I'm in the process of upgrading to Rack and Pinion, essentially I'm adding a R&P like the Steeroids systems. As I was looking at it, I noticed something that is just not sitting right with me. Since the rack is fixed to the frame, the rack steering rods change their angle as the front suspension moves up and down. As the angle changes, so does the distance from the rack to the wheel steering arms. This must result in the wheels going in and out of alignment as the ride height changes going down the road. The shorter the steering rods from the rack to the wheel's steering arms, the more pronounced this problem would be.

What am I missing?

 

In my case the geometry is improoved compared to stock. With Steeroids I no longer have bumpsteer.

~Jay

 

What you are describing is bumpsteer.
The steeroids system has longer tierods(?) and relocated the inner end to reduce the bumpsteer which is designed into our front ends.
The suspension goes through an arc in its travel and the tierod end must go through the same arc or bumpsteer results.
I used an end take off rack and have the tierods angled forward. This replicates the arc the suspension travels at the point the tierod connects to the suspension.
The arc the suspension travels through varies dependant on where you attach the tierod as we have a SLA (short, long arm) design. If you attach the tierod end near the top arm, the tierod will have to be shorter than if used parallel to the lower arm.

So the short answer is you will have to find the correct length for the tierod and mounting point for the inner tierod end to give you zero bumpsteer

 

This topic has been kicked to death several times among Norval, TT, Pete79L98, and myself some time ago....I dunno if a search for 'bump steer' will produce anything or not...long threads....very hot topic...apparently bump steer was not well addressed in the late 50's, when this chassis was designed, probably too much else going on to afford the time.....

it's one issue that a steeroids/similar proper design/install can overcome....as was done in my install, which I did my own...

GENE

 

Simply changing to rac and pinion will not remove the bump from our cars. How have you check it??? Bump is caused by two things.
The slope of the tie rods themselves.
The length of the tie rods.
Rack and pinion might change those 2 parameters but I doubt it.
Do you actually have measurements of bump???

 

Gene I checked a 2002 mustang and it still have 3/4 inch toe in at 3 inch rise.
The ONLY car that I know of that has NO bump is the Viper. They design bump out of it right from the factory.

A tape measure gets you in the ballpark but for really fine tuning you need one of these. It uses a dial gage to read in thousands of an inch the toe change. I settled for .007 over 7 inches of travel.

 

What!? Am I Invisable??

tie rods should be longer than stock, Mine are 13.5" plus the rod ends. 17" total I think... Twin Turbo has an excellent pic somewhere that shows where the inner tie rod must be...

The angle of the rod, Like Norv says is most critical.
Most people say that a little toe out is best as it gives the car some understeer, toe in gives oversteer. I run about ,020" toe out over full bump.

 

I know that other then me you made an effort to build a gage. I know you spent time getting better tie rod sleeves. I run 13 inches plus the rod ends myself.
I am sure Gene just overlooked you in naming names.
I know you did get rid of bump.

 

let me go measure the tie rod length

ok here we are....on the stock rods (i don't think anybody adjusted these since i took them off)....from zerk fitting to zerk fitting ... 14 3/4" on one and 16" on the other? I'm not sure why they are not the same the car was aligned before i took them off....on the steeroids its 17" for both.

 

I measured my car too 17" total center to center also

 

can you measure the old stuff?

 

I just measured my stock stuff. I came up with 15.25 and 15.75. I am unsure of how well the front end alignment was. The car has been apart for so long that I forget how it tracked.

 

I believe that most cars have bump steer if they have much suspension travel. The problem we face with c2 3 is the sorry slave power assist system we have had to face. Jump into a restored 62 chevy or early mustangs with the slave power assist and they all drive the same (badly).

A good rack and pinion system would be nice but for it to really perform to its highest potential it needs to be front steer.

For the money the jeep box is the best solution to our c2 3 chassis design. I installed one 3 years ago and have enjoyed it ever since. It is 2.25 turns lock to lock and has great road feel and feed back.

SSS

 

I cannot measure the old stuff on my car. It's all apart and in boxes. The tie rods were significantly shorter though.

I disagree on both points SSS. While the jeep box is definitly an improvement I think the R&P is a very good solution. Being rear steer is not that great of a loss esp considering there are almost on compliant parts in it so the whole bushing deflection issue is moot.

The drag link design hasn't been used for decades and for good reason!

I do agree that the commercial kit is way too expensive, it can be done for less than 1/2 the cost pretty easily.

 

I have a question for you guys that actually measure bump steer in your Vettes. Do you check bump steer on both driver and passenger side? Is it the same at jounce and rebound suspension travels?

I have a concern regarding the Saginaw 600 gear installations. I wonder about your pitman arm location and height. Is it exactly mirror opposite from your idler arm? I am wondering about symmetry of your linkage system. Of course the proof is that the car tracks accurately and doesn't experience wierd steering motions when driving over bumps. I know that if your relay rod is not symmetrical (parallel and perpendicular to the car centerline and suspension), you might experience a gentle orbiting of the front end as you drive straight down a slightly undulating road.

Jim

 

Stock tie rod sleeves I believe are 10 inches long. I tested with 12, 13 and 14 inch tie rods also and a matching center link for all 4 sets.This is not the overall length but just the length of the center link joining the tie rod ends.

The total tie rod length affects linearity. You might get rid of all toe IN on rise only to find you went the wrong way when the suspension compresses. YOu normally get toe in on rise and toe OUT on compression.
Tie rod length affects weather slope of the tie rod improves both rise and compression or not.

If you start with a stock car, put a tape measure from one spot/hook in a tread and then another spot on the other tire and take an accurate reading. Jack the car up 1 inch, remeasure, 2 inches up, remeasure and 3 inches up and measure you will find the toe in getting greater and greater. To fix this you need to DROP the outer tie rod on both wheels.
Say you drop it 1 1/2 inches and recheck everything and find your toe IN almost gone and maintains toe.

Now the hard part. Pulling the car down. I have a special fixture that does this.
Anyway you will find the car toes OUT as the suspension collapses. You will also find if you take stock measurements collapsing the suspension first, then fix bump for rise by dropping the outer tie rod that you have accually made toe out WORSE by dropping the outer tie rod.
What do you do now?? You fixed toe in only to have toe OUT kill you.
LONGER tie rod sleeves and a new center link fix toe OUT and fix it so when toe in is fixed toe out at the same time has been fixed.

 

Jim I work one side at a time. I install the gage on one wheel after removing the sping, the shock and the sway bar and work on it until I get under .010 or .015 over 7 inches of travel. I then move to the other side and do the same.
This winter I want to recheck bump and at the same time check bump with the wheels turned to see if cornering and bump at the same time affect my handling.

For setting up the Jeep box I set my center drag link exactly level using a level and I had both the idler arm and the pitman are at right angles to the center link.
I put a magnetic level on the center link, squared the idler arm to the drag link the custom made a pitman arm that was at 90 degrees to the drag link and at the same time a height that left the drag link level.
I have not checked bump yet but I will soon.

You can see here that I had to space the outer tie rod down. I have a special tie rod stud that you use with spacers to find out how much you need to drop the outer tie rod. After finding out the amount you weld a block on the end of the steering arm and I bolt it at the same time. AFter the block I fine tune with a washer or two. A welded block is more rigid then leaving the tie rod stud.

 

Great methodology Norval.
Jim

 

Jim When I mounted the box I found a pitman arm that was very close to stock, and mounted the box with with the drag link level and in the stock position.

427, You are correct, the jeep box is not perfect, we are still dealing with old suspension tech, but like I said before after 200000 miles and all kinds of modifications if I could choose only 1 thing to change it would be the steering box.

SSS

 

Jim,
I measured both sides. The rack was as square to the car as I could measure then I adjusted the inner tie rod heights for zero bump. Both sides were within .002" over the entire travel. I then added about .010" of toe out on bump to get a little understeer.

As far as jounce and droop I start at full droop ( no springs ) and then raise the wheel to full compression. With 17" tie rods the curve is very linear With stock rod length there is a pronounced curve to the toe as expected. tie rod length is not to critical, 1/2 inch here or there doesn't make much difference. Tie rod height is very critical a .010" thick washer makes a huge difference.

It drive wonderfully, Well except for tramlining but my understanding is that is due to the tires having large short blocks that do not give at all...

You can see in the pic below, the pass side inner tie rod is a little higher the the drivers side to get the same bump steer