Rack and pinion steering limiter



Last update: 7/5/08

Other articles in this series,

 Go to article, "Correcting CMC designed steering geometry, camber"

Go to article, "Correcting CMC designed suspension to correct bump steer""




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Background
Many production vehicles have mechanical stops mounted on the suspension that limit the spindle rotation. If a limiter wasn't provided it might be possible for the steering parts of the suspension to contact other parts of the vehicle.

After making changes to the steering system or suspension geometry while building or modifying your suspension, it is possible that some part of the wheel assembly etc might then interfere with other parts of the suspension or chassis.



Details of why steering limiting might be required
Some (most?) rack & pinions can move the rack shaft as far as the teeth on the rack will allow it to move. The system depends upon an outside device to limit the maximum amount of wheel angle in a turn.Often when people build their own cars this limiter device is left off or is in the wrong place for the changes made to the suspension.

I modified my steering so that two turns of the steering wheel turned the front wheels the same amount as the old three turns lock to lock did. The rack and pinion itself could still be turned three turns lock to lock though. This caused my Heim rod end mounting bolts to hit the lower control arms when the steering wheel was turned more than one turn off center. (The bolts are 1" lower than the original hardware.)

I realize that limiting the steering the way I did it is nothing new and has been done many times before. But I want to present the details and the precautions that need to be taken for other builders who might not have seen how it's done.



What's involved in doing this change?
Basically "all" you need to do is remove the flexible gaiter from each end of your rack pinion, measure a few things on the rack and make up some spacers to limit the amount of movement of the rack shaft. You then slip the spacers onto the rack shaft at each end and put the gaiters back on.

Sounds easy enough, but you do have to make your measurements accurate so the steering wheel turns the same amount to the lock position left and right and check that the suspension doesn't bind or cause the spindle etc to interfere with other parts of the car.



Why worry about having the steering wheel turn off center the same amount?
The reason is so that the car will have the same turning radius turns left or right. Otherwise you may get into trouble later thinking the car can turn tighter in one direction when it is really the OTHER direction that has the smaller turning radius.



 Considerations and precautions
Some racks may have the bearings for the rack shaft at the end of the rack housing. In this case the spacer can just be centered on the rack shaft diameter and it will limit the amount of travel of the rack shaft. I'd taper the hole ends of the spacer so it doesn't catch on the rack teeth.

Other racks, like mine, have recessed outer bearings for the rack shaft. i.e. the bearing is not at the very end of the housing but is recessed a short distance inside housing. In this case the spacer needs to be made so that it will be a light press fit INTO the end of the housing (or the inner diameter of the spacer should be only a slightly larger than the rack shaft diameter to center the spacer on the shaft to clear the housing).

The reason for this is, if the spacer has a larger diameter hole than the rack shaft and were allowed to lay on the rack shaft it could catch on the end of the housing in a turn and change the amount of lock in that direction. This is not safe!!

So plan on doing a little machining to get the spacer to fit properly either on the shaft or into the housing.



Determining the size of the spacers
First thing is to support both lower control arms so the tires just clear the ground. You need to do this so that the wheels can be turned through their full range of movement.

Next remove the gaiters from the rack. If you have to take the tie rod off the shaft to do this and then put the link back on hand tight once the gaiter has been removed. The outer end of the link should also be connected to the steering arm.

Measure the diameter of the rack shaft and write it down.

A.  If you know how many turns lock to lock you want your steering to have, do this
Center the steering wheel. Now turn the steering wheel to one half the number of turns you want the steering wheel to be at lock. I wanted two turns (total) lock to lock, so I turned the wheel one turn off center. (On my setup, one turn allowed the suspension parts to have the interference clearance I wanted so I was OK to continue.)

Measure the distance from the bearing to the inside edge of the mechanism that holds the tie rod to the rack.

Turn the wheel to the opposite side lock position and take the same measurement.

Write the numbers down as they will more than likely be different from side to side. These measurements are the length of the two spacers you need to fabricate.

There is a picture below that illustrates where the measurement is taken on my rack.

B.  If you want use the maximum number of turns lock to lock do this
Center the steering wheel and then while counting the turns of the steering wheel, rotate it in one direction until the suspension or tire has interference with some object. Take note of the number of turns it took to create the interference.

Re-center the steering wheel and then turn the wheel in the other direction to see which direction gives the minimum number of turns to contact something. Use the minimum number of steering wheel turns as your new lock to lock MINUS a small fraction of a steering wheel turn to allow for some clearance between the interfering parts.

With the steering wheel at your new off center lock turns, measure the distance from the bearing to the inside edge of the mechanism that holds the tie rod inner end to the rack.

Now turn the wheel to the opposite side new off center lock turns and take the same measurement. Write the numbers down as they will more than likely be different from side to side. These measurements are the length of the two spacers that you need to fabricate.



Limiter spacer

To see an enlarged view of most pictures, left click on a picture or right click and select "View Image"

sleeve tube

This is what one of my spacers looks like. One of these sleeves is placed on each end of the rack shaft. The length shown here more than likely will NOT be the same that your rack needs.

Also, the two sleeves will probably NOT be the same length or even the same outer diameter and that may determine how you want to make the spacers. The bearing on the pinion side of my rack had a tapered hole to the recessed bearing. The other end of the rack had a straight sided tube to the recessed bearing.

I decided to make up spacers that were a press fit into both ends of the rack rather than "floaters". I did this because I had a piece of thick walled aluminum pipe that the outer diameter of the pipe could be machined down to fit both ends of the rack housing and the inner hole was much larger than the rack shaft diameter.


sleeve on rack

This picture shows one of the spacers laying on the rack shaft. The spacer outer diameter was machined so it is a light press fit into the rack housing (towards the right of the spacer).

The recessed bearing is positioned about 1/2" inside the end of the rack housing.
sleeve at lock

I screwed on the tie rod end inner retainer (the large, domed piece of metal in the middle of the picture).

The spacer was started into the housing by hand. I then turned the steering wheel so the tie rod inner retainer pressed the spacer into the rack housing as shown here.

After both spacers were installed, I tightened the tie rod retainers and replaced the gaiters.




limiter clearance

This shows how much clearance (~1/4") I allowed between my Heim rod end mounting bolt head and the lower control arm. The other side of the car had the same clearance.

You can see a small chip of paint missing where the bolt head had hit the lower control arm in setting up the suspension.