Measuring Castor on I-beam?

[yossarian19]

I've got no center-return on the front end. I've got new (and greased) kingpins, bearings, brakes, tie rod ends (drag link, too) and a decent-if-leaky rebuild power steering box, good stiff shocks & new spring bushings (old shackles). No damper. Stability is OK but not great.
So, I'm thinking "Add caster"
My thinking is that I can hang a plumb bob off the top of the kingpin and carefully measure distance between bottom of kingpin and the string, record this measurement and math it out to find the castor angle. Make sense?

[mr48chev]

You are pretty much on the right track. The simple thing would be to run it on a front end machine and have it checked but that takes a few bucks in most places even if they don't do any work on it.

You could also use a magnetic angle finder


I picked this one up at ACE after the cover fell off the dial on my old one that I had for 30 years. You can get them at Sears, I think Home Depot or Lowes and Harbor Freight almost always has them in stock. Handy on any build.

The theory is exactly what you figured, finding out how many degrees the top of the axle is leaned back from center.

[nvrdone]

do you have the angle shims between the top of the axle and the bottom or the spring ?
Are they set with the thick end to the rear ? Don't ask me how I know that one ....

[mr48chev]

First he has to figure if it is actually off and then how much it is off and then shim it to correct it to what he wants.

You would need a better straight edge than I used but I was out in the rain a minute ago doing it and the angle finder against it with the straight edge against the bosses on the spindle. That should give a fairly close reading on the caster angle of the spindle.


The reading on the angle finder in the photo showing several degrees negative as the axle is laying on the ground under my frame for my roadster.

[yossarian19]

I dove under the truck and in it's full trim, with caliper brackets & steering and everything, it's a bit "busy" to get a straight edge in there. I'll work on getting a reading tomorrow or maybe later this evening.
Right now, I have no shims in there at all.

Thanks for the help, gents!

[tmoble]

put in the fattest angle shim you can find. install it so it tips the axle or kingpins back at the top.

or, measure the camber with the wheels turned 20 degrees left and then right. difference between the camber readings is the caster.

[mr48chev]

That doesn't always fly and he may not need all that much of an increase in caster to get it right.

Checking the caster with a gauge Is a bit more involved than just comparing camber at 20 degrees in and out That's part of the process but not all of it.

Scroll down to page 152 the front end specs are there
https://www.gmheritagecenter.com/doc...olet-Truck.pdf
It calls for 1-1/2 positive caster sitting empty and 3 degrees loaded. That is why a lot of guys who never haul anything like to run about 3 degrees caster. Much more than that and you are going to have fairly hard steering, It might track well on the highway but you end up working yourself to a frazzle around town at slow speeds.

[Russell Ashley]

When I had the straight axle in my truck I installed some 6 degree shims in hopes of improving the overall drive feel. I couldn't tell any difference in steering effort but I believe it did improve the tracking when driving at speed. I got the shims from Summit and had to trim the width a little to make them fit.