I'm running a Posies front "slider" spring on the front of my '29 Model A. What is the angle, if any, that the spring should set, in relation to the frame? (As far as positive/negative camber) Is there a way to dial this in if the current angle is undesirable? (i.e wedge shim, etc.)
The spring should sit 90 degrees to the radius rods/wishbone when at ride heigth. The caster is a different consideration and should be set and the perches bent to take any twist out of the spring or adjustable perches should be used. Assemble you front end without a spring and find a line from the end of the radius rod to the spring perch at the place you want the axle to be. Mount the spring 90 degrees to this.
The factory Ford crossmembers from 1928 through at least 1934 had 7 degrees built into the stamping. If you are using a home made front crossmember you will need to either weld in or make a wedge spacer that will give you thet angle. If you frame has a radical rake built into it which takes som or all of the 7 degrees out, even more of a wedge should be used.
If your talking about how it sits in your crossmember,I set my crossmember at 5 degrees leaning back.I was told 5-7 is good.Not shure if this is what your refering to though
Thanks for the input. What I guess I should have asked is when the spring is mounted in the cross member (In the free state), how should it set? Please look at the crude drawing at let me know if it should be as shown, or tilted one way or the other. (If tilted is correct, what is the common remedy?)
You really don't have much control over that. When the U-bolts which clamp the spring into place are drawn up tight, the spring will set at whatever angle the inside (mating) surface of the crossmember is setting at. As pointed out, that angle should be between 4 and 7 degrees if the crossmember is installed correctly. However, if the crossmember has been welded in at 90 degrees to the frame, (and many are), all is not lost. A shim the width of your spring (1 3/4") can be made up, 5/16" thick on one side and 1/8" thick on the other side x about 8" long, and then sandwiched between the top of the springpack and the underside of the crossmember.--This will give an angle of 6 degrees, which is just about optimal. Remember though, that it will need a clearance hole in it to accept the head of teh bolt that holds the spring pack together.--The shim does not need to be welded in place. The U-bolts will hold it in place with no problems. I never worry to much about what "rake" the car will end up setting on---there is always enough "give" in the shackle bushings that you can have a couple of degrees difference between the spring angle and the axle angle without causing a "spring-bind" situation. When the full weight of the engine and body is resting on the chassis, with all wheels on the ground,, caster should be dialed in so that the kingpins are leaning towards the rear of the car at the top by six degrees.
God bless you Brian. So when I fab the shim, should I include another "pilot" for the hole in the crossmember?
I do---but any time I had to make a shim, I also had issues with the front end setting a bit TOO low---so the shim was consequently a little thicker, like 1" on one side and 13/16" on the other. That let me drill a clearance hole completely through the shim, then insert a peice of rod the same diameter as the head of the spring pack bolt, about 3/4" deep into the shim, with 3/8" of rod sticking out the far side of the shim.---Then I reached into the hole with my trusty old Lincoln stick welder and plug welded it just enough to hold it in place. This still left a deep enough hole for the head of the springpack bolt to fit up into the hole, and the bit of rod that stuck out the far side located into the crossmember hole.
We get older---we get smarter!!! At least its supposed to work that way. The first rod I built, a '31 desoto, I welded in a square tube crossmember with one side cut out to accept the front spring. Of course, not really knowing much about caster, I welded it in square to the frame. Then, as the build developed, and I was reading every night to try and make certain that I was doing everything the right way, I discovered this whole crossmember angle issue. The chassis was all finish welded and painted by this time, and there was no way that I was going to hack it apart, so I did the shim trick. I was running full fenders, and it just set too darn low in front to look right. The 1" shim cured all the problems, and the car steered, rode, and drove beautifully.---Brian
Thanks agian! It actually looks like I'm gonna ride a little high, so I may have to take out a few leafs.
I talked to the machine shop about fabbing up a shim like this. I'd have more invested in a shim than buying P&J's crossmember. Any of you HAMBers want to make a shim for me at a reasonable price????
Use a flat peice of flat bar 3/16" thick x full width of the crossmember opening.Weld a 3/16" round rod full length of one edge, on top of the 3/16" flat bar. Put it into the crossmember with the rod facing up and towards the engine in the car. Make sure you have drilled a 5/8" diameter hole in the center of the flat bar to provide a clearance for the spring pack bolt. this will give you the tilt you need. The whole thing only needs to be about 10" long.----Brian.
I'll add that the angle of the spring is the castor of the axle, so don't set the spring at 5deg with 7deg on your bones. I made a fixture that bolts up into the stock front crossmember that secures the front axle at ride height (without the spring) then i have a ridgid fixed axle to work my wishbone mounting point etc back on the frame and get the correct angle at the axle. Then i can weld the piecut on the wishbone, remove the axle, axle fixture and add the leaf spring and perch pins and all is perfectly aligned with the bones at factory caster.
Correct me ifn I'm wrong, please. The amount the axle is laid back (such as the 7 deg of stock caster) is measured from pure vertical (the ground or build plane) not at the crossmember. That way you take into account any rake built into the frame at ride height, right? Gary
This has come up again and again. Set the angle relative to the top of the frame. A rake will not have any serious negative effect on the way the car handles. 99% of people who design/build their own chassis have no idea what the final rubber rake is going to be.---brian
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