How do I build some negative caster into this?

If you are going to have any amount of rake in the chassis and use the model A bones, you will definately need to pie cut them to achieve 6-8* of castor unless you want your mounts way down below the frame rail.

 

Pasadenahotrod is correct, the Model A bones are weak compared to the later ones and the way you cut that hole through the middle made them even weaker. I know people use the A bones, but if you take into consideration that age has shrunk down the thickness and strength of the metal already, now you are putting more stress on them, it isn't a good combination.

Don

 

Damn it all. This makes no sense!!!!

 

As others have already mentioned, you don't want negative caster.

 

Before you go making a lot of changes, set the chassis up at final ride height front and rear on a level floor, then check the kingpin angle at the kingpin, not in the centre of the axle. The axle could be twisted, flanges may not be the same width.

 

How bout an update lucky?

 

Scott I have a pair of 38 bones I'm not going to use , you can have them if you want. Larry

 

This is really good info on kingpin caster WITH the rack taken into account. Thanks guys