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Old 06-13-2004, 06:43 PM
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Straight Axle and Rack & Pinion

Ok, I'm back. I posted a few years back about a '39 Studebaker coupe gasser project I had started, regarding a straight axle setup. That project was abandonded shortly after that post but now I'm back on it.
This is going to be a race only car in ET Brackets (Pro class). We've made a custom 2x3 chassis with a 4-link rear, narrowed 9" and coil overs, and when we're closer to putting the body back on, a 12 point cage for stiffness & safety.
I've zeroed in on the axle setup I'm going to use, which is Speedways PN 91339022. This is a tube axle with 4 bar, transverse spring behind design. So far so good.
Now for the Q: Steering. Lots of varied opinions on this. Conventional setup for this appears to be Corvair or Vega with cross steering. But I've had a few opinions regarding using a rack & pinion setup on a tube axle. I'm looking for opinions, experience and any related info on issues associated with R&P on a tube. It would seem to me to be a safer and cleaner install although I would expect some additional fabrication for brackets & such.
I have looked at Unisteers products and have sent them an email chock full of questions. I'm not sure about their Vega replacement setup, I'm more leaning towards the Mustang or Omni manual rack.
If it matters, engine will be set back approx 12" from front axle centerline, mounted with front & rear plates. Total weight of the car should be in the 2000 - 2300 lb range with a 351W.
So, what do you all think? Is the R&P the way to go?

Murff
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Old 06-13-2004, 09:25 PM
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If you go rack and pinion on a straight axle. Back in the early seventies, I built a tube frame lightweight bracket car ( like an early funny car). I experimented with several setups and the one that worked best was with the rack mounted to the axle and hooked to the steering shaft with a slip shaft and u-joint. If I mounted the rack to the frame crossmember I would get major toe changes upon chassis lift (accelleration). I tried to limit suspension travel but it had to be held to no more than three inches total travel.
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Old 06-13-2004, 09:48 PM
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I agree with what you are saying about mounting the R&P to the axle as opposed to the frame. That should allow everything to move as a unit.
I'm also thinking that with the rack on the axle, along with the 4 bar setup should eliminate the need for a panhard bar.
Thoughts?

Murff
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Old 06-14-2004, 08:10 AM
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Should be OK. Ford didn't use a panhard bar till they went cross steer, then it was added to prevent bump steer. On a drag car, the transverse spring and short (stock type) spring shackles should keep everything on the straight and narrow.

Another thing I tried was the early Ford Pinto steering shaft to rack. This is built like a big speedo cable and worked well on the drag car. Tho on a street car I think it would eventually unwrap and fail over time and use. As it wasn't really designed to flex as much as the suspension travels.
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Old 06-14-2004, 11:11 AM
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YOu can do just about anything you can think of but I have one question; Why after going to all the trouble of installing a straight axle for a nostalgia look would you install a R&P, which isn't nostalgia, instead of the proper Corvair?
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Old 06-14-2004, 04:59 PM
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Well. that's a good question. Question back to you: If rack & pinion steering had been as available in the 60's as it is now, would more racers have used it?
I concede that R&P steering is not authentic Gasser equipment. But neither is a lot of other speed equipment.
Now don't get me wrong. I'm not trying to build a case FOR R&P on a straight axle. I'm looking for the opinions and experiences of those that have gone before me. Getting past the appearance aspect, which setup is going to offer more safety, consistancy, ease of maintenance, and affordability?
My mind is not made up. That's why I'm here. You all have good info, and I'm looking for as much as I can get.

Murff
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Old 06-14-2004, 05:13 PM
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There were a few attempts at using R&P w/ straight axles in the mid-late 60s. It becomes a little problematic since a straight axle moves up and down and back and forth with parallel leaf springs so the steering shaft on an axle mounted system is more complicated, having to telescope and articulate. Plus an axle mounted gear adds un-sprung weight which is frowned upon.A frame mounted gear has its own problems. The axle going up and down is different from A-arms since the latter swing in an arc nearly the same as the arc transcribed in the R&P steering arm. The straight axle goes straight up and down while the R&P steering arms swing in an arc, changing the geometry of the front end => bump steer, tire wear?

Conversely the good old drag link system is very simple, rugged and can handle parallel and transverse spring systems fairly well.
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Old 06-14-2004, 05:21 PM
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Just a few comments.

I like the idea of the 'Gasser' look. If you are going for street only, then I would opt for the new rack & pinion that recently came out to fit in place of the more commonly used Vega. It appears to be a well thought out unit. I have no experience with that unit at this time though.

I am against attaching a rack & pinion directly to a straight axle. Although this is formerly the only way a rack & pinion could be used with any success, I believe it puts the straight axle in a bind and would limit the way a straight axle ('I' beam style) is designed to work. Watch what the axle does when the brakes are applied. Best seen on a fenderless vehicle. A straight axle bends and twists when braking, hitting bumps, turning, etc. much like a torsion bar.

If you are going to drag race the car as well as use it on the street, I'd opt for a more traditional side steer box. I prefer the '56 Ford F-100 box over all others.

Good luck with whatever you choose and show us some pictures please.
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Old 06-14-2004, 05:49 PM
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Willys36 & Frisco -

Good points both of you.

The axle I'm using will have the transverse spring, not parallel and a 4 bar radius rods. Wouldn't this setup, with a rack mounted to the tube be inclined to NOT rotate under braking?

It would seem to me that the 4 bar would minimize rotation, and that the bigger issue would be in the axle "falling away" on launch.

And this is going to be race only, no street. Only (planned) turns will be in the pits & return road.

Frisco, I have looked at the Vega replacement rack setup that Unisteer offers. Not a bad looking piece, but if I do end up going with traditional cross steer I will more than likely use the Corvair unit.

Willys36, I saw a polished reversed Corvair box in the classifieds here for $250. Is this a decent price for that piece? I'm really not interested in the polish. The car is going to remain black suede so shiny stuff is not much of a consideration.

Murff
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Old 06-14-2004, 07:07 PM
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Quote:
Originally posted by Murff


The axle I'm using will have the transverse spring, not parallel and a 4 bar radius rods. Wouldn't this setup, with a rack mounted to the tube be inclined to NOT rotate under braking?

The twist occurs from the area of the axle where the radius rods mount, outward and the axle ends and the spindles twist noticeably on hard braking. This is normal and not seen on full fendered cars (because of the fenders). Pretty scary though the first time you see it. With the rack & pinion shaft ends attached to the spindles and the main body of the rack & pinion rigidly attached to the axle, the tie rod ends have to allow for this twist. They are designed for some twisting, but some gets transferred to the shafts and in turn to the main body. Since the main body is rigidly mounted it resists the twisting action. Is it safe? Probably, for your application. Does it also restrict the normal twisting of a straight axle? You betcha! Not what you want to hear I think; but my honest opinion based on what I've seen.

Still like to see some photos.
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Old 06-14-2004, 08:19 PM
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Well, it's beginning to look like the rack idea is falling off of the grid.

And once again I was showing my ignorance and talking out of my hat. Cross steering would be a Vega box while the Corvair would be from the drivers side, correct?

Sheesh.

Murff
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Old 06-15-2004, 12:15 AM
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Quote:
Originally posted by Murff
Willys36, I saw a polished reversed Corvair box in the classifieds here for $250. Is this a decent price for that piece? I'm really not interested in the polish. The car is going to remain black suede so shiny stuff is not much of a consideration.

Murff
That's WAY too much. Get a stock 'vair box and reverse it yourself. Should be able to do it for $50 -$100, max. Reversing the box consists of boring a 7/8" hole in the pot metal screw on cap, putting a shaft seal in that hole, turning the input shaft around and putting a Welsh plug in the old hole in the aluminum body.
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Old 06-15-2004, 03:21 AM
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Quote:
Originally posted by Murff
Cross steering would be a Vega box while the Corvair would be from the drivers side, correct?

Correct for the Vega box and/or the new rack & pinion replacement.

Correct for the Corvair box if it is reversed as Willys explained.
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