Ok let me be detailed about this one. My T-bucket has a Parallel 4-link (Chris Alston Battle Cruser) setup. All big 3/4" Hiem Joints on the bars. I have about 3.5 miles on the car working the bugs out. Lots of new car bugs! To get ahead of potential answers... I built the Frame out of 2x4 Box On a fixture Dead nuts Square. The ch***is is perfectly Square, the front mount of the 4-link is a 2x3 box welded in place The Centerline of the axles front to rear are diagonally measured square to the ch***is and front king pins = to <.015" Coil over Shocks are plumb when the ch***is is bubble level. Mock up and final ***embly went very smooth. I chose a diagonal bar or Drag link. Mounted front DS lower to rear PS Lower. Solid Bar with Chromoly 3/8' Heim joints. So... My "issue" is this. after a test drive around the neighborhood the rear end migrated 1.25" to the p***enger side! The Shocks @ ride height were ****ed about 12 degrees each (lower part towards the PS) So I lifted the rear of the car to investigate... The rear Suspension as it expanded with no weight it settled back center in the car! So what I did was this.. I Pre loaded the rearend 5/8" to the driverside using the diagonal bar to "Pull" it over, went for another ride, came back and it worked itself to being centered in the car. So the rear end is centered in the car, the car tracks nice launches as good as a blown HEMI T-bucket should ever hope to launch. Did I "Rig" a bigger problem I have? Where would be a good place to start investigating" When I let the rear hang free and drop the diagonal bar the rear end centers itself perfect in the car. I can move it left to right very easy but leave it alone just hanging there is nice and centered left to right. I was actually kicking around the idea of adding a Panhard bar to the mix. I dont know if the redundancy is a problem or not? So any pointers will be very appreciated.
Forgot. tomorrows "Agenda" is to break all the nut loose on the 4-bars to see if they all spin equally to check for Binding an any particular Bar.
Everyone I know that tried a diaganol link on the street ended up switching over to a panhard bar or watts link. The set-up seems more for 1/4 mile at a time. All of them that I saw got sloppy after awhile. If you are going to drive it like a street car, a panhard, or watts link might be a better choice.
Can someone explain what a "drag link" on a rear suspension is. I know what it is on a front suspension. To the OP, Panhard bars and Watts links are both tried and true, choose the one that fits/works the best for you and you will not be wrong.
If you mean a diagonal link, that is under the driveshaft, that goes from one lower link, at the front end of the link, to the other link, at the rear end of the link, those are great for drag cars, not so good for those that make corners. Chuck the diagonal link, and put a panhard bar in there. There is a reason that you find one, and not the other, in OEM applications.
pitch the diagonal and panhard it or wishbone it , diagonals work great on a tabletop flat surface but the street has a crown to it and basically ****s the suspension set up .
If you think about it for a moment it becomes obvious that a diagonal link is a Panhard bar. It might be quite a sub-optimal Panhard bar, though, depending on its length in the longitudinal direction as mounted in the car. To locate the axle laterally it must be stressed more than a conventional Panhard bar by a factor related to the angle of the link, and it will moreover be slenderer than a Panhard bar of comparable size for its effective (i.e. lateral) length. And then, a Panhard bar will give you a greater range of options for locating the roll centre where you want it. (On the other hand, taking a diagonal link off the plane of the lower bars opens up the possibility of "projecting" your RC outside the physical envelope of the car, at the expense of some lateral shift in bump: I wouldn't go there, on balance.) Wolfcreek-Steve mentioned a Watts linkage; that's always an option. So is a Mumford linkage: And then there is the triangulated 4-link, of course. All elegant solutions.
Post picture...could be a seized heim. Have one do exactly what your talking....also I've broke a diagonal link on the street....the bracket cracked at bolt and would open up and car would be all over the place
Ned, is there an advantage to a Mumford over a Watts? I'm having trouble visualizing the "animation" of the Mumford linkage you posted an image of, particularly the purpose of the triangular shaped ch***is pivot.
The 3/8" rod ends in the lateral/diagonal link (drag link or whatever) are way too small for a street application and if the bar is sized proportionately it is too small as well. Solid bar is also not a good idea. How far apart are the four link bars laterally? If the link has a small included angle relative to the four link bars any play/flex in its mounts will be amplified. I agree with those who are advocating ditching the diagonal for a more conventional Panhard bar or Watts linkage. What you have now is meant for a drag race application where the majority of the load is on the longitudinal axis of the car. All that it has to do in a normal situation is to keep the car pointed straight. Driving on the street as you are doing adds a lot of lateral load when you turn corners--most of the time a drag race car does that at very low speeds so the lateral G loadings are low. I know that lots of people do it but running rod ends on the street is not a really good idea as you have metal to metal contact everywhere and usually without the lubrication that comes with a conventional tie rod end or the compliance of urethane bushed ends. The street is a lot tougher environment than a race track with lots of load reversals due to chuck holes and patches in the pavement. In a race application the suspension takes a big hit at the launch and shifts but it does not see those reversals and lateral pounding that street car does. Roo
Just a thought... if the rear end manages to jounce around and then settle in a new position over an inch from where it started, but returns to center after some jacking and twisting around, could the links / bars's geometry be so far "off" that the whole deal is basically jambing up - like an over-center bell crank that locks and is unable to return to it's starting position? If so, could modifying their respective lengths in some way take the bind out? Gary
Ok am I missing something? Is there or is there not a panhard bar on the rear end. If there is not then there needs to be either a panhard bar or a watts link like nedd suggested. On a 4 link the suspension links locate the rear front to rear and the panhard bar or watts link locates the rear side to side.
It took me a while, too. The two central pivots only rotate when the axle moves vertically as a whole, i.e. in bump/pitch. In roll, only the two long links move. You'll notice that they describe an instant centre somewhere below the axle. That's the advantage of this set-up and the reason the Locost guys are keen on it: it allows you to put the roll centre at whatever height you want, near, on, below the ground, or anywhere else, by playing with the angles of the long links.
A lot of drag race cars use a diagonal link at the bottom of the four link as described by the OP. It usually is installed by mounting a clevis style bracket via the bolts that locate the rod ends in the four link bars. Most go from the left front to the right rear. Theoretically there should be no lateral movement of the rear end but as noted by the OP this is not the case with his installation. Photos would be helpful in ***essing what the real problem is. Roo
Sounds like you just didn't have your diagonal link properly adjusted before your test drive. I run one on an OT prostreet car, it works fine, however, ANY slack in the heims or the holes in the mounting brackets will cause premature wear with an accompanying noise over bumps.
Another thing to keep in mind is that a parallel 4-link isn't really a free-articulated mechanism in all the degrees of freedom a vehicle suspension needs. The links are free to swing in any plane only as long as they are parallel. As soon as they are non-parallel the axle is constrained to one vertical/lateral position. This means a 4-link can't freely articulate in roll and bump/pitch at the same time. Four-links do articulate in roll and bump/pitch at the same time in the real world only by distributing the usually small stresses involved a**** the links, joints, frame, and axle. The greater the combined axle movements, the more this is likely to be a problem: you won't see a parallel 4-link on a rock crawler. I'd suggest no more than three longitudinal links on any serieux suspension that has a lateral locating device like a Panhard bar, Watts linkage, or Mumford linkage, be they two upper and one lower or vice versa. The single link needn't be at the middle of the axle but it is best if it is near the middle. That also allows all the potential advantages of having the links non-parallel i.e. describing instant centres you can place where you want them for whatever reason.
Thanks everyone for the input! general consensus just backed up my original thought put in a pan hard Bar. Going to be tricky but Ill make it happen! off the computer.. out to the shop where I belong!
OoooK, Just spent some quality time on my back under the car trying to figure out the best way to get a panhard bar in there. A few dilemmas pop up 1: the frame is already powder coated 2: To attach the panhard bar to the driver side frame rail presents 2 problems a: I have ran my wires thru the frame all of my primary feeds and grounds and rear harness are right where I would have to weld/drill b: Its already powder coated 3: Attaching to the rear end housing again a few issues here. a: the entire housing is ceramic coated b: using a pig mount bracket is hampered by the fact that I have a thicker nodular 9" case and the studs barely have enough engagement now to get thru the nylock's There is and pinion support mounts out there but I think those would require on of those "J" tubes and I am not real warm and fuzzy about mounting to the pinion support. So My brilliant Idea is this..... I have a piece of C channel welded between the frame rails already in place 1x3 & 1/4" thick I built it in for dual purpose as a bed rail support on top and a anti sway bar mount on the bottom. The Sway bar got bent pretty bad with the rear end shift so I can count it as gone so out it goes with a nice channel with brackets already welded in place to mount a sway bar! I have 2 options to mount the other end to the p***enger side of the rear end housing both of which involve the 4-link. Option 1 the roundie round guys have an upper tube ch***is mount for a panhard bar I could strap that to the rear of the p***enger side upper bar about 2" from the joint. Option 2 Build a bracket and use the lower open hole in the rear end 4-link bracket (that bar @ that location has to options the lower hole is open. This would give me a panhard bar close to 23" long and be installed @ ride height with approx 15 degrees.
All the joints checked out fine, nothing binding as the car is parked after a ride. going to ditch the diagonal bar and go with panhard bar... see above. thanks
Here are some photos of when the car was in final ***embly. some of the areas I have talked about can be seen here
Question one: how did the sway bar get bent (and where) with the rear end shift--did the Heims get in a bind and if they did why did they not bend rather than the anti roll bar? Question two: Is it just the photos (photo #1) or do the upper and lower bars diverge (in side view) as they go forward and if so, why? On the same subject am I seeing that the top bar forward mount is inboard compared with the lower attachment point? Maybe that is why the bars don't look parallel in the photo. Question three: As the circle track clamp on housing bracket sounds like a good idea how are you going to get the panhard bar past the frame and four link brackets as at full compression on the shocks it looks like the top of the four link bracket will be about level with the bottom of the frame. I know that the bracket is canted forward of the axle center line but the panhard bar will need to be headed that way to get to the C channel cross member.
Answer 1 the arms that come down and have the heim joint/turnbuckel ***embly down to the rear end housing. The Arm itseft from the tube down to the rod ends got bent to the p***enger side. not fun to remove. the 4 link hiem joint are not bound at all Answer 2 the bars I mounted all4 bars on the rear housing in the uppermost option, in the forward mount I mounted the uppers in the top hole and the lower in the bottom home to make the lower bar parallel to the ground or as close as possible. that should cover the side view, no between the bars the rear is 23-1/8' the front is @ 23-1/16 split the difference overall .032" per side taper in, not enough to bind anything. @ ride height (see pic#2) I was thinking of a bracket picking up the lower hole on the 4 link mount option OR a bar mount right on that bar inself about 2" out lines me right up with the C channel. Ditch the bent sway bar and I have a straight shot back to the driver side.
A simple fix is to convert it to a triangulated 4 link by moving the uppers inwards [beside the driveshaft loop on the upper side ] Use bushes at the rear links [ to also get the angle ] and heims at the front for body roll. You wouldn't even need to "cut and shut" the rear end. The instant centre is at the imaginary point of where these 2 links intersect The roll-centre will be high [which isn't ideal from a "road racing" perspective ], but is OK on street cars.
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