Anybody know any facts about reversed four links

First off, this is for air ride and that's not TRADITIONAL. All that will have a problem with that can return to the rest of the forum. My apologies. I would rather you were upset with me than letting my brother make a mistake.

My brother is building a '53 Chevy hardtop. He wants it looowww. He's running a stock 350/350 combo over a Mustang II frontend. The frame has been notched with the Gambino kit. The rear is from a late 70's Monte Carlo that he plans to attach with a 4 link and bags. He's got three little girls and would like to be able to keep the backseat so he would like to reverse the 4 link behind the axle. I know some of the mini-truckers are doing this but I don't know about doing it on a full size car. Any help would be appreciated!

Thanks,
Jerry

 

Most Mini Tucker builders don't know fuck all about suspension geometry.
And they don't care.
All they know is : the lower, the better.


GM used triangulated 4 links on lots of cars. Works well
If he doesn't have room for upper links,
consider a torque arm, like used on late model Camaros.

 

Look at Sellers kit fir the 53/4s . You can keep the backseat for the kids

 

Yeah putting the 4 bars behind the axle sucks because it swings the axle through a weird arc that requires the driveshaft to get longer as the axle swings up and down. You'd probably need a special driveshaft with a long slip yoke or something.

 

why not trailing arms like rod and custom just did? suposedly that was ging to be come a kit

dean moon's moonbeam used backwards 4-link, i guess it must of worked for him

 

ouch, coming from someone who's work i admire that kinda stings. however i realize you did say most not all. i agree we do have those that dont know there ass from a hole in the ground but is it any different than hot rodders and (dare i say this) rat rodders?

as for the reverse setup, it is an option but like someone else said it does cause the pinion angle to roll a great deal more than a traditional 4-link. another option for your friend may be to run the uppers backwards and keep the lowers to the front.still not as good as all forward but a happy medium

 

I'm having this fun at the moment on a 50 chevy, I'm keeping the back seat and trying not to cut the floors too much. I'm going to have to create a couple of tunnels under the back seat for the upper triangulated arms.

 

My $.02...

Let's assume (for the sake of argument) that the link bars would be parallely, equal length, and would form a true parallelogram regardless of whether they were mounted forward and rearward.

IF that were true, then the pinion excursion would be equal in a true parallelogram, the opposing sides stay parallel thru the arc of rotation.

I mention this because if you did mount one set of bars rearward and the other set forward, then you would have MASSIVE pinion rotation, because the only element in that particular geometry that can compensate for the reduced length (effective length) of the bars as they go through their respective arcs of travel is the rear axle...it would have to "rock" on it's mounts...not good.

But, back to your question...there are a number of associated geometries...anti-dive and instant center being a couple...that are integrated into an efficient suspension design, and these all assume that the motive (and stopping) thrust is being delivered through a linkage that is biased towards the front of the vehicle.

Or, think of it this way: The bars are oriented rearward. The vehicle engages in a panic stop. The wheels (effectively) stop rotating...so, where does the inertia that is inherent in the mass of the vehicle want to go? Well, I propose that it wants to rotate up, and forward...and it can...because the rear-facing link bars have provided a convenient "hinge".

Rear facing 4 bars are more than a compromise, they are inefficient and unsafe. I would encourage your brother to REFUSE to consider ANY compromise, and come up with a solution that meets his objectives, but from a reliable, engineered perspective.

 

Perhaps a Terry Satchell rear 4 link would work. In this design the lower control arms form a triangle with 2 attachment points on the axle near the ends and the other 2 ends mounted close to the driveshaft. The upper links go straight forward and are mounted as close to the outside of the axle as well. Here's a few pics. 2 pics are of a bolt in kit for Camaros, the other one is an old Jaguar 4 door with a custom frame.

 

check out www.streetsource.com there is plenty of tech there about the pros and cons of all 4 links its a mini truck mostly site. as far as mini-truckers and shit work i cant agree at all. its like that in any facet of any hobby you have your hacks and you have your serious fabricators. now the v-wagon guys they are real hacks =) j/k

 

While I mostly agree w/that statement, there are a few of us who have built a minitruck or two, and know way more than most hotrodders about suspension....especially when it comes to bags, and 4-links.



Now as for a quick answer to your question on a reverse 4-link... NO.

While there are many answers, and many more opinions, for somone who is learning just run all bars forward, or do a parallel w/a Watts link if you don't want to deal w/upper bars.

Whatever you do don't do "trailing arms, w/a panhard bar"...that is is most ghetto way of setting up an adjustable suspension.

 

You're gonna have to lay the engineering on me for this one, because I'd like to see an actual calculated reason why properly oriented rearward facing linkages are "dangerous".

Is that just code for "I don't understand exactly what's going on in a four bar, so I fear the unconventional."?

The only reason I ask is because these kinds of suspensions have been used for years to great effect in circle track cars. Rearward facing four bars would have a different set of arcs, and thusly need to be approached and tuned differently, but that doesn't make them "dangerous", except when setup by someone who doesn't know what they are doing.

Also, the lower two links forward, and upper two links rearward has been used for years in circle track cars too. We call them a swingarm or Z-link system, and they work just fine thanks.

Can a four bar be setup with the bars facing rearward and be safe? Yes.
Can you do it exactly like one with the bars facing forward? No, certainly not.

Suspension isn't smoke and mirrors, and it isn't rocket surgery, it's engineering, and that means that the answer can be calculated and proven good or bad.

 

True some circle track cars use the "Z-link" but the center section is "decoupled" and does NOT rotate with the "z-link". You actually have to run a torque arm or fifth link to control rotation of the axle housing.

 

Indeed, the swingarms pretty much have to be run with a birdcage, but so what? The addition of a torque arm will not make the suspension worse in any way, and could actually improve it in several instances.

When we ran swingarm cars, we ran pull bars (upper link, running downhill forward to control axle wrap) instead of torque arms. It's a very good suspension system when they're tuned right, but they're also very sensitive to spring rate, so you've gotta carry an army's worth of rear springs (and not be afraid to change them) to keep up with the race track.

The fact still remains that the system he described is viable if properly executed.

 

I have never seen a functioning backward 4-link with any appreciable travel that didnt have problems. Mostly pulling the driveshaft out of the trans.

Can it be done, probably. Can it be done feasibly, probably not.

 

Run the two lower links forward, and the two upper links rearward, as mentioned above. I ran a three link in my IMCA modified, and ran the upper pull bar as a backwards mounted push bar, and the car ran great with awesome forward bite.

 

Then they were using too short of a drive shaft.

With forward facing bars, the shaft moves forward under bump and rebound travel, so you start with the slip-yoke hanging some distance out of the tailshaft and it slips forward under travel.

So, one would expect that rearward facing links would tend to pull the shaft rearward under bump and rebound travel, so you would want to start with the slip-yoke nearly bottomed out in the tailshaft housing.

If the links were the same length in both instances, the slip yoke should not move anymore to rear than it do towards the front. The only thing that would need to change is the length of the shaft between the u-joints.

Just because a particular embodiment of a design was improperly executed and failed, does not mean that the design is entirely without merit.

 

reverse 4 links dont help your suspension at all. all the do is hold the axle in place.

go with a foward 4 link, or a 2 link and a wishbone.


try looking on streetsourcemagazine.com in the ask max section. he gives a pretty good run down of how each 4 link works, the pros and cons. hes the owner of biokustoms and a mechanical engineer i think. so check it out.

 

I'd never put any kids in a car that will drag frame in the event of a failure.

 

I appreciate all the advice, pros and cons. I'll definitely pass the info along. Thanks again and any more info will be well recieved. Especially if you have actual experience rather than guesses.

thanks again,
Jerry

 

About the same answer you got on the air ride forum......

 

This was covered in great detail awhile back... seems the general consensus was it was not a safe way to do things...

 

Yeah, I just checked back and replied to your comment. Thanks for sharing your opinion...

 

I think the GM truck arm would be the best alternative. Simple to install, keeps the bars long and low with good geometry.....Tough to beat in my opinion.

 

look at it this way - Air Ride Technologies doesn't use a rearward setup, and they pretty much have been pioneers in retro-fit air ride suspensions.

In fact, they even say that it's a bad idea

 

I gotta go with this guy.

From a technical standpoint, while the original solution posed may be workable, truck arms are both easy to install and quite robust.

Also, from the safety angle, if you were to apply bump stops in strategic locations, you could prevent the frame from hitting the ground in the event of a catastrophic bag deflation. That's not isolated to truck arm type suspension, but it would be quite easy to do with truck arms.

 

Truck arms are pretty good....

 

Totaly agree if your going to build it build it the best way possiblle. Rear 4-links do nothing for suspension design they only locate the axle.

 

I'd really like to see a circle track car that has any of the control arms mounting reward off of the axle. You will not find a race car that runs such a linkage unless it's "backyard engineered".

The reasons to not do this have already been laid out in a previous post - anti-dive, instant center, unloading of the wheels under braking. Having two forward and two rearward is even worse. BTW, a "swingarm" suspension uses a single forward-pivoting arm - not one one forward, one rear. Motorcycles use a swingarm for the rear wheel.

 

Here is a direct link to Max's article on 4 links. Max over on SSM does know his stuff. There are actually a lot of mini truckers out there that know our stuff. The problem is that those that know what they are doing get bashed so much when we correct people that we just keep our mouths shut for the most part.

http://www.streetsource.com/forum/topic.aspx?topic_id=85853

My suggestion is to do a forward facing 3 link with a panhard bar. Can be done with minimal intrusion and still keep the back seat. Here is a pic of one that Lowboy Motorsports did here in Mesa. It is a wishbone style on a mini truck. You can see the bars under the frame and the upper wishbone. You can also do the upper without the wishbone (just a straigh bar) and do a panhard or watts behind the axle.




Later,
Chad