Technical 49-54 chevy 4-link: Why is everyone cutting the floors?

So i'm looking thru the forum and almost every 49-54 chevy car i see with a triangulated 4 link set up has the upper bars protruding into the rear seat area of the p***enger compartment. lots of extra work there.

is there a specific reason this is done this way? now granted, almost all the cars i've seen have all been done the same way with a big ol giant notch and the bags on top of the axle, laying frame. is that just a case of 'that's how everybody does it' or is there something else going on here? I've seen these frames done without having to cut the floors all up, so what are they doing differently?

 

bump to see if anyone has an answer.... probably the same reason so many people remove the trunk floor. they saw someone else do it.

 

I think Gambino's 4 link is designed not to protrude into the back seat area... I think.

 

I have seen some with the upper links connected to the front of the axle, pretty sure that is the Gambino set up you mention

 

Guessing some of those cars had swiss cheese floors to start with.
1 size fits all 4 link kits could be another reason.

 

Yep, when I went to install my 4 link, I called and talked to Gambino himself. He said that the brackets welded to the front of the axle housing so I wouldn't have to cut the floor unless I wanted in stupid low.

 

If you want to lay frame, even with them on the ftont of the axle, you will have to cut. At least with 6.70-15's.

 

i don't want to lay frame, but why?

 

The upper links will p*** beyond the surface of the floor under the seat.

I have most often made small tunnels to cover them.

My computer is getting the best of me, and I cannot find a picture of a '49-'54 Chevy, but here's a '41. You get the basic idea.

 

yes. i know. but why? why CAN'T you run the upper bars to the rail behind the rear seat bulkhead in this scenario?

I'm honestly not planning on running a 4 link at this point, but i might. either way its just something that has had me wondering since i noticed it 10 years ago.

 

Suspension geometry , you can't just put pivot points where ever you want, it has to stabilize and be in harmony with lower link so the pinion doesn't change drastically as suspension moves up and down , c-10 arms would probably be a better solution for you

 

I was just going to ask about truck arms. That's what I am leaning towards when the time comes but it seems like exhaust routing might be a PITA. Anyone go the truck arm route?

 

You would have radical pinion angle change on suspension cycling with upper bars that short, and you might even have bind.

 

I have put them on a few cars, but not these.

They should work.

 

Hubcaps Hot Rod design in Phoenix has been posting some pictures of their two link set up. Same idea as truck arms; but parallel to the frame.

 

That is a recipe for instsant bind. Those turn the entire rear axle housing into a highly-rigid anti-sway bar.

Not even remotely close to the same idea of truck arms.

Truck arms point to an imaginary point, around which they would pivot, if they reached it. Since they cannot, the arms, by design, actually flex.

That's why box section arms areca no-go, too.

 

I know what you mean; thought about that, too when I first saw them. I wonder if he gets by because his arm to axle mounts have bushings, maybe they flex enough for normal driving.

 

All of the movement must be coming from bushing deflection.

Just because it gets down the road doesn't mean that it is sound engineering.

If it handles fine it is an accident, not a plan.

 

This is Mercedes 4x4 looks to be a bushing deflection concept

Did hub cap copy that design or the early ford 4x4 front links?

Is there a pic of the hub cap garage suspension somewhere?

 

His arms have a dual bushing axle mount similar to MB arm in your picture. I've only seen the pictures of the set-up his shop sells on instagram. Don't know how to borrow a picture from there.

 

I've thought about using this design for a hotrod before with split bones ... If it works in the African safari should be acceptable for a jalopy On the street .. ..
A guy could probably carve on the Benz bones and make them look kinda cool too they're not a bad looking forging kinda ford-esq

 

That is much the same as the Range Rover radius arm, too.

The Bronco also works on bushing deflection.

Either way, all of those manufactures put millions of dollars into ensuring proper handing and function in the exact specific vehicle that these were placed in.

Pulling them out and putting them in a totally different vehicle might "work", but it is not engineering, it is guessing.

If he indeed has engineering data, I will stand corrected, as soon as he posts it all here.

 

And all of those radius arms are FRONT radius arms.

 

Okay…
i'm really trying to understand this just because i'm trying to understand.
so if the pinion angle is supposed to be set for ride height, where does the bind come in (when its laid out?) and if it didn't bind what's the concern for pinion angle (pinion seal damage?)

 

That is a picture of the rear , but how does that matter ? Same rules apply, suspension cycles up and down weather it's on front or back .

 

If you want the upper arms to not protrude through the floor when laid out, then they need to be mounted at a sharper angle, or made much shorter. While this can be done, it will cause the pinion to be at an unacceptable angle almost immediately when the suspension cycles away from static ride height. You would most ***uredly have driveshaft vibration during normal operation. Remember, pinion and tailshaft angles need to be complimentary, within a range.

With triangulated upper bars that short, you will have very little cycling before the bars begin to act against themselves.

If you still want the upper bars to locate the axle side-to-side, the upper bars would have to be at such a sharp angle as to clear the floor, that you would have bind fairly quickly.

The axle will rotate, side-to-side, around the imaginary point where the lines made by the angled upper bars intersect, or at least it will try. If that imaginary point is too close to where the bars actually mount on the axle, due to upper bars being at a very harsh angle, the bars will work against each other, instead of with each other.

With that angle too sharp and you won't just have bind, but you might just bend or snap the link, or bracket under hard braking.

There is a "sweet spot", as putting that point too far away has other issues.

If you just run shorter bars, that reach the frame rails, and don't run them at a sharper angle, then you have an unequal-length parallel 4-link, which does not locate the axle. You'd have to add another axle location method.

Many of these methods have been "pulled off" by some builders. Often times ill-handling is simply written-off as just how hot-rods handle. Many times rods and customs are driven so little that eating bushings is not noticed, as it takes just as long to ruin them as it takes for them to rot.

 

I read someone wrote dig in an article once that Detroit fixes some of their ****ed up geometry by depending on bushing flex , which is the case for these arms , geometry failure made right by a flexible connector...

I usually agree with whatever you write , but I see no difference if this design is used in a Benz, rover or hot rod , well actually the hotrod application would have an easier life as the suspension will only move about 4"

 

Not the same rules. Leading links and trailing links have very different forces applied to them.

What functions well as a leading link may, or may not function properly as a trailing link.

Yes that is a rear axle in the picture. Yes, it is on a Mercedes. Take those links off of a Mercedes, and almost all of the Mercedes engineering goes out the window. Same with taking out the soft Mercedes rubber bushings, and putting in poly ones.

Might work fine, might not.

 

Also lets add the severe driveline vibration caused frome the changing pinion is not just an inconveniace it can be the root cause to pinion bearing failure and transmission failure also

 

Bushing flex is utilized, but it is a precisely known quan***y, and intentionally selected for the application. None of the forces applied to bushings on a Bronco, Land Rover, or a Mercedes will be equal to those of a hot rod.

Engineering is not a guessing game. Guess, and guess wrong, and you might not like the results.

Using arms from a Bronco, Land Rover, or a Mercedes which each easily outweigh a typical hot rod by double, even with stock rubber bushings, and you could again end up turning the rear axle into the aforementioned giant rear anti-sway bar. In a nose-heavy, tail-light hot rod this could lead to some short-soiling handling.