I thought I finished up my 4 link on my 51 shoebox today, but a buddy pointed out what he feels is a major problem. I originally had the upper bars welded to the top of the pumpkin but the angle caused to much pinion change through travel. So I moved the upper bars to each side of the pumpkin on the front side. He says if the tabs are not welded to the top of the rear end that they will rip off under hard acceleration. I am running a 300 HP 302 in the car. So do I once again have to remove the bars and start again? Sorry this is my first 4 link. Thanks in advace guys!
Im no expert but I do not think you will have an issue if the brackets are welded really good to the rearend. Prolly inside and out of the plates. There are many threads on here with the upper bars mounted this way to gain clearance to tho mounts in the rear floor pan and rear seat
I think you will be fine, do a search for the gambino 4 link, i think thats how his ones are set up L
The position is fine. I recomend that you "box" the tabs by adding a piece to at least one side of the tabs to tie them together. It will make them a lot stronger. I may not be an expert, but I've done a couple hundred 4 links in just about any way you can think of.
As an engineer, and a certified welder, I can attest to the fact, if you indeed weld all sides of the 4-link tabs, you should not be listening for this friend for advice, and you will be just fine. Boxing them, like Insane 1 suggests, is a plus, too.
??? ask your friend why he thinks so. Im real curious on hearin his explaination. oh, and make sure o show off pics of the car once the body is back on.
Maybe I might be missing something, how do you set your 4 link up with the ch***is laying on the ground? I am of the understanding it should be done at simulated ride height, with diff pinion angle set in relation to engine and transmission. Never the less, diff mounting location looks ok, as others have said good welds wont break.
I don't see the problem either. As long as the welds are good, it will be fine. At ride height the upper and lower bars should be horizontal. With regards to the pinion angle, if you get adjustable bars, there will be no problem either. There is no need to weld them on top of the pumpkin as it's primary function is to keep the rear end from moving side to side. Here's how I did mine.
Not necessarily. It is perfectly feasible to set up a triangulated 4-link to define an instant centre somewhere near the middle of the car, as one would a race-style four-link with Panhard/Watts linkage etc. In fact that is exactly what happens with an all-horizontal set-up at launch as soon as there is a bit of drop at the rear. The shorter upper bars change angle more rapidly than the longer lower bars, so there is an angle between their respective planes, which defines an instant centre that gradually moves from infinity ahead of the car to somewhere in the middle of the car, as the rear drops. Ideally one would want the instant centre on a line (in side elevation) connecting the rear tyre contact patches with a point at the height of the car's centre of gravity, directly above (or below) the front wheel axis. One saves that initial drop, resulting in a sturdier hook. The beauty of the triangulated 4-link as opposed to a 4-link with lateral locating device or something like ladder bars is that it remains completely articulated and induces no bind. The configuration of the angled and parallel bars also defines the location of the rear roll centre. Here's how to find it: project the axes of the angled bars to their intersection. Now construct a line parallel to the parallel bars' axes through that intersection. The roll centre is where this line intersects the transverse vertical plane of the rear axle. Note that it will move around a bit with roll, pitch, and bump motions. Most triangulated 4-links are set up to put the rear roll centre a bit above the centre of the rear axle, which is a safe bet for most of the front end types one is likely to encounter on a hot rod or custom. If, however, one could get the front roll centre on or slightly below the ground, a rear roll centre only a short distance above the ground would be preferable. There are a number of ways to achieve that, e.g. angling the upper bars the other way around.
My 33 roadster (avitar) has a 4 link with pannard bar and runs well on the street and handles good. I would not set up a 4 link as you have pictured. A well installed 4 link will give you good controlled traction and a decent ride when done right. I dont have a lot of detailed shots of my set up but there will let you see how I did this one and I used chrome molly tubes and Heim joints.
The car was mocked up to ride height and level when I tacked it all in place. I just had to let it down to see if the frame layed out. It was killing me to see it. I also wanted to see how much if any pinion angle change there was through the range of motion. I will box the tabs in as everyone has said. I have come across tons of pics of others done similar so I figured I was ok. Thanks so much for all the positive input guys!
I ran mine on the top of the axle. I know Alex Gambino and many others run it on the front. It didn't make sense to me either.
looks like there is about 4" of vertical separation between your upper and lower dif mounting brackets, is that enough to resist pinion climb?
That is the main issue with mounting the upper links near the axle centerline. It's not so much the separation distance, but the axle wrap is trying to roll the upper link brackets up instead of pulling back on them as it would if they were mounted higher. Yes, there are a lot of 4 links set up the way 51 has them now. It's always seemed to me to be a compromise. I don't think it's the best way to set them up, but it seems to work.
It might be a bigger concern in a dedicated drag car, but this is clearly a cruiser, so it's rarely going to test the limits of the suspension design. Travel is a higher priority here than brute strength. This is a cl***ic case of over thinking things. The safety check box has been marked, carry on.
Nedd, since you have gone to all that trouble to describe what happens, I'd really appreciate a simple sketch or diagram to help me better understand what you were saying. I am sure there are a few other folks out there like me who would benefit from a little more diagramatic info to match the dialogue.
Here you go: Note that it doesn't matter if the angled links are at the top or the bottom, or which way they are angled, the principle stays the same. Grazie bonez!
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