The arrival of the 1974 Chevy Corvette occurred during an abysmal period in automotive history. The period in question actually began in October, 1973 when OAPEC, (the Arab members of OPEC (the Organization of Petroleum Exporting Countries) plus Egypt, Syria, and Tunisia) proclaimed an oil embargo against the United States after the United States came to the aid of the Israelis during a military altercation between Egypt, Syria, and Israel.
While the actual embargo only lasted a few months (it ended in March, 1974, after OPEC received considerable pressure from NATO), the impact the embargo had on the automotive community was detrimental.
Gas prices had soared, and massive fuel shortages had occurred, leaving motorists waiting in long lines at the pumps. In some instances, gasoline was actually rationed, especially in more densely populated areas.
While the embargo was short-lived, it made automotive manufacturers seriously question the value that heavy, fuel-thirsty cars were bringing to the marketplace.
In many ways, the 1974 Corvette would represent the end of an era. Perhaps because of the embargo, and certainly a byproduct of it, The 1974 model would be the last year to be offered with an optional big-block 454 cubic inch V-8 engine. Additionally, all future engines offered with the Corvette would only run on unleaded gasoline – a decision would come in conjunction with the industry-wide requirement to install catalytic converters in every 1975 (and later) model. For its own part, the 1974 Corvette required 91-octane leaded or low-lead fuel.
Lastly dual exhaust would give way to separate manifolds routed to a single catalytic converter, then onward to separate pipes and motors. In fact, the 1974 Corvette would be the last model year that would exclude the installation of catalytic converters.
DID YOU KNOW: RPO YJ8 Cast Aluminum Wheels appeared on early 1974 option lists, but records indicate that none were sold. Since RPO P02 Deluxe Wheel Covers were no longer available, there were no optional wheels or wheel-covers available for the 1974 Corvette
Cosmetically, the 1974 Corvette received a new body-color rear-end treatment that was made to comply with a new, Federally imposed five-mile-per-hour impact standard.
Sheathed in urethane like the 1973‘s front-bumper revision, the skin actually covered an aluminum impact bar that was mounted to the Corvette’s chassis by two telescopic brackets.
The new rear bumper conveyed a smoother, more integrated look, and while it tapered downward instead of upward (as the previous Kammtype rear end had done), it did not harm the car’s aerodynamics. The urethane plastic skin had built in recesses for the license plate and the taillights, and was actually assemble of two main sections that were divided by a vertical, center seam. This detail is unique to the 1974 model year and makes it easy to identify.
Turning to the interior, the 1974 Corvette received only minor enhancements. Perhaps the most notable improvement over the previous models was that the 1974 Coupe now featured an integrated shoulder belt/lap belt assembly for the first time. Shoulder belts remained optional in the convertible models, and if they were so equipped, continued to be a separate assembly from the lap belts. The locking mechanisms in the shoulder restraints also changed design from a pull-rate type (which would catch based on the amount of force applied to the belt) to a swinging-weight type that was activated by the car’s deceleration.
Elsewhere in the interior, the stock inside rearview mirror increased in width from 8 to 10 inches.
Mechanically, a handful of improvements were made to the car. The standard RPO ZQ3 engine’s output increased slightly from the previous model year to 195 horsepower.
The market’s growing preference for performance automatic transmissions resulted in a more durable Turbo Hydra-Matic. Designated by RPO M40, the transmission was no-cost upgrade to consumers and was installed in nearly two-thirds of all the Corvettes built that year.
The radiator was redesigned for more efficient cooling at low speeds. The power steering pump was made more durable via the use of magnets, which were installed to attract (and capture) debris in the power steering fluid.
Downstream from the engine, resonators were added to the exhaust system, which enhanced the tone of the car during operation.
With the newly designed rear bumper in place, the exhaust pipes were re-routed to exit just below the bumper (instead of cut into the rear fascia assembly as before.) Lastly, the alarm activator was relocated from the rear of the car to the driver side front fender.
New for the 1974 Corvette was one of the most bargain-priced performance packages of all-time. The Gymkhana Suspension Package (RPO FE7) cost a mere seven dollars, featured a higher-rate spring assembly and firmer, specially calibrated shocks. This setup – which had been introduced and used since the mid-Sixties as part of Chevy’s popular F41 Suspension Package – provided much improved handling on the 1974 Corvettes that were so equipped.
The F41 itself, which had begun with the Z06 racing option back in 1963, was still available as part of RPO Z07, and included the aforementioned suspension setup as well as heavy-duty brakes.
Given the performance constraints placed before it by Federal Emission Regulations, oil embargos, and a struggling economy, the 1974 Corvette still presented drivers with a respectable level of acceleration and performance.
While it was hard to compare the 1974 Corvette to its slightly older, big-block brothers and sisters, its numbers spoke for themselves.
When equipped with the 250 brake horsepower L82 engine, the ’74 Corvette could accelerate from 0 to 60 miles per hour in approximately 7.5 seconds and reach a top speed of 125 miles per hour while still averaging about 14-15 miles per gallon. Moreover, what it lacked in outright performance it made up for in luxury.
The 1974 Corvette would become widely recognized as a very refined, grand touring car with plenty of creature comforts. The 1974 Corvette defined industry standards by having a near-record sales year. In total, 37,502 Corvettes were sold – 32,028 coupes at a base price of $6,001.50, and a mere 5,474 convertibles at a base price of $5,765.50.
Two-door convertible/coupe, front engine, rear wheel drive
St. Louis, Missouri
Uniconstruction: fiberglass reinforced plastic (FRP or “fiberglass”) body, backboned by a steel cage outlining the passenger compartment. Principal members – underbody, front and rear end assemblies, dash panel and hinge pillars are bonded, riveted, or bolted together and to each other. Hood is plastic with bonded plastic reinforcement. Coupe: two removable roof panels and removable rear window. Frame: all welded, full length, ladder construction with 5 crossmembers. Side Rails and intermediate crossmembers box section; front crossmember box girder section. Eight body-mounting points.
Type and Description: Independent, SLA type, coil springs with center mounted shock absorbers, spherical joint steering knuckle pivots.
Front Coil Springs
Make & Type
10.27 x 3.80; 130.84 x 0.606
Front Stabilizer Bar
Hot rolled steel
.8125 with 350ci engine, .875 with 454ci engine
Suspension – Back
Type and Description: Full Independent rear suspension with frame-anchored differential unit. Position of each wheel established by three links: tubular axle drive shafts, transverse strut rods, torque control arms. Vertical suspension loads taken by transverse leaf springs. Built-in camber adjustment at strut rod inner ends.
Rear Leaf Springs
Number of Leaves
Variable rate 9-leaf
Chrome carbon steel
Length, width, height
48.60 x 2.25 x 2.121
Caliper Disk – 4 Wheel Hydraulic
Delco Moraine, vacuum power unit; integral
Drum diameter, front (in.):
11.75 x 1.25
Drum diameter, rear (in.):
11.75 x 1.25
Swept Drum Area Effective area:
Wheels & Tires
Wheels & Tires Specs
Short spoke spider, welded steel
15″ x 8.00
GR70 x 15 — Blackwall Steel Belted Radial
GR70 x 15 — White Stripe Steel Belted Radial
GR70 x 15 — White Letter Steel Belted Radial
20 psi (cold), 30 psi (hot)
20 psi (cold), 30 psi (hot)
Steering Specs – Manual Steering
Semi-reversible gear with ball-nut driven by recirculating anti-friction bearings, energy-absorbing steering column, steering damper attached to relay rod; two position steering knuckle arm attachment for street and fast ratio steering. Adjustable steering column available optionally.
Wheel Diameter (in.)
Turns, Stop to Stop
37 ft. (outside front), 39 ft. (outside front)
Steering Specs – Power Steering RPO N40
(Specifications are the same as Manual Steering except the following):
Hydraulic; pump powered cylinder assisted linkage
Wheel Turns (Lock to Lock)
1974 Corvette Exterior Dimensions
Hard Top Dimensions
Exterior Dimensions (Hardtop)
Interior Dimensions (Hardtop)
Total Body Width:
Front Track Width:
Rear Track Width:
Min. Ground Clearance
Soft Top Dimensions
Exterior Dimensions (Soft Top)
Interior Dimensions (Soft Top)
Total Body Width:
Front Track Width:
Rear Track Width:
Min. Ground Clearance
Exterior Dimensions (Coupe)
Interior Dimensions (Coupe)
Total Body Width:
Front Track Width:
Rear Track Width:
Min. Ground Clearance
2 – Driver & Passenger
Curb Weight (lbs)
Interior Passenger Volume (cu. ft)
Interior Trunk Volume (cu. ft)
Fuel Capacity (gallons):
4.0 for 350ci. engines (capacity of crankcase less filter – refill)
5.0 for 454ci engines (capacity of crankcase less filter – refill)
Coolant capacity without heater (qts.)
18 for RPO LT1 engine
22 for 454ci. engine
12 Volt, 62AH for 350ci. engines
12 Volt, 80AH for 454ci. engines
Vehicle Assembly Location. S – St. Louis, Missouri
4XXXXX (Eighth thru Thirteenth Digits)
Plant Sequence Numbers.
The last six digits begin at 400001 and run thru 437502, accounting for 37,502 Corvette Coupes/Convertibles built in 1974. Each Vehicle Identification Number (VIN) is unique to an individual car.
1974 Corvette Vehicle Serial Number Plate
For all 1974 Corvettes, the location of the Vehicle Identification Number (VIN) is stamped on a plate attached to the left front body hinge pillar. (See Figure 1 below.)
1974 C3 Corvette Body Number Trim & Point Plate
Location: On the driver’s side upper left-hand door hinge pillar.
1974 Corvette Vin
A01 – Body build date code.
A – Designates the Month (See Chart Below).
A – Aug., 1973., B – Sep., 1973., C – Oct., 1973., D – Nov., 1973., E – Dec, 1973., F – Jan., 1974., G – Feb., 1974., H – Mar., 1974., I – Apr., 1974., J – May, 1974., K – June, 1974., L – Jul., 1974., M – Aug., 1974., N – Sept., 1974
01 – Designates the Day of the Month.
400 – Interior Trim code. 400 – Black (Vinyl)
56L – Exterior Color Code. 56 – Bright Yellow
Codes were often followed by the letter L, but some trim plates had an exterior code preceded by the number 9 with no letter L following.
1974 Corvette Engine Identification & Engine Number
All engines are stamped on the top front of the right-hand bank of cylinder and case.
Engine Identification Example:
V – Engine build location.
T – Tonawanda, NY. (All big block engines.)
V – Flint, MI. (All small block engines.)
0127 – Date Code. Month and Day. 0127 – January 27.
CKZ – Type Designation. CKZ – 350ci 195hp, manual transmission.
(Refer to the Engine Suffix section of the 1974 Corvette Specification Page for a list of all Type Designations.)
Engine Number Example:
1 – Division. 1 – Chevrolet
3 – Model year. 3 – 1974
S – Assembly Plant Designation. S – St. Louis
400001 – VIN Sequential Serial Number
1974 Corvette Transmission Identification & Transmission Number
4-Speed (Muncie) – Stamped on the top right side of the case at adapter.
Turbo Hydra-matic Automatic – Name plate tag on right-hand side of case.
Transmission Identification Example:
WD – Type Designation. WD – 4-Speed / CK – Turbo Hydra-matic
P – Source Designation.
P – Muncie
4 – Year. 4 – 1974
E01D – Production Month and Date.
E – Designates Month (See Chart Below.)
A – Jan. / B – Feb. / C – Mar. / D – Apr. / E – May / H – June / K – July / M – Aug. / P – Sept. / R – Oct. / S – Nov. / T – Dec.
01 – Designates Day of the month.
D or N – Designates Day or Night Shift on Automatic only.
1974 Corvette Factory Options
Base Corvette Sport Coupe
Base Corvette Convertible
Custom Interior Trim
Custom Shoulder Belts (std with coupe)
Auxiliary Hardtop (for convertible)
Vinyl Covered Auxiliary Hardtop
Rear Window Defogger
Optional Rear Axle Ratios
454ci, 270hp Engine
350ci, 250hp Engine
4-Speed Manual Transmission, close-ratio
Turbo-Hydro-matic Automatic Transmission
Tilt-Telescopic Steering Column
White Stripe Steel Belted Tires, GR70x15
White Letter Steel Belted Tires, GR70x15
AM-FM Radio, Stereo
Heavy Duty Battery (std with LS4)
Map Light (on rearview mirror)
California Emission Test
Off Road Suspension and Brake Package
Base Corvette Sport Coupe (1YZ37)
The base price of the 1974 Chevrolet Corvette Coupe without any optional equipment.
A 350 cubic inch, 195 horsepower engine, 4-speed wide ratio manual transmission, vinyl interior trim, and T-tops were included in the base price.
Base Corvette Convertible (1YZ67)
The base price of the 1974 Corvette Convertible without any optional equipment.
A 350 cubic inch, 195 horsepower engine, 4-speed wide ratio manual transmission, vinyl interior trim, and a convertible top were included in the base price.
Custom Interior ( — )
Optional interior trim upgrade that included a number of custom modifications to the base interior.
The custom interior trim included leather seat trim, wood-grain accents and carpet trim on door panels, wood-grain accents on the console, and cut-pile carpeting.
Power Windows (A31)
Factory installed power driver and passenger windows.
Custom Shoulder Belts (A85)
An addition to the standard lap safety belt that crosses over the shoulder for added safety.
The shoulder belts option was included with all Corvette coupes at no additional charge. The option was also available on the Corvette convertible, but at an additional cost.
Auxiliary Hardtop (for convertibles) (C07)
An optional hard-top that could be installed in lieu of the convertible top.
Vinyl Covered Auxiliary Hardtop (C08)
This option allowed consumers to install an auxiliary hardtop on convertible models.
The vinyl covering provided a faux convertible top appearance even when the hardtop was mounted on the car.
Rear Window Defogger (C50)
An optional rear window forced air defogger.
Air Conditioning (C60)
Factory installed air-conditioning.
System includes evaporator, blower, condenser, receiver-dehydrator, refrigerant (freon) tank, air intake assembly and duct assembly for both systems.
Includes an integrated heater.
Optional Rear Axle Ratio
Rear axle ratio selection.
Gymkhana Suspension (FE7)
An optional, heavier-duty suspension system for higher levels of performance.
Included a stiffer front sway bar and stiffer springs.
It was automatically included as part of the Z07 package.
There were no restrictions on ordering this option.
Power Brakes (J50)
Vacuum power assisted brakes; includes dual circuit master cylinder.
454ci, 270hp Engine (LS4)
Optional high-output, big-block V-8 engine.
This was the last year for the 454 cubic inch “big block” engine in Corvettes.
350ci, 250hp Engine (L82)
Optional higher-output, small block V-8 engine.
4-Speed Manual Transmission, Close Ratio (M21)
A close ratio version of the M20 Muncie 4-speed manual transmission.
The gear ratios for the RPO M21 Close Ratio 4-Speed Manual Transmission are: 1st Gear – 2.20:1, 2nd Gear – 1.64:1, 3rd Gear – 1.28:1, 4th Gear – 1.0:1 (Direct).
Turbo Hydra-Matic Automatic Transmission (M40)
An optional, three-speed automatic transmission.
The Turbo Hydra-Matic Automatic Transmission consisted of a 3-element hydraulic torque converter and compound planetary gear set. It was equipped with the following gear ratios: 1st Gear – 2.48:1, 2nd Gear – 1.48:1, and 3rd Gear – 1.00:1.
The M40 Turbo Hydra-Matic Automatic Transmission was a no-cost option with the base 350 cubic inch, 195 horsepower engine, but cost an additional $103 ($97 early in production) when ordered with the 454 cubic inch, 270 horsepower LS4 engine or the 350 cubic inch, 250 horsepower L82 engine.
Tilt Telescopic Steering Column (N37)
An optional, adjustable steering column and tilt-angle adjustable steering wheel.
The Telescopic Steering Column changes the drivers distance from the steering wheel by literally telescoping the steering wheel closer to or further away from the vehicle operator.
Power Steering (N41)
Hydraulically assisted power steering.
Magnets were added to power steering units to attract and collect metallic debris caught in the power steering fluid.
White Stripe Steel Belted Tires, GR70x15 (QRM)
Standard size tires with a special 3/8″ wide white sidewall stripes.
White Letter Steel Belted Tires, GR70x15 (QRZ)
Standard size tires with special raised white lettering.
Dual Horns (U05)
An optional, dual tone horn.
AM-FM Radio, Stereo (U58)
A standard/stock dealer installed Corvette radio.
The radio received broadcast in FM 2-channel stereo, FM monaural, and AM monaural.
16-transistor 9-diode circuitry.
Fixed height rear antenna.
AM-FM Radio (U69)
A standard/stock dealer installed Corvette radio.
The radio receives broadcast in FM monaural, and AM monaural.
16-transistor 9-diode circuitry.
Fixed height rear antenna.
Heavy Duty Battery (std. with LS4) (UA1)
Optional, heavier-duty battery with increased cranking amps/capability.
Map Light (on rearview mirror) (UF1)
Light mounted on inside rearview mirror.
California Emission Test (YF5)
An assembly line emissions test to conform with California registration requirements.
Not available when the LS4 engine was ordered with the car.
Off Road Suspension and Brake Package (Z07)
Stiffer suspension/brake package for more rugged driving conditions.
Available with optional engines L82 and LS4 only.
Required the close ratio, 4-speed manual transmission (RPO M21.)
Z07 was not available with air conditioning (RPO C60.)
It included special front and rear suspension, and heavy-duty front and rear power brakes.
The FE7 Gymkhana Suspension system was automatically included with the Z07 package.
The transition to soft bumpers was completed in 1974 with the introduction of new body color rear bumpers. The urethane plastic skin had built in recesses for the license plate and the taillights, and a vertical center seam divided the two main sections. (Later years are one piece without the seam.) The skin covered an aluminum impact bar mounted on two telescopic brackets.
This was the last model year for the Corvette to exclude catalytic converters.
It was the last Corvette of the era with true dual exhaust. Resonators were added to the exhaust system. Exhaust tailpipes exited below the bumper.
Fuel requirements were 91-octane leaded or low lead.
Radiators were redesigned for more efficient cooling at low speeds.
Shoulder belts on the 1974 coupes were integrated with lap belts for the first time. Shoulder belts remained optional in convertibles and, if so equipped, were separate from the lap belts as before. Also the locking mechanism was changed from a pull-rate type to a swinging-weight type activated by the car’s deceleration.
The alarm activator moved from the rear panel to the driver side fender.
The stock inside rearview mirror increased in width from 8 to 10 inches.
Make: CHEVROLET Model: CORVETTE Model Year: 1974 Manufacturer: CARDONE INDUSTRIES, INC. Mfr’s Report Date: MAY 07, 2003 NHTSA CAMPAIGN ID Number: 03E032000 NHTSA Action Number: N/A Component: SERVICE BRAKES, AIR:DISC:CALIPER Potential Number of Units Affected: 15899
REMANUFACTURED REAR BRAKE CALIPERS, PART NOS. 18-7019, 18-7020, 16-7019, AND 16-7020, MANUFACTURED FROM FEBRUARY 1, 2002, TO APRIL, 25, 2003., AND FOR USE ON 1965 THRU 1982 CHEVROLET CORVETTES. THE SUBJECT BRAKE CALIPERS WERE MANUFACTURED USING IMPROPERLY MANUFACTURED PISTON SEALS. THESE SEALS ARE INTENDED TO PREVENT FLUID LEAKAGE BETWEEN THE CALIPER HOUSING AND THE PISTONS. THESE BRAKE CALIPERS ARE FOR USE ONLY ON 1965 THRU 1982 CHEVROLET CORVETTE VEHICLES. THIS RECALL DOES NOT INVOLVE GENERAL MOTORS CORPORATION OR ANY OF ITS PRODUCTS.
UNDER THESE CONDITIONS, THE VEHICLE OPERATOR MAY NOT BE ABLE TO STOP THE CAR, POSSIBLY RESULTING IN A VEHICLE CRASH.
CARDONE WILL NOTIFY ITS CUSTOMERS AND ALL UNSOLD INVENTORY WILL BE REPURCHASED AND WILL PROVIDE A FULL REFUND TO CUSTOMERS. OWNER NOTIFICATION IS EXPECTED TO BEGIN DURING MAY 2003. OWNERS WHO TAKE THEIR VEHICLES TO AN AUTHORIZED DEALER ON AN AGREED UPON SERVICE DATE AND DO NOT RECEIVE THE FREE REMEDY WITHIN A REASONABLE TIME SHOULD CONTACT CARDONE AT 215-912-3000.
ALSO, CUSTOMERS CAN CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION’S AUTO SAFETY HOTLINE AT 1-888-DASH-2-DOT (1-888-327-4236).
Make: CHEVROLET Model: CORVETTE Model Year: 1974 Manufacturer: HONEYWELL INTERNATIONAL, INC. Mfr’s Report Date: OCT 19, 2007 NHTSA CAMPAIGN ID Number: 07E088000 NHTSA Action Number: N/A Component: EQUIPMENT Potential Number of Units Affected: 121680
CERTAIN HONEYWELL FRAM RACING BRAND HP4 AND HP8 OIL FILTERS THAT WERE MANUFACTURED FROM MAY 25, 2006, THROUGH SEPTEMBER 14, 2007, AND SOLD FOR USE AS REPLACEMENT EQUIPMENT FOR VEHICLES LIST ABOVE. THE AFFECTED FILTERS ARE MARKED WITH A DATE CODE A61451 THROUGH A72571 SEQUENTIALLY. THE DATE CODE AND PART NUMBER APPEAR ON THE FILTER HOUSING. FRAM RACING HP4 AND HP8 OIL FILTERS NOT BEARING A DATE CODE IN THIS RANGE ARE NOT AFFECTED BY THIS RECALL. THE GASKET OF THE OIL FILTER BECOMES MORE PLIABLE UNDER HIGH TEMPERATURES AND PRESSURES.
THIS CONDITION MAY CAUSE INADEQUATE SEALING AND LOSS OF ENGINE OIL, POSSIBLY RESULTING IN A FIRE.
HONEYWELL WILL REPLACE THE AFFECTED OIL FILTERS FREE OF CHARGE. THE RECALL BEGAN DURING NOVEMBER 2007. OWNERS CAN CONTACT FRAM CUSTOMER SERVICE TOLL-FREE AT 1-800-890-2075.
CUSTOMERS MAY CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION’S VEHICLE SAFETY HOTLINE AT 1-888-327-4236 (TTY: 1-800-424-9153); OR GO TO HTTP://WWW.SAFERCAR.GOV.
Make: CHEVROLET Model: CORVETTE Model Year: 1974 Manufacturer: GENERAL MOTORS CORP. Mfr’s Report Date: MAR 22, 1974 NHTSA CAMPAIGN ID Number: 74V050000 NHTSA Action Number: N/A Component: FUEL SYSTEM, GASOLINE:STORAGE:TANK ASSEMBLY:MOUNTING Potential Number of Units Affected: 2937
CHEVROLET CAMPAIGN NO 74-C-13. POSSIBILITY THAT THE FUEL TANK RETURN LINE FITTING MAY HAVE A THIN WALL SECTION THAT COULD BREAK. IF THIS OCCURS FUEL BEING RETURNED TO THE GASOLINE TANK WILL BE SPILLED AROUND THE TAIL PIPE OUTLET AS LONG AS THE ENGINE CONTINUES TO RUN. IF, UNDER THESE CONDITIONS THE VEHICLE BACKFIRES OR SPARKS ARE EMITTED FROM THE EXHAUST SYSTEM, THE FUEL VAPOR CAN BE IGNITED. (CORRECT BY INSPECTING AND REPLACING FUEL LINES WHERE NECESSARY).
1974 Corvette Service Bulletins
1974 Corvette Common Issues
1974 Corvette Maintenance Schedule
The time or mileage intervals indicated on this website are intended as a guide for establishing regular maintenance and lubrication periods. Sustained heavy duty or high speed driving, or driving under adverse conditions may require more frequent servicing.
Additional Maintenance and Lubrication
In addition to the items listed above, it is also recommended that the following items are inspected every 300 miles or 2 weeks, whichever comes first:
Check Tire Pressure
Check Battery Water Level
Check Oil Level In Engine
Remove air cleaner and block throttle and choke in wide open position. Hook up starter remote control cable and insert compression gauge firmly in spark plug port. Whenever the engine is cranked remotely at the starter, with a jumper cable or other means, the distributor primary lead must be disconnected from the negative post on the coil and the ignition switch must be in the “ON” position. Failure to do this will result in a damaged grounding circuit in the ignition switch.
Crank engine through at least four compression strokes to obtain highest possible reading. Check and record compression of each cylinder. If one or more cylinders reads low or uneven, inject about a tablespoon of engine oil on top of pistons in low reading cylinders (through spark plug port.) Crank engine several times and recheck compression. If compression comes up but does not necessarily reach normal, rings are worn. If compression does not improve, valves are burnt, sticking or not sealing properly. If two adjacent cylinders indicate low compression, the cause may be a head gasket leak between the cylinders. Engine coolant and/or oil in cylinders could result from this defect.
The adjustments described apply to all carburetors used, except as noted. All adjustments are made with the engine at normal operating temperature.
Idle Speed (1972-1976)
The idle stop solenoid requires two idle speed settings. The curb idle speed is normal engine idle speed, the low idle speed is set for conditions when the solenoid is de-energized, as when the ignition is turned off. This prevents engine run-on. Idle speed adjustments are made with the engine at normal operating temperature, with the air cleaner on, choke open, air conditioning off, and fuel tank hose from vapor canister disconnected (on later models). Set parking brake and block driving wheels. Disconnect electrical connector at idle stop solenoid. With automatic transmission in Drive, or manual transmission in neutral, turn low idle screw to obtain low idle speeds of 500 rpm, reconnect electrical connector to solenoid and crack throttle slightly, to extend solenoid plunger. Then turn approximately 600 rpm for automatic transmission models in Drive, or approximately 850 prm for manual transmission models in neutral. Shut off engine and reconnect fuel tank to vapor canister.
Idle Mixture (1972-1976)
The idle mixture is factory preset and the screws are capped with plastic limiter caps. These caps allow about one full turn for adjustment. If more is required remove the caps or break off the tabs with needle nose pliers. Adjusting the idle mixture is done with the engine running at normal operating temperatures, with the air cleaner on, choke open, air conditioning off, and fuel tank hose from canister disconnected. Set the parking brake and block the driving wheels. Put automatic transmission in Drive; manual transmission in neutral. Turn in or out one idle mixture screw at a time to obtain smoothest, fastest idle speed; then adjust the other screw to make engine run even smoother and faster. A basic starting point for adjusting screws is four turns out from fully in position with needle just touching seat. Readjust idle speed if necessary. Reconnect fuel tank hose from canister.
Idle Speed and Mixture – Holley 2300
All adjustments are same as previously described except as follows: On models equipped with idle stop solenoid, adjust idle stop solenoid screw to give 1000 rpm, then adjust idle mixture adjusting screw to specified rpm. Turn idle mixture screw in (leaner mixture) until engine speed drops 20 rpm, then turn out 1/4 turn. Disconnect lead at idle stop solenoid (throttle level will rest against regular stopscrew.) Adjust this stopscrew for idle speed of 500 rpm. Do not change setting of idle stop solenoid stopscrew or idle mixture screw.
Fast Idle (1966-1976)
With the transmission in neutral, position the cam follower on the high step (2nd step, 1971-1972) of the fast idle cam. Adjust fast idle screw of Rochester carburetors to obtain recommended fast idle speed. Bend fast idle lever on Holleys. On 1970-72 models, disconnect transmission controlled spark solenoid.
With slow idle speed correctly adjusted, fully open choke and make sure fast idle cam follower is off steps of cam. With dashpot fully compressed, adjust for 1/16″ clearance between dashpot plunger and throttle lever.
Remove the air cleaner and check to see that choke valve and rod more freely. Disconnect choke rod at choke lever. Check choke adjustment by holding choke valve closed and position rod so that it contacts stop. If necessary, adjust rod length by bending rod at offset. Bend must be such that rod enters choke lever hole freely and squarely. Connect rod at choke lever and install air cleaner.
Air Injection Reactor (A.I.R.) – Description and Operation
The A.I.R. system is used to burn the unburned portion of the exhaust gases to reduce its hydrocarbon and carbon monoxide content. The system forces compressed air into the exhaust manifold where it mixes with the hot exhaust gases. The hot exhaust gases contain unburned particles that complete their combustion when the addition air is supplied.
The system consists of: An air pump, diverter valve, check valve(s), AIR pipe assemblies and connecting hoses and fittings. Carburetors and distributors for AIR engines are made to be used with the system and should not be replaced with components intended for use with engines that do not have the system.
The air pump is a two-vane pump which compresses fresh filtered air and injects it into the exhaust manifold. The pump consists of: a housing, centrifugal filter, set of vanes that rotate about the centerline of pump housing bore, the rotor, and the seals for the vanes. The centrifugal filter is replaced by first removing the drive belt and pump pulley; then pulling filter off with pliers. Care should be taken to prevent fragments from entering the air intake hole. NOTE: A new filter may squeal when first put into operation. Additionally, GREAT CARE should be taken in working on the compressor as the aluminum used is quite soft and thin. The air pump is operating satisfactorily when the air flow from it increases as engine speed increases.
The air hoses should be replaced only with hoses which are designed for AIR system use, as no other type hoses can withstand the high temperature.
Check and Adjust Dwell
Start engine then check ignition dwell. With engine running at idle, raise the adjustment screw window and insert an Allen wrench in the socket of the adjusting screw. Turn the adjusting screw as required until a dwell reading of thirty degrees is obtained. A two degree variation is allowable for wear. Close access cover fully to prevent the entry of dirt into the distributor. If a dwell meter is not available, turn adjusting screw clockwise until engine starts to misfire, then turn screw one-half turn in the opposite direction to complete adjustment.
Slowly accelerate engine to 1500 rpm and note dwell reading. Return engine to idle and note dwell reading. If dwell variation exceeds specifications, check for worn distributor shaft, worn distributor shaft bushing or loose breaker plate.
Remove distributor cap, clean cap and inspect for cracks, carbon tracks and burned or corroded terminals. Replace cap where necessary. Clean rotor and inspect for damage or deterioration. Replace rotor where necessary. Replace brittle, oil soaked or damaged spark plug wires. Install all wires to proper spark plug. Proper positioning of spark plug wires in supports is important to prevent cross-firing. Tighten all ignition system connections. Replace or repair any wires that are frayed, loose or damaged.
Disconnect the distributor spark advance hose and plug the vacuum source opening. Start engine and run at idle speed. Aim timing light at timing tab. The markings on the tabs are in two degree increments (the greatest number of markings on the “A” side of the “Q”). The “O” marking is TDC (Top Dead Center) and the BTDC settings fall on the “A” (advance) side of the “O”. Adjust the timing by loosening the distributor clamp and rotating the distributor body as required, then tighten the clamp, and recheck timing. Stop engine and remove timing light and reconnect the spark advance hose.
Inspect each plug individually for badly worn electrodes, glazed, broken or blistered porcelains and replace plugs where necessary. Clean serviceable spark plugs thoroughly, using an abrasive-type cleaner such as sand blast. File the center electrode flat. Inspect each spark plug for make and heat range. All plugs must be of the same make and number. Adjust spark plug gaps to .035 in. using a round feeler gauge. If available, test plugs with a spark plug tester. Inspect spark plug hole threads and clean before installing plugs. Install spark plugs with new gaskets and torque to specifications. Connect spark plug wiring.
Transistorized Distributor (H.E.I. System)
There are no moving parts in the ignition pulse amplifier, and the distributor shaft and bushings have permanent type lubrication, therefore no periodic maintenance is required for the magnetic pulse ignition system.
Distributor (Breaker Point System)
Check the distributor centrifugal advance mechanisms by turning the distributor rotor in a clockwise direction as far as possible, then releasing the rotor to see if the springs return it to its retarded position. If the rotor does not return readily, the distributor must be disassembled and the cause of the trouble corrected.
Check to see that the vacuum spark control operates freely by turning the movable breaker plate counter-clockwise to see if the spring returns to its retarded position. Any stiffness in the operation of the spark control will affect the ignition timing. Correct any interference or binding condition noted.
Examine distributor points and clean or replace if necessary. Contact points with an overall gray color and only slight roughness or pitting need not be replaced.
Dirty points should be cleaned with a clean point file. Use only a few strokes of a clean, fine-cut contact file. The file should not be used on other metals and should not be allowed to become greasy or dirty. Never use emery cloth or sandpaper to clean contact points since particles will embed and cause arcing and rapid burning of points. Do not attempt to remove all roughness nor dress the point surfaces down smooth. Merely remove scale or dirt. Clean cam lobe with cleaning solvent, and rotate cam lubricator wick end (or one-hundred-eighty degrees as applicable). Replace points that are burned or badly pitted.
Where prematurely burned or badly pitted points are encountered, the ignition system and engine should be checked to determine the cause of trouble so that it can be eliminated. Unless the condition causing point burning or pitting is corrected, new points will provide no better service than the old points.
Check point alignment then adjust distributor contact point gap to .019″ (new points) or .016″ (used points). Breaker arm rubbing block must be on high point of lobe during adjustment. If contact points have been in service, they should be cleaned with a point file before adjusting with a feeler gauge.
Check distributor point spring tension (contact point pressure) with a spring gauge hooked to breaker lever at the contact and pull exerted at 90 degrees to the breaker lever. The points should be closed (cam follower between lobes) and the reading taken just as the points separate. Spring tension should be 19-23 ounces. If not within limits, replace. Excessive point pressure will cause excessive wear on the points, cam and rubber block. Weak point pressure permits bouncing or chattering, resulting in arcing and burning of the points and an ignition miss at high speed. Install rotor and distributor cap. Press all wires firmly into cap towers.
Battery and Battery Cables
The top of the battery should be clean and the battery hold-down properly tightened. Particular care should be taken to see that the top of the battery is kept clean of acid film and dirt. When cleaning batteries, wash first with a dilute ammonia based or soda solution to neutralize any acid present and then flush off with clean water. Keep vent plugs tight so that the neutralizing solution does not enter the cell.
The hold-down bolts should be kept tight enough to prevent the batter from shaking around in its holder, but they should onto be tightened to the point where the battery case will be placed under a severe strain.
To ensure good contact, the battery cables should be tight on the battery posts. Oil battery terminal felt washer. If the battery posts or cable terminals are corroded, the cables should be cleaned separately with a soda solution and wire brush. After cleaning and before installing clamps, apply a thin coating of a petrolatum to the posts and cable clamps to help slow corrosion.
If the battery has remain undercharged, check for loose or defective fan belt, defective alternator, high resistance in the charging circuit, oxidized regulator contact points, or a low voltage setting. If the battery has been using too much water, the voltage output is too high.
Inspect for deteriorated or plugged hoses. Inspect all hose connections. On engines with closed element air cleaners, inspect crankcase ventilation filter and replace if necessary. On engines with open element air cleaners, remove flame arrestor and wash in solvent then dry with compressed air.
Check the brake fluid regularly, for as the brake pads wear the level will drop rapidly. It should be replenished only with the recommended fluid. Check disc brake assemblies to see if they are wet; it would indicate a leaking cylinder.
Disc brakes do not need periodic adjustments; they are self adjusting. The pads should be replaced when the friction material gets down to 1/16″. This is when the groove in the center of the pad is gone. Check by removing wheel and looking directly into caliper.
Clutch Pedal Play
Check clutch action by holding pedal 1/2″ from floor and move shift lever between first and reverse several times, with engine running. If shift is not smooth adjust clutch. Free play with pedal released is approx. 1-1/4″ to 2″ and 2″ to 2-1/2″ for heavy duty.
At clutch lever near firewall remove clutch return spring. To decrease clutch pedal free play remove clutch pedal return spring and loosen lower nut on clutch pedal rod; take up play with upper nut. Continue until proper play is obtained, then securely tighten top nut and replace spring. To increase pedal play work nuts in opposite sequence.
Disconnect control linkage at carburetor throttle lever. Hold carburetor throttle lever in wide position. Pull control linkage to wide open position. (On vehicles equipped with automatic transmission, pull through detent.) Adjust control linkage to freely enter hole in carburetor throttle lever. Connect control linkage at throttle lever.
Throttle Linkage Adjustment (Powerglide)
Remove air cleaner, disconnect accelerator linkage at carburetor. Disconnect accelerator return and trans. road return springs. Pull upper rod forward until transmission is through detent. Open carburetor wide open, at which point ball stud must contact end of slot in upper rod. Adjust swivel on end of rod if necessary.
Pull detent switch driver to rear until hole in switch body lines up with hole in driver. Insert a 3/16″ pin through hole to depth of 1/8″, and loosen mounting bolts. Open throttle fully and move switch forward until lever touches accelerator lever. Tighten mounting bolt and remove pin.
EGR Valve Check
A rough idling engine may be caused by a malfunction of the valve. Check by pinching vacuum hose to carburetor with engine idling. If idling smooths out, the valve should be removed for cleaning or replacement if something appears to be broken.
Lubrication – Engine Oil
The car should be standing on level ground and the oil level checked with the dipstick. Withdraw the dipstick, wipe it with a clean rag, replace and withdraw again. The mark made by the oil on the lower end of the dipstick will indicate the oil level. If necessary, oil should be added through the filler cap. Never let the oil level fall so low that it does not show at all on the dipstick. If in doubt, it is better to have a bit too much oil than too little. Never mix oils of different brands, the additives may not be compatible.
Engine Oil Drain and Replacement
Place a pan under the oil pan drain plug and remove plug. Be sure pan is of a large enough capacity to hold the oil. Move pan under filter and remove filter by turning if counterclockwise. Clean gasket surface of cylinder block. Coat gasket of new filter with engine oil. Thread filter into adapter. Tighten securely by hand. Do not overtighten filter. Remove drop pan.
Remove drain pan. Inspect oil pan drain plug gasket and replace if broken, cracked, or distorted. Install drain plug and tighten. Fill crankcase to required level with recommended oil. Operate engine at fast idle and check for oil leakage.
Check fluid level with engine idling, transmission in neutral and engine at normal operating temperature. Add fluid as needed to bring level to mark. Do not overfill.
Every 12,000 miles or sooner, depending on service, remove fluid from sump and add new fluid. Operate transmission and check fluid level. Every 24,000 miles the transmission sump strainer of the Turbo
Hydra-Matic transmission should be replaced. Refill Capacity: Powerglide – 2 quarts, Turbo Hydra-Matic – 7-1/2 quarts.
Raise car on lift, clean dirt and grease from area around the filler plug. Plug is located on side of transmission case. Remove plug and place finger tip inside hole. The oil should be just about level with the bottom edge of the hole. Add oil as needed, using a plastic syringe.
Change cam lubricator end for end at 12,000 mile intervals. Replace at 24,000 mile intervals.
With the car standing level, clean dirt and grease from area around filler plug. Remove plug and place finger tip inside hole. The oil should be just about level with the bottom edge of the hole. Add oil, with a plastic syringe, as needed.
1974 Corvette Dealers Sales Brochure
Download this 1974 Corvette Dealers Sales Brochure for a quick look at the features of the car.