Installing a triangulated 4 bar. Need help

I have searched the forums for hours trying to find information on setting up a triangulated 4 bar setup. First of all, let me say that this isn't the first triangulated setup that I have made. I have done two others that have turned out very well. This one in particular is giving me fits and if anyone can give me help I certainly would appreciate it.

I originally bought this setup for a 31 Model A Coupe that I had. I sold the car because of lack of funds to finish it (not much has changed, but trying harder). I am intalling the rear suspension in my 29 Buick 29-27 4 door sedan. Some of the mods I have made to the car are a 383 stroked LT1 that I am building, 700R4 transmission, a 9" ford disc brake rear, Scott's IFS front suspension and coilovers for the rear.

The frame for my Buick is much narrower that the other two setups that I have completed. It is about 30" outside-outside. I have the bottom bars located and tacked into place. The top bars are a real problem though. In order to mount them at a 45 deg angle as they should be, they would have to be mounted on the very top center of the differential hump which would cause them to have frame clearance problems, and be angled down at the front at a rather harsh angle.

One option that I have thought about is to shorten the upper bars, thus allowing them to be mounted on each side of the hump and "might" possibly solve the problem with the harsh angle of dropping down at the front. The problem with that is that the upper bars will have a shorter arc because of the shorter length and will require substantial modifications to the rear frame crossmember. I am sure that it woud do harm to the geometry of the suspension but I am not smart enough to figure that out.

I can use the upper bars in the current length by changing the angle from 45 deg to approximately 70 deg from the plane of the differential. My thoughts with this would be that it would cause the differential to be less stable from side to side. I would still have to do considerable modification to the rear crossmember but could reinforce it in other ways to compensate. I had the frame boxed but removed a portion of it to get the 45 degree angle but in turn made it worse.

The current length of the lower bars is 29" eye to eye and the upper is 17" eye to eye. How bad will it screw me up to use a 70 degree angle on the uppers instead of a 45? How important is it that the upper and lower bars are parallel with each other? I have never seen any kind of instructions or guidelines to suggest proper installation. I know that some of you guy's have considerable experience in this matter, so this is the place to come.

I want to use the triangulated setup because it looks neater and mainly because I already have it. I have tried to give all the information that I could. It is hard enough to diagnose problems even if you are standing in front of it, much less be email (or forum). Thanks a bunch in advance.

Ed

the bars are not parallel in all the kits ive look at, this is a 4x4 site, big ticket in rock crawling right now, thats my plans for my 4x4 in a few years. this does not answer your question on shortening your bar but it shows you step by step install of the kit, with many pics and explains alot of things.

http://www.universityofjeep.ca/Tech/...or_Install.htm

Not being a expert either i would think 70 degree may lead to some rear end shifting under power. We know the 2 45's hold it at a positive center. My thought would be go to a panhard bar just for the stability for this application. That or you will have to mod the frame to make it work properly.

Where is a engineer when you need one . Hurst there is some great guys here who may have a fix for you. Hang in here and lets see the outcome .

Ed, you need to drop the torch and step back to get a look at the big picture. It is not the suspension which must yield in order to get everything to work, but the frame. Cut the offending frame members out of the way, as well as any offending sheet metal, then re-engineer that part of the car when you have the suspension working correctly.

When a car is built from scratch for instance, all the components are placed where they will work with each other, then the frame is fabricated in order to attach all the components and hold them in place. Not the other way around.

All my books are in storage and I can't repeat the principles from memory, but a short search turned up this explanation for placement and operation of a four bar / four link by Billy Shope on Hotrodders.com:

First, a distinction between four bar and four link:

The 4bar is a parallel link arrangement where brackets at both ends force the bars to remain parallel at all times. The front bracket might be adjustable...up and down..., but the bars themselves are always parallel. With a 4link, the individual links can be adjusted, so that the link pair...on each side...is not necessarily parallel.

And then an explanation of the setup:

With a 4bar and the links parallel to the ground, the squat on launch is excessive. By angling a 4bar up until the bars are parallel to a line...as viewed from the side...which passes through the rear tire patch and the intersection of two other lines, one vertical through the front tire patch and the other horizontal through the car's center of gravity, the car will neither squat nor rise on launch.

With a 4link, if lines through the links intersect anywhere on the previously described line (which passes through the rear tire patch), the car will neither squat nor rise on launch.

Now, my take on it:

As viewed from the side, the car's CG if about the height of the camshaft on a pushrod V8. If we visualize that line as being about 2/3rd's the height of the tire, we can do a simple drawing and see the how Billy's explanation works.

Draw two circles to represent the car from the side, making an attempt to keep the size of the circles and the length of the wheelbase representative of your car. Draw a horizontal line through each tire about 2/3rd's of the way up the tires, running from front to back tire and extending past the tires. Now draw a vertical line through the center of the front tire, from the ground to up past the tire. Now draw a line which angles from the intersection of these two lines down to the contact patch of the rear tire. That angled line represents the line Billy is talking about. With a four bar, you want to keep the bars parallel with this sloping line.

What he says next about a four link doesn't make any sense to me. Maybe you can figure it out. That's about all the help I can be for now, except to urge you to buy this book and teach all of us a thing or two:
https://shop.sae.org/servlets/produc...&PROD_CD=R-146

As much as I despise Panhard bars, I may be tempted to agree with Bob on this one. You could run a single top link straight ahead and a Panhard bar to keep the body from swaying on the diff. If you do that, just be sure to make the Panhard bar as long as is humanly possible and mount it parallel with the ground with the car at ride height. It won't matter if you put a few bends in the Panhard, as long as the attachment points are installed at the same height as viewed from the rear of the car.







http://www.progressiveautomotive.com...m/triangul.htm

Tech TY you just gave me a installation class on my panhard on my 31 .

Watts Link and Four Bar????

I would think the bars could be shortened, 29" is plenty long for the bottom bar. You could mock everything up with some square tubing substituted for the bars. When you figure your lengths, shorten the top and bottom by the same percentage of their total length. IE, 10% shorter would mean 2.9" off the bottom and 1.7" off the top.... On narrow framed cars with triangulated 4 bars, I've mounted the top bar brackets as much as half way up the center section. When all else fails, you could switch to a parallel four bar with a Watt's linkage, I'd have to be really desperate for space before I went with a panhard bar for a street car, though. They work fine on a drag car, but that's about the only time I'll use a panhard bar.... I just don't like the way the load the suspension on cornering....

Thanks for the response guy's. It has been really helpful. Richard, I agree with you that I am going to have to remove the cross member and install the bars as they should be and then re-engineer the cross member for installation. I just hated to do it before I got more opinions.

Dave, I also agree with you that the bars seem awfully long. I bought them several years ago for a 31 Model A coupe that I had. I can't afford to not use them. These bars are very well made, better than the last two sets I have installed. I am hesitant about shortening them because I don't know how they were designed for the geometry of the suspension. I saw a set (installed on a frame) on a web site yesterday that looked just like mine did, but they looked to be about equal lengths on top and bottom. Tops were at 45 deg and both top and bottom were parallel to the ground. I noticed that the ad said that the frame must be boxed. It would help get the 45 deg angle if my frame was not boxed. It would also give me about another 2 inches to obtain the 45 deg angle.

Looks as though I will have to take about 4" off the top bars in order to get the correct angle. If I take 3.4" from the top bar and 5.8" from the bottom bar, that would shorten them 20% and I still have to mount them high, or around mid-way up the center section. I notice in the picture that mooneyeye777 sent on the first replay that the uppers are mounted extremely high on the center section and are not by any means parallel with each other. Looks as though they were designed to mount that way. I didn't know how well it would work if the two bars were not on the same horizontal plane.

I will get out there tomorrow and cut the crossmember (rivits) out. I have to say, there is a great bunch of guy's on this forum to take their time to help people out.

BTW, if anyone is coming to the NSRA Street Rod Nationals in Louisville in August I would like to hook up. I live about 20 minutes from the fair grounds where it is held. I could probably be helpful in finding lodging also. Nothing like having a friend close by with tools, welders and other equipment to do anything that needs to be done.

Ed

Sounds like you have it figured out Ed. With coilovers there's not a lot of suspension movement. I plotted it all out a time or two changing bar angles and placement, not a lot of change in the pinion angle even with the shorter bars. Moving a crossmember is probably the best plan. The most critical part is to make sure that the movement of the rear end doesn't place anything in a bind.

Here's considerable information from Billy Shope concerning suspension setup:
http://home.earthlink.net/~whshope/index.html

With the bars at 70 degrees (20 degrees between the bars, top view), you would have a pretty short life out of your bushings, as this would put a lot of stress on them. 60 degrees works good. 45 degrees isn't necessary to get the suspension working properly, but the top and bottom bars should be about parallel when viewed from the side. If anything, they should be a little closer to each other at the front, when viewed from the side.

Don't use a panhard bar with triangulated four-bars. They will fight each other and cause a bind in your suspension.

OK, I finally got around to getting the tringulated suspension tack welded in my 29 Buick. It looks really good but I somehow am not pleased with it. Because of the narrow frame I had to shorten the upper bars 3-3/4" and the bottoms 6". I did this so that both would be shortened a equal percentage of the total length. The uppers are now 13" eye to eye. Seems awfully short to me, but that is what it took in order to install them at the angle that they were designed to be.
The 9" ford rear is gutted so it is no problem to raise the housing to test the travel. I have not set the ride height as of yet, but from the position that I set the differential initially, I get about 3" travel up. It seems so short. I so far can't see anything that is stopping the travel. I am very tired from a long day and decided to walk away from it and rest.
Actually, the 3" of upward travel will more than likely bottom out on the bumpers after thay are installed anyway. I checked the angle of the housing while raising it with a magnetic protractor. The angle of the housing changes very little while raising it. Actually, just by looking at it you can't see any change in the angle of the housing at all, but by using the magnetic protractor you can tell that it does change a little. Right now anything I said would be a guess because I am totally wore out.
I had to do this twice today. After I got it tacked in place the first time I was looking and found that someone had bumped the differential on one side and moved it about 5/8". I thought about trying to adjust it out but knew better and cut it loose and did it again. I am not about to try and cover up a mistake like that. I knew better than to start welding on it but I was very careful when I first set it up and assumed that it was still OK. In the back of my mind I was telling myself to check it but didn't. Oh well.
I still have to install a bar to mount the top of the shocks on, but that should not be a problem. These short bars look so strange. I will post more updates later.

Ed

Hurst glad to hear you are getting it installed. If you can post some pics so I and some more can learn from your build.