Setting up a hotrod frame
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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.
