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Stock front coil spring height?


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Does anybody know what the height of the stock coil springs are? I'm trying to figure out if mine are stock or aftermarket. Should they say GM ob them somewhere? 

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Ron,

GM selected and installed one of ten possible front coils and one of 3 possible rear coils in each individual first gen Monte based on the total weight of that vehicle including all options.  It had nothing to do with whether that car had a "small block" or "big block" engine as is commonly thought.  You can find the "Free Height" listed for each possible spring in the table below (shown in the second column from the right).

If you have a Build Sheet for your car, check Box 13 for the front spring Assembly Code that was selected for your particular car.  If you have a reasonably optioned 454 car, the code will likely be GQ which has a free height of 18.13 inches.  While the part number is also shown in that table for each spring, I don't believe it is stamped on the spring (unlike Moog springs which do have a stamped PN). 

You can also use a micrometer or digital caliper to measure the diameter of the coil wire (clean it first) and compare that to the spec given in the table.  The overall free height may change over years of use but the coil wire diameter won't.  Good luck.

 

FGMC Spring Specs.jpg

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On 6/29/2020 at 1:19 PM, Dtret said:

I was looking at your list and my tears match (BM) but my fronts don’t (AK). Is that something odd or is that a year specific list. Mine is a 71 SS

 

The table I shared is from the 1970 Monte Carlo Specifications document so it is possible that different/additional spring codes were used in '71 and '72.   Yours is the first build sheet I've seen that has a different code but perhaps there are others.  Maybe someone has the 1971 Monte Carlo Specifications document that shows the table of possible springs/codes used that model year.

If the "AK" code is in the other series of "A" codes, it would be a mid-range spring.  That seems surprising to me unless your SS is a lower optioned vehicle, especially with no A/C which adds more to total vehicle weight than any other option except a big block. 

My big block, 4-speed '70 was a very low option car (not even power steering) and was built with the AO front spring.  A heavily optioned small block car could have a higher total vehicle weight than a low optioned big block car. 

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  • 2 months later...
On 6/29/2020 at 6:37 AM, MCfan said:

Ron,

GM selected and installed one of ten possible front coils and one of 3 possible rear coils in each individual first gen Monte based on the total weight of that vehicle including all options.  It had nothing to do with whether that car had a "small block" or "big block" engine as is commonly thought.  You can find the "Free Height" listed for each possible spring in the table below (shown in the second column from the right).

If you have a Build Sheet for your car, check Box 13 for the front spring Assembly Code that was selected for your particular car.  If you have a reasonably optioned 454 car, the code will likely be GQ which has a free height of 18.13 inches.  While the part number is also shown in that table for each spring, I don't believe it is stamped on the spring (unlike Moog springs which do have a stamped PN). 

You can also use a micrometer or digital caliper to measure the diameter of the coil wire (clean it first) and compare that to the spec given in the table.  The overall free height may change over years of use but the coil wire diameter won't.  Good luck.

 

FGMC Spring Specs.jpg

DTret:  Great information.  I'm working on a frame off and converting to coilover suspension.  I was trying to get a starting point for the spring rates, but here they are.  Would you have the information on the shock travel??  Thanks / Paul

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7 hours ago, Paul C said:

DTret:  Great information.  I'm working on a frame off and converting to coilover suspension.  I was trying to get a starting point for the spring rates, but here they are.  Would you have the information on the shock travel??  Thanks / Paul

Paul,
The 1970 Monte specs I have do not list front shock travel directly, however, I think you can back into it from the specs given.  Here's the data I have:

Wheel travel (design):
     Total                7.92"
     Jounce            3.92"
     Rebound         4.00"
Wheel to spring travel ratio = 1.86

Since the front shock is mounted in the center of the front coil spring, that 1.86 travel ratio should apply to the shock travel just as it does to the spring.  So, 7.92" (total wheel travel) divided by the 1.86 ratio would yield 4.25" of shock travel.  Note that the data above is the design spec so maximum shock travel may be a bit more (but certainly not less).  In any case 4 1/4" of shock travel seems reasonable to me.

The only front shock specifications provided in the 1970 Monte Specs are:

Type = Direct, double-acting, hydraulic
Piston diameter = 1"

 BTW, if you are wondering about a taller than stock coil spring being compatible with a given shock travel, remember that all front coils, once installed, have the exact same working height of 11.7".  The spring rate also has to be considered.  For any given spring rate, a taller spring will simply increase the preload weight (spring height - 11.7") x spring rate #/in.  Greater preload will cause the front end to sit higher and thereby change the transition point between Jounce and Rebound specs but when you apply the 1.86 ratio, that will have a very small affect on shock travel.  Of course, the jounce/rebound ratio on the shock you select will have an affect on ride performance but not travel.  Although that spec is not given, I assume it is 50/50 as most shocks at that time were.

Hope this information is useful.  Someone else may have the exact spec you are looking for.

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  • 4 months later...
On 6/29/2020 at 2:19 PM, Dtret said:

I was looking at your list and my tears match (BM) but my fronts don’t (AK). Is that something odd or is that a year specific list. Mine is a 71 SS

BC98FA92-6574-4BD7-B8A3-13C22F43A60B.jpeg

Dennis,

I finally learned what the "AK" front spring code represents on the Build Sheet of your '71 SS.  Instead of the 10 front springs offered in the '70 Montes, there were only 6 front springs offered in '71.  Codes AF, AH, AQ, GD and GI were dropped and AK was added.

Interestingly, the AK was a heavier/stronger spring than any offered in '70 - possibly in recognition of the total weight of a heavily optioned SS.  The theoretical difference (at the design working height of 11.7") between the AK for '71 and the GQ for '70 is an additional preload of 70 pounds per spring (140 pounds total) reduced by the 1.86 leverage factor at the wheel/tire for an effective additional frontend load capacity of 75 pounds.  They accomplished that with a 21" longer overall length of larger diameter "wire" (.645" vs. .621") and a slightly taller free height (18.38" vs 18.13").  However, the deflection rate of 275 pounds /inch stayed the same so the "ride" feel of the two springs should be the same.

The three rear springs offered both years were exactly the same.

 

image.png.eb6d9578ef7b40d9d81136076a5bdbd4.png

 

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42 minutes ago, MCfan said:

Dennis,

I finally learned what the "AK" front spring code represents on the Build Sheet of your '71 SS.  Instead of the 10 front springs offered in the '70 Montes, there were only 6 front springs offered in '71.  Codes AF, AH, AQ, GD and GI were dropped and AK was added.

Interestingly, the AK was a heavier/stronger spring than any offered in '70 - possibly in recognition of the total weight of a heavily optioned SS.  The theoretical difference (at the design working height of 11.7") between the AK for '71 and the GQ for '70 is an additional preload of 70 pounds per spring (140 pounds total) reduced by the 1.86 leverage factor at the wheel/tire for an effective additional frontend load capacity of 75 pounds.  They accomplished that with a 21" longer overall length of larger diameter "wire" (.645" vs. .621") and a slightly taller free height (18.38" vs 18.13").  However, the deflection rate of 275 pounds /inch stayed the same so the "ride" feel of the two springs should be the same.

The three rear springs offered both years were exactly the same.

 

 

image.png.eb6d9578ef7b40d9d81136076a5bdbd4.png

 

 

That’s great information. Thanks for that. Now I hope I matched the new ones to the “ak”’s. Or else I’m going to bottom out in the front and also have a hell of a rake. Thanks again 

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