Coil Spring Replacement

[david smith]

Is there anyway to find the correct replacement for a discontinued coil spring? No one at Eaton or my local chev. dealer seems to no what the replacement or load should be for #3931824? I have nothing but the part # to go by , the car is a 71 350/no A.C. Thanks for any help

[Gary S.]

Re: Coil Spring Replacement

You might try section 7-4 of the Chevy Parts Manual. There are charts there.

[Joe L.]

Re: Coil Spring Replacement

David------

1971 Corvettes with 350 cid engines originally used one of 3 front coil springs. Cars with a per wheel sprung curb weight of 702 pounds or less received spring GM #3931823. Cars with a per wheel sprung curb weight of over 702 pounds received spring GM #3931824. Sprung curb weight was determined by the option compliment of the car, but, as a practical matter, it was very difficult to exceed the 702 lbs per wheel limit of the 3931823 spring UNLESS A/C was among the option compliment. Cars with F-41 suspension used spring GM #3832518.

I don't understand why your car would use the the 3931824 spring if it is not equipped with A/C, but I suppose it is possible if you have just about every other "heavy" option available. In any event, as far as the 3931824 spring goes, there was never a GM supercession. It remained that part number until it was discontinued over 10 years ago. I am surprised, though, that Eaton does not reproduce it; they are the GM-licensed reproducer of most all of the early springs.

The GM #3931823 spring, which was most commonly used on 68-71 Corvettes with 350 and without A/C, was later superceded by GM #331316. Unfortunately, it, too, was discontinued about 3 years ago, or so. It is reproduced by Eaton and others.

The spring rates for all of the 68-71 350 coil springs are as follows:

GM #3931823 (331316)------ 250 lb/inch

GM #3931824--------------- 264 lb/inch

GM #3832518 (F-41)-------- 550 lb/inch

If you are having trouble locating the spring you need, call Mike Allen at Allen's Stainless Steel Exhaust. I believe that Mike has gotten into the reproduction spring business in the last few years. His number is 219-722-7272.

[Roberto L.]

Great Post, thanks!

[Robert C.]

Re: Spring Rocket!

You might call Vette Brakes. My friend with his 71 has been through 2 sets. He thought he would get the heavy duty set. After an afternoon of disassembly, compression, assembly etc. we finished. His car looked like a rocket on the launch pad. He couldn't see the road, just clouds! The lesson is to make sure you get the lower spring rate.

[david smith]

Re: Coil Spring THANKS

Amazing and appreciated responses, Sounds like the 1823 will be the closest replacement without overdoing it (i.e. THE ROCKET!-Thanks Bob) I'll try Allen, Joe and ask what they might have- Don't have any option that would require that kind of load, but don't know if someone tried to stiffen the ride a bit after.The info you passed will be filed in the permanent folder!!!! Thanks again! P.S Eaton says their specs skip over the 1824, they also thought that was a little unusual.

[Terry M.]

Re: Coil Spring Replacement

Joe, David et al,

Even when the 1823 was last available from the General (with the yellow tags and black part numbers) it was NOT to original specs. The car would sit at least an inch too high in the front.

Unfortunately one will not know the result until the spring is installed. Just the voice of personal experience here. I put the original springs back in. David you might want to consider the need for new front springs before you go through the effort.

Terry

[Joe L.]

Re: Coil Spring Replacement

Terry-----

I think that you may be referring to the later GM #331316 replacement spring. The original GM #3931823 spring was discontinued in 1972 and replaced in SERVICE by the GM #331316 spring. The GM #331316 spring was also used in PRODUCTION for certain Corvette applications after 1972. I believe that the original GM #3931823 spring used a green spring tag with the 3931823 part number and "HS" broadcast code in black print. The GM #331316 spring used a yellow tag with the 331316 part number in black print.

Although GM catalogues the GM #331316 spring as the replacement for the 3931823 spring, I would expect that there exists some difference in the specifications of the two springs. However, I have used the GM #331316 springs and they provided a ride heigth that was perfect, in my opinion. In fact, I liked it so much that I purchased 4 more of the GM #331316 springs for my collection before and after they were discontinued about 3 years ago.

[Terry M.]

Re: Coil Spring Replacement

Joe,

Well it was after 1972 that I did that and the yellow (plastic material as I remember) got replaced with a green tag - judging needs you know - so now I would have to find the sales receipt to verify the part number. Maybe I stuck the yellow tag to the workbench, as I recall they did not come in a box, so there is nothing to check there. The tag on the workbench/tool box would be the only chance of my finding the original part number now. So I guess I am a poor testament to which part number I used.

Glad you were happy with them - I was not. At the same time I was dealing with the unique qualities of replacement rear leaf springs (another long subject for another time). I doubt the rear springs would affect the front ride height that much, but it is a possibility. I ultimately decided the original parts gave better ride height and put them back in. Guess that is what makes the world go round.

Terry

[Roberto L.]

Re: Coil Spring Replacement

I have noticed this situation in a BB which lives here. Owner told me that he replaced at a time the tired coils with new ones. The car seats noticeably higher (one inch or so) than what I think it is normal, although he says it has advantages in bad roads obviously. Roberto, NCRS #30019, RMC

[david smith]

Re: Coil Spring Replacement

Terry and Joe, Sounds like a preference call on the ride height, and I might just keep the old if I really can't match the load height. Eaton say's they will send a set and see if they will work but can I check height by comparing the two before their installed or is everything based on load not an actual physical height difference in the springs themselves? My rear leaf is in need of replacement, i.e. rusted leaves with deep pitting. Alot of sag when on the floor. Appreciate any advice as well. Thanks for the information exchange! David

[Terry M.]

[Duke W.]

Spring design and spring rates

I'll spare you the formula on calculating the rate of a given spring, but it's a function of wire diameter, mean diameter of the wound spring, the number of active coils and the material's elastic modulus, so as Terry said, the unloaded height means little, and also as Terry said, a small change in wire diameter has a big impact because the rate is a function of the wire diameter to the fourth power. Same applies to anti-roll bars. If you have a Chevrolet Power Manual, there is an excellent section on vehicle dynamics if you want to get into the real science.

Terry's comments on torsion bars are well taken. Torsion bars are nothing more than linear springs. I always chucked at Chrysler's torsion bar hype in the fifties and sixties. The physics is the same. It's just a matter of packaging convenience and were you want to feed the spring loads into the chassis.

Duke