i am curious to know if there are any tried and true donors for a steering rack and pinion setup. my space needs for the engine swap are not consistent with the drag link setup my car came with!
i am looking for something with a pretty quick ratio and one that does not require power assist. i would prefer a unit that mounts behind the crossmember but i could probably work it out if it was ahead of the member and offered better performance and parts cost savings to boot. any advice? thanks! mike
In front of crossmember: Miata or Triumph Spitfire have pretty quick ratios. Miata power racks can be easily depowered.
Behind the crossmember: BMW 2002 (I think), Dodge Omni/Horizon.
Before snatching a rack off of something, you will need to know how far apart the lower inner control arm pivots are. Ideally, your rack should have the inner tie rod pivots at the same distance apart.
You might also check these folks: http://www.unisteer.com/
The Porsche 924 had a manual rack mounted ahead of the cross member that was essentially a Rabbit rack from across the pond.
has anyone done one on a fiat spider that you know of?
unless someone has done a similar car it sounds like i just need to spend some time in a pick a part lot measuring racks and spinning steering wheels!
Why not a Fiat X-1/9 or 128 rack?
2002 does not use a rack-and-pinion setup. E21 and later 3-series cars did, I believe.
I've been searching for years for a catalog of racks with dementions for inner tie rod widths no luck yet..
44
Ahead of the crossmember you could use an RX7, S2000. They can be found for sub $100 if you look carefully, and have very quick ratios without the need to be power-assist.
Behind...well, I would think almost any FWD car. I know older Hondas (pre-88) had decently quick steering racks for econoboxes
I have seen a bunch of TR7, and Pinto units in kit cars. There are some pretty compact 80's Toyota ones. They bolt up flat on the subframe. BMW 2002 is a steering box with pivot arms. I have a bunch of TR7 ones here if that will work for you.
Remember that the steering ratio also involves the length of the steering arms.
itsarebuild, I think what you need to do is define the rack and then try to find one that suits. Front steer (rack in front of the wheels) or rear steer? Distance between pivots (hopefully 24", as there are a lot of those out there)? Total travel and number of turns desired?
Dont plan on finding an omni manual rack, they are extremly rare.
itsarebuild wrote:has anyone done one on a fiat spider that you know of?
Slowly working on it. I have seen it done and the last half year or production used a rack the rare 1985.5 models.
Travis_K wrote:Dont plan on finding an omni manual rack, they are extremly rare.
and the ratio was like 26:1, in other words they are the suck. The performance power rack is 14:1, stock is like 20 or 18:1. Get a rebuilt hi-po powered version and depower it, enjoy.
Mopar did make a performance manual rack for a little bit, that was like 20:1, I think it might have been from a Euro model or a Dakota piece, not sure. Those are even more rare though.
Forgot to mention that the early Dakota's are rack/pinion.
all good advice. thanks!
i will take some quick measurements on my arms and desired throw and check some of the ideas above for fit. i may see if i can find any 85,5 units out there too.
thanks!
one more question. it seems like the design of a steering system favors mounting the steering rack ahead of the spindle centerline so that changes in the ride height of the steering rack relative to the ground caused by acceleration or deceleration result in a slight toe in condition. given that i am looking at a challenge car and anything is possible with the right fabrication time should i look to relocate the steering linkages to the front of the crossmember when i make this swap? or is the gain in toe in so negligible that i shouldn't bother? also, as i understand it from my reading so far, the important thing about establishing the pivot point (and thus the housing length) is to keep the link arms longer than the a arm so the link arms travel radius is bigger than the a arms radius. thus reducing the impact of bump steer. is that really the big thing to look at or am i missing something? thanks!
Did anyone mention the location of the steering arms. Forward or backward ? Makes a difference where you put the rack.
Keep the link arms either along a line drawn between the pivot points of the upper and lower A arms or shorter for the reasons you mentioned.
I hadn't thought it through about the benefits of a steering arm in front of the spindle vs. behind the spindle pivot point. Makes sense when you think about it.
itsarebuild, you're describing bump steer when you talk about going toe-in on acceleration. Try to avoid it if you can. It's not really related to front- vs rear-steer at all. The location of the rack relative to the ground is irrelevant, what matters is what the suspension does in droop.
The length of your tie rods - and thus your rack - depends on the height of the steering arm. If they're too long, you'll get bump steer. If they're too short, you'll get bump steer. I've done some diagrams in the past on this - click here and search for "steering rack". Then click the link for page 32.
Pinto/MustangII manual racks are beefed up and served in many different ratios for hot rods and racing.
Escort and Taurus have a rear mount rack and I have a manual rack on my Escort...Lots of Escort guys just depower their racks and get a better ratio.
Not real sure about the geometry as I only learned what Ackerman was about a week ago.
Bruce
itsarebuild wrote:all good advice. thanks!
i will take some quick measurements on my arms and desired throw and check some of the ideas above for fit. i may see if i can find any 85,5 units out there too.
thanks!
The X 1/9 and the 131 both used Rack and Pinion. Best bet would be to find a manual rack from one of those cars (x's were all manual.. the 131 had some power options)
