Four-bar rear suspension: position width? mounting?

For those of you who run four-bar rear suspension, I would like some feed back on a couple things.

1) What is the ideal width to space the mounting brackets on the axle?

The "normal" set-up seems to be a link slightly above the axle center and one positioned below. I****ume this if for torque support, but... I've seen people run BOTH below the center of the axle...

2) What's the limit to how far below the axle centerline you mount the links?

I would appreciate your feedback on this. I'm still working on my frame layout and I need to get these couple things answered before I can continue with the layout.

Anyone running 4-bars UNparallel? How did it work out for you?

 

the one rule of thumb i have been working with is this

"top axle mount slightly above axle centerline, and bottom mount below centerline but (obviously) above the scrub line"

keeps axle wrap down to a minimum, and gives clearance above the axle for suspension travel under the frame crossmembers

running both mounts under the axle would seem to give less support to keep the axle from wrapping up. . . in my minds eye i see the thing "crawling" up over the top bar and causing all kinds of headaches and binding under accelleration... you'd have both bars "pulling" against the torque, and nothing "pushing" against it.

 

In both cases, above and below the axle, you gain more control over the axle as you go farther away. This equals less stress on the parts, however, that stress is transfered to the brackets. It's a balancing act, of sorts. Don't deviate too much from the norm and you should be OK. I think you'll have packaging issues before you have stress issues.

As far as how far apart? As far as possible. When one end of the axle goes up and the other doesn't, there has to be X amount of deflection in the bushing at the rod ends. For the same amount axle twist, there is less deflection farther out.

 

This was basically the theory that made sense to me as well. I think I will be safe if I follow this.

Can someone take a measurement for me on how far apart their brackets are on the axle? Just need a reference for right now.

Anyone care to share their 4-bar set-ups? Pics? 4-bars with transverse spring pics would be good too if anyone has some.

 

Scooter---You can make the center to center of bars whatever you want it to be, but around 6 to 6 1/2" works very well. The main reason that people put the largest offset towards the bottom of the axle is to gain floor clearance. This is the setup I'm using on the roadster pickup, using an S10 rearend and "swap-meet" coils. I run a set of bayonet style shocks inside the coils to hold everything together.

 

Found a more finished picture, shock is not in place yet

 

I noticed you angled them in a bit. How did this work out for you?

 

The coil springs are are the power coaters ... The chrome shocks and the sway bar not yet installed ... the stainless bars are wrapped to protect them ... for now ...

This is a TCI kit ... on a original 32 Ford frame ...

 

Very nice indeed!

Who else sels 4-bar set-ups?? I'm sort of looking for something that doesn't have the shock/coilover mounts on the bracket. I can always cut them off, but if anyone makes them with cleaner bracketry, that would be good.

 

Scooter---I have built 3 ground-up cars with that same basic configuration on the rear locating bars---2 with hairpin type links and the most recent with 4 bars---they all worked great, but I think the 4-link works better than the hairpins. Build your own 4-bar brackets---thats what I have always done. Make cardboard templates, and burn them out of 3,16 or 1/4" mild steel plate.

 

Was thinking of doing that also. I have access to a plasma cutter anytime I want, and this may prove beneficial to get exactly what I want. Will probably do the same for the spring mounts.

I found this website when looking for some 4-link parts sources. Great geometry explanations here:
http://www.thedirtforum.com/4link.htm

Also found this place for some********* 4-link set-ups:
www.suicidedoors.com Someone referred me to them a while back. Super burly links intended for the lowrider scene.

 

by running them unparallel ....you can control where the instant center is ....(as in where the suspension links intersect...and where it is lifting from ...) ....this style works well if you plan on racing or anything like that.....you can also set up your triagulated 4 bar set this way as well ....moving the instant center deal really makes the car hookup better ....lord knows it really makes a gm a/g body work .......brandon

 

Know what you mean. I have some concerns about this though. I'm running a transverse spring, so I have to be careful about the travel of the axle itself. Also, this car is will be pretty much street only, so not too worried about shaving tenths at the light or anything.

That link I posted a bit ago shows some different things with how the instatanous center relates to the 4-link angle... or maybe that was something else I saw... I'll have to look again.

 

A wise man would run parallel 4 bars, with adjustment at at least one end of each 4 bar link for adjusting the pinion angle, and for centering the rear axle square to the chassis centerline. A cheap man would measure carefully and weld the 4 bar ends solid (because its cheaper). Thats what I did---and the hot-rod Gods smiled on me this time---it works great.

 

I'm thinking about running four of these:

http://suicidedoors.com/4-LinkRoundAdjBarwithSuperPivot.php
They're huge! Probably go with 20" length or so. I'll make my own brackets out of some 1/4 plate stock and box each mounting bracket. I'll probably just pick up panhard from speedway way to keep it centered.

 

Here's mine

 

Your set-up brings me to a couple of questions I was already thinking of asking...

1) How long are those bones?
2) Are the aircraft type, swivel rod ends good for this application or should the standard adjustable bushed type be used?

Looks pretty clean... where is that from or did you put that one together yourself?

 

Dont have them in front of me right now, but the "bones" were about 20 inches long. I use the aircraft type swivel rod ends (heim joints) I used them for a lot of years sprint car racing , and in my opinion even the cheap heims(about 12 bucks from speedway) are better than any clevis type end. I raced the cheap heims and never had a failure.
I make all my own brackets cause I just enjoy that kind of work. The rods are DOM tubing that I threaded. Those weld in bungs folks use just look kinda horsey to me.
A days time can save you lotsa dough, but then I could fabricate brackets all day long and enjoy it. I fell offa ladder onto my head when I was eight, though.

 

I want to do a triangulated setup when I do my rear suspension/axle swap this summer, so I want to get as much info as possible before I jump into it.

I see some people have the upper bar mounts on top of the carrier housing, some right next to it, and some just half way down the tube.

Where would it be best to mount the upper bars onto the axle? Or is it more of an angle thing?

 

Scooter---use the microflex bushings from Pete and Jakes----they have a steel inner sleeve, a steel outer sleeve (which your bars weld to) and a urethane bushing in between the two. This not only isolates the frame from road vibration and harmonics, but will allow some flex to prevent bind in the linkages as the suspension works. They are relatively cheap, I paid less than $9 Canadian for one last month to replace an end on my Panhard rod.

 

I'm not sure what you are running to suspend your rear suspension, but you could also consider a wishbone located 3-link. They are real simple to set up, and perform very well.

Suicidedoors sells a custom built to your specs 3-link, heres the link:
http://www.suicidedoors.com/UniversalWishboneKit.php
As a rule of thumb, you'll want the wishbone length equal to, or slightly less then the length of your outside parallel bars. Even with the rear of my sedan bagged with 8" of suspension travel, the pinion angle remains very good.

For a bunch of reasons too lengthy to get into, I had to fab up a bracket to mount the wishbone to the pumpkin. But on a normal axle housing you could just weld tabs to the axle for the wishbone.

Heres some pics of my 3-link. I had Jason at Suicidedoors make it, and as all of their stuff, its super high quality

Should you decide to use the parallel 4-bar, he also offers a real nice panhard bar kit http://www.suicidedoors.com/PanhardBarKit.php

 

Hey Dodge! Glad you buzzed in!

I would seriously consider going the same route w/a 3-link except that I'm going to run a tranverse spring that will be mounted ahead of the axle (won't go into detail why I'm going that route right now). I won't be able to sneak the top link by the spring to make it work. So, I'm going to bust out the 4-link w/panhard. Yes! That panhard looks bad****! I will run that if I go with a weld on. I'm going to run a quick change and may not have that luxury, so I may have to go with a bolt on that mounts just behind the yoke. Like this P&J:

Because of how close my rear frame kick up will be, I can mount the other end right to the inside of the kick up.

 

If you run a triangulated set-up, with the top links attaching to the framerails at the front end and to the pumpkin at the rear end, the closer together the links can be at the pumpkin end, the better it will be---the ultimate best being a perfect triangle (which is pretty well impossible to achieve). The reason for doing this, is that if you do it right you can get away without running a panhard bar. The triangulation of the top links does the job of centering the axle housing in the frame.---goes back to high-school physics---in that a triangle is a rigid structure and can not collapse. In a set-up where the rear of the top links is moved out away from the pumpkin onto the axle tubes, you no longer have a triangular structure---you now have a parallelogram, with the axle tube now being the fourth side of the parallelogram. A parallelogram is not a rigid structure, and your axle housing can now move side to side relative to your framerails, so you need a panhard rod to keep it centered.----simple, eh!!!

 

Simple is right and I've always liked triangulated 4-link, but I don't really like the idea of welding to the aluminum bells of the quick change. For one thing, I don't have a TIG and I'm not planning on getting one for awhile. If I weld to the axle tubes right before mating with the bells than the short side of the parallelogram gets too long and the system is no longer as effective (to be ideal). The other thing I like about triangulated system is the zero-movement aspect. No left to right movement. Unfortunately, I really think I'm stuck with the parallel over the triangulated.

 

Here ya go.

 

Hey C9! Thanks for posting those pics! That's what I wanted to see! You gave me some new ideas just now... What spring are you running back there and how far apart did you weld your spring brackets?

Since I'm stuburn and determined to put my damn spring ahead of my axle, I'm trying to figure out the best way to locate it. I'm thinking I may actually run the spring between the links. I'm going to have to model it before I commit though. The last thing I want is to have the bottom link hitting the spring as the rear comes up. I think can locate the links a little further apart vertically to make it happen.

 

The spring is a 40 Ford rear spring pack.
The top two leafs are out, but will probably go back.
The original second leaf is gone as well and it could go back if needed.
I'm thinking probably not since the car is pretty light in the rear end, maybe a thousand pounds total on the rear tires. (And 1200-1300# on the front.)

Main leaf is a SoCal item, but they no longer sell only the main leaf.
Regardless, any spring shop ought to be able to make one for you.

The brackets are also SoCal and are mounted 44" apart on a 56" wide rear axle - measured outer drum to outer drum.
(A lotta guys are measuring flange to flange and if you do that you need to add 1/8" per side to equal the outer drum figure.)

Long as we're talking brackets, you can save yourself some work by buying them.
Brackets aren't too expensive, especially the single piece ones.
The price goes up when there's some welding on them.

Look for brackets at the usual places. (Circle burner shops carry lots of different ones for cheap.)

Chris Alston Chassisworks sells them separate and in fact the four links you see on the 31 are Chris' 1 1/4" comp 4 links and brackets.
Equipped with the Heim joint looking polyurethane ends.
Got no pics of those, but they should be pictured in Chris' website catalog.
They look like a better way to go than the usual poly bushings.

My 32 runs home-made 4 bars on the outside of the frame and uses a cut down Chris Alston ladder bar bracket on the rear axle.
55" wide rear axle with 10" wide wheels and big tires.
It's a close fit frame to tire, but no clearance probs even when entering steep driveways at an angle.

The parallel 4 bars on the 32 work very well on the street.
The tires bite fairly well if the street is clean, but as DRD57 noted, the rear end does squat a bit.
That's ok though, most chassis builders recommend parallel mounting for the 4 bars - as viewed from the side - for street runners.

The 31 has adjustability in that I can run parallel 4 links on the street and change them as per the instant center bit if I need more tire bite . . . which I probably will since the rear tires aren't too wide and the engine will exceed about 520# torque.
Got a locker in the car as well as the strong Dutchman alloy axles.

Sideways in 2nd gear and lots of tire smoke will be easy.

Not that I would ever do such a thing....

With a little thinking you should be able to come up with a bracket to mount a transverse spring in such a manner.
Keep in mind the springs outer end travels with the rear axle during it's vertical travel so you shouldn't have a problem there.

If you're running a Model A spring and crossmember there shouldn't be a problem setting up the spring brackets.

Install a spring mount to the 4 bar mount.

Don't forget the panhard bar.
Long as you can make it is the rule there.


The pic shows how low the 31 is in the back.
That's the reason the top two leafs will go back in.
If you look close at the above pic of the rear axle 3/4 rear view, you'll see a "wear" pad between spring and crossmember.
If needed I can gain some rear height by inserting a spacer - probably aluminum cuz I got a bunch.

There isn't a whole lot of tire to fender clearance and I want to be able to achieve full rear suspension travel without having the tire rub the inside of the fender.

Rear axle travel is where the transverse leaf system really shines.
Coilovers don't cut it as far as travel goes.

A coil system with separate shock as shown in Brianangus and Deuce Roadsters pics will have a lot of travel as well and a setup like that would work well imo....

 

I meant to add that the tunability factor as far as ride height and ride quality goes is great with a transverse spring.

Moreso than a separate coil/shock setup and way more than the limited travel coilovers.

I recommend highly the installation of a rear sway bar.
Not to be confused with a panhard, I see some folks calling the sway bar a roll bar or calling the panhard a sway bar.

I have one on the 32 and to put it bluntly, I wouldn't like to drive it without one.
You don't need one on the front.

 

Great info!!! Really helpful!!!

Here's what I know so far about the way I have to go... Model A spring (to clear the QC center section) and Model A cross member. I did some quick hand sketches and it looks like I will have plenty of clearance with a link over and a link under the spring. I think if I run a reversed eye spring that might help as well... or not. I may need to run the regular eye to keep the spring from hitting the center section at full travel. I think I may have to custom make all my brackets so I can squeeze everything in just where it needs to be. I would also like to be able to adjust the IC by having a couple extra holes for the links on the frame end. Will have to do some math and some layout sketches to scale to figure out the best set-up for that.

The panhard is going to be a little tricky. I would like to keep it as long as I can, but whatever I do, the only place I have to mount to the frame will be at the rear kick up since there will be nothing to mount to behind that. If I weld to the axle tube, I may have quite a tangle of things and I will for sure have to jog the panhard around some things to make it work. Off the center section behind the yoke will be the simplest, but it will also be the shortest. No free lunch with this one!

 

I really like the simpler design of the 3 point over the 4 point. Now that I am thinking about using a 3 point, I have a couple of questions.

Is the point of the wishbone to eliminate the need for a panhard rod? I don't see how it could be fully eliminated. Seems like you would still get some flex at the urethane bushings at one end or the other.

Could you just use a single straight link connected on the top of the diffy with typical urethane pivot points and a panhard rod? I'm just thinking this would be one less thing to weld to the rear end.