TORSION BAR ADJUSTMENT

Discussion in 'Suspension, Steering and Chassis' started by B'cuda, Jul 19, 2018.

  1. B'cuda

    B'cuda Well-Known Member

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    How much height can you get from the adjusting bolts? Right now about half of the bolt head protrudes below the LCA.
     
  2. J Glenn

    J Glenn FABO Gold Member FABO Gold Member

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    Turn and see;-) Just be sure to make any measurements off something meaningful,
     
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    • Alaskan_TA

      Alaskan_TA Well-Known Member

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      And be ready for a front end alignment when you are done.
       
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      • toolmanmike

        toolmanmike FABO Staff Staff Member FABO Gold Member

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        The lower and higher you go the harsher the ride. Low will hit the bump stops over bumps and too high takes all the spring out of the front end. It will ride like a old wagon.
         
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        • 72bluNblu

          72bluNblu FABO Gold Member FABO Gold Member

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          The bump stops are the only thing you have to worry about. Well, and getting the right alignment numbers.

          Nothing changes with spring rate by adjusting the torsion bar bolts. The car weighs the same, there is no “twist” added to the bars, the adjusting lever just sits at a different angle to the torsion bar hex.
           
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          • B'cuda

            B'cuda Well-Known Member

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            Thanks , I'm trying to get alittle header and tire clearance
             
          • toolmanmike

            toolmanmike FABO Staff Staff Member FABO Gold Member

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            Say what you will. If you crank the bars up it will reduce the travel and produces a harsh ride. Don't ask me how I know. 093.jpg
             
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            • 72bluNblu

              72bluNblu FABO Gold Member FABO Gold Member

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              It reduces suspension extension, of course. Just like lowering the car will put you on the lower bump stops with suspension compression, raising the car excessively will put it on the upper bump stops with extension. So you lose travel in extension.

              But there’s no big change in wheel rate. The spring rate of the torsion bar doesn’t change AT ALL, and the effective wheel rate only changes very slightly.

              But it does that as the control arms move up and down all the time no matter what you do, that’s just because of the effective length of the “lever” working on the torsion bar. The “lever” is always the horizontal distance from the torsion bar hex to the lower ball joint, so since the ball joint moves in an arc it isn’t constant. It’s a small effect, and regardless of the ride height the effective wheel rate is always changing slightly with the angle of the control arms as the suspension travels up and down.

              If it rode harsh, you were either bottoming the suspension out on extension, or getting crappy ride effects from the lousy alignment specs.
               
            • toolmanmike

              toolmanmike FABO Staff Staff Member FABO Gold Member

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              I still beg to differ. But that's what we do here. Disagree and debate. Capture.JPG
               
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              • toolmanmike

                toolmanmike FABO Staff Staff Member FABO Gold Member

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                On a Chevy site. You have what 4 Mopars? Take your choice and jack the thing up and crank the bars up fairly close to the top and go for a drive. Dang right it rides like a lumber truck.

                Capture.JPG
                 
              • Dana67Dart

                Dana67Dart Most undignified way to get to Colorado!

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                Completely agree. the only way to change the spring rate on a streight torsion bar is to shorten it, thicked it, or use another type of steel. A coil spring is also a form of torsion bar. If you cut out a coil you lower the ride height but you increase the spring rate because you have shortened the overall length of the torsion bar.
                 
              • robert flippo

                robert flippo Well-Known Member

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                if you have a good alignment now, just be sure you count the revolutions you turn each one, if you don't like it you can run it back the same amount and a new alignment won't be necessary. As you raise the front the camber on tires go negative(top of tire leans in), as you lower the car you get positive camber (top of wheel leans out ), so if you adjust bolt heads, be sure and get a front end alignment, i know from cranking front of 69 superbee all the way up, front tires went from new to in the cord with 2000 miles, that was 1973, running e-60-15 on front and L-60-15 on back, i was 18 and full of piss and vinegar.,,sometimes the truth hurts, but it may help you not make the same mistake i made...
                 
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                • Dana67Dart

                  Dana67Dart Most undignified way to get to Colorado!

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                  IMHO. A broken torsion bar like that is a manufacturs defect. It had to be twisted past its elastic limit to bend and would have to be brittle to snap. Just MHO but physics os physics
                   
                • harrisonm

                  harrisonm Well-Known Member

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                  IMHO, there is a reason for the factory specific ride height adjustment parameters. They were helping us to get the best ride possible.
                   
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                  • 72bluNblu

                    72bluNblu FABO Gold Member FABO Gold Member

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                    So, you went to a Chevy site to get accurate information on a Mopar torsion bar suspension? Well, surprise, it's wrong. Not to mention, how do you know that guy is right even for a Chevy style torsion suspension? Preload on torsion bar systems is very different than on a coil spring system, and a lot of people try to apply what they know about coil springs to torsion bars.

                    The preload on a Mopar torsion bar suspension comes from the weight of the car. This is not like a coil spring suspension. You aren't adding preload by cranking up the torsion bar adjusters. Take a look at a lower control arm. When you turn the adjusting bolt, it changes the angle of the control arm with relation to the torsion bar lever. It does not twist the bar, it just changes the angle of the LCA with regard to the hex. That's one of the biggest advantages to a torsion bar suspension- you can adjust the ride height without substantially changing the preload. It's also how the offset on the bar sets the ride height range, and why the offset has to be different as you increase the diameter (spring rate) of the bars.

                    The ONLY difference comes from the effective length of the "lever" between the lower ball joint and the torsion bar hex. I've calculated that difference at the extreme ends of the suspension travel, you're talking about a few lbs/inch on the wheel rate, which means you're not talking about a substantial preload difference.

                    I'm not saying your car didn't ride like crap jacked up in the air like that, I'm sure it did. But it's not because you changed the pre-load or wheel rate significantly, it's because you eliminated the suspension travel on extension and hammered the alignment specs.

                    With bias ply tires.

                    The factory specific ride height adjustments were based on the handling characteristics of bias ply tires. So are the factory alignment specs. The camber curves, bumpsteer, amount of caster, etc are all completely different from bias ply tires to radials.

                    If you install radials, the factory ride height adjustments do not give you the best suspension geometry. It's just like using the factory alignment specs for radial tires, except your applying it to the full range of suspension travel. What worked best for ride height and suspension geometry from the factory is totally different than what works best once you install a set of radials.
                     
                    Last edited: Jul 20, 2018
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                    • 72bluNblu

                      72bluNblu FABO Gold Member FABO Gold Member

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                      The description in the picture is wrong for a Mopar suspension. When you turn the adjusting bolt, the lower control arm moves. Not the hex. No tension is added to the bar. Not on a Mopar system anyway, I'm not familiar enough with the design of the Chevy system to say what that one does.

                      But on the Mopar suspension, when you turn the adjusting bolt it doesn't move the hex, it just changes the angle between the hex and the LCA. Grab an LCA and see for yourself. The bar only twists when the weight of the car moves the LCA and the adjusting lever together. Moving the adjuster just sets the angle between the two.
                       
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                      • AJ/FormS

                        AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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                        And the big thing I discovered was that as the LCA rotates up and down,it carries the chassis with it, and so the centerlink too. But the two may not rise and fall in lock step, which introduces bump steer. There is a sweetspot in the curves where this is minimized. And I bet that is where Mopar designed the rideheight to be. On my car the sweet spot started out only about 2 inches wide, one up and 1 down. The outer tierod pivot point was too far out and too low,IIRC. That was year 2000 when I debugged it. Oh and the idler-arm height was wrong too.
                         
                      • B'cuda

                        B'cuda Well-Known Member

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                        Thanks for all the input guys, I don't think I'm going much over an inch in height, it's a 69 fastback with super stock springs in back, and the rake makes the front look droopy with 15s to the top of the wheel opening. Underneath my old style Hedmans pick up grass from the center hump in our dirt road, yeehaa! But since it sounds like an alignment will ensue, I'll probably go ahead with new joints and bushings first, who knows, that in itself may pick it up abit of height.
                         
                      • 72bluNblu

                        72bluNblu FABO Gold Member FABO Gold Member

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                        Bump steer is minimized when everything is close to parallel, which happens significantly lower than where Mopar designed the factory ride height to be. But again, bias ply tire suspension geometry is a different animal that radial tire suspension geometry. The factory did what they did because it was best for bias ply's, and that's darn near opposite of what's best for radials.

                        You'll definitely need an alignment after you change the height that much. If your 15's are at the top of the wheel opening you're probably lower than the factory ride height spec, so raising it up some might not cause as many issues as we've talked about. If you haven't specifically set the ride height using the factory specs, I would wager your current ride height is lower than factory. Suspension settles over time, and kicking the back end up with Superstock springs puts more weight on the front end anyway.
                         
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                        • BigBlockMopar

                          BigBlockMopar BigBlockMember

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                          For the doubters, if spring rate could indeed be easily changed by a simple bolt, why would you think Mopar had torsionbars made in various diameters?
                           
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                          • robert flippo

                            robert flippo Well-Known Member

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                            harrasonm said they set it from factory for best ride ,which is correct, but in the late 60s and early 70s , if you run L60s on back or N50s, unless you raised the front ,about e60s was only tire you could run, and your oil pan was about 4 inches off the ground along with your headers, so on a 70 duster i had L60s on back and F60s on front and raised front about 3 inches to make up for the high riser air shocks for fender clearance on back,also helped raise the front of your traction bars
                             
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                            • mopar505

                              mopar505 FABO Gold Member FABO Gold Member

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                              so with that being said, when you put radials on your mopar today, the factory specs on alignment is useless? or is that a starting point? the person performing the alignment needs to know what? i dont know jack about camber/toe ride height when it relates to proper alignment and am having to soon take my ride to someone.
                               
                            • 72bluNblu

                              72bluNblu FABO Gold Member FABO Gold Member

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                              The factory specs are for bias ply tires. They’re actually worse than useless, because they’re absolutely wrong for radial tires. They're almost opposite of what you actually want. The person doing the alignment definitely needs to know that, but they probably won’t because they probably won't be old enough to know that these cars came with bias ply tires from the factory and not radials. And depending on the shop, they won’t align the car to anything other than factory specs regardless. A lot of the major chain alignment shops will only use the specs in the computer, which are the factory specs.

                              If you're running radial tires on one of these cars, you should be using alignment specs similar to the ones in this chart

                              alignment-specifications-jpg.jpg
                               
                            • mopar505

                              mopar505 FABO Gold Member FABO Gold Member

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                              thanks, that chart will help when i bring it in to somebody. instead of going by there comp, ill hand them a copy of this and go from there. gonna try and find an old school shop also.
                               
                            • mbaird

                              mbaird mbaird FABO Gold Member

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                              I agree with BluNblu that the spring rate does not change.
                              However it is a lot like a rocker arm and I have to wonder what effect the angle of the adjusting bolt to the lever has on the force applied to the torsion bar ? The fact that the aduster anchor can pivot may nulify any effect ... hmmmm????