C3 Spring replacement

[Joe Tutela (46448)]

I have a 1969 390/427 coupe that is in a state of dis-assembly with the engine sitting in the engine compartment but not on the mounts (a long sad story). While I have the engine out, I am going to re-wire and re-hose (vacuum) the engine compartment and I am also going to replace the front suspension grommets and bushings. This seesm like the ideal opportunity to replace the front springs. How do I determine if they really need replacement if the weight distribution is not correct (cannot accurately measure ride height) or should I just not worry about it and replace the springs anyway? I am also seriously considering replacing the rear spring with a single leaf composite is the 330# range, based on my research. Any thoughts or considerations I might have missed? Many thanks and regards...Joe

[Steven Cullen (46423)]

Re: C3 Spring replacement

Joe -

This board is geared toward restoration/preservation, so you might not get any info on the rear spring modification (the Corvette Forum Tech Board is a better place for that sort of thing).

For the front springs, I have a '69 427/435 with original front springs, they seem to have lasted this long with equal side-to-side ride height. I got my car in a similar state as yours.

What do you want to accomplish with this car? It sounds like some modification for improved handling based on the rear spring question...if so, you may want to consider heavier coil springs up front, or even the fiberglass mono-leaf front conversion offered by several vendors.

Steve

[Kent Keech (6201)]

Re: C3 Spring replacement

Joe,

I agree with Steve's post. If you want to modify your car, another site might better suit your quest for answers. As for you rear spring, many here have rebuilt them using new liners available from many vendors. Wile it's apart, clean and paint it (light gray, almost primer color/sheen). Reassemble it with new liners and it should last many more years. Along with new cushions and bushings, your ride height will be almost perfect. Check the archives for more information.

Regards, Kent #6201

[Joe Tutela (46448)]

Re: C3 Spring replacement

Thanks to both of you guys. I guess I explained this poorly when I included the question of the composite replacement. My real question should have been limited to the requirement and methodology to see IF I needed to repalce the front springs at all. Sorry for the confusion and thanks for the direction. I hope this is a better whay to phrase this...Regards...joe

[Jim Trekell (22375)]

Re: C3 Spring replacement

The composite rear springs have been mentioned before on this board. The later model C3 Corvettes came from the factory with the composite springs and starting with the 84 C4s all new Corvettes have front and rear composite springs. My original owner 68 still has its original front springs and are holding up very well for their age. No plans to replace them. I did remove the rear spring years ago and replaced it with Vette Brakes 360 composite spring. I like the ride it gives. I had replaced the rear spring in my original owner 70 Corvette with the 360 composite rear spring because loaded down for a road trip the car would bottom out, it was rare. I like the difference. The 68 and 70 no longer have the Corvette squat when you get on it. The rear spring is about one of the easiest things to change out on a Corvette, it can be done with mufflers in place. Most 63-82 Corvette owners do not change out the spring cushions on the end links, you might try this first and see if you like the difference enough not to replace the spring. Keep you rear spring if you go composite so you can install it for a new owner if that is what they want if you ever sell. Not all Corvette owners that use this board preserve their Corvettes for judging. I have a 68,70,85, and 96 LT4 and have never had them judged at a NCRS event, but I do drive them for my enjoyment. Vette Brakes sells a front spring that is close to what used to offered by GM Parts with the last three part numbers 518. This 518 front spring was used in the optional suspensions. I installed this shorter but larger wire diameter spring in my 70 because the front springs had settled to much for my peference. The 518 spring did not raise the ride height, but it did firm up the front suspension and improved the handling in my opinion. The 518 spring sitting beside the stronger spring offered by Vette Brakes are pretty close to being the same. If you front springs have not settled I would recommend you keep them untill you are dirving your 69 and can evaluate them. If you can see where they have settled enough that the upper coils have been touching, you may want to replace them. Also recommend to go with the original style front rubber suspension bushings not the poly type.

[Duke Williams (22045)]

Re: C3 Spring replacement

330 lb/in is about double the OE rate (and even slightly higher than F-40/41 rate of 305 lb/in) and will cause the car to understeer much more than the OE spring and drastically reduce rear ride compliance. Also, a specially calibrated shock absorber is required due to both the higher rate and a composite spring's lower inherent damping.

Unless coils and leaves have evidence of severe corrosion (in particular look for corrosion notches), they should be fine to reuse, and the rates are well engineering for good ride and handling with the OE anti-roll bars. Springs don't "wear out", but corrosion can kill them.

Though front the coils were not coated by GM, appling a good anticorrosion paint system will protect them, but result in a point loss if the car is Flight judged.

Same with the rear leaves, though they did have a grey paint on the tension (bottom) side only.

I don't know what your research involved, but unless you have a sufficient background in vehicle dynamics to compute roll couples and roll couple distribution for springs and anti-roll bars, you will be better served to keep the OE rates and concentrate on tires, shocks, and alignment if you are looking for higher handling limits and better dynamic response characterisics.

Duke

[Patrick Hulst (16386)]

Re: C3 Spring replacement

As noted elsewhere, if the springs aren't really crusty, reuse them.

Also, unless your original vacuum hoses are in really bad condition, consider re-using them. While Doc Rebuild's hoses are excellent, I'm still partial to the originals and tend to re-use whenever possible.

As long as you're installing new bushings, make sure you get the correct appearing repros. Same for the ball joints. There is plenty of info on front suspensions and correct finishes in the Archives.

[Terry Fiala (21624)]

Re: C3 Spring replacement

Much of the time you can look at the A-arm bushings in a 40 year old car and there is no question they need to be replaced. But, if they have been replaced in the past, there may be some question. Look at them closely and see what you think. If they are torn, replace them. If they are not the original configuration, I would probably take the time to replace them also. Do not tighten the bolts on each end of the A-arm shaft untill the full weight of the engine, etc is on the car or you will damage the new bushings. If you replace the bushings and balljoints, the ride hight will probably come up a bit. If not, I would make adjustments from there by replacing the springs. Take care, Terry