Bad Ast Suspension Conundrum

[astroracer]

I am finally to a point in the Bad Ast (https://www.pro-touring.com/showthread.php?20086-The-BAD-AST-Project-Faze-II/page12) build that I need to make a decision on the rear suspension. All along I had planned to use leaf springs, knowing the Astro springs I had were not going to fit the shorty van.
Now I am thinking three or four link just because, if I am going to spend 3 or 400 bucks on springs, I would rather spend the money on some coilovers and have the adjustability AND tuneability of a link suspension over the "maybe it will work, maybe it won't" aspect of custom leaf springs. The real issue here is I have NO idea what the van will weigh or what the distribution numbers will be until I get it all bolted together and rolling. With a link style suspension I can build that and cobble together some coilovers to get it rolling enough to get some weight numbers.
Any thoughts? 3link? 4link?
Mark

[Bryce]

I built a 3-link with watts. I like my setup.

What are the goals for the Van?

[astroracer]

Hey Bryce,
Goals? It's built in the PT style so it has to be able to do EVERYTHING, right? Well, really, it needs to be drivable. Anyone living in MI. knows what our roads are like so it needs to be able to handle the potholes and rough roads. I know the front suspension is good, it will be tuneable with the coilovers so I want the rear to have the same tuneability. Most of it's life will be on the road BUT, if I get a wild hare, I would like it to be trackable also.
I am thinking triangulated 4 link just to have the extra strength. Any thoughts you have would be much appreciated.
Mark

[dontlifttoshift]

Skip the tri link. There is no reason to deal with the compromises involved, IMHO.....

I don't know your driving capabilities but you got to be pretty good to tell the difference between the two. Its going to come down to packaging. if you have the room up top a 3 link offers the most options for adjustability. I just put a 3 link in my roadster and love it but I didn't put it in there cuz I'm so smart, it just packaged better than a 4 link and way better than the truck arm set up I replaced.

[astroracer]

Skip the tri link. There is no reason to deal with the compromises involved, IMHO.....

I don't know your driving capabilities but you got to be pretty good to tell the difference between the two. Its going to come down to packaging. if you have the room up top a 3 link offers the most options for adjustability. I just put a 3 link in my roadster and love it but I didn't put it in there cuz I'm so smart, it just packaged better than a 4 link and way better than the truck arm set up I replaced.

Thanks for the insight. I was thinking triangulated to try to alleviate dealing with a panhard bar.
I think I have a panhard bar packaged now along with a very stout non-triangulated 4 link design. Last night I ordered 2" & 1.5" dia by .25" wall D.O.M. tubing for the lower and upper bars and I ordered 4 johnny joints from Currie last night, 2) 2 1/2" x 1 1/4 "thrd for the lowers and 2) 2" x 1" thrd for the uppers along with thier matching tube ends. I hope I am doing the right thing here... God this stuff is spendy. And I still need to get coilovers.
Mark

[wellis77]

Mark, where did you order your stuff and what was the price? Feel free to pm that info if you'd prefer. There is a place in Grand Rapids that I get my DOM that may not be as spendy for you. Not sure how far from GR you are.

[astroracer]

Hey Will,
I try to deal locally if I can. I have worked with Alro for years buying aluminum for my model car parts business but they just seem to price themselves out of the picture. The DOM was quoted at almost 3 hundred bucks. That was drops! If they have to cut anything they tack on 30 dollars... I got the tubing from Online Metals for half the price and that includes shipping! O.M. even gave me a quantity discount AND another 5% if I order again within 30 days. I'd be interested to hear what your supplier can offer. I will be ordering 1/4" & 3/16th's plate for all of the 4 link brackets soon.

[wellis77]

I bought some stuff from Taylor Supply last Christmas and it was cheaper than online metals; a stick and a couple drops. Never hurts to try the next time you need something.

[astroracer]

Okay, thanks. I'll check them out.

[astroracer]

I have been burning the late evening oil working on the 4 link design. I ran the geometry points thru a 4 link calculator so I know the suspension is good. It will work and has adjustability.
https://static1.pt-content.com/images/pt/2011/09/08se11_4link1vi-1.jpg
Rear view from drivers side.
https://static1.pt-content.com/images/pt/2011/09/08se11_4link3vi-1.jpg
I have ordered the tubing and Johnny Joints and will get the plate for the brackets ordered after I have the details complete tonight. The hardest part of the whole design was getting a panhard bar in the right location that worked and looked decent.
https://static1.pt-content.com/images/pt/2011/09/08se11_4link4vi-1.jpg
Right now I have the frame hardpoints for the panhard on the passenger side. in your guys experience is there a difference between one side or the other? I know it effects off corner bite but is there any rule of thunb for a street suspension?
https://static1.pt-content.com/images/pt/2011/09/08se11_4link5vi-1.jpg
I have a few more tweaks to make for brackets and such but the design is 90% right now.
Thanks for looking.
Mark

[exwestracer]

Mark,
Unlike the Watts link, the Panhard bar is a true lever against the chassis. The way you have it pictured will tend to plant the LR tire in left turns and unhook it in right turns. This is also affected by the dynamic angle of the bar as installed in your van.

[astroracer]

Hi Ray,
Trade offs I guess. I really don't want the complexity of a watts but I guess that is the only alternative unless I go back to leaf springs... From what I see the "normal" hard point for the panhard mnt is on the passenger side. Left or Right, either way, it causes issues. The design angle right now is flat at the center of the axle tube. I know the dynamic angle with change with suspension articulation. I was hoping the 34" long bar would alleviate some of that. Do yo have any insight?
Thanks
Mark

[Bryce]

A 34" bar with a 3" travel in one direction will have a 5* incline and a lateral shift of .133".

I would build a Watts. It is not very complicated. you obviously have the fabrication skills.

[David Pozzi]

I've driven both & I can't tell the difference between Watts & Panhard from behind the wheel. I think it's a little easier to get an exhaust system past a watts. If you have a GM rear axle with removable cover, you won't be able to access it with watts brackets in the way. For a spring rate, try something close to what the leaf springs are. Since multi-leaf springs are rising rate I start measuring .5" above normal ride height & end .5" below NRH. They will measure much softer at higher ride heights.

[astroracer]

Thanks for the info guys. I am going to stick with the panhard bar for now. A lot simpler and I already have it packaged...
Bryce, I was planning to add bracing to the frame mount. This is how I did it.
https://static1.pt-content.com/images/pt/2011/09/09se11_4link1vi-1.jpg
I moved the upper shock xmbr rearward about a half inch and plated it with the panhard bar mount. I also added a bit of fore/aft with a close out plate on the outboard side of the mount.
https://static1.pt-content.com/images/pt/2011/09/09se11_4link2vi-1.jpg
The axle mount will see some bracing also, I just haven't hit on a good solution yet.
https://static1.pt-content.com/images/pt/2011/09/09se11_4link3vi-1.jpg
Thanks for looking AND responding, much appreciated!
Mark