rear suspension design help needed

[exwestracer]

Originally Posted by wedged

wow. over 80 views and no one has any thoughts ? OK, how about if we pretend it's a first gen camaro instead of a Job Rated Dodge truck ?

Actually, you've probably got a better starting point for a tri-4 link with your truck...

Some general guidelines:

• Keep the lower links level with the ground at ride height.
• Mount the upper links together on the housing, and apart at the frame (complicated explanation having to do with roll center location deleted)
• Minimum of 60deg included angle ("V" angle) between the upper links.
• Upper effective link length should be roughly 70% of the lower links (this is in side view, NOT the actual hole to hole measurement of the angle link).
• Upper link angle (side view) is impossible to determine without more info, but they should intersect ("IC")with the lower link line no further than the front axle centerline (see drawing)

You will find that your narrow frame width will make it difficult to get both the 60deg included angle and 70% link length ratio for the upper links. Stay with the 60deg minimum for stability. You're not going to be looking at a lot of suspension travel, so the pinion angle change should not be a major issue, especially if you keep the intersection (IC) of the link angles in the front half of the wheelbase.

Hope this all makes sense.

[wedged]

Originally Posted by exwestracer

Hope this all makes sense.

Most of it Thanks !. Any particular length for the bars, or should I base the length of the lowers on how long I can make the uppers ? I'm not too concearned about retaining bed space, so I can make my frame any way I need to in order to accomodate the suspension.

I'd like to hear more about centering the uppers on the housing as opposed to centering on the frame, which is what I was considering. It's easier to weld to the axle tubes than to the cast center of the Dana. I can always make a bracket for mounting to the center of the diff. If you don't feel like typing and know of a link, that would be great.

The upper and lower link points on the housing will obviouly be seperated vertically. Is there any specific distance I should aim for ? And should that distance be equally divided above and below the axle center line ?

[ironworks]

For the situation you have a tri 4 link will be tough. I would do a standard 4 link with level lower links at ride height. Make the lower links 30-34 inches long. Make the uppers 70-100% of that length. Set the instant center at about the bell housing of the top hole and just lower the second adjustment hole about .75 of and inch on the front upper mount on the chassis. Then build a pan hard bar that is level at ride height and as long and low as possible. Then mount the shocks as far out on the axle as possible.

This is super basic set up that will get you started, Could you design way more high tech set up sure, But at the end of the day this car will never sit on the Pole at Daytona.

Key points - level lower links and pan hard bar at ride height. The longer the panhard bar. The longer the links the better the ride quality. I have been told that after 34 inches it does not matter. Ideally you want the center of Gravity below the Roll center.

Ready Set Go

[Kenny]

The advice these guys have given is good stuff. The only thing that I would add is the link length...... The shorter the bottom link, the higher percentage the top length should be. So let's say you end up where you only comfortably fit a 20" bottom link, then you will want closer to 20" on the top. That would reduce some of the bind during roll that would be created with a much shorter link. To give a point of reference on that length, it is 19" (if my memory is correct) on 3rd and 4th gen F-bodies. That length seems to work fine as roll steer goes, but longer would theoretically be better.

When working on "bagged" suspension that has a fair amount of travel and using 22" lower links on a shorter wheelbase than yours, the bind from using shorter 18" angled upper links would split poly bushings and kill u-joints. Replacing the urethane with rod ends made the ride quite harsh. Simply moving the upper mounts and going with 22" uppers brought this back where it should be.

Usually these projects "evolve" quite a bit during construction...... So the choice of these upper link mounting styles you choose, and how much pinion angle change you want, will dictate the length ratio...... Of course that is only one man's opinion.

Beautiful project BTW

[exwestracer]

Originally Posted by wedged

Most of it Thanks !. Any particular length for the bars, or should I base the length of the lowers on how long I can make the uppers ? I'm not too concearned about retaining bed space, so I can make my frame any way I need to in order to accomodate the suspension.

I'd like to hear more about centering the uppers on the housing as opposed to centering on the frame, which is what I was considering. It's easier to weld to the axle tubes than to the cast center of the Dana. I can always make a bracket for mounting to the center of the diff. If you don't feel like typing and know of a link, that would be great.

The upper and lower link points on the housing will obviouly be seperated vertically. Is there any specific distance I should aim for ? And should that distance be equally divided above and below the axle center line ?

Yes, figure out the maximum effective length you can get for the upper links with 60deg included angle and build the lowers from there.
If it were me, I'd buy one of those heavy duty steel rear covers they make for the off-road guys and weld the upper link mounts to that...
I just typed the explanation for the direction of the links over on pro-touring, so feel free to have a look... http://www.pro-touring.com/forum/showthread.php?t=73355 The main issue I see with your project is fenderwell clearance looks pretty tight. I think I'd want as little axle movement as possible.

As far as the vertical link separation, it all depends on how hard you are realistically going to hammer the thing... Obviously if you mount the uppers at the top of the diff, you've got some separation built in already. I normally try to keep the lowers feeding directly into the main frame rails, as they are taking ALL the drive force from the axle, so your ride height for the frame would come into play with how far your lower housing mounts are off the ground.

If you decide to go with a straight (4 bar) setup as others have suggested, IMO you have way too much tire (not enough room) for a panhard bar locator.

[ironworks]

Originally Posted by exwestracer

Yes, figure out the maximum effective length you can get for the upper links with 60deg included angle and build the lowers from there.
If it were me, I'd buy one of those heavy duty steel rear covers they make for the off-road guys and weld the upper link mounts to that...
I just typed the explanation for the direction of the links over on pro-touring, so feel free to have a look... http://www.pro-touring.com/forum/showthread.php?t=73355 The main issue I see with your project is fenderwell clearance looks pretty tight. I think I'd want as little axle movement as possible.

As far as the vertical link separation, it all depends on how hard you are realistically going to hammer the thing... Obviously if you mount the uppers at the top of the diff, you've got some separation built in already. I normally try to keep the lowers feeding directly into the main frame rails, as they are taking ALL the drive force from the axle, so your ride height for the frame would come into play with how far your lower housing mounts are off the ground.

If you decide to go with a straight (4 bar) setup as others have suggested, IMO you have way too much tire (not enough room) for a panhard bar locator.

Your correct, but since he has the big wheels he can make the panhard bracket go out into the wheel to increase the length. The frame rails will be pretty narrow due to the wide tires so the angled upper links will be pretty short to have any kind of angle especially if the he does not want to build off the housing.

But either way, both methods will require creative packaging for either the upper links or panhard bar

Chassisworks makes a rear clip that is a nice tri-4, You can buy the links and the axle housing and save your self a bunch of time. They might make a jig to install these parts on a dana 60 housing. We have used this product on quite a few different cars with good results.

http://www.cachassisworks.com/Attach...ons/916241.pdf

[exwestracer]

This is true, but the frame end of the panhard would still be close to chassis centerline. I always try to keep the panhard centered on the chassis, so the roll characteristics are the pretty much the same in left and right turns. Probably doesn't matter, but I figure you can't go wrong doing it that way...just my $.02...

[wedged]

Now we are getting somewhere ! Thanks everyone.

just to clarify a few things:

I will end up with at least 1" clearance from the tire to any body sheet metal, probably closer to 1.5". In the pictures it's at about 1". I'll build the rear axle to be about 1" total narrower than I want and then I can use thin spacers to dial in the final width.

For the mounting the upper links, I had already thought of the off road diff or making a tube bridge over the diff to weld mounts to. There may even be diff covers with mounts already on them, but I have not searched enough yet.

I will probably start with coil overs, but may eventually end up with bags all around. I'm just not sure if I want to add the tank, compressor, etc.

Am I correct thinking the uppers are 60 degrees compared to each other and not an upper compared to a lower ?


I just test drove a pro street '68 barracuda that I put a new set of gears and one new axle into. It's a ladder bar car with heim ends. I'm not putting up with the constant clunking and clanking and that's why I want to use urethane in the truck.

I also have a '68 satellite in the shop that has an Air Ride 4 bar in the rear. I had thought of taking measurements off of it, but I feel that set up is compromised from being ideal in order to be a bolt on kit. So why bother copying it ?

[exwestracer]

You probably won't find a diff cover with exactly the mounts you are looking for, but there are some out there that would be a good start. I wouldn't bother with the bridge on that Dana 60...a 10 bolt is a different story.

You are correct about the 60deg referring to the angle between the 2 upper links.

[wedged]

I made a quick 2d overhead view cad drawing. O-O of the rails at 30.0", upper links mounted 6" apart on rear. I came up with 58 degrees included angle with an effective length of 18" for the uppers. Using the 70%-100% idea, the lower links would be 26" or less. I forgot to dimension the actual length of the uppers.

If i kept the frame rails wider in front of the tires, or had a crossmember in directly in front of the tires, I could make the upper links longer.

I'm going to fiddle around with the drawing and see what i can come up with.