Hot Rods Do you have to pie cut wishbones on the king pin end???

(Talking about 1940 wishbones split on the front of a non suicide front end on a Model A) Do you have to pie cut wishbones on the king pin end or can you leave them un cut and just adjust the tie rods to get the desired caster? Seems like it would be to much stress on the tie rod or the wishbone mount without angling the front of the wishbone.

 

Usually, if you don't cut the wishbones, they will point into the ground with proper axle caster. Not always, but usually.

Modifying the wishbone isn't a big deal if done properly. Is there a reason you don't want to cut them?

-Abone.

 

It depends on how high or low you mount the bones. My frame is pretty low to the ground and I wanted the top of the bones to be parallel with the top of my frame so my bone mounts are about half way up on the frame rail ('32 frame). With the mount in the middle of the rail and the bones set parallel to the frame at ride height I didn't have enough caster (about zero degrees). I did a 10 degree pie cut anticapating a 2 degree frame rake giving me 8 degress of caster.

So yeah, that's what I did.

 

I am not sure I understand correctly. The caster is only dependent on your vertical location of the wishbone mount. I can't see how this would affect stress on the tie rod.

 

I'm running 34 bones on the front of my "A", so I can't specifically give you a yes or no (I didn't in my application). But a lot will depend upon how far up/down you mount the rod end. My guess is if you have short rod mounts (close to the frame rail) you will need to adjust the yoke end. The best thing to do is just mock it up and see where you're at.

 

Tie rods have NOTHING to do with caster adjustment. Period.

 

I know you cant see much, but this is the only pic i have at the moment. I have kinda short wishbone mounts (i wanna say its like 6 degrees of caster now). I just don't like the fact that the spring is mounted square in the crossmember and the bottom of the front end is so pushed foward. So I guess the stress would be on the shackle bushing more so? Is that how most mount or should i cut them to correct the angle of the wishbones, so the whole spring will sit more square?

 

If i understand you right, you have the front crossmember welded in square and the axle is at 6 degrees? The spring and cross member should both be at whatever degree the the caster is set at so there is no twisting/bind.

The angle that the bones are at now looks good, 6 degrees of caster should be fine.

 

No.....not always. The degrees built into the crossmember will change with the rake of the car and the chassis. My coupe has 37? Bones with a 2" lower posie super slide, and off the shelf speedway frame brackets. Caster is 7 degrees

 

I am with you.
You have the stance of the car set.......now you find the spring and the front x member are at different angles. If your axle is at 6, why do you want to change it. You need to change the x member some how to match the spring.

Can you post a better pic of your front end? It looks like your bones are angled down and i want to know how your getting 6 deg of axle angle like that..........unless they are up side down???!!!!!!!

 

My experience has been that if you want to maintain a 6 degree negative caster, the ends of the split bones will be so far away from the bottom of the frame rail that it looks kinda dumb, and puts the bottom of the bracket too close to the ground. That is the reason that a lot of folks pie cut them at the king pin end. Tie rods have nothing to do with caster. If you find that there is a difference in the angle of the spring and the angle of the axle, the cheapest "correct" fix is to put a tapered shim between the top of the spring pack and the underside of the crossmember. This will give the same effect as cutting out the front crossmember and welding it in at an angle.---Brian

 

I was gonna suggest a wedge between the spring and crossmember but Brian beat me to it.....

 

I have to take a better picture, but yeah the crossmember is welded in square( where it was rivited stock) the axle is at 6 degrees by mounting the wishbones foward, so the bind on the spring and shackle is my question/concern.

 

more pics!

 

Yep, thats what you have going on. Do as others suggest, use a shim or go the MUCH more work route, and redo the cross member

 

POSITIVE CASTER, not negative. When the pivot axis is tilted backwards, or the top pivot is positioned further rearward than the bottom pivot, it is POSITIVE caster, TR

 

"and just adjust the tie rods"...........Are ya maybe talkin' about ADJUSTING the TIE ROD ENDS screwed-into the ends of the bones? DD

 

Yes, sorry for the confusion

 

The Model A wishbone has no caster built into the wrist,.. however 1932 and up all have compensation for the caster built right into them, There are a number of things that determine caster (As well as Pinion angle). Sprung weight, wishbone length, Tire size & mounting position of the tie rod end.

When building a chassis I set the frame up on the rake I want to achieve, Then built the engine / Trans mounts and tack them in, making sure that the carburetor mounting flange is level side to side (make sure it's level with the frame, sometimes garage floors are off a little) as well as fore and aft ,.. and install the engine/trans. I have a set of long temporary set-up wishbone mounts, With the engine load on the front, I slide the front suspension into place with wheels and tires,... square it up in the chassis, Clamp the temporary wishbone brackets to the frame,.. and let the engine load down on the spring.

Because of the single pivot point on a split wishbone suspension, the axle will travel in a arch,.. So,.. if you have 6 degrees of caster on a unloaded chassis,.. you might have 8 to 10 degrees of caster with the chassis loaded (or there about). Then I put my angle finder on the top of the king pin, adjust my temporary bracket up or down to get my desired caster,... take the measurement from the bottom of the frame to the pivot point of the rod end,... and build permanent wish bone mounts accordingly.

Having the engine & trans in place, you can find your output shaft angle,.. and set pinion angle accordingly (Compensating for the body and full loaded weight of the chassis). Once again,.. Tack weld everything during build up,.. and when it comes apart for the final time,... Burn everything on the frame with final welds.

There are a number of ways to build a chassis,.. this one works best for me.

***( I know most of you guys know how to do this,.. So,..no offense intended)***

Disclaimer,....
OK guys,.. what I wrote makes perfect sence to me,... but because of a allergic reaction (over the last several days),... I have been taking a LOT of Benadril (sp?) and I'm feeling a little "loopy"



Here is a chassis I built for a friend,... It's not finished,... but you get the idea.


I totally freaked myself out yesterday on this thing,... We measured the wheelbase from the front bearing cap to center point of the rear axle and it was off from side to side by 9/16' of a inch !!! I knew I couldn't have screwed up that bad !,.. So when we got it back to my friends place, I measured Kingpin center to rear axle center,... and it was dead nuts !!

So I'm looking at it, and it hits me,... we just threw together a temporary tie rod on it (in a big hurry),.. so it could be loaded and unloaded and roll straight,.. Well I used the old "Eye ball micrometer" (which ain't working to good these days,...) to put the front wheels straight,... But it ended up having 1-1/2" inches of Toe-in,.... THERE IT IS!!!!,... After removing this little calculation,.. the wheelbase was once again dead nuts side to side. My tape measure doesn't lie,.... But it likes to play little tricks on me from time to time.

Hope all this rambling helps,.... I got to take some more meds.

 

Don
That is kind of what I was thinking also. All you can adjust with your tie rods is toe. But I was waiting for some new wisdom that I didn't know about.

You should build your spring mount with caster in mine. IE if you mount your spring square with the world you will be putting extra stress on the shackles if you use the radius rod to set your caster. You can shim the sprint in its perch to reliev the stress on the shackles if you need to.



That said if you don't get your caster correct you will have an ill handling vehicle. What you ultimately want to end up with is 7 degrees. Maybe a little more but definately not less.

 

You can ramble as much as you want, if you keep building cars like that A. Very nice.

 

This is 100% true, When a tie rod end is used for it's original application,.. But in the case of using it as a pivot point for wishbones,... In a very limited sence, It can be used to squire up a axle in a chassis fore and aft,... Like if your wishbone bracket's from side to side ended up 1/4" inch off front to back. But yeah,.. It has zero effect on adjusting caster. (IMHO)

 

Thanks,.. This car belongs to my friend Ed,.. I would have liked to see it with more of a chop,.. (only 2-1/2"),.. And because the aftermarket manufacturer of the front cross member didn't compensate for caster,.. these shackles are in a little bind,.. So as soon as the chassis comes back to the shop,....
I will put a 7 degree pocket in it to relieve this problem.

 

cut the cross member and reweld .Tack a stiffner above cross member first ,To hold weight and adjust to to same as king pin inclination ,You said 6 so 6 it is ,

 

That original crossmember has caster built in doesn't it?

 

YUP, sho nuff dose !

 

I thought he said he welded it in just as it was originally riveted? So, it should be in correct orientation already unless I am reading this wrong?

 

It's a compensation factor, so the spring, when sitting at 7degrees sits flush against it's mounting surface,... But the pivot point of the wishbone is what dictates how (What degree of angle) it sits in the front cross member pocket.

 

Right! My response/ query was to the suggestions to cut the crossmember loose when it is probably fine where it sits. I just needed some clarification to make sure I wasn't reading incorrectly. Thanks!

Oh, and that's a good looking roadster your building B and C!
The coupe is very nice as well Harm.

 

I guess from reading his original post my understanding was that he was using the tie rod and not a tie rod end on the end of his bones. If you stretch it our very much you are going to throw it into a bind.

Here is an overly simplified picture if the setup the way it should be in a perfect world. Please excuse that it is a little lossy when it shrunk down to fit on the HAMB it blurred it a bit.



Ideally you want everything either parallel or perpendicular. You have a little room to fudge but fudge it very much and things begin to bind. I think that is why we notice so many ill handling or ill riding or both cars is that things are not made to be right in the first place then get fudged too far before all is said and done.