Printable View
I have a 31 Model A stock front crossmember in a 32 stock frame.With the frame sitting level and the crossmember in the correct position I am reading 4-1/2 degrees. I've read that 6 to 7 degrees caster is needed for the car to track straight. Do I need to move my crossmember or will the spring/axle/wishbone combination add a couple degrees to it? I am splitting a pair of 37 bones for this.
No, it is fine the way it is. Anything from 4 degrees up to 7 degrees will work. the six degrees is considered "optimum" and that is the kingpin inclination. Even though your crossmember is setting at 4 1/2 degrees, there is still enought "slop" in the fit between the beam axle, the spring shackles, the spring, and the crossmember to monkey the axle a bit more or less without putting the front spring into a "bind" situation. You'll be fine the way it is.---brian
Thanks, I've seen articles that go anywhere from 5 to as much as 9 degrees, but wanted to keep it as close to the optimum angle as possible.
Ralph
Just to add to this, take into account the rake if any to your build. If the rake is 5 degrees you need to ad that to your cross member.
Ken
That's correct. As an example take a look at the car in this pic and notice the difference between the rake of the frame with "big n littles" compared to the ground. This angle should be figured in to your total cross member angle.Quote:
Originally Posted by Ken Thurm
http://www.hotrodders.com/gallery/da.../nat0281a1.JPG
I am going to go against the grain here, and say that you can forget about the rubber rake. I set my cars up for a 6 degree inclination to the level ground when I am building the car. If the car picks up some rubber rake because of the tire sizes as it evolves, it does not seem to effect the steering and handling of the car at all.
When I build a traditionally styled chassis with wishbones, ford perches, etc, I put the front crossember it with 6-7 degrees of caster, and get a resultant caster of 4-5 degrees with a 2 degree or so rubber rake. Most traditionally styled cars don't have an agressive rake anyways.
For more progressive styled chassis - I actually mount the front crossmember so that the radiator mounting pads are flush with the top of the rails, lowering the car to the max at the crossmember, then run adjustable perches so that you can dial in whatever amount of caster you choose using the radius rods or 4-bars. This way you have zero spring bind, and the front crossmember can be mounted as high as possible in the chassis.
That said, I'm aware of the car that Ralph is trying to build, and adjustable perches and hairpins/4-bars have no place on that car. 6-7 degrees in the crossmember, and pie-cutting the wishbones behind the yoke to get the amount of caster you want is the way to go - been building hot rods that way for 70+ years guys....
I will have to go with SirSpeedy on this one, I'm not looking for a radical rake, but a more traditional look. I am looking at using a posies reversed eye spring (2-1/2" drop) for the stock 37 rear axle. This will put the top of my axle housing about 5-1/2" below the bottom of the "c" notch. The dropped front axle will use a reverse eye as well. Tires will be 6.50's or 7's on stock 36-39 4.00x 16" artillery wheels or '41 steel wheels(I haven't made up my mind) but I really like the look of the Artillery wheel with a 37 hub cap and trim ring.
All that said, I worked on it some yesterday and I modified the A crossmember slightly and got it to sit right at 7 degrees with the frame level to the ground. I also spent another 3-4 hours on the rear crossmember which is almost done except for cleaning up a few welds.
Lets see some pics.... a cool project for this place....haha
Here's a couple. Sorry for the quality, I'm not too good with all this new technology. The rear crossmember has about 15 hours in it so far. It started out as a 1940 with about an 8 inch drop in the center, now it has 1 inch, and it was about 4 inches too wide. I figure it will give me the look of an original crossmember, without having to use the curved spring of the '32. And it will help the car sit a little lower in the rear. I hope to start welding it together this weekend. I'll post some updated photo's when I get it off the frame jig.
I like all of it.
I have picked up a couple of those 35-40 rear crossmember at swap meets over the last year or so, to do that exact same thing with at some point.
Progress! At last it's out of the frame jig, I had a friend come over, who has a 32 that is almost ready for the road, and we knocked it out. I'm really happy with all of it. I had to spend the extra time and set the rear axle in place and see how it would look. The new rear spring will drop it about 2-1/2" and I still have to order the front spring and axle, but so far everything is coming out as planned. Whaddaya think?
Forgot one picture.
That thing looks sexy. Are you interested in a Ford axle? I've got a 48", 2-1/4" perch - about 3 1/2" drop or so....pretty nice.
Well I was going to go with a 37-41 front axle( I have three) but realized with the split wishbones that tire clearance would be a problem, especially if I dropped them, So I started looking at the 32 heavy style that Riley Auto carries, along with the matching tapered spring and Henry Ford style square shank shackles,I already requested a quote on shipping, but do you have any picture and how much would you want for it? Is it Ford or aftermarket?
The I have is a ford axle - I'd be happy with $250 and shipping... email me at tdavis32 @ earthlink.net
I'll get you some pictures if you like.
I would like to elaborate a little more on the front cross member angle and the importance of doing it correctly and the reasons why this is such an important part of a build. I only want to focus on caster and what it does. Other things come into play with this, like the Ackerman theory, but I want to focus just on caster.
Their are two things that directly affect the amount of caster needed in a good handling car. One is the weight distribution of your car, front to back. The more weight you have on the front end the less caster you need to make it handle properly, conversely the less weight the more caster is needed to keep the wheels tracking properly. If you doubt this look at the difference between a top fuel dragster and a supper stock Ford.
The second thing is personal preference, how fast you like the front end to return after going threw a turn and what is comfortable driving on a highway. The more caster you run the less the car wants to turn, so when you make a turn the wheel will center itself more quickly.
I like a lot of caster in my cars, I like it to pretty much drive it self going down the highway.
O.K. I'm almost done. So when you install your cross member all these things come into play. So how much do you need, well like I said before, you need to know the angle of the finished project, rake, weight distribution, and personnel comfort. You really don't want any bind in your front end, this means you need to know what you are going to wind up with. In a '32 roadster with 2 degrees of rake and a stock wheel base with a steel motor and a 4 speed, 6 degrees is good. I use aluminum motors and aluminum 5 speed and I stretch the wheel base so I run about 8 degrees.
Now all of this is just my opinion, things I have learned over the years. Will a car go down the road straight with 2 degrees, yes, probably. But will it be a more enjoyable experience with 6 degrees and no binding, yes, I believe so.
Just some food for thought, I'm nobody, no expert, just somebody who enjoys his Hot Rods.
Ken
It's an apples & oranges comparison I know, but I have my "Z" (strut ft. end) set @ 10°. I was told by Art Morrison anything over 150mph = 10°. Seems to go along with what Ken just said.
Not really it is all the same, in a race car you really want it to track by itself, all you want to do is make slow corrections. Going down the highway the speeds aren't the same but you want the same results. Correct caster is really important. I would run 14 degrees in my pro stocker.Quote:
Originally Posted by pro70z28
Ken