The 1975 Chevy Corvette, along with the automotive industry as a whole, would experience a significant transformation at the onset of the new model year. Because of serious health issues and environmental contamination associated with the use of lead fuel, it was determined that the automotive industry would – and should – phase it out.
Tetraethyllead (also known as TTL, or simply “lead”) was introduced in the 1920’s as an additive to prevent fuel from auto-igniting in high compression, internal combustion engines. While the lead additives allowed engine designers to produce more powerful, higher compression engines, it also produced a dangerous neurotoxin through exhaust emissions, which resulted in many cases of acute, and widespread lead poisoning, especially in children.
Additionally, the lead component was destructive to catalytic converters, which were to become a Federally mandated requirement to aid in the control of damaging exhaust emissions.
For Chevrolet in general, and the Corvette in particular, the 1975 model year marked a turning point in the car’s history. Zora Arkus-Duntov, who had been instrumental in breathing life into the Corvette, retired on January 1, 1975 after 21 years and 7 months with General Motors.
Duntov’s legacy with Corvette started in 1953 when he saw the original Harley Earl Corvette prototype on GM’s Motorama stage in New York. He had come to work for Chevrolet later that same year after writing to Ed Cole with his insights about the Corvette Prototype.
While working on other projects for Chevrolet, Duntov had begun “fiddling on the side” (his words) with the Corvette throughout the 1953 and 1954 model improvements to the car’s overall design along the way.
By 1956, he had been named the division’s director of high-performance vehicle design and development.
While he would continue to be partnered with the Corvette throughout his career, he was not officially named Corvette’s Chief Engineer until 1968. Even so,
Given Zora’s incredible reputation, his history with Corvette, and the legacy, of incredible cars that he was instrumental in developing for more than two decades, there were many who questioned how anyone could fill the hole that was left behind by his retirement.
McLellan had spent most of 1973 and 1974 at the Massachusetts Institute of Technology’s Sloan School of Management at GM‘s direction, and then, with his master’s degree in hand, had returned to Chevrolet as one of Duntov’s staff engineers.
When ZoraArkus-Duntov resigned his post just six months later, it was understood that McLellan would fill the post that he had been so carefully groomed for.
Despite this, McLellan would not have a significant influence on the design of the Corvette until the introduction of the C4 Corvette some eight years later.
The 1975 Corvette look was almost identical physically to the 1974 model. The one notable change to the car’s exterior design was the introduction of a pair of front and rear bumper pads. These pads were integrated into the soft front and rear bumpers with the intent of providing the Corvette with additional protection in parking lots (and similar environments where the car might make contact with a curb, or even another vehicle.)
Beyond the introduction of these parking pads, the structure of both the front and rear bumpers were modified slightly as well. The front bumper now featured an inner honeycomb core which offered added rigidity. The rear bumper received inner shock absorbers to reduce damage in the event of an impact condition.
Lastly, the rear bumper fascia was molded as a single urethane plastic component, unlike the 1974 model which featured two separate urethane assemblies that mated down the centerline of the car.
A significant milestone that was also represented in the 1975 model year had nothing to do with what the Corvette introduced as a new option, but rather what it was about to eliminate as a production option for nearly the next decade.
The 1975 Corvette would be the last of the third-generation Corvettes to be offered as both a coupe and a convertible. Because convertible volumes had continued to diminish year after year, Chevrolet had already considered eliminating the option, but when the government threatened to enact legislation that would have effectively banned fully open cars in the United States after the 1975 model year, it sealed the deal. The decision was made to discontinue production of a Corvette convertible and the last C3 Corvette convertible rolled off the assembly line in late July, 1975.
While the legislature surrounding convertibles never actually materialized, it had given domestic automotive manufacturers the excuse they’d been looking for to discontinue production of slow-selling convertible rag-tops. Naturally, there was a fair amount of discontent by enthusiasts about the decision, especially given that the Corvette had existed as a convertible/rag-top since its inception in 1953.
Despite this, the decision would stand for an entire decade and would mark the last time in Corvette’s history when a convertible was actually less expensive than a coupe.
Engine options for the 1975 Corvette were more limited than any second- or third-generation Corvette that had come before it. While GM did briefly offer an optional big-block V-8 engine, it was dropped very early in the production run, leaving the stock, 165 horsepower, 350 cubic inch engine, and the optional RPO L82 205 horsepower, 350 cubic engines as the only available choices.
Not since the 1955 Corvette model had such a limited number of engine options been made available to consumers. Additionally, it was the first year since 1967 that only a single engine displacement was offered.
Just as there were few changes to its appearance, there were equally few changes to the car’s mechanical and structural makeup. However, 1975 was a significant year, not only for Corvette, but many production automobiles as it was the year that the catalytic converter was formally introduced and adopted by manufacturers across the United States.
The catalytic converter was designed to convert toxic byproducts produced by internal combustion engines into a less toxic substance via catalysed chemical reactions. This method of managing emissions was considered far more efficient than earlier, less conventional emission control methods, and may actually have prevented Corvette’s horsepower ratings from dropping even further than they had.
As a result of the introduction of the catalytic converter, the 1975 Corvette was also the first model not to feature dual exhaust. Instead, the exhaust left both manifolds via a Y-pipe, passed through the catalytic converter, and then split again to a pair of muffler/tailpipe assemblies.
Under the hood was a new, breakerless electronic ignition system known as HEI (High Energy Ignition). Quite different from the transistor ignition systems that had been available previously, the HEI ignition was the first ignition on a Corvette to feature a distributor that did not require a points and condenser setup. In conjunction with the new electronic ignition system, Chevrolet also introduced the first electronic (instead of mechanical) tachometer drive.
While tachometers had previously been driven off of the distributor, the new distributor would receive an electrical signal which was translated into the output seen by drivers on the dashboard. Additionally, the 1975 Corvette was the first model year to feature the “Kilometers Per Hour” subtext beneath the standard “Miles Per Hour” on the speedometer.
Elsewhere on the 1975 Corvette, a headlights-on warning buzzer was added per a federal mandate. An internal bladder was added to the fuel tank to help prevent gas fumes from escaping while also keeping air from entering and/or getting trapped in the tank.
Hood emblems featuring the engine designation “L82” were introduced in 1975, though many Corvettes built that year did not include the emblem.
Lastly, the 1975 Corvette was the final model year to feature the Astro Ventilation system which had been introduced as part of the third-generation Corvette in 1968.
Despite these minimal changes to the car, the 1975 Corvette’s sales numbers continued to rise over the previous model year.
In total, 38,465 Corvettes were sold that year, which was within 300 units of the 1969 model year, which was still – to that point in time – the best production year ever for Corvette.
The coupe accounted for all but 4,629 units sold that year, which once more reinforced Chevrolet’s decision to discontinue the Corvette convertible.
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 15B — Blackwall Steel Belted Radial
GR70 x 15B — White Stripe Steel Belted Radial
GR70 x 15B — 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), 38.8 ft. (outside front)
1975 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)
Coolant capacity without heater (qts.)
19 for Base engine
18 for L82 engine
12 Volt, 78 Plates, 3,250 Watts for 350ci. engines
12 Volt, 90 Plates, 4,000 Watts for Heavy Duty
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 438465, accounting for 38,465 Corvette Coupes/Convertibles built in 1975. Each Vehicle Identification Number (VIN) is unique to an individual car.
1975 Corvette Vehicle Serial Number Plate
For all 1975 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.)
1975 Corvette Body Number Trim & Point Plate
On the driver’s side upper left-hand door hinge pillar.
A01 – Body build date code.
A – Designates the Month (See Chart Below).
A – Oct., 1974., B – Nov., 1974., C – Dec., 1974., D – Jan., 1975., E – Feb, 1975., F – Mar., 1975., G – Apr., 1975., H – May, 1975., I – Jun., 1975., J – July, 1975.,
01 – Designates the Day of the Month.
19V – Interior Trim code. 19V – Black (Vinyl)
10L – Exterior Color Code. 10 – Classic White
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.
1975 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
350ci, 205hp 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
Map Light (on rearview mirror)
California Emission Test
Off Road Suspension and Brake Package
Base Corvette Sport Coupe (1YZ37)
The base price of the 1975 Chevrolet Corvette Coupe without any optional equipment.
A 350 cubic inch, 165 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 1975 Corvette Convertible without any optional equipment.
A 350 cubic inch, 165 horsepower engine, 4-speed wide ratio manual transmission, vinyl interior trim, and a convertible soft 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 Defroster (C50)
An optional rear window forced air defogger.
Air Conditioning (C60)
Factory installed four-season 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.
It was automatically included as part of the Z07 package.
350ci, 205hp 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, 165 horsepower 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 (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.
Off Road Suspension and Brake Package (Z07)
Stiffer suspension/brake package for more rugged driving conditions.
Available with optional engines L82.
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.
1975 was the last year for a Corvette Convertible until 1986.
The 1975 Corvette was the first Corvette to have a catalytic converter.
The bumpers were redesigned for the 1975 Corvette in the continuation of better impact resistance from the 1974 Federal mandates. Inner shock absorbers and two simulated exterior pads were added to the rear bumper. The front bumper added an inner honeycomb core and two simulated pads on the exterior.
1975 introduced High Energy Ignition (HEI) to the Corvette. This replaced the old transistor ignition.
One key feature of HEI is the no-points distributor.
The 1975 Corvette introduced the first electronically driven tachometer, which replaced the old distributor-driven tachometer.
Kilometer-per-hour (kph) first appeared on the 1975 Corvette speedometer as a subset of miles-per-hour.
1975 was the first year for a headlight warning buzzer on the Corvette.
1975 was the first year a Corvette was manufactured with an internal bladder in the fuel tank.
The 1975 Corvette would be the last year for Astro Ventilation.
1975 Corvette Recalls
Make: CHEVROLET Model: CORVETTE Model Year: 1975 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: 1975 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.
1975 Corvette Service Bulletins
1975 Corvette Common Issues
1975 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.
Clutch Adjustment (1975-1982)
Disconnect the clutch return spring at the cross shaft. Push the clutch lever until the pedal is against the rubber stop under the dash. Loosen the two shaft locknuts and push the shaft until the throwout bearing just touches the pressure plate spring. Tighten the top locknut toward the swivel until the distance between it and the swivel is 0.4″. Tighten the bottom locknut against the swivel. The pedal free travel should not be 1-1/2″.
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.
1975 Corvette Dealers Sales Brochure
Download this 1975 Corvette Dealers Sales Brochure for a quick look at the features of the car.