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Puting a 4 link on a unibody???

Puting a 4 link on a unibody???

Puting a 4 link on a unibody???

(OP)
ok this might be crazy but, i'm in the process of putting a ford 302 in a 1992 nissan 240sx. It's a unibody car with independent rear suspension but that is not good enough so I'm wondering the process in changing that into a 4link. i would be using a ford driveline(engine, transmission, drive shaft, and rearend). so if you know of anyone that put some type of solid axle in the rear of a unibody let me know i'm sure a couple of mustang guys did it.  

RE: Puting a 4 link on a unibody???

I've done the reverse a couple of times. You are right the Mustang enthusiasts tended to throw the Cobra IRS away and fit a live axle instead, hence the ready availability of nice IRS modules.

Realistically your main problem is deciding on arm lengths you can package and position that give reasonable control over the pinion joint angle. This is a classic 4 bar link problem, there are many solutions. The V8 supercars over here use long, parallel arms, and then a Watts link. Our sedan used the same (the one is based on the other), but we had a shorter upper arm, angled inwards and down, for roll steer and to help toggle the pinion angle.

You may need to biff the floor to create clearance for the diff.



 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Puting a 4 link on a unibody???

The Mustang guys had it a bit easier than what you have ahead of you, as that car's IRS was designed to fit up to the same points as the stick axle that was concurrently offered.  

I doubt that your car has adequate strength where you'll want the upper link(s)* to attach, and adding only local panel stiffening around any additional brackets may not be enough either.  It wouldn't hurt to 'overbuild' a bit here for stiffness as well as for strength, as you may find you have wheel hop under either hard acceleration or hard braking where there would be some sort of impact factor involved.  At least the few extra lbs would be more or less over the "right" wheels.

* Depending on what you're going to do with the car, you may want to consider a torque arm suspension (a la GM's 3rd/4th gen F-body and a fairly common retrofit to the Fox Mustangs) or a 3-link (as in the latest S197 Mustangs and also a retrofit for the Fox/SN95 axle, and I suspect is also used in Greg's supercars and sedan) instead of the triangulated 4-link.


Norm

RE: Puting a 4 link on a unibody???

Late thought.

The Mustang guys swapped out the IRS for reasons of dragstrip durability, but I'm guessing that's not the environment where this particular conversion is headed.


Norm

RE: Puting a 4 link on a unibody???

You can get 'back-half' kits from Jegs or Summit that come with the trailing arms plus some weld-in frame rails.  They're generic, but that could be a good thing.  What do the drift guys do to the 240SX suspension/drivetrain to make it hold up?  I know that's a popular car for drifting.  I've seen Skyline engines in them.  If the car will handle a Skyline engine, it'll handle a warmed-over 302. There's also a company that engineered an IRS using Ford 9-inch components for muscle cars.  It's actually a Ford design that the beancounters thought was too expensive to put in the Mustang in the 60's.  It's really sweet, but a little pricey

'When in doubt, make it stout, out of stuff you know about.' (It'll help plant the rear tires and give a better weight balance too.)

RE: Puting a 4 link on a unibody???

I read that Ford could've put any IRS on the current Mustang for $400 per car, but their market research showed the drag folk wouldn't have it.

Unless you're drag racing this 240, why would you get rid of the IRS?  What's not "good enough"?

RE: Puting a 4 link on a unibody???

What is the use of the car?
Goran

RE: Puting a 4 link on a unibody???

Norm - no, it is a genuine 4 link, in the Supercars they use long parallel equal length arms. Our suspension was the basis of the Mustang one. There are a few circumstances in which the IRS is better than a beam axle, but a good beam axle is better than a bad IRS most of the time, and cheap IRS tend to be bad.

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Puting a 4 link on a unibody???

(OP)
how about a Solid-axle, with a coil-spring [IMG]http://i283.photobucket.com/albums/kk317/aseaman92/solidaxlecoilspring.jpg[/IMG]
because i was told that the car would handle poor on the road and this would be a bit better.

ok the car is going to be a street/strip but down the road i might just make it into a full out drag car not sure.

I think im going to be tubing it, to free up a bit more space, and there will be a cell going in the hatch of the car so that there is even more space for the diff and suspension components.

the drifters just use a infinity rear end i am pretty sure its a 2.0 or 1.5 lsd not that sure on any of that but i need or i guess i want a possi just so i can launch the car as hard as possible and go straight down the track.

But what i want is a solid drag car with a rear end that will almost never fail so what do you guys recommend for my setup/

RE: Puting a 4 link on a unibody???

I would recommend a Ford 9" centre with drive shaft flanges on axle stubs. Install it where the stock diff is and adapt the heavy duty drive shafts from a V8 with IRS.

f you are serious about your drag racing put in a Detroit locker or an air shift type locker. A Positraction won't cut it.

If you run substantially bigger tyres and/or slicks you will need substantial reinforcement of stock dimensioned suspension arms and their mountings and the chassis platform in those regions.

Normal method for moderate increase is to box in the channel sections and to add thicker plates at the mounting points, but if the power and more importantly the traction increase is substantial, you will need fabricated arms with more robust construction, but same lengths and the mounting points should be on the links that link the font and rear chassis sub frames, or to cross members mounted to the sub frames or chassis links.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

Where are you,  might be ableto hook you up with some chassis fabrication guys

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

A road race car is often using very long 4 link rods, maybe all along the sides of the car, even if inside the bodywork and not visible. This is to free up from "roll lock" that will occure using drag racing style unequallength 4 liknk.

So in your case a shorter rod 4 link is to prefere. It should be adjustable for different instant centre to be able to run unparallell when racing, then go back to parallell when driving home. The trick at the strip is to set "rise" or "antisquat" to produce tire plant during start. Then you should have special Dr shocks where you use the extension dampening to alter the time duration vs force of tire grip. If you got the money, buy doubble adjustable shocks in order to be able to alter the after 60 foot distance grip.
Springs are usually quite soft, and you might even use a heavy swaybar to set off the line side to side preeload.

Get the picture?
Goran

RE: Puting a 4 link on a unibody???

How fast are you planning on running?  The Ford 9" and the Dana 60 are bulletproof axles, but they're kind of heavy.  With a light car and a C-clip eliminator kit, a Ford 8.8" would probably do the trick.  A Mopar 8.75" would work too.  If it sees limited street time, a spool instead of a diff would probably be better.  Sticky tires will shred a weak rear end pretty quick.

RE: Puting a 4 link on a unibody???

would never use a spool on the street.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

(OP)
i live in prince edward island, Canada i know that there is no chassis fabrication guys on the island but if you know any in the maritimes that could be helpful.

im not to worried about weight i will just make that up with a couple more HP and will also make up for it with fiberglass and possible some carbon fiber. I have a 9" already so i might try to save some money and just use it.
i really want to get rid of the IRS so a 9" with axle hubs is not for me but thanks for the good advice.

yeah patprimmer is right a spool is not a option for the road.

but what do you guys think of that 2link i guess thats what it is called with the coilovers it look like the easiest one. the 4link just has to much involved for how much time and money i got.

it would be nice to run mid 10s to 10s if possible but that is a lot farther down the road i'm thinking right now 11s or high 10s.   

RE: Puting a 4 link on a unibody???

Spool on a road car is a PITA, I had one temporarily in a Lotus 6/7 type sports car (i.e. a 'Nota Sportsman'). Not reccommended at all mostly because it will actively try to kill you on a wet road (even at walking pace...).

The one redeeming feature is that if you snap a half shaft you can still get home, but one wheel drive does have some 'interesting' characteristics...

RE: Puting a 4 link on a unibody???

The 2 link is very similar to what I call ladder bars.

ladder bars bind in roll. They also need a Panhard rod or Watt link to control sideways movement.

The bind in roll or a single wheel bump makes them very inconvenient on the street. For dual purpose you need a 3 or 4 link setup with a Panhard rod or Watts link.

I will enquire about fabricators in your part of Canada.  

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

(OP)
hey thanks so i think i would try to go with the 3link because it is a little less complex then the 4link and might take up less space.

RE: Puting a 4 link on a unibody???

NASCAR uses the 2-link with coilovers suspension.  It's a design from old pickups, Chevy I think.  The arms went from the axle to way up near the cab.  My first thought is that if you went with a long 2-link, it would help with weight transfer to the rear axle due to leverage.  Not sure without some study, but that's what my intuition says.

RE: Puting a 4 link on a unibody???

I just shot an image of a Shelby Mustang rear end we are building. No Panhard bar but a diagonal track locator.
www.hemipanter.se very fare down the site. Sorry that my camera battery went drained so there is only ONE image.
Goran

RE: Puting a 4 link on a unibody???

(OP)
see there is a ton of geometry in make a 4link not so much in a 3link and very little in a 2link. SO what do you guys think of a 2link that would go up to under the drivers seat would that be a good setup for a strip/street car? but if you guys think that a 4link or 3link would be better i would need a fare bit of help with the geometry so the angles it should be at and so on.
another question is there any good books or forums on how to build any of these setups?  

RE: Puting a 4 link on a unibody???

I am already on record as saying a 2 link is not suitable for street use.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

There is at least one company that fabricates truck-arm kits for somewhat larger road cars than the 240SX.  Kinematically it isn't as good as a 3-link or a torque arm, but its shortcomings can be mitigated somewhat by careful design.  In larger, heavier cars it is quite predictable at speed - that the various NASCAR driving experiences turn complete newbies more or less loose on real oval race tracks with real hard walls in real race cars cars so suspended ought to be sufficient demonstration.

The lighter your car gets, the stronger I think the argument gets for using one of the other solutions.  Other arrangements may be able to give you a better combination of anti-squat/SVIC location and roll steer with less structural reworking.


Norm

RE: Puting a 4 link on a unibody???

Pat, I was only 21 in 1961 so I did not know that a two link would not work on the street...So, I put an Olds V8 with a four speed Hydromatic in my '46 Ford Coupe along with a '49 Olds rear end (4.10 R&P) with a two link factory GM setup with custom mounting for coil springs.  Worked just fine for the two years I drove it.  Turned mid 12's on Atlas Bucron Cushionairs.  Only problem I had was balancing the Olds rear drum brakes and the Ford front drum brakes...caused a big spin and crash on a wet road.  We learn, often the hard way!

Rod

RE: Puting a 4 link on a unibody???

(OP)
so would this work? http://i283.photobucket.com/albums/kk317/aseaman92/4barparallel.jpg
if it would work, could you explain it like what angles and stuff that is very important. pretty much how do i start?
what parts should i buy to make this go smoothly and successfully with very little knowledge going into this project.    

RE: Puting a 4 link on a unibody???

From what I can see that looks like a 4 link. The upper links are mounted very low so minor compliance will create a significant change in pinion angle. Also the torque reaction from the reaction of the power applied to the axle will have more leverage over the top link.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

Yes, that is a good approach, for a 4 bar.

The angles are important. I suggest you copy one that works, exactly, or else hire someone who knows how to do it, or accept that you may have to modify your design after building it.

Your big problem with attempting to design something is that you probably don't know what you really want, so even if you knew how, you wouldn't know what to aim at. That is not an insult, defining the requirements from a blank sheet of paper is very hard.

The excellent program susprog3d has a template for this suspension.

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Puting a 4 link on a unibody???

(OP)
ok I found a guy that could help me. But what would be better a 4bar or 4link?

RE: Puting a 4 link on a unibody???

4 bar+panhard is what I would prefer, but drag racers seem happy enough with 3 bar + panhard. It probably depends on packaging as much as anything, you may not have the height to accomodate a 4 link, you may not have room for a 3rd link.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Puting a 4 link on a unibody???

Greg, I know you are familiar with the MkI Lotus Cortina's coil over rear suspension

In 1980, I reworked a 3 link plus Panhard that had been fabricated by Strange Engineering of Chicago to a setup very similar to the OEM, ie, using the lower V link (A link to some) and two upper links attached directly above the forward mounting points of the lower V link---Not at the OEM mounting points.  This simplified the mounting system and eliminated the Panhard bar.  It also lowered the roll center a bit.  The OEM problems of broken axle center section was easily corrected with proper reinforcement at the bottom attachment point in combination with the longer upper links...something the Lotus works seemed to miss? Also, to continue along the lines of cleaning up the underside of the chassis, I mounted a 7/8" tubular ARB in the boot with the links going forward through slots cut in the wheel wells to links above the ends of the rear axle.  The bar mounting trunnions were bolted to brackets welded to the rear supports of the roll cage.  I still use this method of mounting the rear bar on our current Lotus Cortina.

Giving credit where credit is due, even after all these years...Help with this setup from Steel Therkelson (one of the Cortina works techs and later for Chapman) His experience was invaluable.

Rod

RE: Puting a 4 link on a unibody???

4 link in IRS car.

Look up how Ford did the 4 link setup on the Mk1 Escorts to convert from leaf springs.  Essentially they cut slots in the floor and welded in boxes.  Simple, quick, and effective.

RE: Puting a 4 link on a unibody???

(OP)
so i just found these clips on bearsperformanceproducts.com and it looks like that i might just get one of them to make my life a little bit easier.
but if i did that how would i make my front end to last? i heard something about capping the frame rails from the front to the back would this work?

RE: Puting a 4 link on a unibody???

Greg

I know plenty of drag racers who are very satisfied with their 4 link designs, in fact, I would think it is the most popular design for cars with rear suspensions.

This link has examples of both types.  

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Puting a 4 link on a unibody???

The four link could be thinked of as  a doubble A-arm system, that is working  in the driving direction.
However, it is not used in top fuel or funnycars, but these are entierly different cars.
Goran  

RE: Puting a 4 link on a unibody???

No suspension at all is still popular in the top levels of drag racing, but it is hardly suitable for the car in the OP.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

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