I need a little help. I started building a frame for my 31 coupe this weekend. I can't determine the front z without deciding on a front end settup. Can a few of you tell me what your settups are and give me some measurements. I am thinking about a spring behind 4" drop axle. I need to know : 1. your settup (preferably spring behind) 2. the measurement of the top of the spring in relationship to the spindles. is the top of the spring XX higher or lower than the spindle? I'll plug in my tire diameter etc. and I can figure out how high to set my front crossmember without having to wait for a front end that I have yet to order..... thanks
This numbers game will drive you crazy if you let it. Here's what I have come up with so far, so sketch this out. My numbers are rough, so take em as you like. I won't bank on anything until I have the parts in hand. Axle centerline is roughly even with the hole in the side of the king pin bore on a typical axle. That's 13" high with a 26" tire. A 4" dropped axle is measured from the bottom of the king pin boss to the bottom of the perch boss. So the bottom of the axle perch should be about 5.5 inches lower than the axle centerline, or 7.5" off the ground. (13-1.5 to bottom of king pin boss - 4 to bottom of perch) Now figure a spring behind axle arrangment will put the spring eyes roughly centered with the axle, or 8.5" off the ground. A typical tranverse leaf is 4 to 5 inches loaded from eyes to top of spring pack, so the spring perch should be about 12.5 to 13.5 inches high loaded. With a stock Model A spring perch, the top of the frame would be in this same area, bottom of frame behind sweep maybe 4 inches lower. That gives frame to ground of something like 8 inches. Step the front perch 3 inches and the frame is way down at 5 inches ground clearance. Situate your oil pan even with the rails and that's driver freindly. That help at all?
that does help thanks. It was a long way of getting there but that's okay. IF I follow your math that puts the top of the spring perch either even or about 1/2" bellow the spindle. I already channeled the body 4 inch and I am using 2x4 box for the frame I z'd the front three inchs (just haven't welded the front on yet) this puts the top of the frame rails 12" off the ground figuring for 5" off the ground at the firewall. I am using 3" round tube for the front cross memeber and figured a suicide perch slightly above that for the spring with the spring behind settup. With the top 6" chop it puts this thing lower than my 62 corvette which is just about right....... Does that all make sense?
strangely, yes. I am aiming for 5" running, but haven't decided if I'll use a stepped suicide perch or sweep my rails. Either way, I'll use the same parts mentioned and maybe play with the spring. I think a mono-leaf would sit lower if any of this math is flawed. I've seen that used with a 1" notch in the rails to put a stock appearing frame in the weeds. There is also room to drop down to maybe a 24" tire for another inch, or go up if you decide it's too low. Good luck. i'll post pics when I get that far. You do the same.
sounds good, I usually don't over think this stuff and jsut go for it, there's nothing I am going to do that I can't undo......
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