STEERING GEOMETRY a technical question

[35ragtop]

Hi all,
I have a 34 pickup with a front end that has been modified. It has 40 brakes (hydraulic), a hotrod style steering arm on the backing plate, a reverse eye spring with reduced number of leafs, a later model tie rod with new ends( not the spring loaded type),16 inch wires (35s).I still get the occasional bout of death wobbles on rough roads. I have also rebuilt the steering box, adjusted to specs. Adjusted and checked several times the toe in. Have not replaced the radius ball but the bolts are tight in.
My question for the gurus is ; Castor angle is altered by the lowering and smaller wheels, could this cause the death wobbles?
Not sure where to look next, hence the castor theory.
thanks
Dave h

[Tony, NY]

Check out the HAMB, sister forum of the Barn. It has been discussed there. Do a search. Also, check out Rod & Custom Aug. 2014 "Cure Speed Wobble & Shimmy" Article

[Bassman/NZ]

An imaginary line running down the drag link should intersect the ball of the wishbone, when viewed from the side of the car. If this does not occur, you have the front axle and the steering pivoting on different arcs. The can be rectified by flipping over the steering arm so that the drag link hangs underneath, instead of sitting on top. I spent a lot of time making those arcs pivot from the same imaginary point, and my car runs straight at 70mph with no effort to steer. Your kingpins and steering box must be A1 also.

[Mart]

No real advice to give, but do you get any bumpsteer? If so you might want to lower the end of the steering arm to lower the attachment point of the ball. You can't just turn the arm upside down, because the drag link will no longer fit. (A RHD one would)

I have the same setup (or similar) on my 33 and do not get the death wobble, but I do get it occasionally on my roadster at low speed. I either stop, or accellerate to get out of it.

Mart.

[Terry,OH]

Make sure the drag link ends are adjusted tight enough. The hair pin steering arm will throw the straight ahead position of the steering box (tightest clearance between worm and sector) and steering wheel off. If you were to have an adjustable drag link the incorrect angle of the hair pin can be corrected by adjusting the length of the drag link.

[Fordors]

Sponsored Links (Register now to hide all advertisements)

Terry is right, the hair pin has the center-line of the rod end perpendicular to the backing plate register surface of the spindle and an original '32-'34 steering arm leads the center-line by about 3/4". Ford designed it that way to give a 90° angle between the arm and drag link with the wheels straight ahead. That can be corrected by fabricating a new, shorter drag link. Remove the d/l at the pitman, turn steering wheel lock to lock and then center it. With wheels straight ahead you can now determine how much shorter the d/l needs to be. That will put your steering box on the high spot and also give an equal turning radius both R and L, as it is possible you were seeing the internal limit of the box in one direction before. Being on the high spot will enhance road feel and give better tracking in straight ahead driving but Dave has a wobble. Usually that points to something loose, or a worn component(s), loose wheel bearings or the alignment. Dropping the front end lessened the caster and I prefer 5-7° and for toe I would start at 1/8". Wheel bearings adjusted OK? King pin bushings fitted properly? Check everything to see that all is tight and it good shape.

[35ragtop]

Thank you for your replies, I will do the things suggested and get back to you. Its a bit frustrating as I have been through the individual components several times, toe in is bang on 1/8 inch. wheel bearings just right, new parts in drag link but that angle suggested by Bassman could be a clue. I have another pitman arm which is cranked and will give me a steeper angle than the straight one that I am using. I will go there next and let you know.
thanks again fellas,
Dave h

[JSeery]

I can see what's wrong from the photo, the steering is on the wrong side!

[35ragtop]

UPDATE
I carried out the alterations as per Bassman 's suggestion, retaining my "modified" pitman arm.( it has been straightened and the ball faces outwards instead of inwards to give me more movement without hitting the chassis). What a difference to the steering! Its lighter to turn, I can let the wheel go and it tracks reasonably well ( slight drift to the side of the road due to road surface camber) but a definite improvement. As for the "death wobble" it didn't happen on my test run over the same road that it has occurred on so we will see about that one.
As for the drag link length and steering box centering, yes you guys are quite right about that too. I was going to make an adjustable drag link but was offered that reversed pitman arm to try. By filing the flats into splines on its inside I was able to position it to give maximum travel in both directions. If I retained the original pitman arm I would have had to shorten the drag link.
Anyway thank you all for the tutorial and I hope others can learn from this too. Let hope my wobble has gone too.
PHOTOS ARE OUT OF ORDER SORRY. N0 1 is after,N02 is before, 3 is after, 4 is before.
Daveh

[Bassman/NZ]

#2 photo is the giveaway. The draglink imaginary extension would be miles away from the wishbone pivot. Looks pretty sweet in #1. Glad you got it sorted.

[supereal]

More often than not, front end wobble is due to a bent wheel or badly out of balance tire. Try moving the wheels to different ends and sides to see if it changes the problem. A bad wheel on the back can cause wobbles on the front, as well. The last time I fought that battle, I found one of the tires had a bad belt under the tread. It set up a wobble that required stopping the car. A different tire fixed it.