need help with my suspension 1970 gmc

[68GMCCustom]

sounds a bit much to me

[redsled87]

Give Larry at Landrum spring a call. I've got to call him when my truck is together with my 496. I'm going to order a set of their drag springs for mine. Their 800 number is,
1-866-703-3154.

[Marv D]

Originally Posted by 68GMCCustom

sounds a bit much to me

Gotta agree with that!
Spring rates are some real rocket science to me, but 1900 pound spring... 3" and ONE spring would hold up your entire truck! Again I'm no suspension expert for sure, but as i have come to understand it....

A 500"# spring will will exert 500# per inch of compression. So at 3" of compression it would hold up 1500 pounds (no geometry included there)

Your front weight of 2250 pounds is TOTAL,, so each side has to hold up 1125 pounds at ride height.

Difference between your "top of the wheel well opening" and full extended you say is 3.375" (but is that the SPRING travel or just the body??? seems REALLY short but OK) Let's say it is the spring.... 1125/3.375 = 333 pound per inch.

The more suspension travel you can get, and the LONGER the spring you can use (soft rate compressed more) will store energy to offer rise at the hit.

But the right way to do this is exactly like redsled said,, ignore my rambelings and call the guys that do this for a living. But do everything you can to give them SPRING length at ride height and at wheels up, AND if possible bottomed out. I missed that one in a set of lowering springs. Thought I had all my ducks in a row and the thing would bottom out on every little dip. There are 'progressive' springs that exerpt more pressure as they are compressed more.
see it is rocket science lol

[bigboybodry]

I see what you mean I just used the calculations in the suspension 101 section and come up with that number. I probably figured something wrong I'll give the experts a call tomorrow and see what they say. Thanks guys for all the help!
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[bigboybodry]

this is the springs that moroso offers and said to pick one

[bigboybodry]

Originally Posted by redsled87

Give Larry at Landrum spring a call. I've got to call him when my truck is together with my 496. I'm going to order a set of their drag springs for mine. Their 800 number is,
1-866-703-3154.

I give Jeff a call and waiting to here back thanks for the help.

[Super73]

At ride height, what is the current compressed height of the spring? Put your tape up the shock hole and measure it that way.

2,250 is the total weight, but it does not take in to account the leverage ratio or what your unsprung weight is.

Unsprung weight on these a-arm suspensions is figured out like this:

100% weight for the following components:
Wheel
Tire
Brake caliper
Brake rotor
Bearings
Spindle

50% of the total weight for the following components:
Upper control arm
Lower control arm
Shock
Spring

Reason it is 50% for this is they are connected to the frame so the weight is shared.

So a stock front end has aprox 250lbs of unsprung weight from the weights I have of stock components.

The leverage ratio if I remember right on the front A-arm we have is right about 1.91 (looked at my old write up).

So, (2250-250)/2*1.91 = 1,910lbs. But that is the total weight the spring needs to support.

If you have a spring rated at 200lb per 1" of spring compression (spring rate), the spring will compress 9.55".. If you start with a 17" long spring uncompressed, installed hieght with all the weight on it should put it at 7.45" compressed height.

[bigboybodry]

the spring measures at 11" like your tread so if I figured right by subtracting the 243lbs for unsprung weight the correct spring at that geometry 1.91 would be a 1908.041666666667 lb spring each? the moroso 47170 spring would be about the same ride height as what is in it now and would work?

[bigboybodry]

the 47170 spring length is 18.625" and a 270lbs in spring so the unsprung weight of 1908.04 / 270lb= 7.07" of compression the spring length 18.625 - 7.07=11.555 of ride height if this makes any sense whatsoever and yes this is way over my head thanks for taking the time and helping me!

[Super73]

What you just posted above looks to be good.

1,910(ish) / 269lb spring = 7.07" of compression

18.65" free height - 7.07" of compression nets a installed height of 11.56(ish).So technically it should sit a little bit higher than it does now.


I would order them through Summit, don't cut them, install them just the way they are and see what that does for your ride height. If they don't work, send them back and let's rethink it.

My math worked on my truck, every truck is slightly different, so hopefully this nails it dead on for you.

[bigboybodry]

Thanks for all the help and good luck on the race! I will be looking for the updated pics/video of your truck.

[bigboybodry]

well I got the new front shocks in and installed they raised the front of the from 27 3/8" to 31 3/4" at ride height what now?

[Super73]

The shock raised the front? Doesn't seem right.
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[bigboybodry]

Originally Posted by Super73

The shock raised the front? Doesn't seem right.
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my bad the new front spring raised the front suspension

[Super73]

Disconnect the shock, roll the truck in and out of the garage, bounce on the front end and see if it goes down. Sometimes the front end can't go down due to the tire draging from the angle of the suspension.

If it is still too high, your options are to either find a different spring or cut those. I would suggest a different spring if it is still too much. I might have some time to look over the spring info you provided. I think I ran the 47140 with 2250 on the front.

The good thing is you have a baseline.


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[bigboybodry]

The springs seem to be to long it has the suspension fully extended with the shock off. Paul is going to send me his old springs and I'm going to try them before I start cutting on these.

[Super73]

Before you swap springs, please take a compressed height with it on the ground. Might be helpful to others as well as help to find the right one for you if Pauls don't work.
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[Super73]

Just found this thread with your weights. I thought we worked it backward.

Disconnect your shock, bounce the front end of the truck, are your headers still on the grund?
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[GMR-PERFORMANCE]

Super, Stop posting until you are back.... enjoy the vacation.. as they say Mahalo.

[bigboybodry]

Originally Posted by Super73

Just found this thread with your weights. I thought we worked it backward.

Disconnect your shock, bounce the front end of the truck, are your headers still on the grund?
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With a 270 lb spring when you add any weight to the front end it just falls to the ground. You can grab the front of the truck and pick it it now. I feel like I am real close just need to drop a few pounds?

[bigboybodry]

Originally Posted by GMR-PERFORMANCE

Super, Stop posting until you are back.... enjoy the vacation.. as they say Mahalo.

I know he isn't on vacation?

[bigboybodry]

truck on the scales with me in it

[Super73]

Originally Posted by GMR-PERFORMANCE

Super, Stop posting until you are back.... enjoy the vacation.. as they say Mahalo.

I am in a bar only after scuba diving for the first time ever. I am enjoying 29* IPA's while Danielle shops and I type. There is no better vacation than great cold brew and helping my fellow truck buddies

Aloha...


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[bigboybodry]

Originally Posted by Super73

I am in a bar only after scuba diving for the first time ever. I am enjoying 29* IPA's while Danielle shops and I type. There is no better vacation than great cold brew and helping my fellow truck buddies

Aloha...


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That's what's up!

[djracer]

Sweet yall get this figured out so yall can help me soon. I am gonna have to drop the front of my son's truck and I want some stored energy.