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Coil overs and 4 links

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  • Coil overs and 4 links

    This on again off again 36 Chevy coupe project is back on again. This is the project car we took over after the car was sand blasted and left in a hurricane in florida. Anyway, playing with building a watts link over the panhard bar, but looking at all the options for shocks and springs is really confusing. Why do a pair of coil over shocks for a VW bug cost less than 100 bucks and the shocks alone for a 4 link end up being close to 150-200 a piece?

    A long time ago I bought a pair of Competition Engineering shocks but when I got them there was a warning for drag race only. They have a 3 click setting for firm, more firm and stiff. I put them on with the 10" springs and the springs hold up the car before the shock compresses. I moved them up about 3 inches and they are now halfway in when the car is resting on the ground. But when I lift the car up again, the spring ends up being about 2 inches away from making contact with the spring again. So I am assuming to control the top side of the rear end movement with the watts link before the spring loses contact with the bracket.

    I just have too many questions that dont get answers. When I call speedway and ask their response was you need to know the length of the shock before they can tell you anything. Well, length of the shock just means where we will weld the bracket on, right? I cant even get into talking spring weights with them.

  • #2
    Yeah those guys won't be able to help you much over the phone. If the shocks are going inside the spring and are too short, yeah that's a problem... Pics?
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    • #3
      just trying to get something up here, cant turn them over.

      Anyway, this is the idea. Its only a 10 inch spring at 250 pound rate and they dont compress at all with no weight on the car. When we go all the way to the bottom bolt holes there is actually a decent height from the ground, but up in the middle where I like the rake, its like a 4x4 build. So getting a better shock with the adjuster is going to go way high unless we go to a way lower rate spring.

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      • #4
        Seems like the spring/shocks are sure mis-matched, in use (at static) the springs should compress about 30% which if your rear axle weight was 1500 lbs or so should happen with the 200# rate, (see; https://www.qa1.net/tech/documents/S...le-Weights.pdf )and at that point the shocks should normally be in about the middle of their travel...that's not going to occur w/ this setup. Since your car is probably going to not have that much weight on the rear a solution would be to change the springs to a 175 or 200 lb. unit and be a little shorter...or move the spring mount on the shock just to get by but I'd presume that's welded on and can't change. It's kinda tough to know if you really have the right springs until the car's complete with all it's weight, until then you're just talking calculations.

        A couple other things, you probably know the four-link at anything other than parallel adjustment will act like a ladder bar on the street (which is not ideal as it puts all roll resistance at the rear of the car and will cause oversteer when you want it least), and those links and springs/shocks should all be as far out to the side as possible, it seems like one sorta is, while still limited by the inside of the frame rail, and the other is mounted considerably inboard. I'd wonder why the builder did that all asymmetrical and figure on some reconstruction there.
        Last edited by Loren; June 15, 2017, 08:15 PM.
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        • #5
          No, I am completely new to this 4 link deal so I dont know squat. Alot of our discussion over this car is did they give up because of the rust condition from the hurricane, lose interest, or just realize they were lost when they welded the rear end together. There were no upper shock mounts, we just tacked those on to try to see where the rear end wants to be so we can work on the fenders. That was the whole exercise of setting priorities, Cant build a fender until we get the car sitting where it wants, but need to know we are on the right path to getting it where it wants so we want to get to the lowest point it could be and know we can go up. So when we have a spring that is 2 inches shorter than the shock is supposed to have and it still does not squat at all, its time to ask questions. So basically, if we had an 8 inch spring on there that was not compressing, we would get to where the point where the proper compression was happening on a 12 inch spring to at least get to that 30% you mention so we can choose the right one later. With the 10 inch you would think its compressed height would be 15% from a 12 inch spring. So just knowing that helps alot.

          The plan was to run the 30x12 mickey thompsons back there, so its a big move outside to get there and since the fenders were junk we figured that is the way to go So since there is so much work left, its good to know what might be completely wrong. The brackets were welded on the rear end housing pretty solid, but I see your point of being too inboard. Seemed all the chassis work was most done, but clearly looks like the springs were mounted close enough in to shorten the rear for fatter tires, but that does not make sense either since all the work was done on the chassis..
          Attached Files
          Last edited by anotheridiot; June 16, 2017, 08:23 AM.

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          • #6
            Someone sure did a stout job of attaching the brackets on the axle housing, however considering the placement I think the builder was just in over his head and backed out when he realized where he had gotten himself. Imagine the forces on all that during a hard launch...or just hitting a good-size pothole...those links need to be out to the side as far as they can go, most cars w/ four-links use a Z/kick-up style frame to put the links in line with the rails, just inside of the tires. The closer they are together, the higher the stresses, and for no good reason. Imagine also the launch force out on the ends and the moment/bending force on the housing from having the links in so far, housings are a little weak where the tubes are welded to the banjo center, although that could be addressed with a back brace as is commonly used. Four-link and ladder-bar brackets have been known to peel off on the housing but not usually with the full-perimeter contact, I doubt the extra sleeving was really necessary, for your purposes that is just going to create a lot of work to get it all back off again.

            What I would do...if it were me...9" housings are cheap enough, the brackets aren't too bad cost-wise, I'd start over with that. Cut the frame bracketry away, keep it but put it back where it should go, as far out as possible and of-course, symmetrical. Maybe do the back brace, and a diagonal link might be the easiest lateral control scheme to package and put the roll center at a reasonable height for street use, although as-noted with the bars non-parallel there isn't really a roll center anyway.

            Is it really worth all that work? Hell yeah, to get a car you'd want to go a hunnert-plus mph in. I always say, half of the parts on the purple car have been done-over at-least twice, including back at the rear end, 'cause it took the first time to learn then the second time to get right. The reward comes when it's all together and working like it should.
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            • #7
              I'm not seeing anything wrong with the set up other then the cross-panhard bar (they move, a lot because of the stresses involved - it's better to tie to the frame and the top of the axle housing). It even has the much-better rod ends. Shocks should be as close to vertical (to the arc of the travel of the rear suspension) as possible. Length of those is fine. You're confusing me with length of spring. Springs are for weight and length is determined by the stroke of the shock. You need at least 2" of vertical travel up to get a decent ride and have enough travel to handle what a car normally sees. I think 200# springs are too much, heck that is my main, front spring on my FJ40. I'd guess you need something in the 75# range maybe even 50#.
              Doing it all wrong since 1966

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              • #8
                Thank you for your suggestions and what you noticed. I can see it plain as day now.

                Yeah, beefed up axle housing. Cut and sleeved some heavy 3" tube over the housing before welding on the brackets.

                I can see what they are looking at though, the offset rear end with the ford 8" and they are pretty close to equal from the center of the housing. They have a drive shaft clearance hoop on the forward support that is centered to the drive line. So when that was set and done, they welded on the rear brackets from the center and when they got to the frame made them straight where they are 3" from the driver side and 6.250 from the passenger side.

                We put the strap to the front side of the front brackets since they had alot of wiggle, just did that while he was finish welding the boxing plates, blasting and getting the epoxy primer on the frame. I will look around for a bare housing we can finish here since it would be nicer to have it a little shorter for these fat tires.

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