Landracing Forum

Tech Information => Technical Discussion => Topic started by: smitty2 on June 23, 2005, 11:42:04 AM

Title: Model A front crossmember
Post by: smitty2 on June 23, 2005, 11:42:04 AM

Greetings All!
 I'm getting ready weld the front crossmember into my "A" frame, and I need some advice as to what angle it should be set at.  I'm using the stock wishbones, and they are split.
 It will be mainly a street rod so I don't need a whole lot of camber... just enough to keep the wheels straight.
 Thanks...   Smitty

Title: caster in model A
Post by: Dave Cox on June 23, 2005, 12:26:59 PM

Hi Smitty, for a street car use 5-7 degrees caster. for the lakes or Bonne, 12-20 works well.

enjoy!

Dave

Title: Model A front crossmember
Post by: smitty2 on June 25, 2005, 11:05:39 AM

Thanks Dave!
Caster... I always seem to get the 2 mixed up even if a picture is right in front of me :D
 I split the difference and used 6 degrees.

Smitty

Title: Model A front crossmember
Post by: jimmy six on June 25, 2005, 10:49:38 PM

I've run 8 degrees in my roadster forever. Top speed is 216 with a 12 port GMC

Title: Model A front crossmember
Post by: Hans Blom on December 29, 2005, 11:35:33 AM

remember to set this with your frame at the rake it will sit when built...Hans

Title: Model A front crossmember
Post by: John Burk on December 29, 2005, 05:26:33 PM

Smitty if the spring is tilted relative to the arc of the wishpone there's bind as the spring compresses . The wishbone angle should dictate the angle of the crossmember .

Title: Model A front crossmember
Post by: Hans Blom on December 30, 2005, 10:01:26 AM

Your axle inclination will dictate your spring and crossmember. If you want 6 deg in your axle, your spring and crossmeber will also be at 6deg, all parallel. You can change your wishbones to fit your frame , common is to pie cut it near the factory weld at the front, put the rear where you need it and weld it up...well. You will always have a little caster change due to the axle swinging on an arc, so longer wishbones the better. Only way to get rid of this is to have a 4 bar or infinitely long wishbones.  It is quite often I see a crossmember welded in the frame flat, after kicking your 6deg in for caster, raking the car a bit, all the sudden you have 10 to 15 deg of miss alignment...bad for poly bushings...

Title: Model A front crossmember
Post by: John Burk on December 30, 2005, 02:22:50 PM

Hans think what happens if the spring compresses 3" with a 6 deg. difference between the spring and the wishbone . There's a 5/16" misalignment between the spring eyes and the perch bolt . The obvious result is a harsh ride  . Correct is for everything from the perch bolts to the wishbone be in harmony and get the caster by twisting the outer ends of the axel .

Title: Model A crossmember
Post by: smitty2 on January 02, 2006, 11:40:34 PM

Thanks for the help guys.
I used 6 degrees, adjustable spring perches, and pie cut the wishbones. The frame is "Zeed" about 5 inches. Not having any real test equipment I put some wheels on, and set the heaviest engine / Trans combo I could find ( 47 Buick straight 8!) on top of everything and yes it bottomed the springs, but no binding!
 I've since moved on to the rear of the car. My biggest problem now is how wide the rear end should be... will have to fit the body onto the frame to see what "looks" good.
 Thanks again for the help, and hope everyone has a good year  :D

Smitty