150# rear coilover spring rate to light?

[skeeterbug]

I am trying to finish up my winter upgrades before local test and tune starts Feb. 3rd. Ended the season with my best ever of 7.70 @ 87mph with 1.70
60', much improved from consistent 7.82 @ 85mph w/ 1.83 60'. Not to bad of an improvement I guess just for raising the trailing arm mounts up and jeep coil spring swap from stiff lowering coil springs. Started seasons end Nov. 2012 with much needed 1-1/2 to 1-3/4 primary header 3" collector swap, dynomax 6" L race bulletts dumping on the pavement. Trying to pickup the short time with a 3.73 to 5.13 Richmond swap, offset some by 28x11.5 to 31x18.5 change. Lost 80 lbs. of interior weight by ditching the explorer buckets and square tubing mounts for one kirkey pro-street cl find. I then decided utilize my other cl score of m/t et fronts, WHEEL TIME, sold my set of 20/22 coy c-5 street wheels to finance the new shiny stuff. This is where the trouble started, ordered 15x5 front and 15x14 revolvers from holeshot wheel (love em, worth every penny) skinned the rears with hoosier 31x18.5x15's. Back spacing is spot on...but the drivers rear contacts the lip of the wheelwell under mild acceleration promting the need for coilovers to fine tune the rear suspension and ride height. I will be ordering strange coilovers very soon just wondering if you all think 150# spring rate will be to light for my lwb fleetside w/ no bed floor at all. Floor will be all aluminum as soon as suspension is finished up. Sorry for the long story but the season is coming and I never wound down.
What spring rate are most of you fellow haulers running?

[Marv D]

Your going to have to be way luckier and smarter than I to get this right the first time. My SOP is to go thropugh 2-3 sets of springs before I get a rate I can work with. I'm DEFINATELY no expert on chassis setup (we do have some great expertise here on this board that I hope chimes in) AND not nowing what your rear chassis weight is,, but I'd think your going to be somewhere in the low 200's before it's done/ I think I went through 4-5 sets of springs to get the suspension reaction I wanted on my 66,, from 130's all the way to 220's and I am pretty sure I have 170's in there now. But the rear of my heap is pretty LIGHT!!! steel bed sides and aluminum bed floor, 2x3 square tube frame rails and battlecruiser 4link bars.

All that to say I have NO IDEA where you'll end up, but don't expect your first spring purchase to be your last.

[skeeterbug]

Oh i expect to try several sets before im satisfied, just trying to get some general idea of where to begin. I really need to weigh the truck im sure that would help alot, plus knowing the weights would come in handy alot im sure.

[skeeterbug]

Here is a few pics of my junk with the new rollers.

[skeeterbug]

[1Bad62Pro/Street]

My set-up:

Competition Engineering #247-2051K7 Rear Coil-Over Shock Kit
250lb springs included.
3-way adjustable shocks
Upper mounts
Adjustable lower mounts (with 6" of ride height adjustment)
http://www.jegs.com/i/Competition+En...051K7/10002/-1



http://67-72chevytrucks.com/vboard/s...d.php?t=551958

Competition Engineering Rear Coil-Over Shock Kits come with 3-way adjustable shocks, upper mounts, adjustable lower mounts, and with or without springs.
They work with a variety of applications, including drag race, Pro Street, street rods, and kit cars.
The upper mounts are finished in black oxide ready for welding.
The lower mounts allow 6" of adjustability in 1/2" increments.
The spring perches and lower mounts are finished with a zinc and yellow chromate plating for corrosion resistance.

Vehicle weight is critical to suspension performance.
So choosing the correct spring rate based on rear end weight maximizes the suspension's ability to function and improve traction.

[Super73]

I have a 14" 130lb spring in my rear Koni's.

Now to your real problem. You are seeing the axle shift from one side to the other under acceleration due to you pan hard bar, not your factory located spring. I saw this in my 63 pick up. i used an adjustable pan hard bard to help fix the issue.

67-72 trucks use a shorter panhard bar than the 60-66 which makes it shift side to side even more.

My advice would be rethink where you are spending your money. A long adjustable pan hard bar will be your friend.


The second thing that will reall help, is a big anti roll bar in the rear. It won't keep the rear from shifting, but it will keep the rear tires loaded evenly and will help keep the right rear from wanting to come up and the. Left rear from wanting to go down. When that happens it effectively make the lower control arms two different lengths now messing with rear end alignment. Not only do you leave twisted, but the vehicle does not drive straight out of the hole.


That's where I would start.
Posted via Mobile Device

[skeeterbug]

I already have an adj. panbar from cpp that i installed long ago when i lowered the truck, there have been numerous changes since then though. May need to check if the axle is centered huh, cant belive i paid it no mind when i had it loose the other day puttting in the new r&p. The rear sway bar i will look into adding, i have noticed my launches are all over the place at times like i was out of the groove. And thats always fun to drive out of even had to lift a couple times last season.

[68racer]

I weighed mine and it came out that I should run 170lb springs. They are good on street and track.

[Super73]

It is really going to depend on the coil over you go with. A coil over that uses a 10" spring is going to need a different spring rate than a coil over that uses a 14" spring.

Another thing to take in to consideration is how much available compression you have on a given coil over. The more the better.

Does the truck squat or rise on launch? That might also help you decide if you want the shock extension in the middle, out more, or in more when the truck is at rest. For example, I have a rather low/long ICG set with my 4-link. This causes the rear to squat on the initial hit and under acceleration. I have my coil overs turned up so when the truck is at rest my shock has a little more compression available than extension.

Just food for thought