Hot Rods How do you get Ackerman with R&P?

I'm working on an early F100 that somebody added rack & pinion out in front of the stock 'I' beam axle and it has tire scrub when turning. Can this be solved?

 

the tie rod ends need to be further out than the king pins.

It can usually be solved, by removing all the previous work, and building it right.

 

Yep, I had to make new steering arms that fit inside the rims. Also if you do that make sure your tie rods are not too long. Bump steer is worse than bad Ackerman.

 

Move the rack to the rear. You want to make the angle of the steering arm to the tie rod to have the angle as shown in the diagram. You can leave the arms alone, just move the rack back. Look at front steer cars. My 1960 Chevy is a good example.

 

does the rack turn the right way for rear steering? they make them two ways...front steer, and rear steer. They move opposite directions.

I would not put a rack on an old truck...use a normal steering gear, drag link, tie rod, etc.

 

Yes, they shouldn't have stuck the R&P on it, it was a terrible mess and I've gotten most of it squared away except for the scrubbing.

 

I shortened the steering arms to right at the edge of the wheel, I was afraid to shorten them more because of the quick turning ratio.

 

Yep, that's the delema. Moving the rack works if you can, mine is already against the frame.

 

Tire scrubbing comes from more than just an incorrect Ackerman alignment.
Negative wheel offset also causes tire scrubbing while going into a turn. The farther the tire is away from the king pin or the center line of the of the ball joints, the more tire scrubbing in corners you will have.

Also, the work to fix any Ackerman problems is identical whether you have a rack & pinion or conventional steering box.
See squirrels drawing above.

Mike

 

Sounds like the time to look for a rear steer rack.

 

Putting a frame mounted R&P on astraight axle vehicle is never good , everytime the suspension moves , the toe in changes..

 

This ^^^^^^^
The rack mounted to the frame with a straight axle is a recipe for mechanical bump steer.
You really need a long drag tie rod [and drag link]

 

As stated, the Ackerman is built into the steering arms. The steering arms angle position gives the Ackerman. Agree that with a R&P you need to be careful of bump steer. Especially with solid frame mounted R&P and moving beam axle. Least of problems is toe changes. Unless hidden, R&P is ugly appearance.

R&P with beam axle just is not a good combination.

 

I swear there are mounts on the I beam axle for the R&P! Glad I wasn't in the truck when they found it that wouldn't work!

 

I would really consider yanking that rack off of the front of the axle and putting a stock gear box like original. The racks are supposed to be mounted on the frame and used with IFS, the steering shaft should not be articulating with the suspension, it will wear out and there goes all of the steering input. Plus it probably looks way out of place on that truck being tacked onto the axle and all.

 

Basic's; Racks don't play well with "I"beam axles.............. Why ,is that racks can't an don't move with axle,excpt if mounted on the axle/not the frame<no thats not a good idea ether !. Racks are made as long as they need to be to fit the inboard "A"frames of IFS{Not "I" beams} ,This so tie rods can move with the "A" frame's in a way to keep bump steer as low as possible. Using a rack in it, as made form with "I" beam=bad engineering. There are some that just cut off one end of a rack=now its just kind of a steering box and use it that way,with a reg. tie rod between spindles/arms. In real life,if you see a rack used with a straight axle/"I"beam=bad planning or just no know how of the way steering works,kind of same for most cowel steering. Things that often should be a red light an need redoing ! Put a box back on it. Both ackermen an bump steer are really good to have very close too zero.

 

Why would anybody put rack and pinion steering on a truck?

Spindles are designed for a specific wheel base any modification to the spindle or the wheel base changes the Ackerman.

 

Ackerman needs to be close and generally headed in the right direction, V towards the center of the rear end. There are plenty of vehicles that use the exact same same same suspension and spindles yet come in at least 3 -5 different wheel base configurations. The Ackerman cannot be perfect on all of those.

A little tid bit of info -
If you study front steer spindles, they are generally deeper or a greater distance from the axle stub to the ball joint center. That gets the Ackerman in the ball park, they couldn't push the tie rod end towards the tire but the could pull the pivots(ball joints) towards the center.

 

As far as general practice and getting close and an easy as pie explanation is concerned -
This is all you need to be drivable and park able without much ass ache.


If you want to understand it, measure it, fix it, get it perfect. You need to wrap your head around this one.

 

Pic's may help.

 

Very true ! . . . . .

 

Gosh I wish you guys could drive the 39 Ford axle car with a rack and pinion that one of our local old time machinists built. Another friend now owns the car and I had the pleasure to drive it once again on our trip to the Frog Follies. No one would ever install a MII front if they did. Just a beautiful driving car.

 

You really need to be careful with generic diagrams like this.
The kingpins are at an inclination, so the height of the tie-rod ball joint centre can alter Ackerman.

The kingpins should be measured at a point which is at 90 degrees to the height of the tie-rod ball joint centre .
Also look at the caster angle, this can create an illusion that the steering arms are too low when checking Ackerman [fooling people into removing some Ackerman on a rear steer axle]

 

Here is a great example of bad acerman A sliding tire has less traction notice the black markshttps://video.search.yahoo.com/sear...=9b7db54239e01a20bb678cb42ab4e318&action=view

 

Yikes!!!!! And the problem is accentuated by the Buick brake drum deal pushing the tire contact patch way outside the king pin axis.

Roo

 

Any way to get pictures of the set up? I'm curious what he did different.

 

Here's what that link gives me
100 plus choices

 

Ackerman angle will be the same no matter what kind of steering mechanism you use. This pic that @31Vicky with a hemi nails it. The tie rod ends are still the tie rod ends and this is the proper diagram to use, simple and to the point.

Note: if you don't have kingpins you use the pivot point or ball joint center.

 

How do forward mounted rack and pinion steering setups avoid screwing up the Ackerman angle?
Even some of the early Chevy pickups and cars with 3 piece track rods in IFS seemed to get away with it.
There must be more to it...

 

It should play my dads 241 hemi rat rod