rack and pinion used with i beam axle..?heard there would be bump steer?

ok..i did a search before before i posted and found nothing...maybe i missed something...trying to get away from the slop of traditional steering boxes..i also have laying around a rack and pinion set up from a 69' jag xke..that was my dad's so i would like to utilize the part ..i currently have it mocked up to the frame to a 46' ford i beam set up...some have mentioned if i do not mount it to the axle it self i will have bump steer??...this puzzles me because it was mounted to the subframe of the Jag so what is the difference?...im no engineer but it seems like it would work just fine mounted to the frame instead of the axle..any info or links would be appreciated..

 

Do another search, lots of info on this topic

 

bump steer would come from the ends of the rack arms traveling in an arc as the axle moves up and down.

the least amount of bump steer for a traditional r/p steering would be a microscopically short rack in the middle of the car, making the tie rod ends equal length and as long as they could be (half the distance each)

since that's not possible, you then have to make one tie rod as long as you can by mounting the rack as far left as you can. Then you use a really long tie bar to have the pass tire control the driver's side tire.

I'd suggest one of those newer single sided rack from whosiewhatsit, but i've heard they dont handle much stress (search Shakypuddin and his gasser 55 build) his broke after the wheel stand.

I've thought about mounting a rack directly on the axle but the unsprung weight addition is the least of the issues. You'd need a telescoping steering shaft that can also handle the fore/aft motion of the axle.

Additionally, when only one tire goes over a bump, you'd get a rotation viewable at the rack input relative to the steering column. -that would be a different form of bump steer-although i dont know how measurable it would be.

-rick


edit: if you're set on using that rack- can the driver's side be snipped off, creating a long passenger side tie rod- then connect the two wheels the traditional way with a tie bar?

 

It works on the jag because it has independent front suspension. As the Jag moves up or down, the A arms pivot at the same point where the rack pivots.

Mounted on the chassis with a solid axle, when it moves up or down, the wheels will get pulled in or pushed out.

Hope I wrote it clear, maybe not.

 

i was hoping the ball joint in the tie rod end would compensate for any horizontal movement of the axle..i have a much more clear picture o now understanding how it works on the..the a rms pivot at the same place the rack pivots...crap what a lot of work for nothing...it seems 69fury has the only way of saving the half ass plan i came up with

 

So, you don't have any way of using a 525 GM box to do cross steer? If you had room, they work great and no slop.

As long as it is a real GM box. I did not say Vega box because most all are offshore junk that you will hate.

 

Faith, of "Deuce of Spades" fame, has a R/P under her '32 Roadster. Apparently it had been mounted wrong so she had "Hollywood Hot Rods" fix it. She as/had a web site, I believe it's www.myhiboy.com where there's a repair thread with photos. It's called a "Unisteer".

 

Finest driving 39 Ford I have ever driven has just that. Citation [it seems] rack mounted to axle, slip joint on the steering shaft. Several of these were made by an old time machinest for his 39 and several other 39/40's in our area. I have never heard anything from those who installed them but good comments. I don't remember all the details as I never installed one, but if you are interested I could provide them.

 

for reference:

http://www.jalopyjournal.com/forum/showthread.php?t=225171

 

i was just up in the barn jumping up and down on the front end and did not see any moment of the tires.maybe it's such a small amount i can not see it...my new front spring is so stiff i can only get the car to move up and down 4" or so ....like i said im no engineer

 

Yes bump steer, and don't do it. Boxes can and will have some play, but new boxes as well as good used ones are around. Mixing a modern rack and a vintage i-beam axle is STRANGE to say the least....some things don't belong together, but i understand why you wanted to try it.

 

Small R&P are mounted on the straight axles of light race cars, like mini-sprints. If weight isn't a factor, it could work, but you need a way to compensate for the steering shaft changing lengths as the axle moves about, like some sort of slip joint or sliding connector or universal. Gary

 

Toe doesn't have to change much before you start changing lanes without wanting to... An 1/8" inch or so should do it. Just a bad idea.

 

Mount rack to the axle? WTF?

 

like i said i have a good amount of time into mounting it to the frame..i was looking at the unisteer systems...maybe one long arm to the passengers side with a tie rod is the way to go as mentioned above..or it's scratch the whole idea and start spending money on a f-1 box or crappy vega box..just an idea i tried without much experience..thanks for the helpfull advice

 

Are you set on cross steeer? Is side steer an option? There are many boxes for side steer Mopar, Ford, Corvair, Chevy truck...etc

 

Here is a fresh made 32 with R&P steering and a straight axel. Ran it uo to 85 so far and all around town and no bump steer. My 33 has a straight axel with the old style vega box and it soon will be changed over to R&P

 

can you get some specs/pics? many would be interested in a way to do this if the geometry is solid.

 

love to see the set up...

 

Could there be some confusion here between Unisteer and a regular, two direction rack? Gary

 

I put a power rack and pinion on a 53 F100 a few years back for a guy. It was a kit from No Limit Engineering. Rack mounted to the axle and had a telescoping steering shaft. Worked very well but "road feel" was very minimal. Steered very well and didn't have any noticeable bump steer at all. System was very similar to many of the big over the road trucks.

 

I mounted a Pinto R&P to my '32 Ford axle and kept the OEM Pinto flex shaft. Like a big speedometer shaft. Everybody would see that flex shaft and expect it to fail. Millions of Pintos never did. Nor has mine in there since 1978. No bump steer. PS. If you really don't understand why a frame mounted R&P will result in bump steer, perhaps steering, suspension work should be farmed out.

 

I used a Pinto flex shaft on a build once too...and it worked perfect.
Since then i've heard there was a big recall on them as they tended to separate in normal use!
I guess its another example of "what you don't know won't hurt you!" Hahaha

Regardless...I'd run a rack on the axle if it was required.
Gotta make sure your turn radius isn't affected though.
Accepted word is that some racks will make it much wider apparently.

 

Uhhh...YES!

You cannot mount a rack to the frame and hook a tie rod to either spindle on a beam axle like you would an IFS setup.

You CAN mount the rack to the axle as long as there is a safe slip shaft in the steering linkage and the geometry is correct. We do it on all 800+hp, 150mph supermodifieds, and have for 30 years.

You can mount the rack to the frame and use 1 drag link across to the opposite end of the axle (unisteer), but the rack needs to be as short as possible. Just using a wide rack and short tie rod will result in bad bumpsteer.

You should use a box and drag link, as suggested above.

 

my 27 has a ibeam i made and a geo metro rack, with air ride, lots of toe in and out and it has rode fine, blown sbc been over 100 plenty of times in the last 5000 miles.


no it is not ideal, but neither is a straight axle for high speeds and rough terrain

 

That's the traditional way to do it, why not do what you know will work?

 

I'd really like to see some pix of these kinds of setups. Gary

 

Gary ---- here ya go.
Has a slip joint as mentioned earlier, and zero bump steer

 

hows that dragster/sand rail rack work? They were not designed to turn that big of tire or carry that much weight? All the ones i have had have 5/16 heims on each end, even the Spe racks that are high quality. your frame looks nice and clean. Any pics of engine and steering shaft?

 

Cool, and thanx. How much travel in that rack? Gary

PS I was really sniveling for some super modified chassis pix!