Getting racked - Lateral-g Forums

69MyWay · #1 03-20-2006, 02:21 AM

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 · #2 03-20-2006, 02:56 AM

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 · #3 03-20-2006, 05:14 AM

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.

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 · #4 03-20-2006, 05:19 AM

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 · #5 03-20-2006, 05:31 AM

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 · #6 03-20-2006, 01:59 PM

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 · #7 03-24-2006, 03:28 AM

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 · #8 03-24-2006, 03:36 AM

Quote:

Originally Posted by 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?

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 · #9 03-24-2006, 04:15 AM

Quote:

Originally Posted by 69MyWay

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 · #10 03-24-2006, 04:35 AM

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.