My car is apart and looking in the empty engine bay there is a lot that I want to do while there is sooo much space. I would like to do my own rack conversion, but reading all of the post about this it sound like this condition is a problem which I've never heard of. I did a conversion on my father inlaws 37 olds and it worked great. So if someone can explain this I'm sure I'm not the only one. Thanks in advance.

Chris

 

Bump steer is when the wheels toe in or toe out by themselves do to a change in the suspension height.
If you jack a stock vet up but measure toe in before jacking and then raise the car about 3 inches at the bumper and again measure toe you will find a massive toe in condition. It could be up to 1 inch of more toe in.
If you could compress the suspension the same 3 inches you might find 1 inch or more toe OUT.
Driving down the road at high speed and you go over the crest of a hill, the type that makes your stomach flip. You get alot of toe IN. The car then comes down on the other side, the wheels never left the ground but the suspension unloaded alot. ONe wheel has more load on it them the other so when you come down for an instant the toe goes back to normal but since one wheel has more load on it then the other all toe correction can take place in one wheel, the planted wheel sticks and the other wheel overcorrects and takes all the toe correction.
Now the suspension compresses and suddenly you have a toe out condition. Again the planted wheel sticks and the other wheel continues to take all the toe change.
YOu now end up with one wheel taking all the toe corrections so you could end up with one wheel pointing OUT a couple of inches.
The car suddenly veers in the new steered direction and you loose control.
I tested alot of vets and toe changes of 3/4-1 inch at 3 inches is normal.
I tested a 2002 mustang, again 3/4 inch toe in at 3 inch rise.
Toe is affected by tie rod length and angle.
Drop your outer tie rod by about 1 1/2 inch and you will cut toe change in half with this simple mod.
A stock vet needs 3 inch longer tie rods, that means a 6 inch shorter drag link and along with the outer drop of 1 1/2 inches and you are pretty close to no bump steer.
A ruler is fine for rough measurements but at the final stage you need aluminum plates instead of tires, dial gages and no spring installed.

At Daytona a .050 toe change would put you in the wall. STock cars try for under .015 toe change.
I worked mine down to .007 over 7 inches of travel and said enough. I tested 4 different steering setups before deciding on the one that gave me this small change.

 

A bump steer gage

 

Read this on bump
http://www.thedirtforum.com/bumpsteer.htm

 

A dropped outer tie rod done the proper way

 

Okay, so that's why it acts like that going over hill. I should have known there would be a name for that action. I was looking at using a mustang rack and fabing a mount sytem similar to flaming rivers. But you say by lowering the mount at the tie rod end minimizes this. If it's that simple why didn't GM change over the years?

Chris

 

Chris GM maybe wasn't worried about it back then. Why does a 2002 mustang have it. The dodge Viper is the only production car without bump, they designed the steering first.
It is simple to remove most of the bump.
The kits doen't do a good job. They increase the turning radius and don't go far enough

 

You will notice that all production cars, even the Viper I'm sure, have toe out on bump. remember the the outside wheel goes into a bump condition on a corner...
This effect gives the car understeer in a corner. If you have toe IN on bump the car over steers. This is bad because it causes the car to turn more which causes more toe out...toe out is better.

Bumpsteer is caused by both the tie rod length and the angle as compared to that of the spindle. See the diagram on the link above.
Norval solved his by lowering the outer end, I raised my inner, same results.

I have some pics and drawings on my personal page for a home made rack. It's not too hard if you have fabrication equipment ( a hacksaw and a welder )

BTW I seriously doubt you will find an end take off rack that is suitable for the C3, but if you do, we would sure like to hear about it!

Goto to my page, then click on the Rack and pinion conversion link.
http://temp.corvetteforum.net/c3/427v8/

 

Does the steeroids rack conversion remove bump steer?

 

 

For those of us that do not weld, is there a kit? What will I gain in handling? I will be upgrading down the road, as usual I'm doing my homework ahead of time. TIA

Rick

 

Thanks for for the info gentleman. I am 99% sure the vette steering is on the way out. I'll let you know.

Chris

 

What will I gain in handling?? It might save your life. I almost lost mine and the 2 passengers I had with me when we hit a wupdee do??? at 100 plus mph and almost lost it to a very steep ditch. The car went through almost total suspension travel and ended up sliding sideways down the road.
After correcting bump the car has many time gone over the same wup de do??? at 100 plus with various drivers and never is there the slightest twitch in the car. That has become my test stretch for checking steering.

 

Building bump into the car to improve cornering is rediculous. Bump rears it's ugly head over rough roads throwing you from side to side while going straight.
I want no bump in my car and will worry about under or oversteer with sway bars.

 

Norval,
Seeing your pics reminds me of another question. Yours and a lot of the other mods are using rod ends instead of tie rods. How long do these last?

Chris

 

I don't know Chris. I have about 20 or so 5/8th rod ends in my suspension. Once a year I go through everything checking for loosens and replace any rod end that isn't perfectly tight.
I only pay $13 CDN for rod ends and don't hesitate to discard any one that shows any where. Some are original from years ago and some are replaced every couple of years.
'The important thing is does your suspension bind up anywhere? I bet that 99% of all vets on the forum have a binding problem somewhere with there suspension.
I carefully remove the shock and coil spring from each corner and put the wheel through a full range of motion feeling like you would while checking a bearing for any roughness, any sign that things are binding and then if I find a bind find out why and eliminate it.
Other then myself who is running rod ends on their sway bars???
That is a major binding problem. Look at the rubber donuts and you will find one that is pinched out of shape. It got that way because of binding.
The other alternative is to just put on heavy spring, tie the suspension up and call bumpsteer and binding a thing of the past, other vets have it but not mine.
A YES the dodge viper is designed with zero bump steer.

 

Norval and I agree we want nothing to do with bumping stears.....

GENE

 

Gene;
I knew you were going to say that!

Norval, I agree that less is better but I disagree that zero is optimal, a car should understeer just a little, unless your name is Richard Petty.

Evalu8er;
I've had teflon heims on the rear camber rods for a good 5 years, they still look fine. I must admidt though if I put 5k miles on a year I'm doin good!

 

Norval:

I don't want to hijack this thread, but how did you engineer your front sway bar mounts? I have been fooling around the last few weeks and a big concern is the amount of misalignment between the A-arm and sway bar. The A-arm and sway bar swing in two different arcs. The stock sway bar link is three inches from the A-arm to the bar. In this short distance, any misalignment will bind a rod end. I have been trying to come up with an approach that lengthens the links so misalignment is not such a problem.

 

My suspension book recommends no more then, now I am guessing but about .015 or something like that maximum. They also claim that .050 would put you in a wall at high speed.
I want zero and will rely on my sway bars for cornering.
Why would you want a car that is running in a straight line down the road to wander as the front end takes the bumps?? To me that is asking for trouble.
I want my car to track absolutely true in the straight line. Try running at about 130 mph, you want absolutley precise steering, no twitchyness.
Get a rear sway bar to control under/oversteer.
I actually found putting a massive sway bar on the rear one of the best things I did this summer for handling.
I posted alot on going into corners at 100 and hitting the brakes and having the rearend coming around. That seems to have dissapeared with the installation of the rear bar.