Factory springs

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Factory springs

Post by The Dude on Mon Nov 29, 2010 12:58 pm

Just messing around with the cars last night I couldn't help but wonder why the 77 seems to sit lower than the 76 did. I went ahead & pulled one of the springs to check for sagging only to find that the 77 has one less coil. Both factory springs & my HD aftermarket springs have the same diameter coils or at least visually close. The HD is nearly identical to my 76 springs height wise, but the 77 spring appears to be about 1.5" shorter when sitting next to the other two.

Unfortunately I don't have the build sheets available, but I know my 76 was a bare bones car with no options other than AC & a 305 (do those even count? lol). I highly doubt someone would choose the F40 suspension with no other options for the 76, but OTOH I'm sure that something's not right about the 77 having one less coil. Possibly tonight I'll go back & check the double digit spring tag on the 76 to post, but something seems out of place.

FYI, both sets look horribly rusted (I'm thinking stock) & both sets have the factory double pigtails, so no cutting was involved. I guess my rambling is just to inform people to be on the lookout for shorter springs, but does anyone know if the F40 or F41 springs are taller, thicker, or just wound tighter? Curiosity is getting to me again.
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Re: Factory springs

Post by Bill's 74 on Mon Nov 29, 2010 1:22 pm

Rago wrote:...just wound tighter...

Like ME!!


I had an 89 88 that had a "F41" badge on the back. Handled like any other of my 4doors of that vintage. scratch


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Re: Factory springs

Post by The Dude on Mon Nov 29, 2010 1:52 pm

Not sure on your Olds 88, but on older cars the F40 option gave different springs. The F41 option also gave larger front sway bar & a rear sway bar in addition to the springs. The F41 option varied by years if I remember correctly, because I want to say F41 also gave a better steering box in some cars?
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Re: Factory springs

Post by bigredlaguna on Mon Nov 29, 2010 10:10 pm

Check the thickness of the wire itself. I'll bet that the shorter spring has a thicker wire diameter.
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Re: Factory springs

Post by kevinlvy on Fri Dec 10, 2010 5:07 am

bigredlaguna wrote:Check the thickness of the wire itself. I'll bet that the shorter spring has a thicker wire diameter.

check it out first. maybe different in the thickness and may harm the car. are you going for a lowering springs or just retain the old stock springs? would like to see pics of the springs if possible so that others can see em. Very Happy

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Re: Factory springs

Post by The Dude on Fri Dec 10, 2010 10:38 am

Both springs are stock. One came from a 77 Malibu & the other from a 76 Malibu. I also have a third set of aftermarket HD springs that are the same height as the taller factory springs. I might try to take some measurements & pics this weekend.

I'm curious as to how the thickness of a spring coil could hurt the car? I know the HD springs are thicker & all they did to a previous car is improve my launch & raised the rear about an inch.
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Re: Factory springs

Post by The Dude on Fri Dec 17, 2010 3:23 pm

Measured wire thickness last night with a digital caliper, but forgot to take pictures & measure height. Head Bang

Anyways here are the diameters:

Factory coil #1 (taller one): .55"
Factory coil #2 (shorty): .58"
Heavy Duty JC Whitney coil spring: .60"

Here's my est specs for the aftermarket ones:

JC Whitney 68-72 3" lift springs
Coils: 6.25
Coil Spring Free Height: Close to 17"
Coil spring I.D. probably 5.57"
Spring Rate: ????
Wire Diameter: .60"

I'm now assuming #1 to be this:

2773007 # Coil Spring
Coils: 6.13
Coil Spring Free Height: 16.76"
Coil Spring I.D.: 5.57"
Spring Rate: 126
Wire Diameter : .554"

#2 is this one:

2773197 # Coil Spring
Coils: 5.28
Coil Spring Free Height: 14.12"
Coil Spring I.D.: 5.53"
Spring Rate : 166
Wire Diameter: .58"

I don't see it listed for any specific car on our database though. Anyone wanna poke in some numbers & guess the ride heights for these last two? I'll likely go with the JCW springs until I can drop the front down some just because all of the weight loss has made Brown Eye go nose up.
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Re: Factory springs

Post by pila on Fri Dec 17, 2010 11:21 pm

Don't know if this helps here, but I still have all the paperwork from a "77 El Camino I bought new. (had to scrap it in 2009) There is F40 on the build sheet, under HD suspension.

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Re: Factory springs

Post by bigredlaguna on Sat Dec 18, 2010 12:30 am

Calculating ride height for the rear is fairly simple.

1. Get the exact weight that is on the rear wheels.
2. Subtract the weight of the unsprung components.(axle, wheels, tires)
3. Answer is the amount of force that is applied to the pair of springs.
4. You can either divide the weight in half to figure the effect on one spring, or multiply the spring rate times two and use the actual weight to figure the pair of springs.
5. Divide the weight by the spring rate to get the compression distance.
6. Subtract the compression distance from the free height to get the loaded height of the spring.

The only person that has put any kind of actual weight numbers on this forum has been 74Malibu383. So I will use his numbers. I don't know how much an axle assembly weighs with the tires, so I will use a guesstimate to show the math.

The wheel/tire combo will vary from car to car anyway and change the unsprung weight value.

weight on rear tires= 1803 lbs.
unsprung weight (hypothetical) = 250 lbs

1803-250= 1553 lbs. 1553/2= 776.5 lbs per spring

Using spring 2773007
776.5/ 126 = 6.16 inches of compression

Free standing height = 16.76"
minus compression 6.16"
equals 10.60" loaded height


Using 2773197
776.5/ 166 = 4.67"

Free height 14.12
minus 4.67
equals 9.45" loaded height

So there is 1.15" difference in ride height between the two in the same car according to the math.

However, the shorter spring is tougher by 40# per inch. For instance, if you add 300 lbs per spring of cargo The shorter spring will only compress an additional 1.8" and the taller spring will compress almost 2.5".

This formula is only for single rate springs. Variable rate springs get tougher as they compress. I haven't found any information yet as to the rate per inch for variable springs or any formulas to figure it out.
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Re: Factory springs

Post by The Dude on Mon Dec 20, 2010 11:02 am

Neat. Thanks for the info.

I checked the front thickness only to give myself a headache according to your info page. The one set is .67" thick & the other is .69" thick. Both are still in the cars because I'm not going through that kind of hassle just to swap factory springs around for marginal gain. My guess is probably as good as yours on what the .69 springs are.....

In case anyone didn't know, I got myself a new digital set of calipers. Smile They are pretty fun to play with, but also revealing. One car's front sway bar measures .96" while the other is 1" thick. I thought I was crazy so I measured in different spots on each & remeasured coming up with the same results. Seems as if there was some variance in the manufacturing...... They should both measure 1" if I'm not mistaken. The rear sway bar is even more strange measuring out to .87" but appears to be either aftermarket or a chromed original.
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Re: Factory springs

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