Bent vs. Straight Drag link

I had a talk with an old guy while looking at my car. He said it would be much more efficient to put a slight bend or Z in my steering drag link instead of being a heavy angle as it is... was wondering what the correct way was. If any body has bent their steering link ?

 

Good question, I'd like to hear this too, In some early 50's photos I've seen cars with the drag link bent, but in my mind I would think it would allow too much Flex.

Drew

 

Might look better but the geometry would be the same. I doubt you would notice any difference.

 

Here's a piccy of the drag link on my Essex;works fine,no handling problems at all.

 

As long as it is sturdy enough to do it's job, and your "Ackerman"??(spelling) angle is right, I think you could go either way.

 

If the distance from point to point is the same, nothing changes. They travel the in the same Arc no matter what shape.

Dotted line = current straight drag link
solid = bent drag link

 

Exactly right^^^ The physics are the same. And as long as it is stiff enough to not flex it will be fine. I don't think there is a lot of force involved here, after all you are holding the wheel in your hands.
I've had heavy vehicles with a curved-bent drag link and they were factory. And basically the same size tubing as a straight one.

Frank

 

I have a bent drag link on my coupe to clear the front hairpin..........before bending it I made a mock up using stiff wire...........then, inserted a lehgth of rebar i n it before bending it using heat..........it works just fine and I see no reason why you shouldn't do it if you need the clearance........

I first saw a bent drag link on Ron San Giovanni's blue blown flathead roadster........figured if it worked for Ron.......what the hell......

Brucie

 

Here's some fun with draglinks you guys might get a kick out of -- mostly 4WD focused, but fun to scroll through.

In the offroad world, bent draglinks are not really great, but the loads are much higher than would typically be found in a light hotrod. With power steering and your tire against a rock or something, you can really cause some damage.

http://128.83.80.193/scarysteering/index.html

Some of that stuff is pretty scary.

For a light hotrod, yeah it'd probably be ok. Use a thickwall tube, make sure the bend is made with a radius, and not over a sharp edge, and you should be fine.

Just my opinion,
Pete

 

A heavily angled draglink will transfer more bump steer than a Z'd one.....
So the "physics" are not the same....
4x4 guys know this.....hotrodder's should too.......

 

A drag link doesn't know (or care) if it is bent or straight, the distance and angles between the points being connected are the same regardless.

If you bend or shape it for aesthetics or to clear an obstacle is perfectly fine, as long as it is beefy enough to not flex in the application or else you'll have handling bugaboos.

If your geometry is poor you'll have a problem whether it is straight or an 'S'. If your geometry is correct then it could be 'U' shaped and as long as it's strong enough it won't matter.

I've made and modified many drag links and can speak from experience on this

[edit] before I forget, a good reason for 'Zing' or dropping a draglink is because the tie rod style (or rod end) joints have limited travel and may bind if the link were a straight shot so bending the link could be a good thing - although dropping the pitman arm would be better to eliminate the extreme angle.

Al in CT

 

You're right, the draglink doesn't care.......but the spindle that it's connected to does......especially in a cross steer application.......

If the angle is increased in the pic below......bumpsteer increases as well.... a Z'd draglink corrects it.

 

>>> If the angle is increased in the pic below......bumpsteer increases as well.... a Z'd draglink corrects it.>>>

I respectfully disagree. Z-ing the draglink in the pic you posted will help eliminate binding at the joints, and thus help the situation, but will do little with the geometry overall except maybe flattening the plane the links travels a little bit. It's essentially a band-aid.

It would be preferable to lower/move the steering box or pitman arm instead in that deal.

JMHO and gentlemen can always disagree.

When I did truck lifts over a couple inches I *always* dropped the pitman arm to keep the geometry correct.

Same thing when I did a roundy rounder front end, I would relocate the steering box and/or idler arm or fab a new pitman arm to keep the planes right. The end result is that the pivots for the tie rods and steering arms have to be in the right spot or it'll bump steer no matter what shape the drag link is.

Al (ASE and Midas front end/suspension certified in my former life before real estate) in CT

 

Now we're talking about to totally separate things.

A heavily angled drag link means you have your geometry incorrect to start with. A Z'd drag link would mean you are bending the drag link so it clears something in the way, even if the actual geometry is correct to start with.

If your basic geometry is wrong you can put all the Z's in the drag link you like, but the steering geometry is still the same.

 

My wifes drag link is bent on her modified and it works great. No handling probelms whatsoever.

 

Agreed

How about over a "couple" of inches? Say 6-10"?

I disagree.....I ain't no gentleman......

Josh (Certified know nothing, do nothing, know-it-all) in WA......

Never said it did.....should have stated that a Z'd draglink "helps" correct bumpsteer...to a point....but then, this is a bit OT, since I'm referring back to my 4x4 days.....

I'll admit I'm wrong..............It happens quite frequently lately......

 

Re-read Al Napier's post. He's got it right.

One extra word of caution. Make sure you have it beefy enough. Don't take chances with steering.

 

I thought of one little advantage that a slightly bent drag link might have. If you get in a wreck, or hit a wall or a curb really hard, that slight bend in the drag link might save some other components by weakening the straight line strength of the drag link so that it could bend and collapse a little to absorb some of the shock, rather than just be like a super rigid straight pole which would be stronger than the components on both ends. Sort of like how they put ripples in the front frame horns of new trucks to get the frame to accordion and collapse to absorb some of the shock from a head on collision.

A lot of stock cars in racing have bent panhard bars. I always wondered why they would want a bend in them, and thought maybe it was to save the frame and axle from serious damage if they slam the rear wheel sideways into the wall.

Putting a bend in a drag link definitely weakens its ability to push end to end though. The more you bend it, the less strength it has pushing or pulling. But that bend might allow it to bend further if you smash a wheel into a curb rather than break a pitman arm or steering arm off. So it might be a good compromise if it's not bent so much that it weakens it and makes the steering sloppy.

Just my thoughts. I could be wrong though.

 

I didn't think it made much difference from a geometry and physics standpoint, but I wonder if anyone knows why some say that a draglink that isn't parallel with the frame will cause bumpsteer? Is that just an old wives tale?

 

Oh, oh...I may know this one.....

The draglink needs to travel in the same ARC as the axle during suspension articulation/compression/etc, whether it's on a cross steer front axle, or wishbones/hairpins on a fore/aft arrangement....the draglink doesn't have to be parrallel to the frame to travel in the same arc as the rest of the suspension......

 

Hmmmm....maybe bumpsteer is more of a concern on IFS setups. I know that on a straight front axle tracking/bumpsteer is usually due to bad toe-in or worn kingpins. Can anyone answer whether this applies to straight axles vs. independent?

 

As for the bent Panhards bars on race cars, that is usually done to keep the two mounting points in a place parallel with the rear end and clear components as necessary. i have also seen Panhard bars on dirt cars set up to intentionally push the rear end to one side to aid with rear steer. But thats a whole nother subject.
And Sinister is right that a draglink does not need to be parallel with the frame, or ground for that matter, just needs to follow the path of the wishbone, 4 link or whatever locates the axle.

 

Bumpsteer is a big concern on straight axle cars, especially if it's a traditional front to rear steer (not cross steer). If the arc of the draglink doesn't follow the arc of the wishbone, 4 bar etc, it will bump. Try an early mustang box on a split wishbone or hairpin car and you'll have a "come to Jesus" moment. They work great with 4 bars though. It has to do with not being able to get the pitman arm pivot at the right height.

Toe in really doesn't have anything to do with bumpsteer on a straight axle car, the toe doesn't change as the front end travels up and down! and even worn kingpins really don't cause bumpsteer either, just a wandering feeling.

 

It's the "wandering" that I've experience that I was talking about. I guess bumpsteer is more of an "oh shit, which direction is the front end going to take me after hitting THAT pothole" kind of feeling.

I'm thinking I'm probably safe on my '56 Chevy pickup. All I did was reverse eye the main springs and use a 2.5 inch dropped axle with discs installed...everything else is basically stock, including the stock front swaybar I plan on installing. Wait, I DO plan on upgrading to the newer style tie-rod but that shoudn't make any difference.

 

kevin is absolutely correct. The shape does not affect steering geometry or bump steer due to incorrect placement of the pitman arm in relation to the radius rod.

Bending a drag link is just plain bad engineering. You will never see a bend in a factory set-up for good reason. It is the equivalent of incorporating a spring into your steering set-up.

A straight drag link has a very high load capacity up to a point where buckling occurs, whereas the bent drag link starts to bend (elastic or plastic deformation) like a spring under ANY load.
As Kevin stated, the force does not travel along the length like water, but the force will always act along an axis that runs through the two pivot points at the end of the drag link.
Each cross section along the length will experience a shear force and a bending moment equaling M=F*d (d...distance from center line) in addition to the the axial stress.

In a light weight car you may not notice a difference, but it is generally not a good idea and should be avoided if possible.

 

I'm thinking I'm probably safe on my '56 Chevy pickup. All I did was reverse eye the main springs and use a 2.5 inch dropped axle with discs installed...everything else is basically stock, including the stock front swaybar I plan on installing. .[/quote]

With a 2.5" axle and a reversed spring you probably should have your steering arm bent to match the height change and get the draglink parallel with the arc of the leaf spring. I know it really made my dropped F-100 drive better.

 

The pivot point at which the drag link attaches to the pitman arm is about 2.5 inches lower than where it attaches to the steering arm. I guess that since the steering arm arcs upward as it curves away from the spindle it would be easy enough to heat it and bend it down so that the drag link sits parallel...I just wasn't sure whether or not it would be necessary. I'll most likely have it done once i get the whole thing buttoned up and sitting on a level surface so i can take proper measurements. Thanks for all the feedback guys.

 

Never say never......this is a FACTORY Ford part.