Technical Mustang Steering Box "Play" - How Much Is Okay?

I've been trying to sort out a violent low speed wobble that just won't go away, preferably without using a steering damper as a band-aid. All new king pins and tie rods ends, correct alignment, tire pressures, balance, etc.

I have adjusted the Mustang (actually out of a '63 Falcon) steering box so that everything is tight with the wheels straight ahead, but when I turn the steering wheel a half-turn one way or the other the box gains a whole lot of play.

How much off-center play is acceptable? Could this be causing my low-speed wobble?

 

Insufficient information. Please provide a full write-up on the entire chassis, suspension, and steering components, and how, and into what they have been installed.

Wobble is not often caused by the steering box.

 

Pictures, too, if available.

 

Does the play start after you turn it a half turn?
Do the tires turn proportionally to the movement of the box up till then?

 

Yes, and I think I've read 'em all. But "debate" is far different from "solution". I've covered pretty much every suggestion as to what "might" cause the wobble, but the wobble persists. The only thing I haven't done other than replace the steering box is install a steering damper. There have been a gazillion hot rods built without steering dampers that didn't have low speed wobble, so why does mine?

Yes. When the wheels are straight ahead the steering is nice and tight, but without binding or hitching. With the wheels straight ahead and the front wheels off the ground you can shake the front tires and all seems nice and tight, no slop.

But, when the steering wheel is turned to either side the box becomes progressively more sloppy and loose when you shake the front tires. This is not apparent while driving the car, however. Everything seems just fine...until the uncontrolled low speed (under 5 mph so far...) wobble begins. I think the wheels were slightly turned each time the wobble happened, but because I wasn't looking for it I don't remember exactly.

 

Okay, you asked for it...

The coupester's (see my avitar) frame is '29A with coil springs, tube shocks and parallel ladder bars / panhard bar in the rear. The front is 4" dropped tube axle, transverse spring, tube shocks, Ford spindles, old Pete & Jake's (I think...) ladder bar style radius rods. Steering is '63 Ford Falcon (same as '65 Mustang) steering box and custom drag link. The drag link and the radius rods are very close to parallel and very close to the same length, sort of like a 4-bar front suspension.

All the tie rod ends, king pins (bearing-style from Speedway) and stuff is new except for the shackles, but they appear tight and right though somewhat dated.

The front end has about 8 degrees caster and 1/4" toe in. Camber appears to be about 2 degrees positive by eyeball. Tires are kept at 32 lbs all the way around. It runs straight down the road however fast you want to go, hands-on or hands-off. Steering effort is light due to 22:1 steering ratio and the wheel returns to straight by itself (sometimes with a little help the last quarter turn or so). It does not dart or follow road seams even with the dirt track ribs in front and F'stone blocks in rear.

In short, everything is good...until it isn't.

 

Okay, everything sounds good.
You might be able to get away with a little more toe-in if you want it depending on the total weight of the car.
Are all the grease zerks on the suspension & steering properly greased? ( I know, dumb question but I've seen problems caused by something that simple on assembly line.)
Does it have bump stops on the axle for the spindles? Have you played with the bump stops as well as the adjustment on the steering shaft between the box & the steering arm?
Have you drove the car in a circle both left & right to compare the turning radius both ways?
I'm just wondering if the full turning travel of the box isn't "matched up" to the full turning travel of the front wheels.

 

Put the toe at 1/8...1/4 is just toooo much..Caster is high for a light car, around 6° should be enough..Are you sure your Radius rods are not flexing;

 

As chessterd5 suggests, if the steering box was assembled with the sector not in the centre of the worm for a start and fitted to the car there is a possibility you will have more lock one way than the other. Then when the box is adjusted for play from what appears to be the centre , it is infact not the natural straight ahead position, this will give too much free play on the ends.

 

When I bought the car it had this problem, but when I adjusted the box I centered it first, both by counting revolutions of the steering wheel and by jiggling the drag link to locate the "tight spot" at the center by feel. Both of these methods indicated the same center, which is where I positioned the worm when I adjusted the box.

At the center, as I mentioned before, everything feels tight and right. It's when the steering wheel is turned to one side or the other a half turn or more that it starts to get sloppy. I don't know if this is "normal" for the Mustang steering box in this application or not.

 

Way too much air pressure. Try 22psi.

 

Because this is an open wheel car I can watch the wobble as it takes place. The axle and the radius rods don't seem to be involved, only the wheels, tie rod and drag link seem to be flopping around. It's pretty scary to watch!

 

STEERING BOXs ; For sure off center is always going to have more play,that is how boxs are design that way from new,its done that way to make steering in a straight line stady,and steering in a trun EZer an helps the feel. Understand what I just said,there is no way in heven or hell to adjust that out or buy one that is not made that way. Even most racks have tight spot in dead center. Caster combind with rim/tire off set on front can feed back with odd feel if off set is too far out=big scrub with wrong kingpin incline point to ground way inside tire tread{ often seen as brake drum or disk sticking way in the open ,looking like there closer to center of car=misstake by some who think they know how to build a car,but don't.
The front tires you picked cuz you saw them many times before,are one of those miss understud things I beleve that just gets copyed over an over. They were good in the day on dirt track racers an dirtroads,Ok for tractors,but for streetdriving they suck,bad tread for anything but dirt cornering,near no braking grip,to add to those prob,there nearly always out of balance an or out of round. Sorry there not a style thing I like,but at lest I said why vs some BS that we sometimes get. Really any tire can be bad,so check them out carefull,so they will not be the prob.

 

No, it does not have external bump stops. I think the stops are in the box itself. In any case the problem does not occur when the wheels are turned hard over, but only in a mild turn off straight ahead. I'll check the stops later to be sure I'm right on this. Good point.

 

Yes, I get that. My concern is that my box may have too much play off center, and that the excess play may be causing my uncontrolled low speed wobble. Thanks for the input!

 

It would be very super odd for any real extra slop wear to be off center*,if center adjustmint is done.
*Only way would be if box had been used for a long time off center for like 100,000= miles. Its not something too be of concern. You got some great info from other too,but likely your fastist fix with out high tire wear would be a panhard bar from frame to axle or a deadprich on one end of front spring,asomming you already have rim/tire balanced,round an straight with good kingpins.< that is often were a prob is. As a very EZ fix,try tow out of about 3/8in.{YES I said tow out,not in.} just to see if there is no wobble no matter what you do? I'll bet its gone if you try that. + That trick is only a cover up of kingpin or bearing slop etc.,but gives you two things,a good driving car,tell you fix other prob that you now will have more time to find.{ it will wear tires some though} Hope that's of some help?

 

Measure the wheelbase on each side of the car. They should be the same

 

Does the steering wheel shake in your hands when the wobble happens?
Does the pitman arm on the box also move with the wobble?
Does the wobble stop or change when you apply the brakes?

There are not really "stops" in the box. It's just where the worm gear can no longer turn the gear teeth any further either way. The bump stops on the axle should be set up just inward of both these points in the turning circle to keep from hard flexing the box.

 

No, not very much.

Yes. I can't see it move, but I can see the the drag link move so the pitman arm must be moving as well. Also, when I shake the wheels by hand (car elevated on jack at the center of the front axle) with the steering wheel turned to either side the pitman arm moves along with the drag link. I did notice tonight that there is a metallic noise coming from inside the box when I shake the wheels with the steering wheel turned a half turn in either direction. The box itself does not move, nor does the steering wheel. There is no noise when I shake the wheels with the steering wheel straight ahead.

No. Applying the brakes has little or no effect.

 

As close as I can measure doing it myself it's within 1/8" and square with the frame.

 

I think I would recheck the tie rod ends.

 

The frame is not square.

The rails get closer together at the front.

 

Tie rod ends, drag link ends and radius rod ends are all brand new. King pins are also new, the Speedway roller bearing style.

As I was checking it over before I posted I did find one bad one, so I replaced them all just to be sure.

 

Sorry, bad choice of words I guess. What I meant was that the axles are 90 degrees to the chassis center line.

 

I am no expert like some, but I have little problem with the radius rod ends, both length and bend. Seems that in a turn the forces placed on them would introduced some serious deflection??? Everything else has been mentioned or eliminated.

 

Try a different set of frt. tires ...cured mine ..
dave

 

Don't think this has anything to do with your issue...but that style of radius rod requires the axle to twist as the suspension moves. A tube axle won't twist...need to either convert to an I-beam axle...or a 4 bar radius rod.

 

Don't get mad....tube axles and radius rods don't mix, period, if you use a tube, use a four bar. Tire pressure is way too high, try 22 to start, toe is way too much, 1/8 is where you should be. 8 degrees caster is a little excessive, but I wouldn't change it, it'll probably be fine, give you a little more stability at speed. Right now, I blame the tires, but you have to understand that this style of steering can be prone to wobble, not every car does it, my old T bucket did it at 30 or so miles per hour, my friends model a is fine till 55 miles per hour, both cured by a hard stab on the throttle, braking would only make it worse. Like you, everything was new, a steering damper was the cure. I doubt it's your steering box, that wouldn't cause the wobble, if it has too much play, while that wouldn't help, but I doubt it's the cause. The biggest reason guys go to a vega box and cross steer is to eliminate this problem, other than the tube axle-radius rod mixup, looks right to me. Lots of guys run this setup, but because a tube wont flex, somethings gonna break, sooner or later, check for cracks at the perch pin mounts, keep an eye on that area. My advise is to try a damper, I bet that will fix most of it. Nice car.

 

As I mentioned early on, this is a slow speed event - under 10 mph and usually much slower. As I recall all of them were with the wheels slightly turned and were excited by a small (!) bump like an expansion joint. At these speeds the tires are just barely turning so I doubt that a tire design or flaw would be responsible. I will try a tire change, however, and see what happens, but not right away.

Yes, I am aware of the "mismatch" of components you mention. As I've said earlier in this thread the car drives just fine until the low-speed wobble event occurs. If I ever rebuild the front suspension on this car (I bought it this way) I'll likely make the change to a beam axle as you suggest.

I agree. Using the long, curved tie rod ends was the only way I could move the radius rod ends down to gain the caster I needed. When the car was originally built (not by me) it had standard tie rod ends mounted into bungs in the frame, resulting in 1 degree of caster. Proper tie rod end placement would have interfered with the Mustang steering box. The long, curved tie rods ends solved the problem - for now. It is my intent to gusset them once I get this wobble problem solved.

Thanks, everybody, for your input.

 

Good information and advice. I'm with you in that I don't think the steering box "causes" the wobble - which is intense and it happens at walking speed, not while going down the road. As others have said, the cause is the momentary "excitement" of the steering gear by a bump, large or small.

A proper steering gear will not allow the momentary excitement of a bump to build into a wobble. It will dampen or cancel it in some way before it can build into a full blown oscillation. Mine just doesn't do this properly. There must be a reason, I just can't find it.