suspension?

Still, you answered the question I intended to ask, and not the one I actually asked, so thank you. I really appreciate you taking the time to answer my question, Brian. You are a gentleman and a scholar.

 

I know there is a hundred different ways to hang a rearend, but I'm a minimalist. Can I safely use a pair of split front bones with the front ends mounted inwards as much as possible with a transverse spring only? Or will I need a panhard bar or anything else? What would you recommend for the type of ends at the mounting points? Your knowledge is appreciated. Thanks.
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Cooter--Its been a long time since I even seen a pair of model A front bones. One of the problems I think you will run into is that the stock bones aren't going to be long enough, but that is easily fixed by welding an extension onto the "ball end" of the cut off bone. The perfect length is when you can seperate the front ends by 8 to 10" and mount them on the rear tranny mount, or on a dummy crossmember not more than 12" behind the rear tranny mount. Since there is no opportunity for them to "twist" a little bit at the rear axle end, I would probably recomend a Heim end at the front of each bone, with not less than a 5/8" hole and a sandwich plate on both sides of each heim so that the cross bolt is in double shear. That should handle anything up to a 350 cu. inch engine. If you are going to run a hemi or a huffed 350, then you will need to fabricate a seperate torque bar to keep from bending the bones on a hard launch. When running a transverse rear spring you do not need a Panhard bar, but I always run one, because on tight corners you can get bad shackle rock, and if you don't have a lot of clearance between the inside of the rear tire and the body, a tire can chew up a lot of nice paint really quick.

 

Creepjohnny has a question---hi brianangus, I'm johnny,
I've been reading your threads about how to build a hot rod and am VERY impressed. you are very knowledgeable about this stuff!! I had some questions for you if you don';t mind..
I was trying to compare my rod to your info, I have a 30 ford and plan to run it full fendered with a dropped front end and make it have a good low, not slammed stance, 350 combo with 9" rear, on '40 ford wheels and bias.
I picked up a boxed frame and have been preparing it. I want to kick up the rear a simple 2", but don't want to notch or Z the frame, and don't want to cut a hole in my trunk floor, can I loose the stock rear crossmember and run something like a 2x4 piece of steel in place of it? would I have to extend the frame about 4 inches then place the 2x4 on top of the extened part? will that be ok in body mounting and fendering and wheel base?
Any info would be very helpfull, thanks for your time and thoughts!

I had to ask what body style he has, and what he really was trying to do, --finally established that he wanted to drop the rear of the car about 2" without cutting the floor and wanted to run coil over shocks on the rear. This is my answer--

Johnny--I was thinking more last night about what you wanted to do. The model A frame tapers at the rear untill it is only about 2" thick where it attaches to the rear crossmember. In order to take advantage of this, it would be better to lay the 2" x 4" crossmember peices down like I have shown them, but still with the "crook" in them to clear the top of the differential housing. In a stock wheelbase model A the center of the axle falls directly under the center of the crossmember. Before you remove the stock rear crossmember, measure to the center of it from some "witness mark" on the frame (example--rear face of front crossmember). When you put your 9" axle into place, you will use this measurement to establish where your rear axle centerline should be in relationship to the rest of the frame. This will in turn establish where you attach the leading end of the wishbones to the frame. Position the coilovers as I have indicated.---Of course you will have to fabricate brackets off the rear of your axle tubes to pick up the bottom attachment points of the coil over shocks.. You can monkey with the height of these rearend brackets to establish the final ride height of the rear of your car. A good guidline is to have at least 4" clearance between the top of your axle tube and the underside of your frame when the body, engine, and passengers are setting in the car

 

So---I've been stealing pictures again!!! Many people who build a hotrod frame want to make the front end set lower by using a "flat" front crossmember, as opposed to the stock model A style crossmember which is "dished down" in the middle. (see solid model). Now, you can do that, and it will definitly make your car set lower in the front, but there is a caveat to be aware of. A stock model A crossmember will position the front transverse spring far enough below the top of the frame that when the spring flexes on a bump, the top of the spring will never contact the underside of the frame. That is why a stock model A frame has no notch cut out of the underside directly above the spring---its not needed.
When you install a flat crossmember, you have to notch the underside of the frame for spring clearance. (see picture). If you don't, every time you run over even a moderate sized bump, the spring will flex up and hit the underside of the frame, and jar your teeth out.

 

Brian,

On a standard suicide front spring mount (like the one that speedway sells), is there a rule of thumb for figuring out the vertical distance between the spindle center-line and the center of your 3" round tube for a given height of axle drop (i.e. this distance is x with a 4" dropped axle and x+2" with a 6" dropped axle)? I am including a picture of what I mean.

Thanks!

 

Not that I can tell you. I do know that a model A front spring with all the leaves in will "flatten" about 1 1/2" vertically under the weight of a small block Chev engine.--The rest is a matter of adding up dimensions taken from all the components you are going to use.

 

Great info, thank you very much.

 

Hi Brian
Just in the thores of refining a frame design for a build. Have you built any frames that follow the outline of an A coupe body so that in effect it looks similar to a 32 frame but sits just inside the body? Just looking to maximise the interior space on a channeled build which will have a high tunnel due to the channel and a 4" bleed like sweep at the front.

 

I haven't done it but it certainly makes a lot of sense. Set the body on a sheet of plywood, trace the perimeter onto the wood, then use it as a template to bend the frame rails to.---Brian ---(I would sawcut the top and bottom and inside edge of boxed tubing every 3" to make it bendable, then when I have it bent to where I want it, weld up the sawcuts.)

 

Great idea re the the plywood, will post pics of the outcome. Thanks mate.

 

I built a duece style frame for a 27 T tudor using this method. Mine was set up as a highboy, but the same approach would work for what you want.

I'd trace the perimeter of the body, then layout a line inboard from that to allow your jambs and body mounts to clear the outside of the frame.

Devise a way to re-position the tubing on the pattern in the same location/orientation each time you fit it to the template. I had a couple of stop blocks screwed into the plywood.

Then lay the tubing on the pattern, find the place where your layout crosses the tubing and mark it. Saw cut the inside edge and top/bottom of the tube, flex the cut closed and tack weld. Then re-position the tube and find the location of the next cut. Repeat until you get to the firewall, then you'll probably want to notch the outside of the tube to get the right angle from the firewall to the front cross member.

 

This is a drawing for Jeff, who has a 6 1/2" deep frame that he wants to put a 7 1/2" rise in at 45 degrees.---Brian

 

A gentleman named Brahm has contacted me about building a Chev type early frame with parallel leaf front springs. I don't profess to know a lot about this type of frame, but I know that you need that cool upsweep in the front of the frame to clear the front axle. The attached drawing shows how I modified 6" deep x 2" wide rectangular tubing to achieve this on one of the frames I built. It used up three or four good quality sabre saw plades, and required a fair bit of welding, but it did give that style of sweep.--Maybe it will work for parallel leaf springs as well.---Brian

 

Hi Brian we are going to start on my frame out of 4x2 Tuesday which will include a bleed sweep at the cowl, 4"dropped I beam with hairpins and the frame rails will follow the inside of the body line so its snug when its 4" channeled, this is the body thats going to be built. Will post pics as we go.



In the rear I will be running 4 bar set up with coil overs. Tyres are 28" and I want the bottom of the body to be 6" from the ground (ie the same as the bottom of the frame). Im just struggling a little trying to work out the rear kick up. This is what I have come up with so far based on your previous posts...

(Axle centre line will be 14") + (diff housing diameter/2) + (4.5 inches to allow for travel etc) - (6 inches as thats body hieght from ground) = (hieght of the kick up) ???????

In relation to the 4 bars, if I was run them parrell like in the pic below and attach them to the angled parts of the kick up and that is at 45 degress, will the 4 bars be too different in length to work?

In this instance will it matter if the frame is almost as wide as the body as Im trying to maximise the internal space for the car and hence the 4 bars are out near the ends of the diff?

I assume I will also need a panhard bar (not sure if thats the correct term) in that instance?



I have a 32 chassis and the rear 4 bar are triangulated, would that be a better option and if so what will I have to consider in that instance?

Thanks again for all your help.

 

Your frame will be 24 1/2" to the top of the kicked up section. (14+2+4.5+4) It will be 10" from the ground to the top of the main central portion of your frame rail. (6+4). that means your kick up will be 24.5-10=14.5" from top of main central frame section to top of kicked up section. Make your kick up at 60 degrees off horizontal. not 45. This will take less room lengthwise and you can keep the front of your 4 bar mounts pretty well in line. The kick up in the frame should start about 3" behind the back of your ass when you are seated in the "driving" position in your car---that will give you room for a seat-back between your back and the floor )--the floor follows the kick-up) Yes, with parallel 4 bars, you will need a Panhard rod. I have never built a frame using triangulated 4 bars, so I can not advise you on that issue.---Brian

 

Ah bugga, forgot to come back and look at this thread....

Thanks so much for you for your work Brian. I built the frame at 45 There are some pics in the build thread below. Hoping it will still work out OK...

 

Great and informative thread Brianangus!
Just curious if you've ever used a dead perch for the front and/or rear cross spring and if this could effectively be used instead of a panhard bar?