Thread: Bump steer.

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Get prepared Dave, several hundred viewers are screaming .........THAT"S A PANHARD BAR!!!!!!!

Here is a picture of what is sometimes called a "sway bar", which is shorthane for what is more accurately called and anti-sway bar, and then if you talk to a suspension engineer/designer it should really be called an anti-roll bar.

Briefly, to function properly an anti-roll bar is attached to the chassis in two points, and the axle at each end. One comment on an anti-roll bar on the rear only is that it can often cause "push steer" (for want of a better term) becuse of unequal roll centers front to rear.

Okay, the site wouldn't take that pic, let's try this one.
This is a set of front and rear aftermarket bars.

Heh heh heh....I hate to admit it, I had to look up pitman arm, panard bar, and drag link.

I'm not a front end Guy.

There is a bar (whatever it is ) that goes from the frame on the left side, and connects to the front end on the right hand side. I do know one thing....I got gouged a hundred bucks to get that mutha chromed.

Daver.

I don't think you have a bumpsteer problem as much as you may have overly stiff springs/shocks and too much tire pressure.

Especially so tire pressure.
More than likely you have springs that are close to what's required and I'm guessing you have aftermarket coilovers in the rear.

Not sure what tire size you're running either, but your car probably isn't too much heavier than my Highboy 32 roadster.

Depending on the tires in use, pressures ran from 12-20# in the rear and 26-30# in the front.

The 35# (most times) max load rating pressure molded into the tire isn't always what you want to use.
Many folks do and end up with a rough riding and ill handling car.

What may be happening to you is the same thing that happened to my 32 when it was on the road.
Hit a bump equally on both sides of the car and the steering wheel did not react - indicating no bumpsteer.

Hit a similar bump on a curve - a taller than usual tar strip on a cement road for example - and the rear tires instead of doing their share of the cushioning left the road, centrifugal force due to the curve would bring the car sideways and when it came down it was pointed in a slightly different direction.

Nothing dangerous and easy to compensate.
Lowering tire pressures cured the problem.

My stock height short bed 63 Chevy half ton did the same thing on that particular curve, so it's not always the hot rods that do it.

I checked the panhard bar, and it was neutral. It fact it was dead neutral "to the thread' with full weight on the car.

The pitman arm (steering arm) is fully two inches below the drag link. The drag link and panhard bar are in pretty good alighnment with one another. I guess I'll just heat that baby up, and bent it right on the car.

There is a road out here, 55 mph....that is like a roller coaster. Speed driven is more like 65. When you hit the bottom of a dip and compress the suspension the car goes one way....when you come over the top of a hump and the car gets light, it goes the other way. Bumpy roads are no fun at all, because the car is all over the road.

If bending the pitman arm doesn't correct it, I may just chuck it and get the rack and pinion set-up. I do prefer the looks of the old fashioned set-up though.

Daver.

"The pitman arm (steering arm) is fully two inches below the drag link. The drag link and panhard bar are in pretty good alighnment with one another. I guess I'll just heat that baby up, and bent it right on the car."


Do that and the heat will destroy the seals, probably damage the heat treat on the pitman shaft, boil out the steering box oil/grease and more than likely you'll end up with an elongated hole on the pitman shaft side of the pitman arm.

Looking at the posted pic and noting how low your steering box is, it looks like the draglink and panhard bar are at different angles.

If you think the panhard is at fault, remove it and drive the car.

The rack and pinion will not cure your problem.

What are the caster and toe-in set at?

If you're not running enough caster and the toe-in is neutral that could be part or all of your problem.

A man of few words I see....

OK, I'm gonna give myself the "Duh Award" for the day.
Why not take that ball joint connector on the steering arm, and put it on top....instead of on the bottom.

Daver.

You gotta brush up on your automotive terminology. The reason that you can't put the "rod end" in from the top is that it has a tapered shank that fits into a tapered hole in the Pitman arm. If you try to put it in from the top, the tapers won't match.----note that you can buy Pitman arms with reversed tapers to do exactly what you are suggesting.---once in my miss-spent youth I actually cut the end of a Pitman arm, flipped it over, then welded it back on, on a 56 Ford truck that I had installed a 390 Thunderbird engine in, and I needed the extra clearance for the oil pan. (I did the exact reverse of what you are suggesting).---Please don't do that!!! Mine never broke, but sometimes even dumb kids get lucky.

I'm pretty sure it's a tapered hole/stud, so that won't work. I might be wrong, though.

If there's a taper, why not flip the pitman arm over then. Isn't the pitman arm a straight spline affair ? BTW, that arm isn't the one on the car. I traded in that one for a chromed one.

Daver.

The spline on a Pitman arm is a tapered spline, if its fitted to a Vega or Flaming river, or Mullins steering box.

"Hydrogen Embrittlement.- Embrittlement of a metal or alloy caused by absorption of hydrogen during a pickling, cleaning, or plating process."

"Hydrogen Embrittlement: Steel fasteners exposed to hydrogen can fail prematurely at a stress level well below the materials yield strength. Hydrogen embrittlement occurs in fasteners usually as a result of the part being exposed to hydrogen at some time during its manufacturing process but it can also occur through in-service corrosion. Electroplating is generally considered to be a major cause of hydrogen absorption in steel fasteners due to the release of hydrogen during this process. Higher strength steels are more susceptible to hydrogen embrittlement than lower strength steels however it is considered that there is no lower strength limit. However, as a rule of thumb, steels below Rockwell C 35 are considered to be far less susceptible. Tests such as the incremental load hydrogen embrittlement test can be completed to assess if hydrogen embrittlement is present in a batch of fasteners."

" Finally, chrome plating is notorious for hydrogen embrittlement. If you don't know how to properly relieve the embrittlement, you can turn hardened steel parts like springs, steering linkage, and fasteners into brittle glass."

The Duece Factory has a stainless pitman arm and it has a taper on both sides so it can be installed either way as you are hoping for.

I agree with C9X...take off the Panhard bar and see what happens. If you have the same result, then you know your Panhard bar isnt at fault. But I would imagine it is. Again, I had a TCI unit and it did not help. It gave when under pressure due to its inferior design (no slamming here, just my opinion...which I am entitled to since I payed good money for the POS) and when it bent they claimed it was my set up, not the bar...funny how I replaced it with the exact length bar from the Duece factory and my problem was solved.

One last thing I remembered which was a huge lesson for me in my teens. The front spring was squeaking so I foolishly (remember I was a teen at the time) took the spring and perch bushings apart and greased them up good the night before a buddy and I set out for Colorado Springs and the Rocky Mountain Nats. Boy did we figure out quick how stupid this was. We actually changed lanes when a trucker rolled by or a strong wind current blew across the road. So I mention this only to say dont over-do-it on the lube and realize others have been here and made mistakes too. But thats how we all learn...Right?

I would also suggest the tire pressure idea is a good one too. These narrow cars are very light up front and this tends to exaggerate the issue.

Here is a link which might help as well.
http://streetrodderweb.com/tech/0304sr_upfront/

Good luck and let us know what you find out!