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straight axle w/ rack and pinion

Discussion in 'The Hokey Ass Message Board' started by mrconcdid, Mar 6, 2013.

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  1. mrconcdid
    Joined: Aug 31, 2010
    Posts: 1,157

    mrconcdid
    Member
    from Florida

    OK guys, no drama. I saw a frame mounted rack and it caught my eye, I ask a direct question and through the bickering it got answered. Thanks for the information and insight
    godspeed
    Mrc.
     
  2. ken1939
    Joined: Jul 5, 2008
    Posts: 1,558

    ken1939

    The problem with that rack unit you can buy to replace your vega box is you will have less lock to lock due to the design. I have a freind who has it on his 32 roadster and hates it. turning radius is bad.

    I would go Mustang or Vega. I would love to have a real rack up front for the control that everyone spoke of, but there is alot of extra engineering to make that happen with a real full rack unit.

    My next build will probably get a mustang with traditional steering.
     
  3. Must be a full moon! There's a lot of it going around today. ;)
     
  4. bobw
    Joined: Mar 24, 2006
    Posts: 2,368

    bobw
    Member

    Ok, like Billy Joel said, "I didn't start the fire", I just wrote about what I built and how it has worked for me.
    I spent 34 years working as an engineer, maintenance manager and mechanical & electrical engineering manager. As a result, I'm very disciplined in the work I do, the way I build. When coming up with an approach to something that is atypical I analyze the system, do several mock ups, test, change, etc. My installations are not willy nilly, shoot from the hip systems.
    Metalshapes, you have every right to think I am wrong, in spite of the facts I've presented. Your opinions and conjecture are yours, and it's obvious you passionately believe what you are saying. No need to apologize for the insult, you've done it to me before. I figured if I offered my experience on this thread I would take one or two across the bow from you.
    Yes, I think it's best if the overwhelming majority of the car builders on the HAMB use tried and true components and designs. The blueprints for traditional hot rods are well established. Stick to them.

    Weld on, boys.
     
  5. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,698

    metalshapes
    Tech Editor

    I could care less about what you do on your car.

    Its obviously wasted effort to try and change your mind.

    But maybe one or two people that that would try this on your recommendation can get some food for thought before they do.

    That is enough of a goal...
     
  6. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?
    Member

    Either way, on the axle or even worse on the frame isn't an obviously bad enough idea just looking at it? I mean really it's just chassis geometry 101A. Draw it and look.
     
  7. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,142

    Mr48chev
    ALLIANCE MEMBER

    Both Hotroddin and Metalshapes gave excellent explanations of why that is a terrible idea.

    As basic as I can make it the Rack and pinion is designed to work in conjunction with an independent suspension. The tie rods between the ends of the rack and the steering arm on the spindle are of an equal length to the lower control arm so that they move with the lower control arm. That is the way steering linkage is designed on all independent front ends and it works on them.
    With the I beam axle the whole axle goes up and down as a unit. When you mount the rack and pinion on the frame the tie rods work to pull the steering arms in and push them out changing the toe in constantly as the vehicle negotiates the streets. This causes the bump steer. Meaning that you drive down a road your tires are constantly changing toe in and not only causing bump steer but eating the tread off the tires in the process.

    If you can't comprehend that concept maybe someone with cad can actually draw up diagrams to explain it. It's past my bedtime as I have to get up at 03:00 to go to work.
     
    Last edited: Mar 6, 2013
  8. bobw
    Joined: Mar 24, 2006
    Posts: 2,368

    bobw
    Member

    You don't mount the R & P on the frame, you mount it on the axle. Mounting it on the frame can be deadly. That's just chassis engineering 101A.:)

    Hey, I wouldn't even try to change your mind, MS. I don't care if you don't care what I do with my car. Never said I did. I'm way beyond caring about what you think. I do know that you are an experienced and talented builder. Just maybe you don't know everything, eh?

    My only mission here is to inform the readers of this thread of what I've done and how it worked. If that inflames you, sorry.

    Guy asked about mounting a r & p on a straight axle and I cited my experience. If it hadn't worked well for me I would have posted that.
    [​IMG]
    Another POS with a R&P mounted on the axle.
     
    Last edited: Mar 6, 2013
  9. n.z.rodder
    Joined: Nov 18, 2008
    Posts: 1,016

    n.z.rodder
    Member

    Here's another Don't DO It. It's actually illegal here in N.Z. to have a R&P on a solid axle. You will never get it on the road it's so dodgy.

    Scotty.
     
  10. Halfdozen
    Joined: Mar 8, 2008
    Posts: 612

    Halfdozen
    ALLIANCE MEMBER

    Nice looking car, seems to have a very long pitman arm outside the cowl- wrong pic maybe?

    Far too many people build a front end setup without having the necessary knowledge. Generally, the combination of a straight axle and a rack and pinion is easier to do badly, than well. When mounted to the axle, the height, and fore and aft location of the rack in relation to the outer tie rod ends is also critical, not to mention the considerable increase in unsprung weight.

    bobw, what did you use for the telescopic coupler that joins the steering column to the rack?
     
  11. bobw
    Joined: Mar 24, 2006
    Posts: 2,368

    bobw
    Member

    Darn! I blew any credibility I might have had by posting the wrong pic.:rolleyes:

    Halfdozen, I have used a few different shaft/spline arrangements. But I like the double D shaft and sleeve with 6" of engagement. It only moves in and out about 3/8" on bumps so it retains lots of engagement. If you visualize a torque tube rear axle moving up and down the spline on the u-joint at the transmission output shaft moves in and out. Usually not more than a inch. It doesn't bind even with the torque of an engine being applied and taken away in rapid order. A straight axle might move as much as 2" up and down, generally not more than that, so with proper alignment of the rack's pinion to the steering column and correct placement of a u-joint(s) the in and out movement in minimized. The torque you apply to the steering wheel with your hands is much less than what a non-binding slip joint on an transmission output shaft sees, so not much chance of a rotational bind. The rack is parallel to the axle and placed in the same location the original tie rod occupied.

    Please note: I did not suggest that anyone do this. I merely told of my experience. If you live in NZ or anywhere else this modification is illegal, don't do it. If you are unsure of how safe it is, don't do it. If an expert tells you it is stupid and anyone that does it is stupid and is sure to die in a wreck, and you trust him, don't do it.

    There's really no advantage to using a R & P on a straight axle compared to tried and proven steering setups. Again, at the beginning of this fiasco I never said there was nor did I suggest anyone do it. This is a set up that I found interesting and wanted to see how it worked. If it wouldn't have worked for me I would have cut it off and followed the herd.

    If you have steel wheels and drum brakes, a heavy Deuce axle the contribution to unsprung weight by the R & P is pretty low. Remember, it replaces a tie rod and a drag link on cross steer set ups. So there's some weight offset there. Unless you are building a cute little light weight sporty car the unsprung weight addition shouldn't be noticeable. Again, if unsprung weight is a concern for you, don't do it.

    My Fiat pictured back a ways no longer has the straight axle/rack set up. It now has a home made A-Arm front suspension and a 3 link with a Watts link in back. I won't be putting that up for inspection here.:D

    The chassis that was under the Fiat is now under a 406 sbc powered Crosley station wagon.

    I guess I'm lucky to still be alive, doing all this crazy stuff.:)
     
  12. Wow, seems like we go through this discussion every couple of months. Like anything dealing with steering or brakes, not knowing what you are doing can very likely get you (or worse, someone ELSE) killed. Rack on axle is a great way to be different, but unless you're trying to solve a particular space or geometry problem, why bother? It's definitely not "traditional"....

    Over the years I've built a LOT of rack on axle setups for race cars. The sliding shaft deal isn't the greatest, but I've found that the old Datsun Z car splined shafts are tough as nails. Lately I've gone to the under-dash shafts from BMW sedans as they are easier to find and sealed up better.

    The trick is to anchor the shaft (heim mount) and place a u-joint at a point where the shaft arc will closely follow the motion of the suspension. This minimizes any sliding motion. Our cars have close to 30" of front tire (no kidding) and pull around 3G in a corner, so there is plenty of load on the steering system. They are ALL rack on axle design, and failures are very rare and usually due to improper maintenance. Keep an eye on the splines, clean and re-lube them regularly, and don't make them work harder than they have to.

    The photo is NOT one of my builds, but it shows the relative geometry I was referring to.
     

    Attached Files:

    Last edited: Mar 7, 2013
  13. And how much Wheel travel do they go through? What concerns me about this design for the street is 4, 5 or more inches of wheel travel, with rapid movement, especially when hitting real world junk like a big pot hole causes quite a bit of movement of the axle. That mean more spline movement, but also the axle will move the location of the shaft that i would think would cause quite a bit of steering wheel movement in turn.

    Not arguing - Asking :D
     
  14. mrconcdid
    Joined: Aug 31, 2010
    Posts: 1,157

    mrconcdid
    Member
    from Florida


    I saw this pic (cropped out the car on purpose) and was wondering how it worked?
    Since I am the OP, this seems to be the answer I was looking for. All this other B.S. is just that.

    There maybe differs of opinion on this subject but I can clearly understand the 2 different paths of the tie rod vs the axle take.

    Thanks
    Godspeed
    MrC.
     

    Attached Files:

  15. MrC,
    We are all trying to give you our best information, and yes everyone has an opinion. Here's mine... That setup in post 44 is the WORST possible way you could set up the R&P. Note that each tie rod connects to the knuckle independently (no cross tie rod). As the axle moves up and down, both tie rods will move in an arc, but the wheels are moving vertically, so you will have constant toe-in change throughout as the suspension cycles.
     
  16. Ford Freak
    Joined: Jan 5, 2005
    Posts: 826

    Ford Freak
    Member

    ^^^What he said x2^^^
     
  17. pitman
    Joined: May 14, 2006
    Posts: 5,026

    pitman

  18. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?
    Member


    Sorry, I know I sounded a bit short in that answer, but it's something that is asked over and over, and the answer will always be the same.

    I went through this deal with a good friend up in Washington about ten years ago. He asked the same question you did and I said "NO". I explained exactly what I did to you, and low and behold a month later when I got up there - there it was - a rack mounted as you described! He said "See, it works"! Without saying a word I stepped up on the frame and started bouncing up and down. As I did you could see the tires toeing out by at least a half inch with each compression and rebound. We cut it all off and set it up with a steering box the next day...
     
  19. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,142

    Mr48chev
    ALLIANCE MEMBER

    MrConcid, sometimes we come off as a bit harsh but if you were to read posts by Hotroddin, Metalshapes, Need Louvers ? Exwestracer and myself on other threads and there hundreds to read the one thing you will find is that we all advocate building safe cars that people can actually drive. A couple of them have shops where top rate work is done daily another has a long background in racing, I'm just a former shop teacher who spent a number of years before that as a front end alignment specialist.

    Right now there are more guys throwing straight axle "gassers" together than there was in the 60's in the heyday of the straight axle gasser. Just as there was then there is a lot of suspect work done now and the vehicle in your photo is a prime example of that.
     
  20. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    langy
    Member Emeritus


    I've fitted quite a few axle mounted racks, if you set them up correctly and use a Jaguar steering UJ they work brilliantly and you do not need a slip joint, you have to see a Jag UJ in operation to understand how well it works.
     
  21. Best advice would be to always follow factory (any factory, not just the brand you are building). They hire engineers who are trained in the proper manner, and lawyers to make damn sure it don't break.

    Ask yourself: Has there ever been an R&P setup on a solid axle, and you'd find out, no, there has NOT been. EVER.

    Next, draw it out. Make it move. See how wrong it is on a physical level.

    Why do people do it?? Lack of proper training and way too much hubris.

    How do they get away with it?? Simply put, they lie. Just like your buddy tells you he gets 47 mpg in his Tahoe, Hot Rodders lie about how nice (or not) their car drives. The ultimate clue is: ask them to let you drive it. They won't.

    Lastly, lack of suspension travel (common in oversprung solid axle cars) masks bump steer by the simple reason of no suspension travel = no bumps.

    Cosmo

    P.S.
    No, I DON'T believe your car is OK with a chassis-mounted rack. No amount of empirical evidence will ever prove this right, and there exist no engineering drawings to prove otherwise. The whole concept is wrong on a basic engineering level.

    P.P.S. The first racks were installed in 1936 on Citroën Traction Avants. Just in case you were wondering if the technology were concurrent. It was.
     
  22. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,698

    metalshapes
    Tech Editor

    I did a quick Google search, and found some pics.

    Yes, that would solve it...

    Thanks Langy.
     
  23. willymakeit
    Joined: Apr 13, 2009
    Posts: 1,326

    willymakeit
    Member

    Can you post a picture? I looked it up but would like to understand it better.
    Thanks in advance.
     
  24. special-k
    Joined: Mar 24, 2009
    Posts: 45

    special-k
    Member

    Cosmo you better never look up Freightliner R&P mounted on front axle on google or you'll find that a major company DOES use it. I would think a company that makes equipment that weigh many thousands of pounds and has lifespans of millions of miles would have found it to be safe alternative.
     
  25. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    langy
    Member Emeritus

    The people that say chassis mounted rack doesn't work are quite correct but a axle mounted rack works brilliantly if set up correctly.

    I will have a look for a pic but basically it's the UJ fitted to the early xj's but all the early Jags have them (xk's for us market I believe) the UJ is there to absorb movement in the rubber mounted subframe, the UJ sort of moves in and out therefore getting longer or shorter, it has around 1" of travel before it becomes out if round.
    If the column input is set fairly horizontally there movement will be less than half an inch.
    I had this on my old 29A Coupe that i ran in the 1980's, It had a Ford Escort rack mounted on a dropped tube axle, this car would run reliable 10.6 quarter miles and I did a shootout for a magazine where it went through a slalom course 5 or 6 seconds faster than any other car, it handled brilliantly when you consider it was a pro street street & strip car.



    [​IMG]

    [​IMG]

    [​IMG]
     
  26. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    langy
    Member Emeritus

    I found a pic of the Jaguar steering UJ.


    [​IMG]
     
  27. There is a world of difference between CHASSIS mounted and AXLE mounted.

    You missed it.

    I didn't

    Cosmo
     
  28. willymakeit
    Joined: Apr 13, 2009
    Posts: 1,326

    willymakeit
    Member

    Ah Ha That makes sense. Thanks
     
  29. jtm_elcamino
    Joined: Feb 17, 2013
    Posts: 43

    jtm_elcamino
    Member
    from Uvalde Tx

    a friend of mine is diong this setup on a 48 chevy rat rod. ill get some pics of it and see how hes doing it
     
  30. Heny Young
    Joined: Jul 25, 2019
    Posts: 1

    Heny Young

    First timer here. Your insights are indeed food for thought and the result has saved me from potentially making a poor desision! Thanks to every0ne; both pro and con.
     
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