I have a 1930 Ford Model A closed cab pickup with 4" dropped tubular axle, front disk brakes, tubular shocks, hairpins, and Vega cross steering. It shimmys at 30 mph, so need to align it enough to drive to town to get it aligned by an expert. How can I do this? Thanks. Larry
There aren't very many adjustments on these old car front ends. You should adjust it to have 1/8" toe in when the full weight of the car is on the wheels,. The axle must be setting "square" to the centerline of the ch***is, and the kingpins should both be tipped back at the top end between 4 and 6 degrees, with the full weight of the car on the wheels (not jacked up). The axle "camber" is not adjustable without bending the axle itself (something which heavy truck front end shops are capable of doing), but unless your axle has been damaged at some point, the caster should be built into the axle "as purchased".
You should only have to align the toe-in to drive it a short ways. Without getting technical about it, measure outside of front of the wheel to out side of the back of the wheel and get it as close as possible. 1/8 inch either way won't hurt to drive it 20 - 30 miles. The shimmy however, could be something else. Typically it is loose parts somewhere. Have seen extreme cases of excess caster (like 10 dgrees possitive) causing rough road shimmy. Don't remember you specifying what frame you have, but many A frames don't even have caster built in to the front spring setup, so if you bolted it straight up with no bind on the springs, you probably have little to no caster. I'd recheck the front end first. BTW. I have 3.5 degrees of positive caster on our 28, with a 4 inch dropped tube axel, and I don't think it is enough. Still has a bit of wander to it. I've heard 7 is a good number for this front end. Camber, by the way, has little or ne effect on steering, just tire wear and some cornering effects.
Make sure everything is tight. Tie rod ends king pins etc. One thing I found back on one of my old builds that the castle nuts they gave me for the spindles when backed off to put a cotter pin in they allowed the bearing to be too loose. That caused a shimmy . Tires and balance play a factor too. Set the caster at 7 degrees and toe it in 1/8.. Dave
If you're needing some technical tool-type help, check out a previous post done during the HAMB Tech week. I posted about a toe setting tool that I make for about $1.50. Search for "Redneck Teck" or something close to that and it might be helpful for you.
See a couple of answers while I was typing. I don't want to hijack this post, but take it one more step. Can anyone confirm the 7 degrees positive caster I've heard? I have an old fashioned truck shop that aligned mine. They seemed to think their 3.5 degress by the old fashioned hand method could read higher on a new electronic machine, or maybe this 30 year old equipment isn't as accurate as it used to be. Anyway, we had to leverage the front end (4 bar setup) to get 3.5 degrees.( My frame is a 25 year old TCI model. Likewise the Super bell dropped axel is that vintage. ) My concern is, putting too much twist on the front springs, to get it up to 7 degrees. Should I be shimming the spring hangar at an angle to get rid of twist? If I had built in Caster angle, would it be measurable along the front crossmember as an angled spring perch, or in a difference in angle on the axel itself?
The king pins are new. The dropped tubular axle, spring, and hair pins are new and from Speedway. I am new to this. I guess you adjjust the tie rod to get the tow (bottom of tire goes in?). Aren't the hairpins where you adjust the caster to push axle forward of back? Help?
You want to take a tape measure if thats all you have and find 2 spots front and rear on the tire (front of crossmember rear of crossmember) that you can measure and at the same height front and rear to check the toe.. Catser can be checked with a magnetic protractor on the king pin top or the top of the spindle next to the king pin. Dave
To adjust the toe in, loosen off the clamp or jamb nut at each end of the tie rod (which runs from spindle to spindle) and turn the tie rod--you may need a small pipe wrench or a pair of vice grips to do this. The tie rod ends should be a left hand thread on one end and a right hand thread on the other end, so turning the tie-rod body will effectively lengthen or shorten the distance between the tie rod ends---this adjusts your toe-in. You should see the same type of threaded ends on your drag link (which runs from the 'steered" spindle to the Pitman arm on the steering box.--You can turn the drag link body to "center" your steering wheel. The caster angle is adjusted by turning the threaded ends in your hair-pins in or out. The caster angle should not exceed 6 degrees. The toe-in is measured at the front (leading side) of the tire, level with the center of the tire, and should be 1/8" less than the same measurement taken at the rear (trailing side) of the tire, which again is measured at the same height from the floor as the center of the tire. These dimensions should be taken with the car setting on the floor, nothing jacked up. Measure the toe in (usually from one of the tread lines on the tire that will be consistent all the way around the tire---measure from the same tread line at the rear of the tire. A magnetic based angle finder (the mechanical type with the hanging pointer) can be used to set the caster, and if you want it to be super accurate, you can buy a magnetic based angle finder with a digital read-out--but they cost about $200 and you don't really need that degree of accuracy for what you are doing.
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