rack and pinion question

BBShark -
Nice CAD work. SW I guess? Do yo have the FEA module too? Be nice to check the loads on the mount, but I have no idea what you'd use as a starting load.

Just wanted to comment on the nice work.

Cheers - Jim
 
IMG_1339.jpg

It actually looks like DS went out to put out the best suspension upgrade. Interesting to see how it performs.
 
That is a sweet looking well thought out sub-frame/adapted bit of gear! The tow links could bring a bit of body damage however.
 
:ripoff:
phantomjock said:
That is a sweet looking well thought out sub-frame/adapted bit of gear! The tow links could bring a bit of body damage however.
Click to expand...

Yes, I think they set out to one up the competition. But, it's not going to be cheap (my guess).

Anyone recognize the rack make/model?
 
As far as bump steer is concerned, I read that you need to have to tie rods pointing at the IC, which is the imaginary line from the ball joints to the center of their inner mounts. Where those lines intersect is the ic. So this is by no means parallel to the lower control arm.

http://www.hotrod.com/articles/ctrp-1001-bump-steer-explained/

Length wise the tie rod ends need to intersect with the lines coming formed between a. the inner mounts of upper and lower arms and b. the ball joints.of upper and lower arms.
I'm not sure how good our system is. It's hard to judge things while everything is on the car.
 
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Belgian1979vette said:
As far as bump steer is concerned, I read that you need to have to tie rods pointing at the IC, which is the imaginary line from the ball joints to the center of their inner mounts. Where those lines intersect is the ic. So this is by no means parallel to the lower control arm.

http://www.hotrod.com/articles/ctrp-1001-bump-steer-explained/

Length wise the tie rod ends need to intersect with the lines coming formed between a. the inner mounts of upper and lower arms and b. the ball joints.of upper and lower arms.
I'm not sure how good our system is. It's hard to judge things while everything is on the car.
Click to expand...

The IC intersection is essentially correct and my description of this geometry as a parallelogram is also essentially correct. The IC length is 4 meters at ride height and the outer tie rod is about 30-40 mm below the lower ball joint center. Sure "no means" parallel but so close that the two are basically identical (and a great starting point). Also consider the IC moves based on suspension travel and that changes the position of the pickup point for the inner tie rod. There is no fixed point that intersects the IC with suspension travel.

If you lay this out you will find that both are not completely accurate but they are both so close, your splitting hairs (and much better that stock).
 
one suggestion on the bracket

BBShark, essentially all the steering loads are transferred to the driver side mounting plate. The loads are along the axis of the rack and are applied perpendicular to the mounting plate. The flat plate shown in the CAD drwg is not very stiff in that direction. I would recommend that you consider a gusset perpendicular to the plate running from the bottom mounting bracket bolt to the area on the bottom of the frame where the 4 bolt holes for the ram/damper mounts to better react the steering loads. There is a picture of this design in MYBAD79's post on his rack conversion.

Grampy
 
The old school bump steer correction substituted a long threaded rod with a tapered end to substitute for the outer tie rod joint. Spacer shims were used to position a heim joint lower than the factory location.

Since you are making a new center link to fit the GA rack you can change the height and change the center to center distance of the inner pivot points. This freedom along with the old school bump steer kit plus some experimentation with a bump steer gage should allow you to establish the new inner and outer pivot locations needed to minimize bump steer.

Look at the work of others it appears that the tie rod center to center distance wants to be longer than stock so the center link would be narrower. Also the inner tie rod joint wants to be as close to the oil pan as possible and the outer joint wants to be lower.

Gunther has done the bump steer tests. Perhaps he would share his findings.

Grampy
 
Grampy said:
BBShark, essentially all the steering loads are transferred to the driver side mounting plate. The loads are along the axis of the rack and are applied perpendicular to the mounting plate. The flat plate shown in the CAD drwg is not very stiff in that direction. I would recommend that you consider a gusset perpendicular to the plate running from the bottom mounting bracket bolt to the area on the bottom of the frame where the 4 bolt holes for the ram/damper mounts to better react the steering loads. There is a picture of this design in MYBAD79's post on his rack conversion.

Grampy
Click to expand...

There is lateral gusseting on both sides of the left hand bracket and the inside of the right hand bracket as well as axial stabilization from two mounts (on the right hand side). It's not going anywhere.
 
Grampy said:
The old school bump steer correction substituted a long threaded rod with a tapered end to substitute for the outer tie rod joint. Spacer shims were used to position a heim joint lower than the factory location.

Since you are making a new center link to fit the GA rack you can change the height and change the center to center distance of the inner pivot points. This freedom along with the old school bump steer kit plus some experimentation with a bump steer gage should allow you to establish the new inner and outer pivot locations needed to minimize bump steer.

Look at the work of others it appears that the tie rod center to center distance wants to be longer than stock so the center link would be narrower. Also the inner tie rod joint wants to be as close to the oil pan as possible and the outer joint wants to be lower.

Gunther has done the bump steer tests. Perhaps he would share his findings.

Grampy
Click to expand...

The link I posted seems to suggest the location of the joints need to intersect with the lines from the arms pivots and ball joints. I don't think it would be correct to place the inner joint below the oil pan.

Does someone here have the measurements of the stock location of the various suspension points ?
 
Sorry for the confusion Yves, previous experiments report the inner pivot should raised vertically. The oil pan is the vertical limit so the pivot should be to as close to the oil pan as practical.

Grampy
 
Belgian1979vette said:
The link I posted seems to suggest the location of the joints need to intersect with the lines from the arms pivots and ball joints. I don't think it would be correct to place the inner joint below the oil pan.

Does someone here have the measurements of the stock location of the various suspension points ?
Click to expand...

I'm not explaining myself. There is no "common" intersection (using the IC) of the inner pivot point of the steering links. Try laying this out on paper. The IC defined by the upper and lower arms moves in and out and up and down with the wheel. The only way you would have a common intersection would be if the outer steering arm was in the exact same point as the lower ball joint (x, y). It's not.

You are going to end up with rods that are 1 1/2 to 2 inches longer. That is the closest you will get.
 
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