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Discussion Starter · #1 ·
If I'm on the highway running 65-70 and go over a bridge or dip, the front suspension bounces side to side. It makes the car act like I'm whipping the steering wheel left to right real fast. I'm suspecting a faulty shock but they are only about 6 months old. I replaced the a-arm bushings and the idler arm bushings. The ball joints are all tight and have been replaced. The tie rods have no slop in them either but are original. I'm very experienced in front end rebuilding on tri-5s but this is the first time I've had one rock side to side. If I'm on the turnpike running 85 and hit the bridge, it gets down right SCARY. If I hit the brakes it stops immediately. C O N F U S I O N
 

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Trifive Automotive Electrical Wiring Expert
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It sounds like front end alignment. Insufficient toe in can cause the wheels to want to go in opposite directions, causeing the oscilations.
 

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What did you use on the idler arm, bushings or bearings? My 57 was rebuilt using the bearings and the loosened up after 5-6 months of driving. I have done had to rework it due to slop in the steering, kind of like you are describing.
Terry
 

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It certainly sounds like tie rods or idler arm. Rather than being loose one could be binding up. Maybe you just need to slow down. :sign0020:
 

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Funny you mention this. My Willys CJ2A does this exact same thing. Scare me to death when it did the first time. I still can't figure it out. I have huge tires on it though 33". I even put a Rancho steering stabalizer on it and that didn't help. If you figure it out. Please let me know!
 

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Toe out will do this more than in but either will do it if excessive - the tires are running deep in their slip angles (the max amount of steer that can be given to a tire without it changing direction or loosing traction), bump steer gets introduced and weight shifts even more. As weight transfers so does traction and the side with more weight will always get more steerage effect until it's slip angle is completely exceeded. gets worse with no sway bar or bad sway bar bushings. Braking will increase traction on both sides (discs more equaly) and stabilize the shifting. On race setups harder braking is required to help entry if you have high ackerman (gains toe out when steered) because of this.

I recall the tri's bump steer out and rebound in? What that means is that if you are at 1/8 inch in at rest, when you bump (compress the suspension) it could go to zero. As static toe IN is typically to force the wheel to run parrallel - zero toe - when they are loaded (being forced forward against mechanical resistance) it sounds as if you are toed out and the result is tires that get to "pick their path" based on road surface! This is worse with low profiles - less forgiving sidewalls mean lower slip angles.

Just to cover all bases I would check all wheel bearings and ball joints (even new ones can go bad) - something is bump steering more than it should by geometry if it ain't your static toe!
 

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scary 56

Had the same thing happen to on a 55 I used to own. I'd hit a dip in the road and and the car took any direction it wanted. It also wandered all over the road when braking hard. Pretty scary. Redid all bushing, also brand new ball joints and had front end alignment done. End of problem.
 

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"I recall the tri's bump steer out and rebound in?"

From what I know the bump steer isn't too bad with the stock suspension geometry. The exact situation may be a matter of tolerances, in other words the parts YOU have on YOUR car.

Do you have any measurements or details that would confirm your statement?

Not arguing, want to learn.
 

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...The tie rods have no slop in them either but are original. ... C O N F U S I O N
This is where you need to start.

You MAY have what we call in Jeep land "death wobble." Bump steer is a little different than death wobble. But it's hard to tell sometimes.

737Pilot sounds like he has death wobble. You know because it scares the crap out of you and you literally think that you are going to die.

Even though you can't feel any play in your tie rod ends, you should replace them. 50 years on original suspension and steering components is not a good thing.

Have you changed the height or swapped out OEM parts for performance parts?

It's my personal opinion that you will be chasing your tail if you don't replace those TREs first.

E
 

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Do a google search on "Death Wobble" It is very common in the 4x4 world. :anim_25:
 

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oscilations

If I'm on the highway running 65-70 and go over a bridge or dip, the front suspension bounces side to side. It makes the car act like I'm whipping the steering wheel left to right real fast. I'm suspecting a faulty shock but they are only about 6 months old. I replaced the a-arm bushings and the idler arm bushings. The ball joints are all tight and have been replaced. The tie rods have no slop in them either but are original. I'm very experienced in front end rebuilding on tri-5s but this is the first time I've had one rock side to side. If I'm on the turnpike running 85 and hit the bridge, it gets down right SCARY. If I hit the brakes it stops immediately. C O N F U S I O N
I had this same problem with a Brand New 1976 Chevy Van. The problem is too much negative caster. You can drive for weeks and it never happen. But when you hit the right spot the front wheels start oscillating like crazy. Almost got me killed before I found the problem. Dealer could not figure it out. I final put it on front end machine my self and took out some caster.
 

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It's broke

Yep it's broke. But probably not expensive.List of my humble opinion suggestions; 1, jack the car(and safety stand under framerail) and check the ball joints with a helper to work the bar use a big bar lifting up and down on the bottom of the tire slightly sometimes catch bad ball joints better with helper. Then while still jacked have helper work some more, hold side of tire then work back and forth rapidly, if all tie rods and ball joints are tight and without slop, then step two. 2, While still jacked give your helper a rest and grab tire yourself at top and bottom, try to move back and forth checks wheel bearings, if all is still tight go to step four. 4, have a helper grab sides of tire and rapidly wiggle side to side while you check the rest of the steering idler arms inner tie rods and pay close attention to the steering box pitman arm. if all is still tight then step five. 5, check other side the same way, if you still have a helper, if all is still tight then let the car down and go to step six. 6 check steering box play by having helper turn slightly right and hold steady pressure, then on your command very very slowly turn left while you watch the difference in the input shaft and pitman shaft. some people just saw the wheel back and forth to look for slop, to each mechanic is a preference. if all is still tight then seven. 7 pull the shocks and check both at the same time. if shocks are good, I would say do what we should have done to start with and mark the coil spring pockets to make sure they are not too short and moving when you hit a bump, and also I would make sure the A Arms aren't freezing up in the bushings two things that could happen on a new build or restomod, I would spray some "compatible" slickum on the a arm bushings first then go drive awhile cause it may save some unneeded exercise. On alighnment I would say check caster especially, could be. And all that is based on I really don't have much info on your front end set up(my fault, too lazy to check archives and fairly new here)so kinda generalized info that is my simple minded way of trying to help. A Arms
 

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A guy on a swedish car forum had this issue (on a '32 rod) and was recommended to try other wheels with different offset (more stock like). The ones he had on had the wrong offset (don't remeber if it's called positive or negative offset). That solved his problem. Did you have this problem before you changed the wheels on the '56, Hafrod?
 

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Having spent some time with rods I would be looking at the geometry. Have you had it checked properly? I would especially be looking at caster and toe.
 

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"I recall the tri's bump steer out and rebound in?"

From what I know the bump steer isn't too bad with the stock suspension geometry. The exact situation may be a matter of tolerances, in other words the parts YOU have on YOUR car.

Do you have any measurements or details that would confirm your statement?

Not arguing, want to learn.
Absolutely correct - what you have on your car and how you have the thing aligned is the determining factor.

All drag link style twin arm suspensions bump steer one way or the other. What causes it is different lengths when comparing lower ctrl arm to tie rods. The longer the arm (or tie rod) the wider the arc. If exactly the same length there is no bump steer as the suspension travels up or down (they would create equal arcs). However that also means that the space between the two lower ctrl arms inner bushings must be identical to the length of the drag link!. This is all cool but as the drag link is made with a curve to travel under the engine - over time it tends to straighten out (hence some of the need to adjust toe) - even as little as 1/64 inch makes a difference. AND the bushings on the lower ctrl arm tend to settle closer together over time also changing total bump steer.

Basically if the steering links are ahead of the spindle centerline (front steer) and the tie rods are longer than the lower a arm (which is normal to see a need to shorten them over time to keep it in toe) - it will steer out when the wheel travels upward and in when the wheel travels downward (rebound). On a rear steer the opposite is true. Front steers tend to toe in over time and wear while rear steers tend to toe out. Toe in is MUCH more squirrly than toe out!

The reason camber effects bump steer is simple - as you move the upper ball joint in to create more camber - you must shorten the tie rod to get the toe back in! Caster also effects bump steer - the more castor you have the more camber is gained when steering - so bump steer is effceted more during a turn with higher castor than when driving straight. Negative castor will make a car REAL squirrly in a turn and dart from left to right without settling to center even on a smooth road.

When all is tight and toe is correct - bump steer is hardly felt by the car (you will still feel it in the wheel tho). But as the front wears and especially if toe is not correct it becomes very noticeable as the tires fight each other's slip angle and can make directional changes faster than the drivers response time - and with no coresponding kick back in the steering wheel. Rear steers are more forgiving which is one of the biggest design features that makes the 1st gen camaro such a desireable clip for sportsman and late model stockers. In race cars when the rules allow it they use heim joints so that they can add or subtract spacers between the tie rod end and steering arm (or drag link). When the rules disallow heims they mock it up and have tie rod ends made with the ball studs at the specific length needed to accomplish this.

Now unless you are racing, SOME bump steer-out is wanted - and the higher the center of gravity (or the softer the spring rate of your sway bar) the more you want. This is a safety feature in the design so that if the average driver (including grandma) gets into a corner a tad too fast the car will steer out on the outer tire faster than the ackerman (thus gain in total toe out) as it rolls (transfers weight to the side opposite the turn direction) so that it overruns the front slip angles (called "push" in racing terminology) and not only scrub speed faster but is forgiving enough to not just toss the back around faster than the driver can steer into a slide (recall Ralph Nader's angst over the Corvair). Rear steers use more ackerman for this reason.

So no - the designed in bump steer is not bad in the tri's - but with wear, incorrect toe settings AND (heres a biggy) a heavier engine on worn stock springs meant for a lite weight 6 banger (more body roll, bump AND rebound inertia) - they tend to wear into a bump steer issue. And the fifties (ALL cars) were engineered with tons more ackerman than the seventies into today (part of Detroits reaction to Nader's "Unsafe at Any Speed" was to take out ackerman and introduce more rear axle steer by using shorter rear control arms). (ackerman defined using left turn example - the left tire steers slightly more than the right in order to follow a tighter turn radius thus keeping both tires in the center of their slip angle)

With rack and pinion its FAR easier to get to exactly what you want - especially with the high end units that have slotted hole (or a set of offset slugs) to locate the tie rods to the rack at the right place to have equal ctrl arm and tie rod lengths.

When I was a teenager I helped a good friend of mine who circle raced a 55 convertable - spending hours getting all the bump out from that front end - in racing bump in is better than out! But he LOVED that geometry - it has a bunch of anti dive so he could drive in to the corners further and the brakes would actualy hold the front from driving into the ground!
 

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Discussion Starter · #18 ·
It was toe out. I climbed back under it with my curtain rod and rechecked it. It was out a little over a 1/4 inch. Reset it and took it on a long drive. It is fixed and drives alot better. :tu
 
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