The Jalopy Journal
Discussion in 'Traditional Hot Rods' started by hardtimesainit, Nov 30, 2017.
When you tie it in a knot?
I don't know too many guys who will cut a crossmember loose to rotate the spring pocket for a caster change.
If the frame is being built most chassis builders will set the crossmember so the crossmember is close to the target caster with the ride height and rake and variables under consideration. Some after market crossmember have a few degrees already in to accommodate. After its all done and final caster adjustments are made and it's no longer in that theoretical alignment. Big BUT and a for sure IF - if the car gets built and sold and the next guy changes stuff like tire size or ride height he's not going to cut the crossmember to get the spring pocket rotated for a caster change.
From a purely theoretical and completely perfect (impossible) stand point the springs perches would be and stay parallel the the axle. Picture the axle assembly bolted to the crossmember but the crossmember not attached to the frame. Since the axle needs to roll the top back to get get caster the top of the spring will roll back, the crossmember will not only roll with the spring but also slide back in the frame as well. So now it's all purely perfect, right? Ok don't drive it because the suspension movement puts an oscillating bind in the perches. Again impossible.
How much twisting is considered a bind?
It subjective but if one can not get the parts together or change out spring bushing it's too much.
In a perfect world that is somewhat true but I'd say that few guys are going to rework the front crossmember or change it to be able to set the caster.
There other ways to go about it including making a wedge to to on top of the top leaf or run the not so attractive but effective adjustable spring mounts.
It's still down to the simple fact that the car needs to go on an alignment rack and have accurate measurements taken. Then a decision on how the adjustments are going to be made needs to come about. If It were me and I had to load the car on a trailer and haul it to Boise or even further to find a shop that knew old cars that's what I'd do.
One thing on checking the toe in. The hacks always come up with the set the boards or straight edges next to the tires and measure. To me that is rather amateur and not all that accurate. I worked in a couple of shops that didn't have much more than a front end rack with a pair of swivel plates and a caster/camber gauge and the prescribed and pretty accurate method is to raise each front tire a few inches off the surface, set something in front of the tire to hold your hand steady and hold the tip of a pencil to the center of the tread and rotate the tire so you get a line all the way around the tread. That will compensate for any runout in the wheel or tire along with giving you an exact place to measure from front and back. It takes a helper holding the other end of the tape but is simple, quick and easy and accurate.
You'll know when the spring is in a bind 'cause it will ask for $50! Sorry, couldn't resist.
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Bending the spring binds the shackles and that creates problems. Alchemy, your engineering prowess is phenomenal.
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Hmm, maybe I'm wrong and it is like rocket science ! Well, trying to locate a shop. Only question that I can think to ask that is germane, is...do you align old car front end ? What if shop wants to bend front axle: heated or cold ??
At that point you know you are in the wrong shop. It has been mentioned that you can lower the mounting point of the wishbone. I know you raised a concern about it becoming a hazard (too low) but I think you can do that and still not foul the scrub line. Buy a magnetic angle finder, park car on level pavement and place angle finder on front of axle where perch pin boss is. Take reading and let us know what you get.
They make caster shims normaly used for parallel springs but could be used between a cross spring and the cross member.
Every time I drive over a bump in the road I am "bending" the spring. Who's to say a little front to back is worse than up and down? And I'm not talking Kevin Bacon (six degrees of separation) stuff here, I mean a degree or two. If your shackles are bent they are either too loose or too weak. Maybe your axle position forward to back is not optimum and could be adjusted to reduce the shackle bind.
I talked with a local old timer who ran an alignment shop for decades. He said the best way to set the toe on a solid axle car is exactly as you described. That is how they did it since the beginning of time.
Toe is set by tie rod adjustment. The problem the OP has is caster and only caster. The B/L tire change raised the rear and lowered the front which decreased caster. All other settings remained the same. I think his caster was at the minimum amount and the B/L swap put it beyond the acceptable range but without knowing what it is you can’t correct it.
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It should be noted that measuring the toe angle must be done at spindle height. Camber can effect the toe measure if measured otherwise.
You need the car setting on a level surface. This one is up in the air so ignore the actual reading put pay attention to the placement of angle finder
Angle finder checking caster
Flat on king pin.
Above Checking camber
On rotor, or straight edge on front of tire
Below is king pin inclination
Flat on King pin.
'from beginning of time'....
Well, I think that that is true, as when a youngster, I was shown this same...draw a 'center' line with chalk/pencil method. As such, I used to think...hey, I wonder if these bald tires and shaky loose parts makes any difference and whether the line will be straight/accurate. At least I was thinking on the right track, eh...ha ! I felt lucky to have bald tires that held air, and didn't blow out from the '50 ford jumping up/down on the highway.
Thanks, that helps. Hm, wonder if HF has that gage ?
That "flat on the king pin" doesn't exist on many king pins. My roadster I purchased from a previous owner who had purchased it as a rolling chassis, and it has either chromed or SS king pins with a somewhat domed top to the king pin. Alignment shops have degreed turntables and camber gauges that , used in combination with each other, can read caster.
I don't have either, and I have Buick drum brakes which negatews the use of angle finder depicted above. Still a few guys around here that understand how a straight axle front end works that I could get to check caster if I had a problem, and I would do so if I needed to check caster really accurately.
But in about 65 years of fooling with old straight axle Fords, etc. plus setting and building up dirt oval track cars, I can judge fairly well about caster by the way that when turned left or right, the inside wheel should have much more positive camber and the outside wheel much more negative camber with positive caster.
Then later on working with my son on competition dirt oval go karts which have no springs, I had to learn how caster can also influence weight jacking in the turns!
If you have loose parts don't worry about alinement fix the parts. The minute the parts move the alinement just went out the door.
I believe this also.
How about every time tires are changed, is the same true ?
If you have loose parts ball joints king pins or tie rod ends any movement in these parts from they where when the alinement was done changes things especially the toe setting. The alinement will be fine until you move the car. Tire changes are fine unless the height is changed a lot. On double wish bone cars ride height will make big changes in alinement..
That's why the experts say you draw the line on the center of the tire, take the car off the jack, roll it foward a couple feet to "set" the wheel in its forward position, then take your measurements.
Thanks for input on proper process.
Anyone familiar with a process where different degree sized 'wedges' are used to correct caster ? One shop has advised that this may be one method whereby he can correct cster.
Divided by 2, to work out caster angles.
There are some , I have just done this, as I wasn’t happy with some spring bind that I saw happening.
The wedges are used with straight axles and dual, parallel leaf springs, between the spring and axle, not for transverse single springs.
In extreme cases, where the angle must be changed a considerable amount, there could be spring bind problems severe enough to warrant some work on the front crossmember on a transverse setup, but it isn't common. usually results from some radical alteration involving cutting the frame or crossmember, or a rake of extreme degree from more than just normal B&L tires.
Thanks for that info. Hm, wonder why he would suggest such possible use , as I informed him that I have a stock type straight axle '30 ? I'm going to see a couple shops next week, we'll see and I'll let ya'll know what I find.
Well, I said that I'd give you guys some feedback.
I located a GOOD front end/frame straightening business (41 yrs).
Someone here said to ensure that parts are in good condition, etc....
All my front end parts were/are fairly new. The problem turned out to be LOOSE parts ! I thought that I checked /re-checked for loose parts. But, a little hard to see everything without a little help...i.e.-someone to shake front end and someone to observe. Shop owner did easy stuff first (golden rule, eh !). After tightening everything, he found that front end was with=in specs and that I have , what he said , glass belted tires....'Get rid of those and put steel belted on' ...his advice. I subsequently put on some steel belted tires and it is again a pleasure to drive. tight/right ! It is a '30 model A and drives like one ! No more following road irregularities !!
We have all seen the photo of a Ford axle twisted up like rope. I feel it is acceptable to twist the ends of the axle slightly to alter the caster. Look at how much the axle twists & caster changes when cranking the steer wheel on a side steer car with dropped axle, car sitting still. Also, from a side view the front spring should be 90 degreeangle from the trailing arms. The correct spring angle has nothing to do with axle caster. If nothing else it takes a bind off the shackle pins & they will take grease better. Greg
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