Front springs

[71Dragtruck]

Alright, seen alot of talk lately about front springs for best weight transfer on here. And low and behold I'm doing alot of changes to my setup this year, now I know if it works don't mess with it, but I'm sure knowing my current setup that it wll be better not worse.

Right now my truck does hook and has fairly good weight transfer for a LWB. I run 1.52 60's and have pulled a front tire on launch. Most of this is due to my rear setup as my front is not set up for drag racing. I run all stock frontend with 3" drop springs and Bell Tech drop shocks.

Now down to business, I'm going to tubular front arms, 3" drop spindles and QA1 R series adjustable rebound front drag shocks. The best plan that I can come up with for ease of installation and the ride height I want is a stock LD front coil spring.

UNLESS anyone knows of a drag spring that will fit the stock spring pocket that I could use. I don't want to have to mickey mouse in a spring, so it would have to be a direct bolt job.

[Super73]

Do you know the weight of the front end? If not, do you have a local scale that will allow you to get front / rear axle weights? This can be done at the track too if there is a scale. Weigh the truck, then just the rear of it. But it would be prefered if you were in it.

"Drag springs" are simply long springs with a low spring rate. The reason they are set up this way is to store energy. The more preload on the spring, the more stored energy you have. Then you can use the shock to tune the rate at which the front rises.

Spring rate is the amount of weight it take to compress a spring 1" So a 300lb spring that is 10" long, would be 8" long with 600lbs on it and 6” long with 1200lbs.

The trick is to compress the spring as far as possible with out inducing coil bind and leaving a little room for upward travel IE hitting a bump in the road.

You can determine coil bind simply. You can either call the spring MFG and ask them what compressed height is or, measure one coil with a caliper, count total coils and do a little math. Now I like to add a little wiggle room here and add one extra coil. IE if you have 12 coils, do the math like you have 13. ( 0.47” * 13 = 6.11 compressed height).

Control arms induce a leverage ratio. That can be figured out fairly easily by taking a measurement from the ball joint location to the LCA shaft that the arm swings on. Then take a measurement to the center of the spring location from the control arm shaft. Divide the spring number in to the LCA. This is what's known as leverage ratio.. (stock stuff on my 63... 9 / 17.25 = 1.91) I would assume this to be the same through the early 70’s but double check.

Now this is where things get a little tricky. You have a 14.5” 350lb spring with a compressed height of 7.3” and you need to now if this will work. It’s all going to depend on unsprung weight.

This is weight of:

Wheels
Tires
Brake assembly
Spindle
Bearings

1/2 of the following parts
Upper control arm
Lower control arm
All tie rod ends
Springs (but then divided again by leverage ratio)
Shocks (but then divided again by Shock ratio)
Sway bar end links

Take your total front axle weight and subtract the unsprung weight. Divide that by two. Multiply that by the leverage ratio. This is the weight the spring needs to support.

2,260 Front weight
200 Unsprung weight
2060 is the sprung weight
1130 is each side
Multiplied by your leverage ratio 1.91 = 2,165

That would compress the spring a total of 6.18” making the spring 8.32” at ride height. Leaving .98” of travel before coil bind.

This is about where my truck is. I have about 2” of preload on the spring before the truck is lowered to ride height.

It’s a lot to figure out the right spring. But if you new the static weight of the front of your truck I could probably ball park a spring for you.



Here is a little spread sheet I threw together some time ago trying to figure out what will work for me.

http://73-ls1.com/63truck/weight_sheet_revision_2.xls

Some things that need to be know about this sheet..

1) Red Areas should be left alone..

2) This is currently set up for my trucks rear suspension. There might have to be some slight changes to the equations depending on your suspension set up (IE 3 link it won't compute the UCA for the rear properly). It takes the individual weights of the control arms and then doubles them in the final eqution showing unsprung weight. It should work however for a 4 bar, 4 link, truck arm, Ladder bar ect. It also uses a panhard bar in the equation so a ladder bar with a Z bar or a watts link set up might need the adjustments as well.

3) The front suspension equations are bases on a double A-arm suspension. So a strut set up might not work right or it might if you leave the UCA weight out.

4) If the drive shaft weight looks funny, ignore it. I divided it by 1/4 but it is multiplied by 2 in the final equation. So it does represent 50% of it's total weight.

5) "Max Control Arm Drop From Ride Height" is the amount the spindle would fall before maxing out suspension travel jacking up the front end (hope that made sense)..

6) All mesurements in the sheet are guesses right now. I have some weighing to do.

7) Axle centerline has to do with the truck arm suspension. The LCA goes past the rear axle center line so I tried to figure out the actual unspring weight by adding that in there. You'll more than likely put that to 0.

[71Dragtruck]

I do know the part about how a drag spring works, rate and such. What I'm in search of is a spring that will cross refrence over and fit into my truck. As you allready know nobody makes one for our trucks, but is there a spring for something else with the same dimensions in a drag type spring, and hopefully a selection of rates to choose from.

Also since you have done your homework on this subject and I was hoping you would chime in. The front of my truck is a total of 2352lbs. at the moment ( unfortunately that's without me ). If you want to get really exact LF=1195, RF=1157, LR=879, RR=898 this is with 3/4 tank of fuel and full nitrous bottle. Total weight 4128lbs. ouch!

The rear end is 4-linked with coil overs so springs and such are simple back there to work with and the choices are endless, the front is another story.

I plan on weighing it again after my planned changes:
aluminum front brake calipers (new ones 5lbs. ea.)
glass hood
tubular arms
loose extra bumper brackets, brake shields and such
aluminum master cylinder

and in the rear:
fab 9", aluminum center section, disc brakes, spool (replacing 12 bolt, posi, drums) not sure of any weight savings here.

Truck has stock disc rotors, no sway bar, tires are 20lbs. each, front rims are 15x6" Draglites (not sure of weight but very lite) Front shocks extend to 14", so suspension travel in the front has room to move, and I have different sizes of upper stops to adjust this if need be.

So with that said, I would like a spring that will compress to about 1/2 less then stock height light duty springs for the desired stance. A bit lower would be fine as I can always use spacers under the spring.

I tell you the next major mod I do is going to be a new front cross member with coil overs, that would make this SOOOOOOO much easier, tuning options endless, and my truck much lighter too!

[Outlaw72]

WOW...I got some work to do!

[Outlaw72]

71 Dragtruck......how is your rear suspension set up?

I would kill to run some 10.70's!!!!!!

What was your 1/8 ET and mph on that 10.77 pass?

[71Dragtruck]

Originally Posted by Outlaw72

71 Dragtruck......how is your rear suspension set up?

I would kill to run some 10.70's!!!!!!

What was your 1/8 ET and mph on that 10.77 pass?

Not sure what it was, our track doesn't have 1/8 mile timer lights. This year I hope to make it to another track that has them, it's also IHRA so maybe I can throw in the 250 jets and run a 9 sec pass.

My rear end is 4-linked with coil overs, so spring rate and adjustability are real easy back there. I've ran faster but had to let off because I was bracket racing, I ran a 1.56 60' on the 10.77 pass, and cut 3 1.52's in a row the one day on what felt like 10.6 sec passes but had to let off all 3 times. I was braking hard enough at the end to make 10.86 at 109 mph, I'm usually 10.77 at 124 mph. So going off that I'm sure I would have been in the low 10.6's.

[Super73]

A bit lower would be fine as I can always use spacers under the spring.

Music to my ears.. Gat a spring that is actually lighter than you need, then use a spacer to dial in the ride height you want.. Adds preload and more stored energy.. But one thing I noticed trying a spacer bellow the spring is it causes it to bow. You don't want that. Put it on the top as it is flat in the perch.


The best thing about summit is you can buy 3 sets of springs at once, put them in, see where they sit. If you don't like them, send them back..

Here are a few to look at.. But keep in mind they have a 3" inside diameter. I don't know what stock is. On my 2.5" ID ones I am using, I made a little keeper out of some 1/4 plate steel 2.5" exhaust. Drill a hole in the center of the plate with a 1 1/2" hole saw. Weld a 2" piece of the exhaust tube to the plate. The plate sits in the bottom of the LCA with the 2.5" tube welded to the plate. The exhaust tube sits in the spring center and keeps the spring from shifting.

http://store.summitracing.com/partde...5&autoview=sku

http://store.summitracing.com/partde...5&autoview=sku

[71Dragtruck]

Originally Posted by Super73

A bit lower would be fine as I can always use spacers under the spring.

Music to my ears.. Gat a spring that is actually lighter than you need, then use a spacer to dial in the ride height you want.. Adds preload and more stored energy.. But one thing I noticed trying a spacer bellow the spring is it causes it to bow. You don't want that. Put it on the top as it is flat in the perch.


The best thing about summit is you can buy 3 sets of springs at once, put them in, see where they sit. If you don't like them, send them back..

Here are a few to look at.. But keep in mind they have a 3" inside diameter. I don't know what stock is. On my 2.5" ID ones I am using, I made a little keeper out of some 1/4 plate steel 2.5" exhaust. Drill a hole in the center of the plate with a 1 1/2" hole saw. Weld a 2" piece of the exhaust tube to the plate. The plate sits in the bottom of the LCA with the 2.5" tube welded to the plate. The exhaust tube sits in the spring center and keeps the spring from shifting.

http://store.summitracing.com/partde...5&autoview=sku

http://store.summitracing.com/partde...5&autoview=sku

Thanks for the info, I guess I'm just going to have to do some fabbing and make some spring holders.

[Super73]

The nice thing is they are simple to make..

[bighead]

Thanks for posting some good spring info guys. Has anybody tried using a Moroso Trick spring in the front of one of these trucks? Seems it may work using one of 71's centering pads. What do you think?

[djracer]

Originally Posted by bighead

Thanks for posting some good spring info guys. Has anybody tried using a Moroso Trick spring in the front of one of these trucks? Seems it may work using one of 71's centering pads. What do you think?

I have tried them on my old 71 street truck but I had djm controlarms at the time and it was too low and the spring seemed to move around in the pocket some. I think with something to keep them in place they would work well. They definately help the weight transfer. I need to work on the weight transfer and antiroll on my 67 drag truck!

[71Dragtruck]

Originally Posted by djracer

I have tried them on my old 71 street truck but I had djm controlarms at the time and it was too low and the spring seemed to move around in the pocket some. I think with something to keep them in place they would work well. They definately help the weight transfer. I need to work on the weight transfer and antiroll on my 67 drag truck!

Were they drop arms? How much more did they drop over the stock springs? My control arms are stock height and I'm going with a 3" drop spindle so just wondering where it would sit with that combo and a set of trick springs?

[57sailplane]

thats what i was going to try before i went to a mustang II front end. they make springs to fit chevells and novas and such so i would think you could make them fit.. on a deal like this i would definatly call them and they could give there idea on it all..

[bighead]

57, is the Mustang 2 an aftermarket one like fatman's or home built? I'd sure love to pull a bunch of weight off the front!

[57sailplane]

i went the home built rout. don't no how well it will hold up yet but i think it will work fine. i built it to bolt in so i could remove it if necessary. i bought everything off of evil-bay, including the heidts universal 60" cross member. i got the tube upper and lower a arms and the 2" drop spindles with the big Chevy disks. the only thing i don't have yet are the qa1 coil over shocks and springs. what i do have cost me just at 1000 dollars including the polished rack and pinion. so i saved a bunch compared to a fatman and i also went lower then you can go with theres. here are some pics.

[djracer]

71 Dragtruck where are you getting your tubular a arms?

[71Dragtruck]

Originally Posted by djracer

71 Dragtruck where are you getting your tubular a arms?

They are CPP arms that I bought off a board member.

[djracer]

the a arms were 2.5 inch drop I think. You might try the trick springs before you install the spindles. It would be too low with the drop spindles.

[71Dragtruck]

Originally Posted by djracer

the a arms were 2.5 inch drop I think. You might try the trick springs before you install the spindles. It would be too low with the drop spindles.

Thanks I might give them a try.

[71Rat]

i spent some time with a moog spring book one day and figured out 72 big block nova springs fit within a 1/2 inch of my stock springs ride height. the truck i did it in was a sb long bed and you could grab the grill and lift the front end a good 4 inches. i know a bb weighs more but it might be work a shot the springs were 60 bucks from my local speed shop.... the only problem is the factory spring is a pig tail on the top and the nova is square cut but mine doesnt move around

[aggie91]

bookmarked....

[71Dragtruck]

Well since this thread all my stuff has totally changed again, from different 4-link and rear end out back with now it's 3rd coil over change with different rate springs for the 4th time.

In the front after the tubular stock type setup, I removed all those parts and went with IFS front crossmember, rack, and coil overs in the front, weight of the truck is now 3700. Also different brakes on all 4 corners.

Now cuts 1.39 to 1.40 60's off the foot brake, and runs 10.18's on a 180 jet, that's as fast as I can tune it at the moment as I only tech for 10.00.

Next change I'll be making is adding a drag race anti roll bar to the back.

[19671972C10]

Cool. I want to do coilovers on my 72 with tubular a-arms.