Pest or cholera - leafs or trailing arms what's better above 120mph?

[kingcrunch]

Aloha,

for my project i am trying to decide between pest and cholera, bettern known as leaf springs or trailing arms. And i would like to ask for some help with that decision.



The situation is as follows:
I want my 1985 Dodge D150 shortbed pickup truck to run a 170mph top speed and handle good on the Autobahn (i am located in Germany) where we have stretches of road where it's legal to run that fast.
I also want to compete on the race track (Nurburgring, etc.) and local autocross (we call it "slalom") events.

Now this thing has 2.5" wide multi-layer leaf springs from the factory with the fixed attachment point in the front.
No sway bar, no parnhard bar, spring over axle setup (could easily be changed to spring under axle), no staggered shocks (and they are pretty far inboard).

I have been looking at C10s and admire the simple coil spring and trailing arm setup and i think that could be installed on my Dodge aswell.
All that's needed is a crossmember for the arms and a crossmember for the coils, both pretty easy to build and if i use the stock Chevy arms (reinforcing them a bit) easy enough to make road legal.

A road legal vehicle is very important to me.
Local laws prohibit welding on the frame completely, so no welding on attachment points for 3- or 4- link setups, no IRS setups (which would require a much more rigid chassis than i can achieve anyways).
Sadly this also outrules a custom chassis because the identity of the vehicle is bound to the frame.


Now that the limited range of action has been described, what could be better for my application?

Thanks in advance for all input. All help is appreciated.

Alex

[RobNoLimit]

Hi Alex. Although leafs could do it, I'm not sure how predictable they would be at speed, especially in the back of a P/U with all of the wind buffering. The one change I would make is with the panhard rod (locator). The OE rod is rather short, and mounted too high, raising the roll center. You will want the longest panhard bar you can fit, and about as low as you can get it. There are many examples of bolt-on brackets and braces that mount the panhard bar down at the level of the trailing arm. Good luck, and please post picts of you on the ring.

[Zspoiler]

Think NASCAR Truck series.

[F-Body International]

Here is what the Camaro/Firebird people do with well performing leaf springs...

Installing some spherical bearings in the front leaf spring pivot point of the leaf spring is known to help it articulate, react faster and keep the pivot point located. Check out Currie Enterprises "Johnny Joint" for this. Some aftermarket high performance leaf springs also incorporate this in the rear leaf spring pivot point.

Delrin or Delalum in the rear pivot point on the frame.

Build a solid leaf spring pad plate for the rear end to lock on the leaf.

Run a nice two, three or four way adjustable shock absorber.

Some run a Watts Link but that might not be allowed for modification in Germany. That's another option you might be able to add to a leaf spring setup.

Good to see someone on here from Germany Alex. I have family members that live around Stuttgart and I've been there a few times. It's a great country to visit!

[kingcrunch]

Thanks a lot!

I have been thinking about spherical bearings in the leaf eyes but it's hard to find bearings that actually fit the springs that come with the truck.
The bushing has a 1" OD, most kits for the application are larger than that. Doing that would require custom made springs.

I ditched the idea of spherical bearings and began thinking about delalum bushings on all 6 attachment points, but i fear this is like adding a too large anti-roll bar to the rear.
That's when i read that leaf springs have very little rear steer and it's hard to tune the roll center because the attachment points would have to be moved...

I think i will have to aquire some more data to see if the trailing arms from a C10 would actually fit in the frame and where i would have to mount the springs before making this decision...

[F-Body International]

1" seems awfully small for a truck spring. You might want to double check the size. Let us know.

There's an AFCO Chrysler piece that's 1.490"
http://www.speedwaymotors.com/AFCO-2...ing,23537.html

[68Formula]

1" seems awfully small for a truck spring. You might want to double check the size. Let us know.

I know, I thought the same. Then I did a lookup on Rockauto, and it looks like it may be correct.

[kingcrunch]

I know for a fact that my W-series (solid axle front, 4x4) trucks had 1.25" front eyes but i am not sure if the same counts for the 2wd trucks aswell.
So it's either a 1" or a 1.25" OD bushing. The large bushings were used on passenger cars. I would have to see if i can mix and match a spring pack with a car main leaf and truck additional leaves...
But in all honesty, i think the trailing arm conversion has more and easier tunability in it... i am not a 100% sure that's the route i want to go but the leaf springs don't have as many pro's left.

I compared frame width and it looks like the Dodge frame is 37.68" all the way from the rear to the transmission crossmember, from where it necks down in two steps to 29.88. That is inside the C-channel.
The D150 frame is 2.27 flange x 6.06 height x .156" thickness.
That means it's effectively 37.992" wide in the rear and 30.192" wide in the front, which by the way is why i can't use the C10 crossmember.

According to the specs i found, the rear section of the C10 frame spreads out to 37.81". Close enough to find room for coil spring mounts.

[kingcrunch]

There seems to be some kind of confusion about the actual length of stock C10 trailing arms.
I figure it could matter less to me since i am placing my own crossmember in the frame where it needs to go with the set of arms i will eventually buy.
But i could not manage to find information on the spacing of the two crossmember mounts and the angle that the spring perches on the axle housing have in relation to the axle housing.
Anybody have these measurements available?

Thanks,
Alex