I am bagging and building a parallel 4 link with a track link for my 55 Olds. The lower links are 24 1/2inches bolt to bolt and the mount at the rear end sets them about 5 1/2inches below the rear end. To prevent the 34 inch upper links from having to be mounted through the floor up under my back seat, I have decided to run them to the back. My question is I can either mount them on top of the rearend and they will be around 8 inches above the lower links but not parallel with them at ride height. Or I can mount them under the rearend which will put them right at 4 3/4 inches over the lower links and will be perfectly parallel with the lowers. I have seen some that have all 4 links under the rear, I just am not sure if 4 3/4 is too close and would give me alot of pinion movement. I know the further apart they are the less pinion movement I will get, but I just figured them being as close as possible to parallel at ride height would give me less movement even though they would be mounted closer together. Any suggestions would be much appreciated. Thanx Dustin
I would strongly recommend not running your bars towards the rear. It really is a bad way to go for many reasons. Heres a link to some info from AirRide Technologies that will shed some light: http://www.ridetech.com/techarticles/air4linktechinfo.asp That being said I would either do what needs to be done to make it work installed forward, or consider another method to locate the rear. The one thing that I am confused about is what type of four link you actually have. You say its a parellel 4-link, but the upper and lower bars are usually the same or very near the same length on a parellel set-up, yet you say yours are 24.5 and 34 inches, so I am confused a bit as to what you actually have
Dodgerodder is right... There is no reason for your upper link to be longer than the lower on a parrallel 4-link setup. You could actually make the uppers shorter and/or lower the front-upper mount point such that the links have an imaginary convergence point somewhere ahead of the CG. The later setup will give you slight anti-dive geometry but also induce a little more pinion movement than a parrallel setup. All of this depends on if you want the car to handle well or just look cool...
Rear facing four link bars are always a bad idea. There are a lot of forces in play when it comes to locating a rear axle and the rear frame section does not have the stregth to withstand them. Further hindederd by deep C-notches or frame bridges weakening the frame over the rear axle. Not to mention the suspension design ramifications. Even parallel four links travel in an arc, they just keep the pinion angle the same throughout that arc. And this one would be BACKWARDS! The suspension would have a tendancy to steer the rear axle just as if it were installed correctly but as the outer wheel compresses in a turn the links would pull the compressing wheel back slightly and cause oversteer. Likewise, one bar forward and one bar rearward creates what is known as a Watts Link. These systems are great for locating the axle side to side or if you have a rotating collar around the axle for those locating bars and some sort of Torque arm to control axle rotation. Without it you will get exaggerated pinion angle changes.
no on the rear bars, there are many reasons not to do this . There is nothing wrong with having bars that are not the exact same lenght. The only drawback with real short bars is the adjustments aren't as gradual.As if a 12 inch bar is moved one hole for adjustment it may be the same as moving a 24 inch bar two holes. Not a big deal on a street car.
there are some things that shouldn't be messed with, like re-inventing the wheel..........go with the established design.
Just generally speaking, I think if it was absolutely necessary to run the upper bars of a 4-link from the rear forward to the axle then all four 4-bars should be run that way. It's not unreasonable considering 4-bar front beam axles s run that way. It may do wierd things to the hookup though because the bars will be pulling the chassis from the rear instead of pushing it from the near-center. THat's all C/G nd moment of inertia stuff and a different book to write, though.
He does not mean all four links to the back, only the tops. Bottoms are forward facing like normal giving a neutral setup. If they all face face forward like normal on this car the front mounting points are going to be far from optimal or he would have to lose the back seat. I know that both forward is best and will plant the rear on exceleration etc, etc, etc... and that both facing rear unloads the rear end which is a no-no. I have done numerous suspension setups over the last 15 years and have researched the topic for longer than that. THe top back/bottom rearward setup gives us a neutral setup. This is going on a 55 olds custom and will not raced or autocrossed so it only needs to be a safe daily driver. The Bars are different lengths because he originally wanted to do a traditional triangulated 4 link. We can change the length of them as needed. What we really need to know is if the 4 3/4 inches between the upper and lower mounting points are enough space to prevent axle twist? Many companies such as ART Morrison sell mounts that have both mounts on the same side as the axle so that is not a question. Not to be rude but we are looking for info from folks like ElPolako who have a true working understanding of suspension and chassis design theory and function, not opinions. Sorry for any confusion.
Dear terminably confused, To begin with, Who rattled your fucking cage? You obviously only read every fifth word I wrote. If you've got so much fucking experience, then why do you need to ask how do do ANYTHING (who the fuck are you anyway?) If you READ what I said, and had any capability to reason, you would know what I said is reasonable.
Dear Dr J, 1st - I was not referring to you or anyone specifically so calm your ass down. 2nd - While there are some very knowledgable and great people on here that I respect tremendously there are also a ton of dumbfucks that reply to every thread and know nothing except what they read in old Skool Rods or pull out of their ass. 3rd - Your comments about all links running to the back because the front ones do shows which catagory you fall into. 4th - That was a lovely mature comment about "who the fuck am I" and" why do I need to ask" etc..etc.. again showing what catagory you seem to fall into. 5th - Id your read some of the other posts or any chassis book down at the bookstore you would know that you don't know what you're talking about. 6th - To answer your question I am a 34 year old Chemistry and Physics teacher that happens too have built 15 plus custom vehicles over the last 15 or so years. Not that I give a shit what some shit talker behind a keyboard thinks. I'm not here to talk shit, if thats your thing, look me up if you get to Texas. If I did offend any of the folks in the other catagory I apologize, that was not my intention. Thank you ElPolako and anyone else who answered. If you ask 30roadster or some of the others on here that know me they will tell you that I'm really easy to get along with and not a shit talker. I think they would also say that I'm very knowledgable about cars and specifically suspensions but noone knows everything. Again thanks for any info you've provided or may post after reading this.
To the transgression of trying to teach pigs to sing, I plead guilty. "Very strange people, physicists - in my experience the ones who aren't dead are in some way very ill" --Mr Standish "The Long Dark Tea-Time Of The Soul" by Douglas Adams
Dustin. Lay out your proposed idea to scale on some graph paper. Then scribe the arcs of the links and see what it does. Remember the points welded to the axle don't move relative to each other, so if the arcs want those points to move further apart than their fixed distance, then you're binding at that point. Also think about what the axle wants to do when the pinion gear is trying to climb the ring gear and see where the forces are transfered to on the frame-It can be figured out.
I'm with DrJ here, you are coming across like nobody has any good ideas except ElP. I agree he is an expert so if his is the only opinion you want, then give him a call and leave your drama off the board. But wait, you didn't even ask the question, droplord49 did. So who the fuck are you in this project?
Calm down fellas, LowB is my brother and although he comes off cocky, he means no harm. I think he started off just trying to say that I/we are not new to the adjustable suspension world, we just have not set up one this way before and I wanted to get some informed opinions. I didn't just PM Elpolako because I know that there are others here with as much experiance. So please no more drama, I just wanted to know if 4 3/4 is to close at the rearend.
OK, Here I go. The Watts linkage deal is a bad idea. That is running the top bars back. The axle will have to rotate as it moves up and down. The difference in this rotation from opposite wheels will tear something out. The 4 3/4 inch is short as you know. If you go this way use the 3/4" drag racing hiem joints. The polyurathane stuff will not carry the loads. I would do something like NASCAR does. Trailing arms from a 60's chevy pickup. They mount really low and work. Mount the forward ends as close together as you can. Wide mounting individually stresses them and is not good. Hope you get it worked out!
I just measured the axle out of a 90hp Volvo and the arms are about 6-1/2" apart, but at the frame end they are closer together. Yes this does and will change the pinion angle some. You might be able to clear your floor pan with the upper arm and still have it pvot off the top of the rear axle if you make a "drop" in it like a dropped axle, or like the upper control arm on the Miller Ford Indy cars, only turned fore and aft, and then bend back up to as high as you can on the frame end, clearing the seat pan. Maybe the diagram below will read. the rear axle is the middle O on the left. |º\ |O \___________/º |o______________o I usta run the R&D and product development department for a world-known physicist, so I'm familiar with their occasional intensity.
Both forward, parallel bars, same length, doesn't 'plant' anything. There is no 'kickdown' with parallel four bars. It just holds that axle from rotating. The planting only occurs if the bars are not parallel and give ladder bar type geometry. the Watts linkage style, with one bar forward, one rearward, will rotate the axle as it raises and falls, and with 4 1/2" centres it will rotate a fair bit. What happens when just one end of the axle raises, like when you go over bumps out on the highway? The axle will try and twist at the end that raised up, but stay still at the other, and something will tear.
I already apoligized if I offended anyone. I'm not the one that got my panty's in a wad. I should have said Droplord49 was my brother but didn't think it should matter. If you read what I said above I said " folks like ElP" and " Thanks ElP and anyone else who responded". If you don't fall into the same inteligence range as them I am also certified to teach Special Ed and can teach you some strategy's to help you be successful. I will choose not to respond to shittalking keyboard jocky's anymore because their not worth the effort, and seldom understand the response anyways. To them my last response is " A truly wise man is a man of few words" . Morrisman-- Thank you for that insite. That is the type of info we were looking for. Were kinda to the point that we've looked at so many options that I know we are not seeing the whole picture anymore.
I would also suggest doing it on graph paper, to scale, and see what it does through suspension travel. A local guy had a '61 Ford wagon done that way, and the pinion angle change with travel was way excessive. It always had a vibration from the angles, and the u-joints don't care for it too much.
Well I referenced a circle track builders guide and it says that what I am trying to build is called a Z-link and is used quite often in the dirt track world with much success as long as the links are as long as possible and the upper and lower links are parallel with the ground(at the furthest point of their arch) at ride height. I have decided to move the upper links mounting point to 7 inches above the lowers with should give me plenty of axle roll controll without causing to much stress on the links. I even made a 1/1 scale model out of a sheet of plywood, some cardboard cutouts and some nails and I got very little pinion movement. I think it is going work quite well, but if it doesn't I will just put the leafs back on it, radius the fenderwells and start building it into a gasser. Thanks for all of the advise and sorry for causing alittle drama.
droplord... what works on a race car don't always work on the street. a race car is regularly inspected, a street car not... race karts don't have suspension at all, but you wouldn't build a car that way... read what morrisman said again, it's the most important point: building your suspension this way will fatigue the welding areas that mount the bars to the axle. watts link = fatigue. fatigue = break. break = crash. crash = bad. thus, watts link = bad. sorry dude, find another way.
here is a suspension set up we did to mess with all the people who said it should not be done. It is a triangled four bar with the top 2 bars running backwards. Plus we took a Toyota pick up torsion bar set up and cut it down to fit. It rides bitchen and is all adjustable. Scott
It charges fine as long as it gets driven. You should see it with the bike chain guard I cut down to fit. Ill take a picture. Scott
I'm not saying it won't work, but it depends how well you want it to work. You can't deny the geometry is basically wrong in this set up, but poly or rubber bushes can take a fair bit of the strain out of the system. Depend on what type of roads you use it on to, and how much suspension travel you want. Try lifting the axle up and down with no springs or load on, and watch what happens to the pinion angle. I had limited rear seat room on my Morris, so I used an ultra short four bar, but mounted the rear end pivots behind the axle. It makes no difference to the operating geometry, but keep it all working with no binding and makes the bars as long as possible. Actually, there is binding in the bushes as one wheel raises, but that is because the actual bars have to rotate a little longtitudinally. That's typical with four bars of any description. I made mistakes, and would do the the whole thing on a bigger scale if I built to this design again, with more distance between top and bottom bars. The axle plates were originally cut for a smaller axle and I was too lazy to remake them. I left holes in the front plates to allow for later changes. I'd also make the whole chassis wider at the rear, no reason to keep it parallel like I did all the way from the front.
why dont you just go with a 2 link instead..muuch easier to deal with..no pinon problems to deal with...the way it works is keep the leaf springs in place..add the 2 top bars to the top of the rear end has close to the chunk as you can get them ..then face the front of the bar as close to the leaf spring purch's as you can you are going to have to get some 2x4 tubing an run it from frame rail to frame rail..to get close to the purch'es..then after thats all welded in place cut off the rear of the leaf spring right behind the u bolts..thats called a 2 link set up...the rear end never moves and the pinon stays perfect..much cheaper and alot easeier..if you have any ? about a 2 link or the way i tried to explain it..call or go to any race car shop..they can help you a good bit..just remember to leave it stock position and then work with the top bars only..afterwards cut off the leaf spring..perfect for putting bags on to...
I'll be the first > I AM a confessed IGNORAMOUS when it comes to multiple link suspensions so I am curious about one thing , o.k. two things . lol . If a guy decides to run a Z-bar set-up with the links for and aft , how much variation in pinion angle could one expect in 3 1/2 to 4 inches of suspension travel? Also , is there a formula for considering the difference in that variance based on the length of the bars ? I apologize if I missed the answer to this in the middle of all of this info .Most of this is greek to me.I am curious about this though and find all of it incredibly interesting in that it all appears to be useful in some context . thanx fellas. swaZZie
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