View Full Version : Four link placement questions

03-25-2006, 09:25 AM
I'm designing and building my first chassis. It's a bit different from a traditional chassis built car as it's going under a unibody car (front wheel driver getting a rear wheel drive conversion). I'm questioning the placement of the four link rear suspension. Keep in mind another oddity of the car is it's being widened...a stock ford 8.8 out of thunderbird is being widened 4" on each side (8" overall). With that in mind I've been told and it make sense to me, to get the four link mounted out as wide as possible on the rear axle, which puts it outside the rear "four link" bumped frame rails. This was the plan until I realized the coilover would need to go on an angle under the bumped rails. I've seen that before, what are your opinions on that? Another issue with suspension outside the frame is looks...this car is more "show" than "go" so it needs to look good, the rear floor will have a bunch of plexi to show off the suspension etc. Here is a view of the four link outside the rails.

Another option is to put the rails out as far as possible (I have 36" outside for either the rails or four link) and move the four link inside...this looks much better and the coilover will be vertical which I would think is ideal for the suspension? The only thing this option has against it that I can think of is I just moved the four link in almost 3" per side...is that an issue? the outside of the backets would be just over 30" apart. Here's a view of it.

Here's a shot of the overall chassis. Might not be as beefy and braced alot I see but like I said it's going under a unibody...those main long runs down each side sit flat on the floor of the car and will be welded or bolted to the unibody rails. The driveloop and front "bumper" and rear "bumper" crossmembers also bolt or weld to major parts of the car (haven't decided if I want to weld it yet). Any major issue you guys see with it?

Thanks guys!

03-25-2006, 03:01 PM
I would need some more information for a good answer.
what are you doing with the car or what are your expectations of it?
if you are drag racing that having the links inward a bit would not be so bad. if you are road racing then you do want the links out as far as can be. you can tilt the coilovers and that is ok but remember you will soften then by doing so. let me explain that, if the spring is straight up and down then you will get 100% of the spring rate and 100% of the shock dampening. as you tilt the coilover you will get less. for example, if you tilted the coilover 45 degrees the spring would feel conciderably softer than if straight up, so you will then have to go a heavier spring and heavier dampening to get the same result.
in short, it is ok to tilt the coilover a little for application fit but do not go too much as it will start to hurt you. and yes for the best reaction you will want the springs out as close to the end as you can.

on another note. I was looking at your frame design. if you are going to have a full unibody sitting on top of that chasis and you will not be cutting out the whole trunk area, then you may not need to extend the frame beyond the rear springs. this can sabe weight and make fit easier if there is still enough material in the body to suport the rear section and the bumper.

what car are you working on?
have you concidered the 8.8 out of a lincolin town car for the width


03-25-2006, 06:05 PM
THanks guys, I appreciate the time. The car is a 97' Ford Probe. Goals...well the project is kind of an exercise in pushing myself to do alot of stuff I haven't done before...that's kind of how I learn and helps me be more efficient on easier stuff I do for my clients. The car will most likely be a trailer queen but if I can somehow get it inspected and on the road she may drive around a bit but no road racing...it might see a drag strip once just to get a number and dial in the engine. I have cut all the sheetmetal out of the rear end up to the unibody rails but it didn't have any strength. I had to also cut the rear unibody rail to get down to ride height (axles tubes were hitting) but I "c-notched" them before I did to keep some strength before it's bolted to the chassis, I'm doing the same to the front end now. I may not go back behind the rear coils as far as the solid model shows but the bender will need that much length to make the final bend, I can always cut them off once I get them. I hadn't thought of a lincoln rear end...I got the thunderbird rear basically for free and measured a couple other's (mustang, trucks etc) and they were all pretty close to this one so I went with it, but I'll check into the lincoln, thanks for the tip.
I did forget to the put the panhard bar on the solid model, good catch Richard :) I'm using this kit from TCI http://www.totalcostinvolved.com/productdet.cfm?prodID=831 which comes with a panhard bar. I'm leaning towards putting the link inside the rails, I loose the width and it may not be as functional on corners but it looks a ton better in my mind (envisioning what I will need to do to show off the rear end) and simplifies a few things for me. I hadn't thought about the coilover being on an angle being a good thing but it makes sense...I can incorporate that into either design so I'll plan on a bit of angle on the inside the frame rail design.

03-25-2006, 06:30 PM
I you are going for a race look the 90% of the time the 4-link bars are directly under the frame rails. There are a few reasons for doing this. One is ith is easier to do you sheetmetal work. It also alows you to place both the frame liks closer to the tires.
I have a couple of questions? Frist what size tire/rim combo are you wanting to run. Next why would you have to widen the 8.8. I have installed that rear end in a lot of different vehicals and have never needed to widen the rear. If you need a wider rear I would look at an 8.8 from an F-150. It should be aas wide as you need. Also most of the time they will come with a posi and all the trucks have 31 spline axles. Tilting the shocks on an angle would make for a much more street friendly ride. If you give a few more details about what you are wanting to do I am sure that we can help point you in the right direction.

03-25-2006, 06:33 PM
hi there i think if you are going to a four link i would build the frame rails up high and mount the four link under the frame rails and possibly use some rubber bushed rod ends ,now remember a drag race style 4 link will be noisy ,not corner real good, plus other guirks? i think i would mount the lower bar straight ahead and try to triangulate the uppers ? your coil overs can protrude through the floor and attach the upper mounts to a crossmember off of rear kickers ? i hope i havent confused you good luck mike "carryallman"

03-25-2006, 07:05 PM
The F-150 I measured was pretty close in width to the thunderbird rear I have now, that was the main reason I just stuck with this one. Widening the car was one of the first design goals of the car. Alot of my clients have sad looking tasteless "wide body kits", this car will have what I consider a real "widebody kit" so I need a wide stance to work with. Oh, the wheels are 19" with...35 series tires I believe, I forget, I've had them for awhile. Like I said, it's a bit of a different project than most of the hot rods being built around here :) I've also seen the race/drag style four links with the links under the frame rails, part of the reason I went with this kit from TCI is how low it stays. The drag style kits eat up the entire rear of the car, this is staying nice and low so far. My main business is custom car audio so I need some space to show off equiptment and make a tastefull interior (another trend I see in my client's requests that bugs me...tasteless gaudy interiors). I still need it to look like a car inside once done...not a drag car with huge tubs in the back :) I have it mocked up a bit if a picture would help, I'll take one tonight and post later.

03-25-2006, 09:27 PM
how wide are you making this that you cannot just go with a wheel with the width and ofset that would allow you to use the rear as is.

also, what engine are you using? in many states if you stick with the same year engine and keep all the emissions for that year (say a 5.0 or 4.6) then you can go through smog as the year vehicle it is.
you can also usually go to the newer engine by undating the emisions to the year of the engine as long as it is newer than the car


03-26-2006, 05:35 AM
I see. You are going mostly for the tunner look with a rear wheel drive. i understand. I have used the TCI kit before and was not very impressed with the results. I would suggest using a Trangulated 4-bar/link system. It will still give you the look you are after plus you will not need a pan hard bar or track locator. If you still like the look of the paralell 4-link then I woul suggest the one S&W Race Cars make. It is a very nice kit. Installs nicely and has a good ride. I have installed several of these on street rods and have been well pleased.
S&W Race Cars (http://swracecars.com/street_rod_4bar.asp)

Peter Miles
03-26-2006, 08:53 AM
I would suggest using a Trangulated 4-bar/link system. It will still give you the look you are after plus you will not need a pan hard bar or track locator. If you still like the look of the paralell 4-link then I woul suggest the one S&W Race Cars make
Donnie, the main page at that link says:
The suspension experts at S&W Race Cars have just made it easier to install a four bar suspension under your street rod. S&W's street rod 4 bar is fully adjustable and features high strength polyurethane ends for a smooth, quiet ride. Precision cut brackets and a 2" x 3" rectangular front crossmember round out the package. Simply add a panhard bar and your favorite coil-over shocks and you're all set

Were you suggesting that the S&W parallel unit did not need a panhard bar or that a triangulated unit would not? As I reread your message I think that you are saying the latter but I just wanted to check.

03-26-2006, 06:44 PM
The trianguler will not need the pan hard bar. the S&W 4 bar would require a pan hard bar.