Thread: Bump steer.

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I have a nasty bump steer in my model A. TCI frame, vega
box. I was going to convert to the TCi Uni-steer rack and pinion set-up, but I want to see what you Guys have run into....and I wanna check out a couple things before i start ripping and chucking expensive parts.

Any bump steer stories/cures, fellas ?

Daver.

Your panhard bar should be parallel wiyh the steering rod. The axle is moving in a different arc than the tie rod end, causing the wheels to turn as they move up and down. Lower the driver's side end.

Further thought--if there's room under the engine, you could bend the pitman and raise that end of the drag link.

Originally posted by R Pope
Further thought--if there's room under the engine, you could bend the pitman and raise that end of the drag link.

I'll go along with R Pope on bending the pitman arm up to match the angle of the panhard.

Another way out is to get one of the flat aftermarket pitman arms that are a direct replacement for the Vega arm.
What's nice about these is, the pitman can remain flat and the draglink's tie rod end can go in from the top due to the double sided taper in the aftermarket pitman arms.

Be careful you don't end up with the pitman being one of the lowest front end components. Catch the pitman on one of those tall gas station manhole covers and it's gonna tear things up.

If you do heat and raise either the stock or aftermarket pitman be careful and do not elongate the holes at either end.

What will happen with a bent pitman is:

The steering ratio will be a touch slower - which means less steering effort.

The draglink will come back a little bit and no longer be perfectly parallel with the tie rod - as viewed from the top.
This doesn't hurt anything and the difference in angularity will be very small.
Getting the tie rod parallel with the panhard - as viewed from the front or rear - is the important part.

In fact you could wait until you actually drive the car before making changes.
You may not have the bump steer problem you think you have.

I have the same setup you have on my 32 except the aftermarket pitman is bent a bit.
Bump steer is not a problem.
Nor is shimmy.
With 6 degrees postive caster and 3/32" toe-in plugged in the car handles very well. (1/16" - 1/8" is the usual toe=in recommendation.)
Keeps up with sporty cars on the twisties.

Originally posted by DennyW
Looks like your pitman arm is way to long, and you have it hooked to the end of the wheel arm. Thats max shock.

You lost me here . . . the draglink goes to the aft hole on the right side steering arm.
I'd be inclined to think there is less shock when the right wheel hits a bump or whatever.
That due to less leverage by the wheel on the arm.

Long panhard bars are better than short ones.
Especially in the back where they tend to end up too short if you use the typical aftermarket rear axle housing mount - or worse yet the really short mount that bolts to the carrier bolts.

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Aside from that - and maybe it's just me not understanding what DennyW is talking about.

Are you running steering stop nuts on your kingpin locks?
If not you should be.
The steering should stop - or bottom out - on the steering stop nuts and not on the internal stops in the steering box.
Relying on the steering box's internal stops leads to damage in the steering box.

If your stop nuts were purchased in the last few years they are probably the right length (1 3/8" including the thick washer).
I point this one out since some steering stop nuts are too long.
Usually the stainless aftermarket ones that were available in the mid-80's up to the late 90's.
And they may still be out there with the thinking being, the car builder will cut them down to the correct length.

I ended up with a set of the long ones and found the car had a very wide turning radius.
After cutting them down - twice - .120 each time I ended up with the stop nuts at 1 3/8" (which is how long they are nowadays) and a car that had a fairly sharp turning radius.

It can be a juggling act to get everything set up right - IE: steering stopping on the stop nuts, draglink the right length, steering wheel straight when traveling straight ahead etc. but it can be done.
All it takes is a little trial and error.

Don't be surprised if you have to shift your pitman arm one tooth on the pitman shaft to get where you want to go.

One last one and I'll shut up.

You can make your own steering stop nuts out of a couple of Chevy mag lug nuts.
Try to find stainless ones, but good quality chrome works ok.
(Chevy lug nuts are 7/16 - NF and so are the kingpin lock bolts.)

Cut them down to size and get a couple of thick AN style washers to go underneath.
A lathe is ideal for cutting them down, but a thinking guy using a modicum of care can do it with a hacksaw, file and square.

In general I agree with the comments about parallel between the drag link, tie rod and panhard bar, verticle and horizontal. One word of caution is that that would be with the front end fully loaded weight wise, not in the current "stripped down" condition. Obviously the panhard will flatten out when the frame comes down on the suspension. That's also the best time to adjust it's length, not when it's unloaded.

I see your backing plates are fairly well exposed, but can't tell from your pick how wide your rims are. If you've got the requisite king pin inclination at 6 or 7 degrees as Jay mentioned you may be getting some induced steering by too much positive offset on the wheels.

I have ran a vega cross throw steering on 3 rods that I have built, and have never experienced bump steer on any of them. I use an aftermarket pitman arm that measures 6 1/4" center to center, is perfectly flat steel 7/8" thick, and install the drag link rod-end from the bottom side. I fabricate my own Panhard rod, and as the other gentlemen advise, I set it up to run parallel to the drag link and tie rod when the front spring is under full loaded condition. I mount it to a bracket on the underside of the drivers side framerail, and to the batwing on the passenger side. I try to run 5 or 6 degrees of caster, (kingpin tilted towards rear of car at top), and whatever camber is built into a Superbell I-beam 4" dropped axle. The spindles I have always used are stock 40 Ford units with the stock steering arms, set up exactly as you have shown. I use an aftermarket Model A spring with reversed eyes, and "normal length" shackles. The steering boxes are mounted so that the input shaft (on the steering column side) is tipped up at an angle of about 10 degrees from the frame at the rear side of the steering box. I can't imagine why you are having a bump steer problem. The only thing that I can think of is this---do you have a panhard rod on the rear axle, tied to the rear-end and the passenger side of the frame? that would do it. (the rear Panhard rod should always be pivotted off the same framerail as the steering box is mounted to.

I had a nice big reply going, and I lost the SOB. (I hate that)

Simply....look at my pic in post #1. Now that the engine, ect. is in the car....the sway bar (don't say panard bar) is about level. I thought that this was the culprit.

If you pull "up" on the frame, it will pull the steering on the RH side wheel to the right no matter how long, or short the steering arm ( don't say pitmann arm) is. If you push "down" on the frame, it will push the steering on the RH wheel to the left....no matter what.

Raising, or lowering the steering arm will help in on direction....but will make it worse in the other direction.

It seems to me that this system won't work right, because of the pushing or pulling by the steering arm on the RH wheel, with the steering wheel held straight....and the front end moving up and down. (bump steer)

....no matter what.



Daver.

Why not say Panhard rod and Pitman arm?---That is the correct name for those components. As far as pulling or pushing side to side, that is why you endevour to keep the panhard rod parallel to the ground. If you consider that maximum overall front axle travel is limited to about 3 1/2" vertically, then from normal "at rest" condition, the axle travels only 1 3/4" up or down from "at rest" position. If you assume the length of the Panhard rod to be 30", then the resultant kick sideways will only be 0.051" (less than 1/16"). That amount of sidethrow will not cause bumpsteer.

The front end in your photo - except for the panhard bar angle - is exactly like many other front ends on hot rods.

They operate with a high degree of success and as Brian says, the side deflection of less than 1/6" will not be noticeable when driving.

You may as well use the correct terms to describe the pitman arm and the panhard bar.


Fwiw - a sway bar is a whole other thing and you do not show one in your photo.

A front sway bar is not required on these lightweight cars, but a rear one is.

That's whether you run coilovers in the back or a transverse spring.

The sway bar makes for a good handling car.
Without one you'll get excess body lean and a lack of hard cornering abilities.

You may think you're never gonna push this car hard, but with the horsepower (HP) you're gonna have up front there will be times the car wants to get a little sideways and the sway bar helps there.
There's always the emergency avoidance maneuver to consider, you want good handling in that situation.

And then there's the sporty cars you meet up with on the twisties.
Kinda embarassing when one of these drops in behind you on a twisty mountain road and you can't get away - or even keep up regardless of your HP levels.

As far as going to the single sided rack and pinion set-up, your basic steering linkage geometry isn't going to change so you'll still have minor bumpsteer.

I understand as well that the rack travel in these doesn't allow the car to turn as sharp as it will with a steering box.

Daver,


I understand your concern with the "nastiness" of bumpsteer. And I will go out on a limb and say that some cars are just worst than others even though if set up the same they should all act the same (dont ask me why this is...but it just seems to be reality).

Before I rebuilt my sedan, I had terrible bumpsteer due to the front end was one of Pete & Jakes first series axle/steering set ups. I worked on that thing for months trying to eliminate it before I installed a panhard bar.

When I rebuilt the car, I found 4 things which totally eliminated the "white-knuckle" and "puckerin" anxiety I found when driving the car. These were:

(1) Installing a large diameter (in other words strong...I too had a TCI bar and it did not do the job so I bought a stainless Deuce Factory bar and it has worked flawlessly.

(2) Installing the Unisteer Rack & Pinion unit (which may not have done anything for the bumpsteer, but it sure made unbelievable improvements in the steering as it feels just like a go kart without the "play" of the vega. I only add this as you mentioned you were thinking about it. Again, well worth the $.

(3) I installed a anti-sway bar from Chassis Engineering. And while I have fenders which help hide the ungliness of the bar, it sure helps the car track well. I am running all the chrome and stainless goodies like you so I might suggest using CE's as a guide to bend up a stainless bar, or have their unit chromed. Then it will blend in with your the rest of your front end.

(4) and finally I installed one of the anti-bump shock absorber from SO-CAL. Believe it or not, this really helped. And considering the costs, it was well worth it too.

So, to sum it all up, today I have no fear passing an 18 wheeler, around a corner, in the wind, with my family in the car. It tracks as if it wasn't a dropped axle car.

Let me know if I can help with any other information.

You got to Drive 'em!

Troy

Look at the front end again, there is a sway bar there. I didn't adjust it with the weight on the front end, that may be the problem. It might be pushing the front end to the right. When the weight comes off the car over a rise it is real bad.

I want to check the sway bar, and have a look at the alighnment
and such. I appreciate the help so far, I really need to get to the bottom of this. The steering is like a go-cart as it is, and frankly
it is unsafe at speed, if you have dips, cross winds, and oposing traffic (trucks) on a two lane road....it's difficult to keep it between the lines.

Daver.

Here's the sway bar.

That is not a sway bar. That is a Panhard rod. Totally different animals.---You do not have a sway bar.