corvetero

How do I do know wether my car has Gymkhana suspension option or not?

I'd like to low the car, so I need to know it.

BTW. You can post your better option to low the car...not looking for performance, just 2" lower look.

resdoggie

Gymkhana suspension will have a 7-leaf spring vice the standard 9-leaf spring. You can cut one coil off the front springs to lower the front 2", give or take a bit. Use longer spring bolts in the rear, 8" or 10". Or, buy a suspension kit in the after market.

jb78L-82

SB C3 will have a 7/16 inch rear GM style sway bar if it has the gymkhana suspension.

hunt4cleanair

The 1974 Gymkhana did not include the rear sway bar...it became standard equipment in 75.

If the shocks are original, they will have part numbers. Look for GM# 4984577 (front) and 4984578 (rear). If the front springs have a green/yellow tag it will read AA. And as mentioned, the leaf spring will have 7 leafs, not including the spacers.

Hope this helps!

Sluefoot

My '79 w/ the Gym. suspension, has a 1-1/8" dia. front sway bar....I believe the non-Gym. has a 7/8" dia.....but I'm not sure about the setup on a '74.

jb78L-82

Looks like that is true about no rear bar in 1974 for the gymkhana cars but the GM heritage center info below is VERY nebulous about the gymkhana sport suspension in general...only mentions base suspension front springs of 260 and rear of 170lbs (which BTW is ridiculously soft for a sports car...my 78 L-82 Gymkhana car currently has 550 fronts and 360 lb rear composite). There are no specifics sited for the gymkhana suspension cars in 1974 which is odd....

https://www.gmheritagecenter.com/doc...t-Corvette.pdf

Another thing that is odd is that my buddy in college had a 74 L-82 4 speed car (bought used) and it DID have a 7/16 rear factory bar with the gymkhana suspension...something is not clear here.....

hunt4cleanair

Corvette did not get on its diet until 1980...the 1978 was the heaviest Corvette ever and weight added to suspension requirements.

corvetero

FYI, my car has 13/16" front sway bar and none on the rear.

The rear spring is a 9-leaf one. Here you are a picture.





It's a 74 L-82 4 speed.

jb78L-82

The 78/79 corvettes were the heaviest with curb weights of 3500 lbs (1978)and 3480 (1979) roughly without options but for all intensive purposes the same heavy weights. The weights of the earlier C3's contrary to popular opinion are not that much lighter, especially with the BB 454 which are way heavier than any SBC C3 with options:


Corvette's 427 big-block became a 454 for 1970.
The LS5 version delivered 390 bhp for just $290 extra.

Vehicle Specifications
Convertible
Coupe

Wheelbase, inches
98.0
98.0

Length, inches
182.5
182.5

Width, inches
69.0
69.0

Track, inches
front: 58.7 rear: 59.4
front: 58.7 rear: 59.4

Height, inches
47.9
47.9

Curb weight, pounds
3,720 Convertible (base weight)
3,425 Coupe (Base weight)

Even the early 70's SB C3's were in the base curb weight range of around 3250-3,400 lbs without options. The BBC C3 handling issue is more the weight distribution than the actual weight (53-54% front: Rear 46-47%). SBC generally are around 50:50 % weight distribution and the reason Duntov preferred the SBC C3's for handling....

The base suspension 1979 C3 (all base C3's are VERY softly sprung regardless of the weight requirements) had VERY soft springs for its heavier weight: 295lbs fronts and 192 lbs rear...way too soft for a sports car.

corvetero

Interesting information

hotrodnick

Interesting for sure,

jeff602

74 small blocks with ZO7 had a 9/16 rear sway bars, they are rare only 47 built

hunt4cleanair

That's partially correct...Z07 was only available for the L82 smallblock in addition to the LS4. So Z07 was not available for the L48. And the rear bar was equpped per the base suspension. So the LS4 was equipped with the 9/16 rear sway bar while the L82 was not equipped with a rear bar.

jb78L-82

That's interesting about the Z07 option....I can't recall what size rear bar my college buddies 74 L-82 4 speed gymkhana car had since it was the early 80's when he owned the car but he definitely had a factory rear bar....

To answer the op's original question on lowering the car:

Cut the front springs either 1/2 or 1 full coil in front and use 8/10 inch bolts on the rear steel spring for the rear.

Putting the factory gymkhana suspension on a 74 is easy (I would recommend the 78-82 F-41 settings):

front springs 550 lbs (base suspension is I believe 350lbs)
rear steel 7 leaf spring of 292 lbs (base suspension is 192lbs-9 leaf)
Front bar-1 1 /8 inch (base is 7/8 inch I believe)
Rear GM style Only sway bar 7/16 inch (no rear bar base suspension)
Bilstein HD's or Sports

A better gymkhana suspension like I have had for many years with superior ride AND better handling:

Front 550lbs coils cut 1/2 coil for lowering
rear Composite 360 lbs spring
Bilstein HD's Front with poly bushings on top
Bilstein Sports rear
factory 1 1/8 inch front bar with all poly bushings
rear 7/16 GM style bar with poly bushings
Competition adjustable strut rods with heim joints
Front Spreader bar-Speedirect

LT1M21Vette

Does anyone sell coils that will lower the car without cutting, or is that the proven recipe?

jb78L-82

I have used both Midamerica and ZIP Products for front coils shorter than stock:

http://www.mamotorworks.com/Corvette...lalom-602512-1

http://www.zip-corvette.com/68-82-c3...l-springs.html

hdal

JB,your poly bushg install didn't make the handling/ride to firm and sorta jumpy? I removed blue poly's from a friends 71',he complained about to hard ride especially over RR tracks. I have a 78"S/A/L-82 with stk Gym susp and think it rides & handles perfect. Hdal

jb78L-82

Not sure I know which poly you are referring to? Poly on the front shock towers did not firm up the ride but just increases the effective time of the front shocks. Poly bushings on the sway bars did not make the ride bouncy/firm but just makes the sway bars effectively act like bigger bars with rubber bushings. I do have poly upper and lower front control arm bushings and these do make the ride firmer BUT do eliminate much of the front slop in the front suspension...firmer but more solid along with the front spreader bar. The competition adjustable strut rods with heim joints (no bushings in the rear struts) did make the ride firm but not harsh.

The secret to making the C3's handle/ride/steer better is to eliminate all the slop in the stock C3 suspension, mostly from all the rubber bushings, front and rear, and the terrible 255/60/15 rubber available today for these cars.

The biggest contributor to a bouncy ride on my C3 were the 360 composite with the wrong shocks for a composite (KYB Gas A just) and the 255/60/15 balloon tires. Switching to Bilstein HD's all around helped immensely with the bouncy ride in the rear but eventually I switched to Bilstein Sports in the rear only (30% stiffer than the HD's) to quell the rear bouncy ride on the highway. Switching the rims to 17's and 255/45/17 ZR ultra high performance summer only tires finally completely eliminated the bounce and shockingly greatly improved the ride overall about 8 years ago....35 years of trial and error one change at a time has resulted in a C3 sport suspension that is simply head and shoulders over the stock gymkhana suspension.

A few years ago a neighbor of mine, not a car guy with a lexus LS430, went for ride in my 78 and he was shocked at how well my C3 rode (firm but not harsh) and the terrific handling....he thought that all C3's rode like trucks.

The last piece of the 78 upgrade is the rear trailing arms that are original...the TA bushings are worn and the rear wheel bearings have play...this winter....I have completely rebuilt and upgraded the OEM stock designed suspension to maximize the suspension's original design/intent with the same components but improvements over the last 35 years. Success!