Cowl steering/drag link?

does a drag link, from a cowl setup, at a steep of an angle to the steering arm, cause a low speed wobble issue, i think it doesn't know the difference, if it does pls explain in plain English

 

Normally the effect of a drag link running at an angle relative to the radius rod is BUMP STEER. This is caused when suspension travel changes the distance from the front steering arm to the pitman arm. (The drag link swings thru a different arc than the radius rod.) Do you get the wobble on smooth pavement? In this mode there is little or no suspension travel so it shouldn't affect steering. If you do then other things may be suspect: caster angle, toe, or loose joints/kingpinst.

 

just at a slow speed when you hit a little bump, if you use the brake while going over the bumps, it doesn't wobble..all the front end is new 7 degrees caster,toe in 1/8 have Had it 1/8 out plus more, no difference. steering box centered, and mounted tight,i havnt tried it at faster speeds yet to see if will still happen ove the bumps.

 

Been thru this before, is this caster wobble or bump steer? If you can go down a straight flat surface road and the car wobbles randomly it is usually a loose component, balance or alignment issue. If you can go down a straight flat surface road ok but upon hitting a bump, rise or drop on one side, the vehicle steers erratically, it is a steering issue. As stated before the angles of the steering rod and the angle of the radius rod have to rotate in conjunction with each other. if one operates in a radius different from the other you initiate a steer effect to the vehicle. Because your steering arm is pointing downward it is creating an arc that operates in a different radius than the arc created by the level radius rod. So every time you hit a small bump the two different components travel different arc distances and produce a steer effect. This steer effect is perceived as a wobble where it is only the vehicle trying to return to a neutral state. You have to change the position of the steering box to locate the drag link more parallel to the radius rod.

 

Can you post some pics of your set up.

 

so this is wrong

 

Does it change any if you drop the drag link into the bottom hole in the pitman arm?
That should take several degrees out of the differences in angles between the drag link and the split bone.

From seeing the photo I'd venture to say that it goes against the generally accepted angles of proper steering linkage design. Truthfully, we don't know if any of the three cars you showed drive any better than yours does at the moment.

One reason that I am going back to an independent front end on the 48 is that I am tired of wrestling with the current setup. I'm not even suggesting that you change suspension but tweaking what you have to make it drive right will make driving the car a whole lot more fun and allow you to relax a bit when you are driving it.
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your bump steer would be alot, an easy way of checking your bump steer is to bounce the front end by standing on it and watch the steering wheel whip back and forth.

 

Never have had any personal experience with cowl steering, but everything I have read or heard from what I considered good sources about side steering, either cowl or frame mounted, says to keep the drag link as close to paralell to the radius rod as possible. And I've been fooling around with hot rods and race cars for over 55 years.
To me cowl steering is for race cars such as track roadsters and modifieds where the steering box is much lower in relation to the steeering arm. This makes it much easier to keep the 2 more paralell.
Dave

 

Chances are you won't get it to work right at that angle.
The easiest fix may be to relocate the steering box.
Another possibility might be to go to a race car power steering
mounted in the same location.
You can then run a longer pitman arm and steer as easy as you want.
They are adjustable for effort and feedback. They are available in different
ratios also.

 

Well yes but the angle of the drag links are less severe than yours so while they look similar they react a lot slower so the bump is not as noticeable. Here is a quick explanation of your problem in relationship to the arc created by the drag link in relationship to the radius rod movement.


Sorry for the sideways picture I rotated it but must have saved the wrong image.

 

My steering arm has been modified so that the drag link is on the same plane. Before anybody says something, this has been on the road for 10 years without any problems and the steering arm extensions are aircraft material with grade 8 bolts. Opps...just noticed the tacky AN fittings!

 

**** has explained it in detail but, basically, for side steering to work well, the drag link should be parallel to the radius rod AND be nearly the same length (Vertical centerline of pitman shaft same as verical centerline of radius rod pivot). Any deviation from either of these conditions will result in SOME bumpsteer. The greater the deviation the greater the effect. Side steer will probaly NEVER be perfect; why do you think even Ford abandoed it (on p***enger cars) in 1935?

 

you might try to clarify your symptoms better

I dont think you are describing the effects of the steering arm.....Bump steer will be there at any time with any bumps and will pull the steering wheel the same time the suspension moves up and down......

It sounds like you are describing what most people call "death wobble" there are a lot of threads on here about it.

This is my setup:

 

Raise the mounting location of the radius rods to the body. You'll have to then adjust the angle of the king pin.
Lengthen the steering arm to drop the attachment location, so that drag link is closer to parallel with the radius arm.

Also since the drag link and the radius arm are different lengths, being exactly parallel, may not be optimum. The ones you referenced all have the lengths almost equal, thus parallel works.

 

the closer the steering box end of the drag link is to the center line of the front ends center of rotation the less bump steer you will have, everywhere else is a compromise, this can only happen with your car is going straight and as soon as you turn the bump steer appears, i wish i could make it more plan, everything about being parallel and such is just confusing, this is on a split bone/hairpin setup only, a four bar is different.

 

i dont have any problem with bump steer to speak of, its just the low speed wobble, it gets going over small bumps in the road , unless i put my foot on the brake alittle as i go over them then it doesnt do it...

 

Sounds like bump steer to me.

 

i thought that bump steer is when you are going down the street and hit a place in the road it would make the car move to one side or the other as you are driving,

 

Looks to me in the pics of your steering that your headlight and your header are determining your angle?

 

If the shake starts at a very slow speed. Go to a big enough old parking lot
with pot holes unhook it and try it.

Yeh I know I think to much, poor mans thought.
reading this you can see why I am poor.

 

thanks i should have thought of that, find a place thats big enough the let me go faster over bumps to see if its just at slow speeds that it happens, keeps me away from others to test it...

 

I'd like to point out that in the third pic you can see that the drag link is pretty close to the same angle and close to the same length as the suspension linkage. Both links travel in the same arc set up this way. Bump steer should be minimal set up this way.

 

Before you go any futher with the issues you have,fix or replace that steering arm angle. This is never going to work right. The steering rod needs to be more level to the drag linkl to work right.

 

Yup. Make that drag link level. When I built mine, I looked around at sprint cars and just kind of copied their geometry. Seems to have worked out very well for the 11K miles that it's been in use.
Pat

 

The " drag link level" - thing is just wrong, unless your front suspension is a four link, in which case you could a more or less bump-steer free steering set up if the drag link length is the same as the suspension links.
If you have a radius rod / wishbone type of front suspension, the ideal configuration is when a line drawn through the drag link would p*** through the pivot point of the radius rod (in the side view) and also improve the more similar the two lengths are. Just use ****'s sketch in the post above and draw it up for yourself. Draw different positions of the suspension. The less distance between the two different circles, the less bump steer you have.

 

would someone explaine, bump steer, and death wobble to me.....

 

bump steer can have different symptoms, most likely with your setup you can verify it this way. Go out to the car and stand up on the front driver side frame horn and jump up and down flexing the leaf spring and making the suspension travel thru its arc.....at the same time look at your steering wheel, I bet it rocks back and forth. While driving if you hit a bump in the road at speed you would also feel that same tug back and forth on the wheel while the suspension compresses and expands until the suspension calms back down to a smooth ride.

Death wobble can be described as a vibration that begins and then gets worse as it starts to build off of its own energy as the suspension works back and forth in an almost uncontollable vibration....sometimes the only way to stop it is to mash the throttle or brake. This is common on Ford Super Duties that are lifted with no steering stabilizer....Ford even sent a letter to all of its super duty owners explaining the symptoms and the cure. (Yes they are straight axle too)

 

death wobble is like an uncontrolled shutter or shiver, i bump or stone or
something sets it off and the front wheels go into an osculation, not unlike a speed wobble on a motorcycle and it may not stop until you slow down, bump steer is when the geometry of the front end steering is off, on your car when the suspension is compressed your tires will turn to the left, as the suspension un-compresses the wheels will turn to the right, when going around a corner with the lean of the vehicle you get the same effect, going around a right hand corner will cause your wheels to turn to the left, going around a right hand corner will cause the wheels to turn to the right, so the term "bump steer" is not really a good way of describing this effect, i have a 45 gmc with a drag link on a very steep angle and it is quite a trick to drive.