What rate leaf spring for my Mopar?

[mrn2obelvedere]

Im having a tough time visualizing this...could you post a pic of this?

[Bryce]

real quick crude CATIA model

[mrn2obelvedere]

Ok...but those are just spring clamps...they don't really allow much leaf to leaf movement.

I will keep this in mind though as a potential tuning tool....it seems easy enough to fabricate something like that, and adding/removing leafs should be a snap.

[autoxcuda]

Ok, here's what I have decided to do for now. I am going to run the stock leafs for the time being and try to focus on other aspects of the suspension first. I am going to replace the shackle bushings with solid units, and I will replace the front spring bushings with these nifty Afco pivots that I purchased. These give a solid connection but still allow the spring to twist (if the spring can't twist then it binds and affects the spring rate).

Some people consider the added rate of the leaf spring twist a benefit of a progressive rate. A sway bar if you will.

The plain bearing aspect of also helps locate the rear laterally some. The uni-ball will allow a little more float from side to side.

[rrunner68]

You can make them pretty easily. Just some flat stock of 1/4" by 3/4" wide. Drill two holes and bolt together. When i did this I used stainless bar and stainless fasteners. Just make sure it is a tight fit on the bolts. the bolt spacing (not hole spacing) should be the same width of the spring. I used 5/16" socket head cap screws.

Not all of us have the awesomest hardware section in the county at work you know.......

[mrn2obelvedere]

We all have the awsomest hardware section in the world...everyone should know mcmaster

http://www.mcmaster.com/

[mrn2obelvedere]

Some people consider the added rate of the leaf spring twist a benefit of a progressive rate. A sway bar if you will.

The plain bearing aspect of also helps locate the rear laterally some. The uni-ball will allow a little more float from side to side.

Yes that makes sense, but I have a sway bar already, and I am using a panhard bar as well. I am using the solid bushings/pivots because I think this will help the suspension move more freely, while at the same time more positively locating things.

[Norm Peterson]

Yes that makes sense, but I have a sway bar already, and I am using a panhard bar as well. I am using the solid bushings/pivots because I think this will help the suspension move more freely, while at the same time more positively locating things.

Once you add a PHB, I don't think you want to be positively locating the leaves in the lateral direction. If anything, you'd want to let them be able to move laterally a small fraction of an inch.


Norm

[John Wright]

[deleted list of questions]

[Bryce]

Not all of us have the awesomest hardware section in the county at work you know.......

Whats up man? Ya, Im pretty lucky. Thats why I work there one day a week.

McMaster is really expensive tho. But they have everything and same day shipping.

[mrn2obelvedere]

Once you add a PHB, I don't think you want to be positively locating the leaves in the lateral direction. If anything, you'd want to let them be able to move laterally a small fraction of an inch.


Norm

Hence the Afco pivots, these will allow the springs to move around while still being mounted solidly.

[High Plains Mopars]

So what t-bar/S-bar combo do you want to run up front?

[mrn2obelvedere]

I'll tell you what I have already and maybe I can go from there.

I have upgraded the front end with magnum force adjustable UCA's, and I have a 1-1/8 diameter sway bar. It is an Addco. I am in the process of modifying the Addco setup to remedy the mickey mouse (at least in my opinion) mounting configuration. I will replace the sway bar links with a solid rod end setup of my own design, and I'm trying to find nylon or teflon sway bar bushings but have not gotten very far with that.

I still have not selected shocks for the car. There are a number of brands that I am looking into but I can't get any good comparative information on them. The ones I know of are Bilsteins, Koni's, Spax (of which I don't even know how to acquire), and QA1. With the shocks, I'd prefer to have something that is externally adjustable, as I know that I am too lazy to be taking shocks apart to change the valving.

I probably won't go with large diameter wheels, I really like the vintage trans am look with the minilites, or I might go with a set of Aero race wheels. I know this limits my tire selections, so when I get to the point where I'm ready to autocross the car I will have to find a set of race rubber for 15" wheels, but I'm pretty sure I'll be able to find something.

[Norm Peterson]

I will replace the sway bar links with a solid rod end setup of my own design, and I'm trying to find nylon or teflon sway bar bushings but have not gotten very far with that.

I doubt that there's enough stiffness or noise benefit to be had in the bar to chassis bushings that would take polyurethane out of the running. As long as the bushings are the right size, there won't be much compression between the poly and the bar (which is what develops the friction that ultimately leads to something squeaking when motion occurs).

I probably won't go with large diameter wheels, I really like the vintage trans am look with the minilites, or I might go with a set of Aero race wheels. I know this limits my tire selections, so when I get to the point where I'm ready to autocross the car I will have to find a set of race rubber for 15" wheels, but I'm pretty sure I'll be able to find something.

This may depend on how far up the food chain you're looking at competing in. There is at least one 275/50-15 R-comp tire (see Hoosier R6, which is more of a road-race compound than specifically intended for auto-X), but not a lot more. Most of the more recent cars that fit into FS and ESP have been running on 265/45-16, 275/40 and larger 17, and 285-up 18 R-comp sizes.

You might have better luck with real racing slicks, or in finding 17" wheels in the same pattern as the 15" Minilites/Aeros/etc.


Don't get me wrong - I'd really like to see a couple of 275 and wider 15" sizes in something like Nitto NT05 or Toyo R1R for thge street and in a shorter profile R-comp for auto-X.


Norm

[mrn2obelvedere]

[QUOTE=Norm Peterson;604747]I doubt that there's enough stiffness or noise benefit to be had in the bar to chassis bushings that would take polyurethane out of the running. As long as the bushings are the right size, there won't be much compression between the poly and the bar (which is what develops the friction that ultimately leads to something squeaking when motion occurs).

The bushings I have for my end links are rubber, and even poly will deflect a great deal more than a solid connection IMO. I would at some point like to make the setup adjustable, and this arrangement I have will greatly facilitate that.

As far as wheels go, I'll cross that bridge when it comes to pass. My car has a long way to go before I have the guts to show my big porky car at an autocross event dominated by miatas and civics. For the street at least, I will go with some decent street compound tires on 15" wheels. Perhaps I can find some decent lightweight 17" wheels for auto-X use later on.

[Norm Peterson]

Are you talking about endlink bushings or the bushings at the chassis brackets along the torsional section of the bar itself?

For endlinks, poly isn't the best option for at least two reasons. It's soft enough to trade away some sta-bar effectiveness. And it's stiff enough to let suspension movement start bending the endlinks if it is overtorqued on installation to improve the stiffness situation.

Many OE sta-bar installations have moved away from the split bushing design, probably because you can't easily/cheaply improve both of the above conditions at the same time without going to a still stiffer/heavier/bulkier bar.


Norm

[High Plains Mopars]

If your fabricating all your parts, then there is no practical limit except your skills and wallet.

However, if you dealing with the original architecture and the associated bolt on components, then selection options change.

If you are going autocross, then you will likely end up with 1.22 t-bars and possibly a 1.25 sway bar, but like I said before, mopars do not have the selection of front end rates that ford and chevy coil spring cars do, so you rear wheel rates will largely be dictated by what you run up front, if you are staying with torsion bars. At that point, spending the effort to make the rear sway bar adjustable will probably yield better dividends than having an adjustable front bar. Or, simply bolt in an adjustable Hotchkis rear bar. So, if you can tell me what your front combo is, or is going to be, I can tell you what your rear combo will need to be to keep things somewhat in balance.

However, the addition of a panhard bar in the rear may have already put your car in an autocross class that you need to look beyond t-bars and 15" rubber to actually be competitive. I am somewhat ignorant of SCCA and NASA classifications for solo, so perhaps a reading of the rule book is in order. If your talking Goodguys autocross, then anything goes there.

For shocks, might also consider Varishock. Monotube design and available in multiple stroke lengths with single and double adjustable capability. Not too hard to find distributors for them either.

[Brads70]

Good reading here guys! ( Brads70 from Cuda-Challenger.com)

[Brads70]

Multi-leaf springs are rising rate. A Hotchkis or other steel leaf at 175 is going to resist squat more than a mono leaf at the same rate. I would go with a 225 composite leaf. Look at what rates a car with your weight and rear coil conversion would use. A 3 link coil sprung first gen Camaro would be in the 250 to 275 range, assuming a fair amount of rear tire, horsepower, and traction. You could go lower on a lower HP car.

What does the rear of your car weigh?

Great advice David! I bought 175# hyperco composite springs and they were way too soft, easily bottomed out on the pinion snubber. Just changing them out for 225# over this winter.I found the Bilstein RCD shocks can't handle the composite leafs though. They react MUCH quicker than steel and bounce. I know this is an old post but thought it might save someone else time and money some day.