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C4 Rear spring code/rate conversion chart?

84Turbo

Well-known member
Joined
Nov 5, 2008
Messages
60
Location
Florida
Corvette
'69 ZL-1 5spd, '84 turbo 6spd
I put a C4 suspension under my '69, and I'm looking to stiffen up the rear. To tell me what springs I'm looking at while wandering around swap meets, I'm trying to find a chart that has the spring three letter broadcast code (not the vehicle RPO code), and the rates. Anybody seen a chart like this?

thanks,
Mike
 
Not on one chart.
You have to cross reference the spring rate and the year model it came in from the commonly available suspension chart against the factory parts book that gives the factory spring codes for each year.

Exp
The heaviest rate rear spring is the 87.5 (N/mm) rear spring from a 84 Z51 equiped car
Listed as BMH is the GM Y body parts book
 
Try this data.

C4 Spring Code Chart

compiled by Hib Halverson
©2007 Shark Communications

Preface Notes:

1) GM had two RPO subsystems during the C4 era. There were engineering RPOs and marketing RPOs. What consumers knew as Z51 or Z07 was actually a combination of the FE3 (96) or FE7 (84-95) HD suspensions with other performance-related options. Some GM parts data refers to FE3 or FE7. When those RPOs are listed, it refers to cars optioned with either Z51 (84-91, 96) or Z07 (92-95).

2) In MY89-91, Selective Ride Control (SRC), which many refer to by its RPO, FX3, could be ordered in combination with Z51, however, a little-recognized production change which always occured in those MYs when those two RPOs were ordered together was a downgrade to base level (FE1) springs, front lower control arms and stabilizer bars. In those MYs the only conditions under which FE7 was present were; 1) if the car was ordered with Z51 and without FX3 or 2) it was an 90 or 91 Corvette Challenge car.

3) For MY92-95, FX3 and FE7 was added. A new RPO, Z07, was released for this combination. For MY92-95, FX3 was, also, available as a stand-alone option.

Coupe, front

HMZ 84 w. Z51
BMB 84 base, 85-87 with w. Z51
HKX, HMP 85-87 base
FHA 88-91 base, 89-91 w. FX3&Z51
FHB 88-91 w. Z51
AA 90-91 w. ZR1
FSS 92-95 base, 92-93 w. FX3
FSK 92-95 w. Z07
FSM 92-95 w. ZR1
HA 94-95 w. FX3
22173028 96 base
17999032 96 w. Z51

Convertible, front

HMN 86-87
FHC 88-91 base, 89-91 w. FX3
FSR 92-95 base
JA 94-95 w. FX3
22173029 95 w. FX3
17999031 96

Coupe, rear

BMF 84 base
BMH 84 w. Z51
NYR 85 base(?) 86-93 base, 89-90 w. FX3&Z51, 90-91 w. ZR1
NYU 85-91 w. Z51, 92-95 w. Z07
RHY 92-95 w. ZR1, 96 w. Z51
RHZ 94-96 base

Convertible, rear

RCA 86-96
22112254 94-95 w. FX3
 
I appreciate the information! :thumb
 
Hib,

I've got a front spring sitting on the shelf, with the FHU broadcast code. Can you give me some info on it?

Thanks again!
 
HIB

According to this statement "In those MYs the only conditions under which FE7 was present were; 1) if the car was ordered with Z51 and without FX3 or 2) it was an 90 or 91 Corvette Challenge car."

I had a 1990 parts vette which was not a challenge car since it lacked the challenge car RPO.

It however had Z51/FX3/FE7 it used FE1 springs, had a ZF6, J55 brakes, 30 & 26mm sway bars ... RPO label vin matched cars vin as well. It was a black on black coupe.
 
HIB

According to this statement "In those MYs the only conditions under which FE7 was present were; 1) if the car was ordered with Z51 and without FX3 or 2) it was an 90 or 91 Corvette Challenge car."

I had a 1990 parts vette which was not a challenge car since it lacked the challenge car RPO.

It however had Z51/FX3/FE7 it used FE1 springs, had a ZF6, J55 brakes, 30 & 26mm sway bars ... RPO label vin matched cars vin as well. It was a black on black coupe.

At some time in its 22 years, someone retrofitted the bigger stabilizer bars. Good thing it was a parts car because, with the big front bar and the soft rear spring, it would have understeered terribly. It's also unlikely the car's bars were a mistake at the plant because the 26-mm rear bar did not go to production until the following year.
 
At some time in its 22 years, someone retrofitted the bigger stabilizer bars. Good thing it was a parts car because, with the big front bar and the soft rear spring, it would have understeered terribly. It's also unlikely the car's bars were a mistake at the plant because the 26-mm rear bar did not go to production until the following year.

FE7 is the larger bars isn't it? I have a 90 FE1 but it has same spring codes as what the 90 parts car had but has much smaller sway bars
 
DSCF0303.jpg
 
Here you can see the larger front sway bar and rear sway bar. The rear sway bar makes my fe1 ones loon like a paper clip and the front is much larger as well. This was all from a low mileage wrecked 90. Don't think anything was changed on it and this is the way it came.

DSCF0414.jpg


DSCF0416.jpg
 
FE7 is the larger bars isn't it? I have a 90 FE1 but it has same spring codes as what the 90 parts car had but has much smaller sway bars

FE7 was the combination of HD front lower control arm bushings, HD springs and large stabilizer bars.
 
FE7 was the combination of HD front lower control arm bushings, HD springs and large stabilizer bars.

This one had all of the above however like I said it's springs carried the same codes as my 90 FE1. The rear spring is NYR can't remember the front though so I can't imaging anyone would go through the hassle of using FE1 springs on a FE7. As for the lower control arm bushings they seem the same as any other vettes bushings that I have seen.
 
This one had all of the above however like I said it's springs carried the same codes as my 90 FE1. The rear spring is NYR can't remember the front though so I can't imaging anyone would go through the hassle of using FE1 springs on a FE7. As for the lower control arm bushings they seem the same as any other vettes bushings that I have seen.

Actually it was no unheard of for someone to buy a used Z51, hate the ride then downgrade the springs. Those types of folks seldom drive hard so they'd never push the car enough to notice the huge understeer from the big front bar and soft rear spring.

On FE7, the front lower control arms use higher-durometer rubber, ie: they're less compliant than base FLCA bushings. The arms are ID'ed by "Z51" embossed on them. The FE7 (Z51) bushings were never serviced. Only way you could get them is on a new car.
 
Actually it was no unheard of for someone to buy a used Z51, hate the ride then downgrade the springs. Those types of folks seldom drive hard so they'd never push the car enough to notice the huge understeer from the big front bar and soft rear spring.

On FE7, the front lower control arms use higher-durometer rubber, ie: they're less compliant than base FLCA bushings. The arms are ID'ed by "Z51" embossed on them. The FE7 (Z51) bushings were never serviced. Only way you could get them is on a new car.

But I have read z51 for 90 was unlike 84-89 and wasn't a high spring rate code. This car also had a 2 1/4 rack compared to my 2 1/2 lock to lock one.
 

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