1. 11.2

    11.2 Well-Known Member

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    I bought a longacre gauge and tried it out today. I’m either doing something wrong or I have an issue. Here’s my findings. Seems pretty basic but maybe I’m buggered up.

    - Passenger
    - Compression.

    .5” .055.
    1”. .090.
    1.5” .115.
    2.0” .150

    Drivers
    - compression.

    .5” .050.
    1” .095.
    1.5” .110.
    2” .200
     
  2. AJ/FormS

    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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    Is that set at the factory ride height?
     
  3. 11.2

    11.2 Well-Known Member

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    I can’t answer that at the moment. I will check tomorrow though. It’s crazy, My toe changes enough that you can see it when you put a straight edge on the rotor. It’s toed in at full compression and toed out at full droop. And the longacre gauge confirms that.
     
  4. 11.2

    11.2 Well-Known Member

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    And FYI. the droop measurements are very similar to compression
     
  5. AJ/FormS

    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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    What parts have you changed?
     
  6. 11.2

    11.2 Well-Known Member

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    Pretty much everything. Stock k member, tubular uppers ( cap ), boxed lowers, firm feel box, 11/16 tie rods, hotchkiss strut rods. Stock spindles. I have a set of hotchkiss uppers I’m going to install eventually but I don’t think they will change bump steer without their bumpsteer kit.
     
  7. AJ/FormS

    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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    Well that's it then. If you changed your caster/camber settings from stock, then you are guaranteed to have introduced the bump steer, guaranteed.
    Sit down, have a beer; you got some work to do, you can't drive it like that.
    Here are some helps;

    Technical Articles
     
    Last edited: May 10, 2020
  8. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    For comparison, this is a car lowered 1" with stock spindles...
    Screen Shot 2020-05-10 at 7.01.29 PM.png

    It's pretty hard to read, the original chart is listed here as well as a chart for the B or FMJ spindles https://www.hotrod.com/articles/mopp-0503-swapping-a-and-b-disc-brake-spindles/

    With numbers like yours there's something pretty dramatic going on. You should be able to lower the car and change the caster and camber pretty significantly without inducing numbers like that. When you were installing those suspension parts did you also replace the lower control arm bushings? Check the K frame for cracks or damage, especially at the LCA pivot tubes? What procedure did you use to determine the length on the adjustable strut rods?

    As for the CAP upper control arms, those things are garbage. If your plan is to run Hotchkis UCA's, install those before you put it back on the street. CAP UCA's have failed catastrophically due to poor welds.

    Do you have your current alignment numbers?
     
  9. 11.2

    11.2 Well-Known Member

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    Last season I found a crack in lca at pivot shaft. I repaired, welded k frame and new lca bushings. I’ve had the cap uppers for over ten years and 20,000 miles, so far so good but yes, plan is to change to hotchkiss. I didn’t do the alignment/ setting of the strut rods, I had a shop do that.. is there a way to check without alignment machine ?
     
  10. brian6pac

    brian6pac Well-Known Member

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    You need to move the outer tie rod up, and to do that you need to lower caster or raise the front of the car. here is a chart from a mopar racing manual and you should read the whole manual to figure out what to to and how to do it. This page is the opposite of what you have I believe but you will get the idea.

    img500.jpg
     
    Last edited: May 11, 2020
  11. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    Oh boy. Did you specify what the alignment settings the shop should use? Are we talking about a shop that does custom alignments and suspension work or a tire shop? Most places that do alignments these days will only set the specs that are in the computer, and wouldn't have the foggiest idea what to do with an adjustable strut rod.

    You don't need a machine to check your alignment, but you will need some kind of caster/camber gauge. A set of toe plates would be handy too, but not necessary. If you have a nice smooth concrete floor and some dish soap you can get by without a set of turn plates.

    You're jumping the gun, without knowing what his caster is even set at or how the length of the strut rods was adjusted telling him to change the ride height and caster is completely premature. Suspension parts have been repaired, aftermarket parts have been installed, there are a lot of things that could be contributing to this issue.
     
  12. 11.2

    11.2 Well-Known Member

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    I don’t know the exact alignment specs but they are somewhere in the range of
    Toe in - 1/8
    Camber - negative 1
    Caster - positive 5

    I don’t know the method used setting the strut bars. My plan is to find out how to set strut bars, double check alignment and check bumpsteer again.
     
  13. brian6pac

    brian6pac Well-Known Member

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    There you go caster is way too high
     
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    • brian6pac

      brian6pac Well-Known Member

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      If you read what I said that he needs to read the whole front suspension racing manual to understand what he needs to do and how to do it.
       
    • brian6pac

      brian6pac Well-Known Member

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      72bluNblu
      You can disagree all you want but the fact is when you change caster you change the height of the steering arm and that is what changes bump steer. I have never seen a mopar with a alignment spec that even comes close to +5* caster. I don't even know what kind of car he has so I can't tell him exactly what to do but the theory is the same for all.
       
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      • 72bluNblu

        72bluNblu FABO Gold Member FABO Gold Member

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        Ok, so if those are the actual alignment numbers the shop that set them might actually know what they're doing. Again, what kind of shop is this? What did they say about installing the adjustable strut rods?

        Has the ride height of the car been changed at all since you had the alignment? Because that changes the settings.

        The process for setting the length on the strut rods is actually pretty much the same as checking the bump steer. Remove the shocks, remove the torsion bar adjuster and plates so the suspension can travel through its full range of motion bump stop to bump stop. Then raise and lower the suspension through its range of travel, seeing if there is any binding or resistance as you go. If the strut rod is the right length the suspension will move up and down freely, especially through the middle of the range. As you get to the extreme ends of travel before you hit the stops there may be some additional resistance, especially if you have rubber LCA bushings as the rubber in those is twisting to allow the LCA to move. If there's binding everywhere the strut rod is the wrong length. And if it's binding a lot at the extremes of travel its probably the wrong length. You want to start with the strut rods set so the LCA is perpendicular to the frame rail, if it's pulled forward or pushed back the strut rod is the wrong length. The goal of setting the length of the strut rod should be no binding of the LCA through its travel. Adjusting the length of the strut rod does change the caster setting, but changing the caster setting shouldn't be the goal of adjusting the strut rod, that should be binding.

        Only for a drag race car. If this is a street car with the intention of having better than stock handling it's just about perfect.

        Oh BS. The front suspension racing manual is for drag racing. Pretty much everything it describes is for a drag car, NOT a street car, and some of what it describes would be the WRONG way to set up a street car. I mean seriously, /6 torsion bars, checking the toe pattern at 1" raised suspension so it's the same as through the traps, setting 0 toe to begin with, only checking the rebound toe changes. That's all great for a drag car, but none of it is applicable to a street car.

        Zero toe change is also pretty much impossible. That's one of those theoretical deals for designing suspension, it's not something you get in the real world. And not on a street car. Even the graphs they use in the manual aren't realistic. 4" jounce to 4" rebound? Explain how you get that on a car that only has about 5" of total suspension travel.

        And the front suspension racing manual doesn't cover what to actually DO about most of those changes.

        Mine has +6.5° of caster. It's not possible with stock parts but with aftermarket suspension pieces it's not that hard.

        When you run wide, modern tires on the front increasing the caster increases the stability of the car. All aftermarket UCA's have additional positive caster built in. Radial tires need more positive caster. The factory alignment specs are for bias ply tires, and are WRONG for radials.

        Most aftermarket tubular UCA's have an additional +2 to +3° of caster built into the geometry for that reason.
         
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        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          Well, Since we do not yet know OPs goals or application or even what car he has;
          I'll say this; having put 150,000 mostly street miles on my 68 Barracuda,IMO,
          3.5* caster was just fine; and .5* camber was just fine;And the 1.03 bars were just fine too.
          My car is a streeter, driving on the street, where I can never trust the road to be worth chit for traction, so there is a chitload of skating involved, often at both ends.
          When skating, the suspension relaxes and settles into skate-mode, and the only thing that matters is that you picked a decent line, with no obstructions or objections to where the car is going to end up, despite your best efforts not to go there. lol. At that point I might as well just be a curling stone, cuz I am more or less just along for the ride. This is what makes a streeter so exciting for me. Never knowing. Every trip is an adventure, every corner a dare, every almost crashed it; an OMG moment.
          If this doesn't happen to you,............... IDK, check your heartbeat, cuz I fear it mighta stopped.
          But in all those miles and all those hours, I never once stopped to ponder if I needed just a lil more caster, or a lil more camber, or a lil more tire.
          Well, not totally true;
          One time, just one summer,I wondered if a lil stickier tire would help me; one time, I wondered. Four weeks later, if that, those fancy tires were bald and gone, and the Barracuda was back on streets; and I never looked back at the time I spent on those stickies. Didn't even miss them. The only thing they helped, was to almost ruin my paycheck.
          The take-away for me was/is; It's way easier to correct bumpsteer at 3.5*, than at 5* on a system that was never designed to run more than ~1.5,lol.
           
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          • brian6pac

            brian6pac Well-Known Member

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            It really doesn't matter if it's a drag race car, a road race car, circle track car. The theory of bump steer is the same for all, that is all I am saying. As for 0 bump steer being impossible you are very wrong. I have set up my car with a rack & pinion out front and it has "0" bump steer through out the entire travel. I also set up the famous Red Alert Chevelle to "0" bump steer because they put a big oil pan on it and they bent the idler arm and pitman arm down to clear so we had to adjust the outer steering arms to match. My friend had a late model circle track car and they ran 0* left and 2* right side caster with a manual box, with a power rack they ran 3* and 5* and this was on a 1/4 mile and 3/8 mile tracks. I don't know why you think a drag race set up wont work on the street other than I run my camber at 0* Toe at 1/16" in and caster at around 3*, worked perfect for me on the street.
             
          • 72bluNblu

            72bluNblu FABO Gold Member FABO Gold Member

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            The term is literally "near zero bump steer". For most applications less than .030" is acceptable, for racing applications it's usually under .010". But neither of those are actually "0". Or 0.000”, because that’s what that would mean. Like when Ehrenberg talked about measuring bump steer with a piece of plywood and a piano hinge for the Green Brick article. Must be fancy plywood to be true within .010”.

            And of course the application matters. Reducing the bump steer is a lot harder if you have more suspension travel like with a street car. And there are always trade offs. Like running 0° camber with radial tires on the street is dumb. I'd rather have .030" of bump steer with -.5° camber than "0" bump steer with 0° camber, because if you have to go around corners you want your tire patch to stay parallel to the ground on the outside where the weight is, and 0° camber doesn't do that.

            Caster for narrow front tires like used in drag racing is different too. A couple degrees positive is all you need to keep you from feeling like you're driving a shopping cart. Put 275's up front and it's not enough, adding positive caster improves stability. Just look at the alignment specs for a modern car. A Challenger SRT8 calls for -.5° to -1.6° camber, and between +8° to +10° caster. Yeah, +10° caster. Yes, I understand that is not the same suspension design and it is designed to have those numbers. But the wide front tires are why those numbers are that high (they aren't specific to the Challenger, look at a modern mustang, or any other RWD modern car for that matter).

            capture-jpg.jpg

            So no, your drag set up is not ideal for the street. Not enough negative camber. Barely enough positive caster, dependent on what your tires are. And who knows what your ride height looks like, or if your torsion bars can keep your suspension off the bump stops with your average pot hole. If you're driving to Dairy Queen maybe that works, if you're going for a rip up the mountain in the twisty's it's piss poor.

            Regardless, bump steer is a moving target. Just saying "the caster is too high" is silly. Yes, caster changes the bump steer. So does the ride height. So does the camber setting. So can things like adjustable strut rods, repaired LCA's and K-frames, aftermarket UCA's, etc, etc, etc. The OP has made a lot of changes to his car from stock, and that's fine. He doesn't have to set the stock alignment to get his bump steer under control, he needs to investigate further, make sure nothing is broken/cracked/binding or installed incorrectly, and go from there.
             
            Last edited: May 12, 2020
          • GMachineDartGT

            GMachineDartGT Senior Member

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            That’s a lot of movement, but it’s in the right direction. Toe out on droop will help the inside wheel steer into the corner reducing under steer. I’d try dropping the outer mounting point.
             
          • 72bluNblu

            72bluNblu FABO Gold Member FABO Gold Member

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            Exactly! If you're going to have bump steer, better to have it in that direction.

            Like everything with setting up a suspension there are always trade offs. Sure, bump steer is bad in general and you want to minimize it as much as possible. But not having enough positive caster can be bad too. So can not having enough negative camber. And the camber curve matters too. Some of those things can be a trade off, it's a balancing act that changes depending on how the car is used, how it's set up, and even the preferences of the driver.
             
          • autoxcuda

            autoxcuda Well-Known Member

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            When I checked mine, I needed to remove spacers to make this 100% theorically perfect. But mine was allready at the lowest setting.

            Luckily, my numbers were very good. The circle track and road course chassis builder told me just to leave it.

            Edit: Just an FYI, 0.082" is only a little over 1/16" toe out at 3" compression. And 0.114" is only a little under 1/8" toe in at 3" rebound/extension.

            I run probably close to 4 TIMES the spring rate a drag car does with my 1.14" T-bar. So I might only see those 3" numbers in a few corners on a road course

            7590606-BumpSteer2_2_12Md1.jpg

            7780202-CopyofIMG_3582.jpg

            7590683-BumpSteer2_2_12Md2.jpg

            7590664-Hotchkis7_27_10TVSbuildSm29.jpg

            7590697-CorrectedBumpSteerChartLFInitial.jpg
             
            Last edited: May 15, 2020
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            • HemiDenny

              HemiDenny HDK Suspension FABO Gold Member

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              to get zero bump steer is a hell of a feat when dealing with three different arcs, especially with two of the arcs (LCA / UCA) being vastly different due to their length(s).

              I was always under the impression that the reason for raising the car when doing an alignment was because when ANY car is moving under power, drive-line torque causes the front suspension to raised slightly.....ballpark 1" . The way I see myself when driving....I'm always going thru the traps.
               
            • 72bluNblu

              72bluNblu FABO Gold Member FABO Gold Member

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              Exactly on getting to zero. Possible? Sure, if you're willing to sacrifice every other setting to get it. Likely? Nope. Especially not on a street car where the other alignment settings are also important. It's all a trade off.

              The only way the 1" raise would be true is if you're at WOT and accelerating. If you're maintaining a constant speed the car will be at ride height or close to it with aerodynamics. Mild acceleration won't raise the car that much. And torsion bar diameters would play a big part of that too, with /6 bars you might get that much rise. With 1.12" bars like mine, nope. That amount of weight transfer would not be 1" of suspension rise.
               
            • HemiDenny

              HemiDenny HDK Suspension FABO Gold Member

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              Those 1.12 bars must make your front end stiffer than a wedding pecker.....hope not to offend, just a common technical term used in most hot rod shops
               
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