Getting racked

[69MyWay]

Just now wrapping up the rough-in installation of a 97 Grand Am rack in my 69 Vette.

I won't have time to get back to it until this weekend. I will be running a pair of passenger side tie rods from the 97ish grand am. I can't start to bump steer test it until after those are in. Having to get lengthened adjuster bolts for the tie rods.

The new tie rod assembly will be coming from the center of the car (longest possible tie rod length). This should help reduce bump steer issues.

http://mcspeed.homestead.com/Rackinstall.html

[69MyWay]

BTW, if it looks too low...no worries. Notice the sidepipes on the driver side. The rack hangs no lower then them, and my oil pan is deeper than that!

[Twin_Turbo]

Why in the center? sure, if you put them in the center you get the least angular difference over the suspension travel, however you can also put them in the correct posiyion so they have the same angular change over travel as the steering knuckle has resulting in absolute 0 bumpsteer.

Look at this picture, it's all about extending the ball joint to cross shaft lines, where they cross you have your instantaneous center, then from there go to the steering arm. Where all this intersects the line between the 2 cross shafts is where the tie rod end should be, the angle can be fine tuned by spacing the steering arm side. It will be difficult and time consuming to do but you should be able to get it very close to ideal, that sure makes fine tuning easier later on 9w/ bumpsteer measurements) I did all that with the entire front clip off the car, much easier that way and I know you won't be able to do that.

http://www.thedirtforum.com/images/bsdrawing.jpg

What they call "alternate" position is where the tie rod will roughly be, slightly lower than the lower control arm.

Where it says line 2 you see the inner pivot for the tie rod, THAT'S where the hole in your rack's center plate should be. I know you spoke to Norvalwilhelm about this, look at his pics, that's exactly the position of the eye on his center link, he modified the stock one to reposition the mounting hole.

Don't worry about line 1, it's purely theoretical, there's no way the line will be in the same plane as the 2 balljoitns since the steering arm is further back and you have to accout for the ackerman geometry putting the steering arm hole slightly further inboard from the spinde steering axis.

[69MyWay]

That is a great explanation of that diagram. I have been looking at it from Corvette Forum and not 100% sure how it lays out.

Was speaking to my buddy Dave at www.tropiczoneracing.com this weekend about different angles, etc.

I won't know anything until I can get the gauges set up to run the tests. I am going to start in the middle and work my way out. I will need to build a center mounting plate to change the height and position of the inner tie rods.

Thanks for the info and the explanation.

[Twin_Turbo]

That's the neat thing about the center take off, if you get it wrong you can simply build a new center place. I have a front steer end take off rack and because of the fixed tie rod end locations on the rack shaft you have to position the entire rack dead accurate on the frame, if you get it seriously wrong you're screwed. There's some adjustment possible by shimming the rack and the tie rods ends but nothing more.

How did some of the guys over on CF do their bracket? The only 2 I've seen are mrvette (gene) and keith (427 / corvettengineering) and I think both went to the put them in the center approach right??

Looking at the plate from speeddirect it looks like they have or tried to put the holes in the correct position (although it will differ from car to car due to tolerances, frame sagging and so on)

[69MyWay]

You are exactly right about the steeroids and the other guys that built the center plate with the inner tie rods offset to center them and position them in a more correct location.

I will already have the GA tie rods so I am going to have some fun hooking them up and measuring. That won't cost anything but time and I can get an idea where it sits now.

[Twin_Turbo]

Chris, I saw your pics over @ DC.. why did you decide to put the inner mounts where you put them? Are you aiming for the geometrical approach or the reduction of angularity??? (putting them centered and as close together as possible)?? If it's the 1st, look at the speed direct bracket, from the pics it looks as if they have it about right, yours looks to need the inner mounts moved 2" or so outboard.

Can you shoot a pic from the front where you can see both the upper and lower cross shafts as well as the rack bracket?

[69MyWay]

Chris, I saw your pics over @ DC.. why did you decide to put the inner mounts where you put them? Are you aiming for the geometrical approach or the reduction of angularity??? (putting them centered and as close together as possible)?? If it's the 1st, look at the speed direct bracket, from the pics it looks as if they have it about right, yours looks to need the inner mounts moved 2" or so outboard.

Can you shoot a pic from the front where you can see both the upper and lower cross shafts as well as the rack bracket?


Are you talking looking straight down above the X member or from under the front looking back?

BTW--I intend to re-visit this once the car is up and running. There is no doubt this will work to hold it togethe and I can always rebuild the center bracket later and swap different tie rods. Without having the engine in I have been having to disconnect the front spring to get the A arms to swing into the natural drive position. I am ready to move onto the hydraboost now and hope to drop the engine back in there very soon. No more time budgeted to this right now.

I only have one dial indicator and setting up on one side of the rotor (with the spring and sway bar undone) moving the spindle up and down, so far it looks good. With the engine back in I can support on the control arm and bounce the car and check for bumpsteer movement.

[Twin_Turbo]

Are you talking looking straight down above the X member or from under the front looking back?

BTW--I intend to re-visit this once the car is up and running. There is no doubt this will work to hold it togethe and I can always rebuild the center bracket later and swap different tie rods. Without having the engine in I have been having to disconnect the front spring to get the A arms to swing into the natural drive position. I am ready to move onto the hydraboost now and hope to drop the engine back in there very soon. No more time budgeted to this right now.

I only have one dial indicator and setting up on one side of the rotor (with the spring and sway bar undone) moving the spindle up and down, so far it looks good. With the engine back in I can support on the control arm and bounce the car and check for bumpsteer movement.
No, looking at it from the front like the other 2 pics you took, but then hold the camera at ground level or so and aim it up so you can capture the rack, the lower control arm cross shaft and the upper 1 in the same shot. It should be possible. Doesn't matter if there's a bunch of stuff in the way, jsut so that these points can be seen and an evaluation of the geometry can be made (although crude)

It will work to hold it together but you will hate to drive the car with a lot of bumpsteer especially on rough roads.

[Twin_Turbo]

Here's a crude chop of one of those pics you posted, the angle is a little weird to properly show it but it should be apparent why the inner tie rod mounts should be moved outboard. I'm not saying this to rain on your parade or soemthing but if you build it as close to perfect as you can now that will save you a lot of time when measuring bumpsteer with dial calipers, to be able to do that you already must be pretty close to where it should be. Otherwise you'll end up redoing it many times. The ideal tie rod length can easily be deter mined just by measuring under the car, err on the short side because there's plenty of adjustment in the tie rod ends (thread)

I know it's a rough sketch but this does show why the rod ends should be moved outboard, not take a look at the steeroids bracket. I can't tell exactly from the pics or measure it but it sure looks like they either have it correct or very close.

http://i1.tinypic.com/s474uc.jpg

http://i1.tinypic.com/s474w3.jpg

[69MyWay]

No, looking at it from the front like the other 2 pics you took, but then hold the camera at ground level or so and aim it up so you can capture the rack, the lower control arm cross shaft and the upper 1 in the same shot. It should be possible. Doesn't matter if there's a bunch of stuff in the way, jsut so that these points can be seen and an evaluation of the geometry can be made (although crude)

It will work to hold it together but you will hate to drive the car with a lot of bumpsteer especially on rough roads.


Seeing what you have done on the photo-chop better helps me understand the other drawing.

One curious question I have though. How does the Grand Am work so well considering the geometry is out of line with the flow of the inner pivot point?

Fixing it this way won't be hard at all. It can easily be done with a larger bracket and custom tie rods.

[Twin_Turbo]

What do you mean with this:
" How does the Grand Am work so well considering the geometry is out of line with the flow of the inner pivot point?"

The rack has nothing to do with the inner pivots, that's all done w/ the center bracket.

[69MyWay]

What do you mean with this:
" How does the Grand Am work so well considering the geometry is out of line with the flow of the inner pivot point?"

The rack has nothing to do with the inner pivots, that's all done w/ the center bracket.

The grand am does not have a bracket in the center. The grand am inner tie rod connects to the center of the rack. The lower control arm on the grand am is much shorter than a Vette (although the upper is handled with a strut).

My point being, it doesn't fit the model of the center line going up from the inner lower control arm bushings, etc.

[Twin_Turbo]

Oh, that..yes the grand am attaches them to the center, where steeroids mounts their bracket. The grand am one works beause of the reduced angularity effect but why would you go that route if you can do a much better job? The grand am arms would require a really wide bracket on the rack, the vette w/ the long lower arms relativly close to each other gives you the opportunity to do it with a center plate to put the rods in the geometric right position and that way you have a real advantage over the other wya, which is only reasonable at best.

[69MyWay]

Good info on the different designs Twin Turbo. One other difference is the knuckle for the tie rod to attach on the Grand Am is at the extreme top of the wheel area. Don't know what role that places in geometry of the syspension, but it is exactly opposite of the way it has to install on the Vette, since we have to put it very low on these cars.

I put the engine back in yesterday.

I now know better why I was able to connect with only two U-joints as it is clear my rack is lower than most. It is not a problem though because it is still higher than the low part of the oil pan.

I have more room than I thought to custom fit a different center bracket and tie rods. It really helps to have the engine it at this time to know where any interference items may be located.

Finished build the hydraboost yesterday as well and will be installing that soon. It will be easier to come back and tweak the tie rods after I get the car running again and can move it around a bit and then focus only on tweaking this aspect.

My list is shrinking, but I still have 100 other small things to do that are simply time consuming and minor detail in nature.

[69MyWay]

Yipeeeeeeeeeee!

Got the car fired up this last weekend. The power steering is smooth as butter! The reaction is ultra quick and tight. I have driven it around the neighborhood about 2.5 miles or so and I love it.

As far as bump steer...tie rod relocation, etc...that is still on the drawing board. I have half a dozen other small items to get online INCLUDING getting the hydroboost working then I will re-work the details.