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I do not believe there are any modifications required to go between fiberglass and steel springs. At worst you'll need longer bolts if there isn't a 'make up block' in the current fiberglass spring stack where it is held onto the center section.
Would there be any ride height change if you swapped the fiberglass to steel?
I don't believe there would be a ridge height change directly associated with the GEOMETRY of the swapped spring. I do know that some C3 Corvettes sit WAAAY too high in the rear, and I do not fully understand why that is.
If I put 6" bolts in the rear of my car, it looks bad. Rides too high. I run 8" bolts in my car and it's just about perfect. I ran those same 8" bolts in my steel spring.
I will offer that my rear ride height was nearly identical between my steel spring (a 9 leaf unit, I believe) and my 330# VB&P fiberglass spring.
If you don't want to mess with the bolts, or if the 8" bolts don't get you where you want to go, some folks have also experimented with removing one of the "upper" (shorter) springs to further alter ride height or final spring rate.
Lots of options. Usually there's a little bit of fiddling involved to getting things just perfect on an individual car.
Last edited by keithinspace; Feb 1, 2016 at 12:36 PM.
I don't believe there would be a ridge height change directly associated with the GEOMETRY of the swapped spring. I do know that some C3 Corvettes sit WAAAY too high in the rear, and I do not fully understand why that is.
If I put 6" bolts in the rear of my car, it looks bad. Rides too high. I run 8" bolts in my car and it's just about perfect. I ran those same 8" bolts in my steel spring.
I will offer that my rear ride height was nearly identical between my steel spring (a 9 leaf unit, I believe) and my 330# VB&P fiberglass spring.
If you don't want to mess with the bolts, or if the 8" bolts don't get you where you want to go, some folks have also experimented with removing one of the "upper" (shorter) springs to further alter ride height or final spring rate.
Lots of options. Usually there's a little bit of fiddling involved to getting things just perfect on an individual car.
Since you have had both the steel spring and the fiberglass one on that same car, how would you rate the difference in the ride and handling between the two?
My '81 is a garage queen as I have owned it for 5 1/2 years and have not put more than 1500 miles on it in that time. It goes to local car shows and an occasional 10 mile run to keep the fluids circulating.
I think anything would be better than the hard bottoming out I have noticed since the rear spring started failing.
My steel spring was well sprung and in decent shape. The plastic between the layers was older, so it didn't operate quite as smoothly as it should. Just an old spring in decent shape.
When I completely rebuilt my rear end, I actually restored my steel spring. I had no issues with using it. I sandblasted it, put new plastic in it, and greased each layer of the 'sandwich' to make sure everything slid together really nice.
Perhaps it was the grease that messed me up. What ended up happening is that the second spring from the bottom...the next-to-longest one...ROTATED and "un-nested" from the bottom spring. Since there are no real clips or stops to keep it from twisting, I actually found it odd that this type of thing doesn't happen more. Fortunately, this happened close to my house. I rode on the rear bump-stops the mile or so to my house.
Whatever the case, the mantra I follow on my car is "if it breaks, remove it and replace it with something better". So...I ordered my fiberglass spring.
I can honestly say that the ride is GENERALLY the same. My car rode pretty smooth before and it rides smooth now. It doesn't seem to 'bound' quite as much.
If I had to say where the biggest difference is, it is in the really, really, really, really small bumps. The ones where my old spring didn't quite feel like moving against itself. The fiberglass spring just moves. Soaks up every little bump. The ride quality is generally the same, but there is noticeably less harshness over SMOOTH roads, if that makes any sense.
The weight savings didn't hurt my feelings. Probably shed 30 lbs from the back of the car.
That's the best way I can answer the question. Hope it helps.
Last edited by keithinspace; Feb 1, 2016 at 08:42 PM.
My steel spring was well sprung and in decent shape. The plastic between the layers was older, so it didn't operate quite as smoothly as it should. Just an old spring in decent shape.
When I completely rebuilt my rear end, I actually restored my steel spring. I had no issues with using it. I sandblasted it, put new plastic in it, and greased each layer of the 'sandwich' to make sure everything slid together really nice.
Perhaps it was the grease that messed me up. What ended up happening is that the second spring from the bottom...the next-to-longest one...ROTATED and "un-nested" from the bottom spring. Since there are no real clips or stops to keep it from twisting, I actually found it odd that this type of thing doesn't happen more. Fortunately, this happened close to my house. I rode on the rear bump-stops the mile or so to my house.
Whatever the case, the mantra I follow on my car is "if it breaks, remove it and replace it with something better". So...I ordered my fiberglass spring.
I can honestly say that the ride is GENERALLY the same. My car rode pretty smooth before and it rides smooth now. It doesn't seem to 'bound' quite as much.
If I had to say where the biggest difference is, it is in the really, really, really, really small bumps. The ones where my old spring didn't quite feel like moving against itself. The fiberglass spring just moves. Soaks up every little bump. The ride quality is generally the same, but there is noticeably less harshness over SMOOTH roads, if that makes any sense.
The weight savings didn't hurt my feelings. Probably shed 30 lbs from the back of the car.
That's the best way I can answer the question. Hope it helps.
Can anyone tell me for sure that they are interchangeable without cutting/welding? I am a fairly good mechanic when replacing bolt-on items but do not do cutting and welding.
As long as you use a steel 9 leaf spring, for a 78-82, it will be a direct bolt in. 80-82 rear ends used the same mount plate and bolts, for both the steel and fiberglass rear springs. 78-82 rear springs are 2 1/2" wide, while 63-77's are 2 1/4" wide.
Chevrolet switched to the fiberglass rear spring, to save weight, as part of it's efforts to meet the Federal Governments fuel mileage mandates. The fiberglass spring only weighed 8 pounds, compared to 44 pounds for the steel 9 leaf spring.
As a clarification, 81 Corvettes with an automatic trans and standard suspension, came with the fiberglass rear spring. Automatic 81's with FE7 Gymkhana suspension, F51 Heavy Duty Shock Absorbers, or ZN1 Trailering Package, all came with a 9 leaf steel rear spring. 81's with a 4 speed came with the steel 9 leaf spring, regardless of the suspension.
The manual and automatic transmissions were available with both Federal and California emission equipment. The only difference was that Federal automatic cars came with a 2.87 rear axle ratio, while California auto's came with a 2.72 rear ratio, and the 2.87 was offered as a "performance" ratio. All 81 4 speeds came with a 2.72 rear axle ratio.
For 82, all Corvettes came with an automatic trans, both Federal and California. Like 81, standard suspension came with the fiberglass rear spring, while the optional suspensions used the steel 9 leaf spring.
As long as you use a steel 9 leaf spring, for a 78-82, it will be a direct bolt in. 80-82 rear ends used the same mount plate and bolts, for both the steel and fiberglass rear springs. 78-82 rear springs are 2 1/2" wide, while 63-77's are 2 1/4" wide.
Chevrolet switched to the fiberglass rear spring, to save weight, as part of it's efforts to meet the Federal Governments fuel mileage mandates. The fiberglass spring only weighed 8 pounds, compared to 44 pounds for the steel 9 leaf spring.
As a clarification, 81 Corvettes with an automatic trans and standard suspension, came with the fiberglass rear spring. Automatic 81's with FE7 Gymkhana suspension, F51 Heavy Duty Shock Absorbers, or ZN1 Trailering Package, all came with a 9 leaf steel rear spring. 81's with a 4 speed came with the steel 9 leaf spring, regardless of the suspension.
The manual and automatic transmissions were available with both Federal and California emission equipment. The only difference was that Federal automatic cars came with a 2.87 rear axle ratio, while California auto's came with a 2.72 rear ratio, and the 2.87 was offered as a "performance" ratio. All 81 4 speeds came with a 2.72 rear axle ratio.
For 82, all Corvettes came with an automatic trans, both Federal and California. Like 81, standard suspension came with the fiberglass rear spring, while the optional suspensions used the steel 9 leaf spring.
gbvette62,
Thanks for the great info. I will go ahead and order a steel 9 leaf spring and get rid of that splitting fiberglass one.
FWIW I would never go back to a steel rear spring on my 78 after having a 360 composite on the car since 1986...No exhaust wrap, no split spring...just a superior ride and handling rear spring to the OEM gymkhana rear steel 292 lb spring. There is a very good reason that GM ditched the rear steel spring permanently after 1982 and has never looked back with the C4.C5, C6 and now C7 vettes...and it is not just for weight savings over the rear steel springs. The composite has many advantages over the steel spring:
1. Allows much higher spring rate with minimal loss in ride quality...my 360 composite is firm but not harsh at all in terms of ride quality. The 360 composite is far superior in ride quality to the 292 spring
2. The composite will never sag...mine is perfect after 30 years on the car
3. The composite has much better suspension response than the steel spring
4. The composite weights 8 lbs versus 45 lbs for the steel spring
Disadvanatges:
1. Can split from harsh treatment or road debris damage
2. Can split from heat from the exhaust although my spring is about 2 inches from the duals and has no issues with no special wraps/treatments after 30 years
3. Requires a top quality shock to dampen the spring correctly...my 360 has Bilstein Sports for proper damping...Bilstein HD's that I had were not adequate with the 360 spring
My 78 with 550 front springs, poly everything up front including control arm bushings, Bilstein HD's up front only is MUCH softer riding than my 10 Z06 and 12 Lexus IS350 F Sport!
I agree with that logic since the replacement composite springs cost 2 or 3 times as much as the metal springs and would not pass NCRS scrutiny I think I will go with a metal replacement spring if it will fit my '81 with automatic transmission.
Can anyone tell me for sure that they are interchangeable without cutting/welding? I am a fairly good mechanic when replacing bolt-on items but do not do cutting and welding.
I changed my metal spring to composite a few years ago and it was a direct fit. VBP 330lb composite. Removed my steel spring and bolted up the composite. On thing to remember is the factory composite springs had a heat shield to protect it from the exhaust heat. Since mine didn't have the heat shield I wrapped my pipes that run under the spring with header wrap.
I'd also change the mounting bolts (4 in on the diff), the mounting plate and the bushing/bolts at the trailing arms. It took me longer to get the car up and down on jack stands than it did to actually replace the spring. In all about an hours worth of work.
Factory steel springs like my 78 gymkhana spring also have/had a gm factory heat shield. When I changed to composite in 1986 I used the factory heat shield as well. Unfortunately, many of these have been ditched by owners over the years. Steel springs came from the factory with heat shields starting in the Mid 70's
Factory steel springs like my 78 gymkhana spring also have/had a gm factory heat shield. When I changed to composite in 1986 I used the factory heat shield as well. Unfortunately, many of these have been ditched by owners over the years. Steel springs came from the factory with heat shields starting in the Mid 70's
The problem is that many owners when they make changes to their C3's discard some parts and indiscriminately eliminate others when they do projects which almost always is a mistake....GM put certain parts in places for a reason...heat shields for STEEL springs is a good example....not just for composite as most people think......
Over the years I've broken 2 steel springs in a 74 and 75 corvette. I've had this 82 with well over 100k and never had any problems. It is a little softer than the steel but now they come with a few different ratings. The ride height can always be worked out with the links and bushings. The biggest plus is weight savings and no rust. Durability IMHO is the same if not better than steel.
The 81/82 composite was very weak .. 192 lbs....and was gms attempt to give the c3 a nice soft ride....I would look at a 300lb composite at a minimum..
Eckler's says their 300 lb composite "Replaces a 9-leaf stock and rides VERY soft. Suggested for use only on small blocks." Volunteer says their 330 lb mono "provides high performance ride and handling characteristics w/o harshness," while their 360 lb mono is a "replacement for gymkhana rear spring." Given the spread on these ratings (300 - 360 lb) and their descriptions, 192 lbs doesn't sound right. Not saying you're wrong, but what's the source of your information? Also, does anyone know the standard rear spring rating back in the early '70s?
Eckler's says their 300 lb composite "Replaces a 9-leaf stock and rides VERY soft. Suggested for use only on small blocks." Volunteer says their 330 lb mono "provides high performance ride and handling characteristics w/o harshness," while their 360 lb mono is a "replacement for gymkhana rear spring." Given the spread on these ratings (300 - 360 lb) and their descriptions, 192 lbs doesn't sound right. Not saying you're wrong, but what's the source of your information? Also, does anyone know the standard rear spring rating back in the early '70s?
Gmheritagecenter.com
Everything you would want to know about each C3 is there....BTW-looked up the rear spring rate for the composite on the 81 C3...I was wrong...its 172 lbs/in.....I believe the base composite on the 82 is 198...you can look it up yourself if interested but as I said before, the spring rates were VERY soft.....
Everything you would want to know about each C3 is there....BTW-looked up the rear spring rate for the composite on the 81 C3...I was wrong...its 172 lbs/in.....I believe the base composite on the 82 is 198...you can look it up yourself if interested but as I said before, the spring rates were VERY soft.....
Thanks, I didn't know about those archives until now. Unfortunately, they don't answer my questions about these springs.
The first image below is from the '82 spec manual. It shows the spring rate as 183 lbs and the rate at the wheel as 122 lbs. Looking at an earlier '72 C3 (second image below), it's listed as 85 lbs at the spring and 121 lbs at the wheel. How can they be almost the same at the wheel, but so different at the spring? And how is it possible for a Corvette to have an 85 lb spring?? I'm obviously not interpreting this info correctly.
Well, I looked up the '71 to see if the 85 lbs at the spring for a '72 might be a typo. I was thinking maybe they left off a "1," and it should be 185 lbs. However, the '71 is rated 140 lbs at the spring, and 123 lbs at the wheel. That didn't help one bit...
Over the years I've broken 2 steel springs in a 74 and 75 corvette. I've had this 82 with well over 100k and never had any problems. It is a little softer than the steel but now they come with a few different ratings. The ride height can always be worked out with the links and bushings. The biggest plus is weight savings and no rust. Durability IMHO is the same if not better than steel.
Chevrolet had issues with the rear springs used from 74 to around 77. The main leaf broke on all of them, usually right by the large bolt hole. In the late 70's and early 80's, a friend of mine had an ARCO station (remember them?) and specialized in Corvette work. He kept a couple 9 leaf springs in stock, because he was replacing one or two broken ones a week, always on rubber bumper cars.
I broke the rear spring on my 35,000 mile 74, in 1980. It was 8 o'clock on a Sunday night, in pouring rain, on a deserted highway in the Jersey Pine Barrens, and long before anyone had cell phones.
Thanks, I didn't know about those archives until now. Unfortunately, they don't answer my questions about these springs.
The first image below is from the '82 spec manual. It shows the spring rate as 183 lbs and the rate at the wheel as 122 lbs. Looking at an earlier '72 C3 (second image below), it's listed as 85 lbs at the spring and 121 lbs at the wheel. How can they be almost the same at the wheel, but so different at the spring? And how is it possible for a Corvette to have an 85 lb spring?? I'm obviously not interpreting this info correctly.
A Spring rate is NOT a spring deflection rate....these 2 terms are different. The spring rate is the force to move the spring 1 inch. The spring deflection rate is I believe the amount of weight the spring is designed to carry when deflected a certain height....They are NOT the same.
Most C3's as stated earlier and again now had way too soft steel spring rates IMO and the composite were VERY soft as well giving an extremely cushy soft ride. The base suspension steel spring on 78 C3's was 192lbs....very soft in an effort to preserve some semblance of decent ride with the raw characteristicss of a steel rear spring. A composite allows MUCH higher spring rates with minimal losss of ride quality (my 360 composite rides 10X better than the OEM steel Gymkhana 292 lb spring) and superior suspension control.
The second picture above for your 72 does not give you a spring rate but a spring deflection rate which is not a spring rate...I am sure some engineers can convert the number for you with the right information and equations.
The source I gave you conclusively verifies that the composite 81/82's had extremely soft rear springs...I believe the composite 82 gymkhana was a whopping 198 lbs which is Cadillac soft......
I may go to a 420 composite with my 550 front springs if the rear 360 ever "wears" out (it won't) or splits from severe duty or road damage (maybe some thing will happen). I spend some much time on certain topics since after 33 years of C3 ownership and lot of experience with certain components on these cars, I try and keep the record straight and prevent misinformation..
