Triangular 4 bar set-up

Just for review. When setting up the angles for the uppers in a triangular 4 bar, what are the most extreme angles that are acceptable? I am setting up a tri-angle 4 bar in a fairly narrow frame (26-1/4" inside). To keep from shortening the uppers too much, I need to know how far off paraelle to the frame rails does it have to be?
Next question: How close together can the two pivot points be together for the same two upper bars on the differential mount? Right now I have them tacked in place at approximately 10" between centers. I can move them closer together to obtain a longer distance between the differential mount and the frame. My only concern is that it may interfere with the differential / body clearance. That is something I can work on for clearance issues if necessary.
I was working on my project and had to have a third open heart surgery that took me out of commission for a while. I want to see this thing finished before I die.
Third question: Is there a ratio that is recommended for the length between the upper bars and the lowers?

Thanks, Ed

Hurst01,

Hope this helps. On my 34 ford I tried to duplicate the dimensions from the 66 GTO that my rear came from. For the upper bars the original bars were aprox. 16" long and 13" between pivot points, center of 1 bar to the next at the diff. housing was 6 1/2 to 7 ". At the frame rails the center of 1 bar to the next was 24-25". The bars also angled up some what from the rear to the rails; I don't have the angle but it was whatever it took to put the end of the bars nearly even with the top of the rails. For the bottom bars the originals were aprox. 25" long and 22" between pivot points, and the frame mounts made to keep the rails parallel to the ground. The spread of the bars at the diff. was what ever needed to keep the bars perpendicular to the rear and mount to the rails. I used the coupe for nearly 20 years with that set up and am using the same dimensions in the rebuild. If there were flaws in this set up I was too stupid to see them.:rolleyes:

Jack.

You should try to keep the upper and lower pivot points at the frame one directly above the other if possible and try to keep the upper and lower bars as close to parallel to each other as possible. I would also suggest that you make the triangle bars come as close together at the center as you can because they will make the best track or sway bar that way.

Just my 2 cents
Walt

These are on a 51 chev,, a wider chassis that you are working with,, but maybe you can get some prespective of how to place the bars and mounts,

I found it is best to angle the top bars as much as possable, to keep the R/E in its correct location,,,

Ok, Lets see how this works out. When I first bought this tri-bar setup, it was for a 30-31 Model A Coupe. It already had a differential mounted with leaf springs and someone wanted to buy it. I sold it because I never figured I would have to money to build it. I kept the Tri-bar set up
With the existing length of the set up, the top bars were about 3/4 length of the lower ones. Feeling that they engineered the lengths this way for a reason, I had to shorten the bars to where they would fit this application. I figured the ratio between the uppers and lowers and shortened them proportionately.
Since I had never set one of the tri-bar set ups, I assumed the the uppers would be at 45 deg angle from the differential to the frame. This would not work because it would make the uppers about 6" long. I wound up with about 38 deg angles. This still makes the uppers fairly short, about 13" center to center. The lowers are about 22-3/4". I shortened them a percentage according to the over all length. I did not just take so many inches off each one.
I figured that the uppers needed to be as close to 45 degrees as possible to keep the sway to a minimum. I have since seen them with much less than that for what-ever reason. If I could make the upper at say around 30 deg it would be able to be somewhat longer. That 13" length on the upper bars look strange. I fear that a 30 deg angle may allow a bit of side to side movement.
I am afraid that the short length will cause a harsh ride or possibly handle uneasy. I have been told that I need a 4 bar set up with panhard bar. I like the triangular-bar set up.
I started this set up a couple of years ago and then began having more heart problems. I had my third open heart surgery in May of last year. I want to get this taken care of. I am putting this in a 1929 Buick. I have about $12,500 tied up in this car and if something happens to me it will be given away for practically nothing. I have to get it far enough along that it will bring something if I am unable to finish it. I have the IFS mounted solidly in the front, motor mounts are there and a short block 1995 LT1 sitting in place with a 700 R4 behind it. Everything is aligned where it should be. The master cylinder is just clamped in place waiting to be tacked and/or drilled and bolted. The cross member is sitting there holding the transmission up. The engine is waiting for the install of the 383 stroker kit.
I had to quit working on it because of heart problems. I am doing half decent now but have been told that there are no more options for me should more problems arise.
I am disabled Vet and Journeyman Machinist and Certified Welder. I finally have some machinery that I can make anything I want with it (just in time to die (LOL). I still have to do a rebuild on the 9" ford rear and install a 3:70 gear. The rear is good but has around a 2:54 gear. This won't work well with the LT1 and the LT4 Hotcam I have for it, especially with the 1.6 roller rockers. I shouldn't have bought all that. It was really unnecessary. But, at the time I wanted it, so there it is. Time to quit feeling sorry for myself and get it done.
I am wondering about moving the rear of the upper bars closer together. I don't see any reason that it would not work and this would allow me to use longer lengths on the top bars. But, it could cause a problem with the differential pre-load, I don't know. This is why I am asking for ideas. I am thinking that the uppers do more then hold the rear in the center and keep it from shifting. How would this affect torque? Can anyone see if it would hurt to leave it where it is? So far it is just tacked in place. Is is within 1/64th of an inch of being dead nuts of factory specs of the original wheel base. The rear wheel looks to be too far forward but the wheelbase is right on. I have thought about moving the rear end back between 1 to 1-1/2" so the rear wheels would be more centered in the wheel well.
Anyone else have any ideas?? Times a wasting.

BAD RAT.

What is the angle of the upper rod in relation to the frame? That looks to be where I am at right now.

Don't worry about the health issues, VA told me 20 years ago I only had 5 years to live and the next stroke would be the big one...Had 3 since and still kickin'!!:LOL::LOL::LOL:

The top bar length is a bit short, could just cut it, weld in a slug for strength and a bit more tubing, maybe extend it to about 18". I've ran them at that length with no problem. I also run my top mounts up on the housing instead of the tubes to improve the angle. Same setup I'm building on the 'maro, lower bars are 23" and the top bars are 18". Don't recall what I set the top bar angle at, seems about 35 degrees. Pictures of it in my gallery if you're interested.

Quote:

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Originally Posted by Hurst01

BAD RAT.

What is the angle of the upper rod in relation to the frame? That looks to be where I am at right now.

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Hurst,, not sure of that angle, I no longer own that car. but I am guessing maybe 30*
I just ran the bottom bar as straight as possible to the frame and the top bar at the most angle that would work, and keep the mounting points close,, That was for a air bag setup.. and it works great,, air ride has more up and down movement than any other suspension, and this one doesn't bind up at all...
if you notice,, the front pivot points are close in proximity to being one above the other, on the same plane, not necessarily the same horizontally,, The top angle doesn't have any set degree setting,, No matter what angle you set the bars at,, it will hold the R/E in place, as long as there is one on each side,,,,,,,,,,is that confusing you even more?

I have to agree with Dave, worrying about your health will just speed up that trip, none of us want to take,, I'm 72,, and try to keep my mind occupied with positive thoughts, like the cute blond that lives accross the street:>)
I basicly have the same reason for getting my projects done,, If something happens to me .. at least my wife can sell the cars for a decent price and have a little nest egg, but mostly because I want to drive em,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,ALOT

I believe that I still have the pieces that I cut off. It would be a simple matter to thread the pieces I cut off, cut a threaded 5/8-18 grade 8 bolt (might be a 3/4-16) screw the two pieces together and weld them and machine or grind them back down. I am also a certified welder so I fully trust that I can weld them to hold.
I figured that there was an engineered ratio between the uppers and the lowers. I have my upper mounts on the differential tacked so that the mounts are even with the top of the diff housing. I thought about putting them closer together but was concerned about the clearance above the differential. Giving it another look, I think I have plenty of clearance. By moving them closer together I can lengthen the rods and still keep a reasonable angle of the the uppers.
The idea of the angle should be, as I understand, to keep the differential from shifting side to side. The less angle, the more possibility of movement. I would hate to go less than 30 deg. I will see if I can get to it in the next couple of days and see what I can do. I want everything to be right before it is welded. I appreciate everyone's input. It always helps to kick ideas around in unfamiliar territory. BTW, thanks for the pictures from everyone.

TCI has a page with measurements for their triangulated 4-link setup on different chassis. Also, I was told by a well known chassis builder to keep the distance between brackets at the rear end as narrow as possible. I placed mine as close to the 9 inch pumpkin as I could get them. I was very surprised at how free this setup works through the suspension travel. I think you are correct in keeping the upper links as long as possible.

the closer the upper rear mounts are together the less bind in the whole assembly

you also can widen the lower rear mounts to improve the overal angle--they DO NOT HAVE TO BE PARALLEL!!!!!

If you can , get a look under a Mustang at an 8.8 for angles and lengths

Just replace the links you cut with some tube that has an inner id that is tap size for 3/4 threads--11/16 or .6875----cut to length and tao one end rh and other end lh

In theory 45 degrees is the ideal angle for triangulated upper bars. 20 years of GM intermediates all had this setup. I came pretty close with mine (about 42). The difference in length doesn't seem to matter all that much, as long as it's not too radical. I have two cars with this setup and I don't see that much bind. Since most of our cars have at most 3" of suspension travel I don't see a problem. But then, I could be wrong...:LOL:

Hurst01,

We need a update and some pics of your progress.:):)

Jack.