Getting a more "correct" steering ratio write up

[Grubby]

Disassemble both racks and remove the existing ERA rack from the car.

1. Remove outer tie rod from steering knuckle. Get accurate measurements and toe/steering wheel angle will be maintained.
2. Remove large end of boots and unscrew inner tie rod ends. The small end of the boot can stay in place.
3. Disconnect steering shaft U-joint from steering rack input pinion.
4. Remove the two bolts holding the rack to the chassis.

On the bench

5. Remove tension plug from steering rack. Count the turns so you can put the same tension on the rack when you re-assemble.
6. Remove pinion outer boot, then use a small screw driver to remove the inner seal. Use some RTV on it during reassembly to ensure no leaks.
7. Remove snap ring and then pull pinion up and out.
8. Slide the rack gear out of the steering rack housing.

After both racks are taken apart you will need to have the quick ratio pinion machined to print.

Then reverse the process installing the quick ratio pinion (modified) and quick ratio rack gear into the ERA housing. Reinstall the ERA modified tie rods to the new assembly. If you took good measurements your toe and steering wheel will be correct. If you missed, you will need to adjust toe and steering wheel.

I used string alignment and toe plates to confirm I was still in good shape, before driving.

When reinstalling the steering rack tension plug, I found it needed to be backed off about ¼ turn. This makes sense as the new pinion gear is larger diameter than the old one.

I decided it was wise to use the ERA rack housing, to be certain to maintain the designed bump steer.

Using the quick ratio rack from Flaming River risks creating a bump steer issue. It has mounts that are roughly .600” forward and .125” lower than the ERA rack. If the rack just needed shimmed forward, I would have used it with a shortened pinion.

The negative is the part of the pinion that rides in the bushing will not be heat treated at the top .125”, as it will be machined away. The feature is .500”. Therefore, .375” of the feature will still be hardened and .125” will be a bit softer. I think it is a non-issue.

The changes to the input pinion include shortening the splined end to match the short pinion and shortening the gear end by .125”. I can supply prints to any that want them.

Results; Measured steering ratio went from 22.5:1 to 15.3:1. Turns lock to lock went from 3.3 turns to 2.4 turns. Note the ERA Subaru racks were 2.7 turns lock to lock.

ERA standard rack is Flaming River 1502-3X3. It is a Mustang 2 rack shortened 3” with short pinion (20:1). ERA modifies the tie rod ends.

The custom Flaming River rack is ordered via special order form. The rack looks to be a Fox body Mustang rack shortened 3” with long pinion (15:1).



John

[Tommy]

The EM Cobra I used to have had C4 Corvette front suspension and power steering. With a 15.5:1 ratio and Hoosier racing tires the response was lightning fast. It was probably too fast for comfortable street driving, but was ideal at the track. Fortunately for me I was used to flying a jet that required a very light touch to avoid overcontrolling it. I liked it. . . . Very good write up.

[Ezpilot]

For those of us who have a Mustang II front suspension, I just ordered a quick ratio from Johnny Law motors. 16 inch center mount. It should be here in about a week or so. I'll post any issues I might run into...161 BUCKS!