builder,
I have posted an answer to this about 5 times and deleted it....lots of variables. This might be a "semi-easy" way to do it. Assuming you still have the backing plates and drums on, you could snap or draw a line down the exact center of the axle itself. This "center" has to be the same "center" as the spindle/kingpin center. Use a straight piece of square tubing or wood and clamp it to the backing plate.
Measure out a 3"-4"-5" triangle...this will give you a true right angle, or 90 degrees. If you do this on both ends, the spindles will be straight with the axle centerline, which is what you want. If 3"-4"-5" isn't enough, you can use multiples of these numbers. Use whatever fits nicely on the axle and your straight reference piece clamped to the backing plate.
After you weld the knuckles (a [censored]) and set it in your trailer frame, center it exactly side to side, then pull a tape from each spindle end to a common point on the tongue. When this measurement is the same, the trailer should track right behind your rig. I'll bet there is an easier way and we'll hear about it real soon.
Now you can see why I hesitated in my reply...good luck!
Stuart.
