[Turbo84]

I'm putting the C4 rack in my car at the moment. Trying like an SOB to get it set right to minimize bumpsteer issues. Once I get it (the brackets) tacked in, I'd like to make a few measurements. Just for comparison purposes, how bad is the stock C3 steering, specifically the bumpsteer numbers? I recall you did a bunch of work on your car a while back to correct this.
Thanks,
Mike

 

[mrvette]

U trying to do a C4 rack, front steer, in a stock C3 suspension setup??

or U replacing the whole damn thing with C4 components like some guys do??

if U just replacing the rack, I don't think it's possible....

whole kahuna, yes....

 

[yellow73sb]

I believe it was something like 3/4 on an inch :surprised

 

[Strider]

I believe it was something like 3/4 on an inch :surprised

Yes it was. 3/4 inch toe in. You can CAN use a tape measure at these values. With just 3 inch rise of the front bumper I was getting readings like that. I had the ability to also pull the car down with full suspension and it was just as bad for toe out.
You only need the dial gages when you get down into the thousands of an inch.
I checked a new mustang at the time and found it just as bad.
Try this guys. Hook a tape in one tread and measure across the front as high up as possible to the other tire, any spot on the tread. Jack the car up 3 inches and remeasure the same points. Do not worry about measuring at the back of the tire. The amount you find this distance shortening is the toe IN FOR ONE TIRE Double it for total toe in.

 

[kwplot34]

don't want to hijack your thread, but why is it called bumpsteer?

 

[redvetracr]

don't want to hijack your thread, but why is it called bumpsteer?

read this....

http://www.racerpartswholesale.com/longtech3.htm

 

[kwplot34]

Thank you. :thumbsup:

 

[Turbo84]

Yes it was. 3/4 inch toe in. You can CAN use a tape measure at these values. With just 3 inch rise of the front bumper I was getting readings like that. I had the ability to also pull the car down with full suspension and it was just as bad for toe out.
You only need the dial gages when you get down into the thousands of an inch.
I checked a new mustang at the time and found it just as bad.
Try this guys. Hook a tape in one tread and measure across the front as high up as possible to the other tire, any spot on the tread. Jack the car up 3 inches and remeasure the same points. Do not worry about measuring at the back of the tire. The amount you find this distance shortening is the toe IN FOR ONE TIRE Double it for total toe in.

Thanks for the info. I'm trying to get the rack situated as accurately as I can, but it certainly looks like even if I don't get it in perfectly (an almost certainty that it won't be perfect), I ought to have still improved upon what the tires were subjected to with the stock suspension.
Thanks again,
Mike

 

[Turbo84]

U trying to do a C4 rack, front steer, in a stock C3 suspension setup??

or U replacing the whole damn thing with C4 components like some guys do??

if U just replacing the rack, I don't think it's possible....

whole kahuna, yes....

Whole Kahuna. (See signature below.)

 

[Strider]

two things affect bump. One is the angle or slope of the tie rods. This is corrected by raising or lowering the out or inner.
The second thing is length of the tie rod itself. It is possible to set the angle of the tie rod perfectly to have zero bump on rise and then suddenly find when you compress the suspension it is way off in the other direction.
LENGTH of tie rod affects linearity. Which means correct it in one direction and you correct it also in the other.
Just setting the rack so it works in one direction of suspension travel doesn't mean it works in the other

 

[Strider]

Recvetracr's link tells you about bump steer.
But lets take it to a practical application.

You are flying down the road and go over a rise, the type that you feel in your gut. NOt enough to cause the car to jump over the crest but enough to unload the front suspension and give you that thrill in the pit of your stomach.
Your front end it at full rise and you suddenly toe in badly, say the 3/4 inch.
Now the suspension comes back down into hard compression. Suddenly you go from a toe IN positon to a toe OUT. But the left side landed harder then the right so that wheel has more load on it, better traction and the right wheel suddenly does all the toe change. You go from 3/4 toe in to 3/4 toe out or the passenger wheel just went through 1 1/2 inches of toe change. That wheel suddenly takes it share of the load and you find the car darting to the right, into the ditch. Sure you quickly correct, or hope you do and the car swerved to the left.
You are loosing control, nothing you did , the car steers itself.
You can correct the steering linkage or you can install really stiff springs so you don't go through this suspension change.
I believe is soft springs and big sway bars. My front end travels 7 inches stop to stop. I need zero bump. DO YOU?

And yes at the end you need a bump steer gage with dial indicators but again not in the first stages. I settled to .007 over 7 inches because I didn't want to grind a washer in half.

 

[yellow73sb]

I just couldn't trust the welded center link. I wonder If I could do something to not have the weld it.

 

[mrvette]

I just couldn't trust the welded center link. I wonder If I could do something to not have the weld it.

Welded center link?? the adaptor plate from rack to tie rods??

or input linkage??

:crazy:

 

[yellow73sb]

Welded center link?? the adaptor plate from rack to tie rods??

or input linkage??

:crazy:

With stock steering you have to weld on the tie rod mounts in different places

 

[turtlevette]

if it weren't for bumpsteer, camber changes, play in the steering these things would be no fun to drive at all.

What? Everybody wants to have a boring car?

just put some big ass wheels and tires on it. Thats the bigest thing you can do to make it handle.

You guys are making career projects out of these things. How many hours of driving will you ever get out of them?

Maybe TT's brother will let him drive his car.

 

[yellow73sb]

Hopefully I'll drive mine in spetember. I should be done with all I want to by then. So purely driving after this final tear down.

Also I'm putting it some nicer components like moog and howe ball joints. Make sure Everything Is locked tited also.

 

[Strider]

turtlevette you are flying down the road at 100 mph, 3 of you in the car and you go over the bad bridge, a really woopdy doo??? Whatever and the car goes squirely. You almost loose it and kill everyone.
I spent the time, removed the bump steer. Now I let others test drive the car and tell them to take that same run at 100 mph, over the same rise in the road and drop on the other side and you watch there reaction to hitting it. Absolutely nothing. The car is rock steady, yes the suspension almost totally bottoms but the wheel is rock steady, no swaying, no fitting to keep it on the road.
That is what you get with fixing the bump steer.
I read that with as little as .050 bump in the daytona cars they would not keep them off the way.

As for the welded center link, yes you have to weld something but done right it is as strong as stock.
I will look for a picture.

 

[Strider]

I welded about a 4 inch thick piece of steel to the top of the center link. The weld is long and full penetration. I then drilled 3 new holes 1 inch apart and then using the proper reamer reamed new tapered holes for different length tie rods. You can see the stock lower hole on the outside of where the inner tie rod is attached.
I made up 3 more sets of tie rods. Installed each set, set the toe and then checked bump recording what each set gave me.
I did this with all 4 holes and picked the one with the least bump.
As for fear of breaking the weld. There is over 8 inches of quality weld, both side of the 4 inch block. What are the chances of breaking this much weld???
I little 3/8th bolt is all that holds the tie rod to the center link.
This also shows the stainless plate at the bottom of the crossmember for jacking along with the large nut welded off center for screwing a hook in for towing the car OR pulling it down with full suspension for checking bump
I pulled the picture since it messed up the post.

 

[redvetracr]

With stock steering you have to weld on the tie rod mounts in different places

the fastest vintage racer in the country has a welded centerlink...there is a (very fast) vintage racer from down south that had someone at Penske south make some billet centerlinks on a CNC machine but they are supposed to be heavy.....and most likely pretty pricey. I have a factory centerlink/relay rod.
redvetracr

 

[redvetracr]

I welded about a 4 inch thick piece of steel to the top of the center link.QUOTE]


norval, whats the diameter of that centerlink??