Hot Rods Steering won't centre after cornering.

Hi

I modified the suspension on my ''32 Plymouth, at the rear I put a S10 axle on the 2 parallel springs with 4'' lowering blocks and a stabilisor bar. At the front a Speedway 46'' solid 4'' lowered axle, with hairpins and a panhard bar with a Vega steering box, set up with 7 degrees caster and 1/8'' toe in.

It drives ok but after cornering the steering won't centre, what am I missing or does a solid axle does not do that so good.

Leen

 

1/8" sounds generous.
7 degrees should be good.

 

The 7 degrees should be relative to the ground at normal ride height; if this was set with the car level (on stands or a lift), any rake once the car is on the ground will reduce the caster.

 

Yep and it sounds like too little caster to me. If it were not new I would say that the king pins needed grease.

 

the 7 degrees caster is when the car is on the street, that's what all the guru's recommend, and that is the degrees I welded the crossmember in... All is brand new and have all the greasee they can swallow..

 

If you disconnect the drag link at the steering box, does the steering wheel turn freely? If not fix it so it does. Next make sure the wheels will turn easily left and right by hand with the drag link off. If all of the above is free, you need more caster.

 

more caster or check the steering box for any stiffness also check king pins. stop by your local alignment shop and set it up and just check it out. on the alignment rack you can check the caster you cant always assume it fine just by measuring it. sometimes you can check it with an angle finder you can get one at home depot for a few bucks it will get you close it only has to be off by a little to make a difference.

 

As BJR stated, disconnect the drag link and with the tires in the air you should be able to turn the wheels from left to right very easily by pulling on the tire its self, if you cant, you may have king pin or tie rod that is hanging up. Remove the tie rod from each spindle to isolate location of problem. If they are free, your steering box maybe adjusted too tight or there maybe an issue with it internally.
You should be fine with 7 deg caster. Hard to tell from the pic, are those radils or bias ply tires? If radial then you have too much toe, should be 1/16"

 

No mention of what spindles you are using.
Self centering is also influenced by king pin inclination.
Less KP inclination will require more Caster.

 

No mention of Mr. Ackerman and his principle yet. Do your steering arms point to the rear axle pinion when the steering wheel is strait on? I know not a good explanation of the ackerman principle, but google can explain it better. Anyway your steering should return to center. Good luck. -Dave.

 

Simple approximation for designing Ackermann geometry
A simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the center of the rear axle.[2] The steering pivot points are joined by a rigid bar called the tie rod which can also be part of the steering mechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the center point of all of the circles traced by all wheels will lie at a common point. Note that this may be difficult to arrange in practice with simple linkages, and designers are advised to draw or analyze their steering systems over the full range of steering angles.
Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low-speed maneuvers. Some race cars use reverse Ackermann geometry to compensate for the large difference in slip angle between the inner and outer front tires while cornering at high speed. The use of such geometry helps reduce tire temperatures during high-speed cornering but compromises performance in low-speed maneuvers.

 

Well he does have a 46" /4" drop speedway solid axle and those use ford spindles and all ford spindles have same king pin inclination, like everybody else.

Ackerman has not much to do with steering returning to center at all.
It's geometry for turning and the tighter the turning radius the more important it becomes.

Have you ever noticed while sitting stationary and turning the wheels to full lock that the cars chassis will actually rise and on return will fall back down ? That's the effect of combining caster and king pin inclination while turning. In order to get the return to center it first needs to rise and then needs to be free enough that gravity will assist the return.

 

Solid axles work good, but I've had trouble with CHINESE Vega boxes. One spit the balls out inside while trying to back into a parking spot and the other clicks when unwinding from a tight left turn. Get a Flaming River box or a 525 box.

Make sure the tie rods and other parts aren't bumping each other or binding.

 

Ackerman is important, but doesn't influence self centering.

 

2 things.. Make sure everything is greased well.. And I never heard of an axle being backward.. If there is such a thing, how do you tell???

 

I've always had it stuck in my head that king pin angle on a solid axle was essentially the same thing as caster. But a couple folks here have mentioned the two terms as if they are two different dimensions. So what exactly am I missing here?

 

You're missing the facts. On a Ford axle king pin and perch pin are parallel. There is no backwards.

 

https://www.google.com/search?site=&tbm=isch&source=hp&biw=1024&bih=646&q=king pin angle&oq=king pin angle&gs_l=img.3..0i10.1582.5533.0.6649.14.14.0.0.0.0.101.1170.13j1.14.0.msedr...0...1ac.1.61.img..0.14.1161.E4KJ2SirOxw

King pin angle

 

https://www.google.com/search?site=&tbm=isch&source=hp&biw=1024&bih=646&q=king pin angle&oq=king pin angle&gs_l=img.3..0i10.1582.5533.0.6649.14.14.0.0.0.0.101.1170.13j1.14.0.msedr...0...1ac.1.61.img..0.14.1161.E4KJ2SirOxw#tbm=isch&q=caster angle

Caster angle

 

Well that clears things up pretty well. I was picturing king pin angle on the wrong plane, like it the same as caster angle.

 

Do aftermarket axles matter which is front or rear???

 

If he is using spindles other than Ford, they could
have a different king pin angle, and require more Caster.

 

King pin inclination angle would be found on a blueprint for fabricating parts.

Caster angle is found on an alignment rack at the tire. Its the roll of the axle.

A camber is the sum of king pin inclination and spindle's axle center line relationship.

 

Another possibility, there should be bearings between the axle and spindle.
IIRC, the bearings go under the axle, so the carry the weight of the car.
If they were installed on top of the axle, seen it done, the extra friction
might reduce the self centering effect.

 

The axle would also need to be adjusted , heat and bend to get correct camber.

 

That's my thoughts here.

Too much wheel offset for the king pin angle . Giving it too much positive scrub radius.
Meaning : the centreline of the king pin inclination intercepts inside the centreline of the tyre.

So there is more drag on the outside 1/2 of the tyre causing it to want to toe -out.
When you turn a corner [eg: left] the caster plants more load on the outside edge of the LH wheel which drags itself around more.
The weight on the RH tyre also tries to Toe-in [turning left] due to the caster angle.

If the OP bolted on some FWD offset wheels [to test it ] the problem should diminish

Adding a shitload of caster [so the vertical weight is greater than the drag ] is a patch up fix that works, but it is heading into "death wobble" territory.

 

Ford switched the betting location around someplace in there.

Cheap ass china bearings will do it too.
The wheel free of tie rod and drag link should move very easy. Just about flop

 

Kerry: The front wheels don't look like they have a ton of offset.

 

We are also assuming the spindles turn freely,
meaning the king pin bushings are not too tight.

 

When working with old cars I learned two important things 1) assuming is the mother is f@ck ups
2) never doubt an olde Mechanic in a old cars question.

I can only agree with @Uncle Ian! Check it over ones more, in every part.

Ad more info on your set up! Did put shim under the axle? Did you heed and bend?

My first boss always told me, if it worked before you screwed with it, you c0cked it up! Fix it, again! Sign