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Technical Straight Axel Rack & Pinion

Discussion in 'Traditional Hot Rods' started by Buzoom, Dec 22, 2016.

  1. BamaMav
    Joined: Jun 19, 2011
    Posts: 4,867

    BamaMav
    Member
    from Berry, AL

    If you'll think about it, neither does the stock cross link on a straight axle, it goes up with the axle. I may be missing something, but it looks to me as both move in the same arc as the wheel end. The center steer rack allows for a tie rod that is almost half the distance across the axle, so it would react slower than the short tie rods of a conventional rack, but half again as slow as a full cross tie rod link.
     
  2. I've read a few threads about this only out of curiosity.
    Consensus is it can be done and work fine with the slip shaft.
    I still haven't seen anyone answer the question why??
    Look at the pic a couple posts up. Nice looking drilled straight axle. Love it. But then there's an ugly rack behind it?? I really don't get why?
     
    Montana1 likes this.
  3. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    langy
    Member Emeritus

    The rack allows far more precise steering really just by design, I would only do it on a fendered car as don't like the look but I guess it's horses for courses really, it's a very common modification here in England as our roads are so different to yours


    Sent from my iPhone using The H.A.M.B. mobile app
     
  4. I can see the benefits and the cons are there as well.
    I think the unisteer guys tried to get the best out of the benefits and leave the worst of the cons and then wound up with their own set of issues to be swallowed in a compromise.

    The biggest down fall of the idea here is trying to adapt a production steering rack specifically designed for a completely different type of set up and intigrated into another specifically designed type of set up and the two are completely different. All of What's needed is rotational direction transferred into linear.
     
    RICH B and pitman like this.
  5. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,227

    Ned Ludd
    Member

    Parallel to the ground isn't really pertinent, but it's a good basis to set up from. The critical thing is that the crosslink in a cross-steering set-up has to mimic the movement of the Panhard bar as closely as is practical. That's why I advocate using one tie rod only from the rack, plus a conventional tie rod linking the spindles, plus a Panhard bar.
     
  6. TR Waters
    Joined: Nov 18, 2006
    Posts: 1,439

    TR Waters
    Member
    from Vermont
    1. Early Hemi Tech

    People keep asking "why?". Why a crate engine? Why a T-5 trans? It goes on...and on....and on...........:confused:
     
  7. gnichols
    Joined: Mar 6, 2008
    Posts: 10,969

    gnichols
    Member
    from Tampa, FL

    I'm planning a rack on a dropped axle for my next build, an A coupe. I'll be using the lightest rack I can find, like a Sweet or Stiletto, with enough throw. It will be connected via a slip joint to a small, frame-mounted power servo in order to keep as much weight off the axle as possible. Since the car will have an I-4, I don't expect much of a problem rigging up the entire steering system - getting around motor mounts or headers - as the intake is on the left side of the engine. The reason why you say? Racer-ish stuff I dig (some Indy cars used this back in the roadster days) and of course there would be no bump steer. And then there'd be less crap out in the wind than cowl steering (though that may be my fall back design Walter Mitty Wanna-B racer wise). I also figure that getting rid of the extra cross steering link, the steel steering arm, at least one tie rod end, and that boat anchor Vega box can but only help a little in both overall weight savings and also really help to unclutter the front of the frame around the engine. Gary
     
    Ned Ludd likes this.
  8. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 8,210

    theHIGHLANDER
    Member

    That "why?" thing? Probably this answers why we ask "why" (thanks to "The Old Motor")
    [​IMG]
     
  9. RRichFox
    Joined: Nov 15, 2016
    Posts: 63

    RRichFox

    I don't know nearly as much as most of the people who answered you here already. But I do know I used a Pinto R&P on this car in '78 and it is still on the car and works fine IMHO.
     

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    grumpy32 and AHotRod like this.
  10. Thanks gnichols, for sharing some real reasons why. May not be something I'd ever choose but I see your way of thinking. Crate engines and T5's have obvious advantages.
     
  11. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,640

    thirtytwo
    Member

    I've put uni-steer in a couple good vega boxed cars , I felt very little difference , I think people might imagine a big difference after spending all that money on the setup (placebo effect?)

    I suppose if I was trying to go 70 mph through some switch backs and twisty roads I may feel different , but I think if that's what your shooting for , a transverse spring axle car may not be your best choice either
     
    shawnsauto1 likes this.
  12. gnichols
    Joined: Mar 6, 2008
    Posts: 10,969

    gnichols
    Member
    from Tampa, FL

    Makes sense, 32, as I don't think there is any fundamental difference between Vega cross steer and Uni-Steer'd cross steer. IE no improvement. Gary
     
    shawnsauto1 likes this.
  13. iafraser39
    Joined: Aug 2, 2009
    Posts: 163

    iafraser39
    Member
    from Warmland

    I'm using a unisteer rack in my 28 model A RPU. Powered by buick 401/425 nailhead and a st400sp. work fine, had nothing but trouble with the vega clone. No bump steer or road shock and its just like power steering.
     
  14. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,227

    Ned Ludd
    Member

    Racks are fairly light, so I don't think unsprung mass is a deal-breaker in the scheme of things. Nor are the slip-joint/packaging issues insurmountable. My main concern with the rack-on-axle arrangement is that relative roll movement at the front axle is transferred to the steering wheel.

    Even a roll-stiff, high-performance chassis tune might see 3½° of roll at the limit of adhesion. That translates to about ½" of movement at the steering wheel rim. More pedestrian states of chassis tune will produce greater steering wheel movement because the greatest anticipated roll angles will be correspondingly greater. (Likewise, if warp stiffness is decoupled from front-axle roll stiffness there might be situations where front axle roll movement exceeds overall roll by a substantial margin.)

    My question is, does it really matter? Or do you learn to anticipate the difference between body roll and steering angle, so that it still feels right? Indeed, does this difference not make it easier to get a feel for body roll? Or does negotiating bumpy curves at speed cause all kinds of bump-steer effects originating in the position of your arms relative to the seat? I couldn't say. What has been your experience, Langy?
     
    Last edited: Jan 1, 2017
    langy likes this.
  15. toxic waste
    Joined: Dec 18, 2011
    Posts: 383

    toxic waste
    Member
    from Iowa

    What works the best is a Ford pinto rack and pinion and the Ford pinto steering flex shaft . This works great with no wear problems.
     
  16. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    langy
    Member Emeritus

    I never noticed much roll in mine as I fitted a sway bar on mine which kept it pretty tight in the bends, I never encountered any bump steer of any kind, i was aware to it when I set it up correctly in the first place.


    Sent from my iPhone using The H.A.M.B. mobile app
     
    pitman and Ned Ludd like this.
  17. tj
    Joined: Aug 19, 2006
    Posts: 501

    tj
    Member

    Have a unisteer on my 33 - it's ok but loose steering radius. Had a 525 on my 36 and loved it. Would prefer 525 over the Vega.
     
  18. Loss of turning radius is easily corrected, see post 21 first page
     
  19. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248

    Hackerbilt
    Member

    I used one once on an off topic car. Did what it needed to do.
    Since that time I've heard they were very unreliable and not approved by any sanctioning body in motorsports.
    Besides...they don't do anything some DD shaft and U-joints (or the Pick a Part equivalent) can't do just as well.
     
  20. RRichFox
    Joined: Nov 15, 2016
    Posts: 63

    RRichFox

    That is what I have on my 32 pictured on page 1. SCTA didn't like it, but I pointed out the millions of Pintos running around. Bumping curbs. Hitting pot holes. And never heard of a failure. After I retired the car from SCTA events and took it to the nostalgia drags SCTA banned them from further use. Never heard a solid reason. They just didn't like the look of it, I guess. Still on the car 38 years later.
     
  21. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248

    Hackerbilt
    Member

    I'd say if its mounted almost straight it should be good.
    Once you go to some angle its in a constant bind and always working those flexible little wires against each other and that unforgiving crimp on either end.
    Once a few start to break the failure of all the others still stressed will ramp up.
    Ultimately though, I would say the big issue might be not KNOWING when you are approaching total failure!

    A U-joint will bind/click/pop/rattle etc as it gives out. A slip joint will also rattle and give some noticeable play.
    I doubt either will happen with a twisting cable.
    You likely won't know its gone till your going off the road...
     
  22. toxic waste
    Joined: Dec 18, 2011
    Posts: 383

    toxic waste
    Member
    from Iowa

    Just do it right and don't use a R/PM on a straight axle. All around a box would be better .
     
  23. RRichFox
    Joined: Nov 15, 2016
    Posts: 63

    RRichFox

    Yeah. I remember all those Pintos going off the road because the flex shaft failed. Sometimes I would see two or three on the way to work. I should add that I mounted my R&P behind the axle, as I thought in front was ugly. This required a reverser box so that the steering wasn't backwards. I used oil return pump gears from a CF6 General Electric engine that had been removed and replaced. Had a lot of them available at the time. Mounted solid to the frame at the bottom of the steering column. At the same plane as the rear of the hairpins. So the flex shaft would move in the same arc as the hairpins and axle. Otherwise some of the wear speculated about above may have been a concern. But it seemed common sense to do it this way and lacking learned persons to tell me it would not work. I just did it. So far so good.
     
  24. RRichFox
    Joined: Nov 15, 2016
    Posts: 63

    RRichFox

    PS. The current blue roadster has Franklin steering. Now that is traditional. I'm sure some one can tell me why it's unsafe.
     
    grumpy32 likes this.
  25. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248

    Hackerbilt
    Member

    Don't be a smart ass Rich.
    I hold you to a much higher level and I wasn't challenging you anyway...just making an observation. ;)
     
  26. RRichFox
    Joined: Nov 15, 2016
    Posts: 63

    RRichFox

    Fair enough. But how many if any, Pintos have you heard of having a failed steering shaft? I don't remember any. I remember the gas tank fails. And we all remember the Audi throttle auto WOT stories. Corvairs falling over all the time. But the steering shaft fails are some thing I hear conjecture about a lot. But not examples. Since I had one, I became sensitive to what seemed unfounded repeating of something that could happen, but I never saw. You, yourself used one with no poor results. But you heard someone say that they heard some one say that they heard it was unsafe. So it must be true. Or maybe you have actual knowledge of a failure. In which case I welcome you sharing your experience.
     
  27. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248

    Hackerbilt
    Member

    Nope...definately no first hand knowledge of failure.
    I heard grumblings back in the 70's about them having issues but no personal experience.
    I do have concerns...just from the fact that Ford discontinued its use (in a vehicle they made for 6-7 more years) after just 2 years.
    Also, the banning from various Sanctioning bodies is a concern, especially when you consider just how much more use a road car gets compared to a competition car.
    Another thing is, Pintos were using little 13" tires so there wasn't a whole lot of stress being transferred thru the cable to start with.

    A big question mark for me as well is very simple and doesn't involve physical structure at all.
    A flexible cable type of steering connection, IF it works reliably and for as long as we would like, would be extremely cheap to supply and manufacture.
    No forged yokes...cross shafts...roller bearings...double D shafting...support bearings. Nothing....except a steel cable crimped into some tube.
    Inexpensive as dirt.

    Yet nobody that I know of in the aftermarket duplicates it.

    Are they afraid to jump on that boat???
    Seems like it...and I'm not at all sure why, so thats a big concern.

    Bottom line...just because you and I got away with it 1 time each is not a good reason to recommend it to the masses. :)
     
  28. Fordors
    Joined: Sep 22, 2016
    Posts: 3,540

    Fordors
    Member

    Just like with a u-joint you can exceed the recommended angularity. IIRC Borgeson says no more than 30* and though I've never seen a spec on the Pinto flex coupler too much of an angle can't be good for those either.
     
  29. CraigR
    Joined: Jun 20, 2008
    Posts: 375

    CraigR
    Member
    from California

    RrichFox - I'm sure you used the Pinto piece sensibly and as such it's lasted, though I have personally seen a Pinto cable shaft fail - but not in a Pinto. I believe Ford stopped using them in the Pinto due to possible failure concern, but I think they were more of a vibration damper, not being used change the angle of two shafts in place of a U Joint?
    However the one I witnessed was being used in place of a U joint in a Model A tourer at the base of the column to enable a 30 or so degree angle change to the intermediate shaft. Customer stopped at the shop concerned about the fraying and wanted to see about replacement options and make sure it was safe to take his family out in that weekend. I couldn't believe how bad it was frayed. Because he'd driven it there he didn't seem to worried about how bad it was until I spoke to the boss about having the guy sign something to the effect that we advise him not to drive it any further. That freaked him out enough that he decided to limp it into the shop & leave it there. It didn't even make it that far! As soon as he tried to move it from the spot he'd parked it in the last wires cried 'enough'. Borgeson to the rescue!
     

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