omc_logo
GT "Things to Know"

Opel GT "Things to Know" (Top Ten List)

This is a list of 10 things that Opel GT owners (or, persons buying an Opel GT) need to know. 

All vehicles have their idiosyncrasies -- the Opel GT is no exception -- but with specific attention and repairs, including use of OMC tech tips, more time can be spent driving and enjoying your vehicle.

1) Identify What Year It Is

Knowing the model year of an Opel GT, with its VIN number (located on the firewall plate — as seen on right — GT model numbers start with either "94", "77" "0Y0"or "93") or by certain parts types, will help you to know what major year-to-year parts or service procedure changes apply to your vehicle.

To learn more, click here: "What Year Is It"

opelvehicletag02

2) Inspect Body and Drivetrain Condition

The Opel GT is now a 30+ year old all-steel unibody vehicle, so when inspecting a GT for purchase you need to check for rust. Try to purchase cars you can see in advance (when not on Ebay), and pay closer attention to vehicles "doctored" for sale by dealers.

The areas of common treatable rust are below the battery mount area in the front belly pan and behind the rear wheels, Difficult rust repairs are located in the floor pan near the rocker panels, below the windshield, and on the doors above the mid-line of the exterior panels. Be wary of GT's from the Northern US, as suspension bolts also rust solid and the upper shock tower rusts through, in critical stress areas.

Also avoid body damage -- Use a magnet to locate "bondo" body-filler areas. When damage is in in the rotation area of the GT headlights, it can be very difficult to repair. Door and side panel repair is easier, with  used sheet metal replacements. Generally, we suggest buying a higher-priced undamaged GT over lower-priced GTs requiring repairs to rust or damaged areas.

Verify the engine will turn over, by removing the spark plugs,squirting a teaspoon of oil into each cylinder, then use a 19mm wrench to rotate the front crankshaft bolt in a clockwise direction. In some cases it takes a few days for engine to move freely.

Also verify vehicle can be moved, by pushing it to loosen grip of the brake and transmission/clutch and rear axle parts. Inspect critical rubber suspension and torque tube parts. If battery is available, check wiring and operation of light circuits. Tow vehicle home on a 4-wheel dolly or flatbed for added safety. To learn more about towing, see the Oct. & Dec. 2005 Blitz.

rust_areas

Typical rust areas to inspect on Opel GT's:

CIRCLE shows extensive rust area in GT body.
SQUARES show treatable front & rear areas.

gtdrawing

3) Decide on Mechanics or Do-It-Yourself

Many mechanical repairs on the Opel GT can be done by the owner, presuming a reasonable skill level, correct parts, some metric or special tools, instructions, and some time for the job. The advantages of this approach include saving the costs of mechanic's labor, and learning about your GT as you go along. GT owners have found doing this can be personally empowering!

Others have hired professionals to work on their car. The advantages are that they can bring certain expertise to the job (particularly recommended for machine work on engines and transmissions, and for skilled paint and body work).

wrench

To avoid getting burned on GT service by mechanics, always:

-Research the reputation of the shop (ask prior customers)
-Meet and question the mechanic doing the actual service work (not just a salesman or shop owner) and judge by his attitude, credentials, work area and tools (ie ask to see his torque wrench),
-Insist the mechanic read written "tech tip" procedures prior to starting a job (particularly when unfamiliar with Opels)
-Get written time and cost estimates in advance of starting work
-Expect more repair work in the middle of a job (ie rusted bolts)
-Rely on machine experts to do  rebuilds (engine, trans, axle).
-Report unresolved complaints to government agencies or BBB.

Also learn the difference between the value of a "rebuilt" GT (with parts replaced as needed) and a "restored" GT (all parts reconditioned or replaced with new parts), before authorizing a repair job of several thousand dollars (that in some cases may exceed your wishes or the resale value of the vehicle).

bad_mechanic

4)  Acquire Service Manuals

No single Opel Service Manual contains all the information you need to repair your GT, and not even the factory manual is 100% correct (which is why OMC "tech tips" were written).

The best combination (in general) is the 1971-1973 factory Opel shop manual combined with the aftermarket "GT Owners Workshop Manual" and a reprint of the Electrical Schematic, but this can vary with the actual model year of parts in your GT.

To learn more, click here: "GT Service Manuals"

gt_manuals

5) Inspect & Repair Critical Components

Your first priority should be safety, which begins with awareness. The Opel GT headlight wiring (at the moving mechanisms) must be replaced if it is the original 30+ year-old set. The factory Rubber insulation breaks off, which causes short circuits (damaging pricey headlight relays) and in some cases catches fire.

The area to inspect, under the headlight lids, is shown at right.

GT Headlight Rewiring instructions are here: "GT Headlight Rewiring"

headlight

The Opel GT ignition switch is prone to internal carbon buildup and sudden failure, which immobilizes the car. This scenario can be put off, by carefully disassembling the steering column and cleaning the interior switch with WD-40, and/or installation of a protective Radio Shack #275-226 4-prong relay (shown at right) in the starter circuit.

Diagnosis & Installation instructions for this relay into the GT starter circuit are found here  "GT Ignition Switch"

Also inspect the vent hoses attached to the gas tank (behind the spare tire area) which are prone to disintegration, causing release of dangerous gas vapor in the vehicle interior. Also lift the GT, so other component systems like exhaust & suspension, can be fully checked before operation. If the rubber brake hoses appear stiff and wheel cylinders leak, it's a good idea to just replace them.

auto_relay

6) Restarting Procedures

Generally it's a good idea to just go ahead and replace all the fluids and filters in a newly-acquired GT: This includes the engine oil, transmission oil, rear axle oil, and brake fluid. Flush the cooling system to remove internal scale, and particular attention should be given to cleaning out the gas tank, fuel hoses and carburetor. Replace the radiator hoses, fan belt, & battery. Check water & fuel pumps for leaks. Once engine turns easily, check starter operation.

Once engine is turning, perform a compression test to verify a minimum measurement of 125 psi in each cylinder. (This may also require a valve adjustment, to maximize compression output). Opel 1.9 Engine Compression Test instructions are here: "Opel 1.9 Engine Compression Test"

comp_tester02

7) Identify Parts Differences and Availability:

Try to shop in advance of your needs, as high demand sometimes causes delays in availability for certain GT parts. Make a list of parts you want or need to purchase, then check the parts types match those actually on your car.

Examples of parts to inspect and write down for reference:

Cylinder head: Does it have solid or hydraulic type lifters? Is it a early 10 or late 12 bolt style? Does it have 3 or 4 camshaft bearings?

Rear Axle: Does it have an early or late model shafts and wheel bearings?
Parking Brake Cable and Rear Shoes: Are early or late model parts installed? (Shown at right)

Condensor: Does it have a square or round-hole type insulator?

Additional Information available at: "What Year Is It"

rear_brake02

Example GT Rear Brake Shoe Styles:
Early Style (ball & folded lever) at Top. Late Style (hook and stirrup) at Bottom.

rear_brake2

8) Daily Operation Tips:

The original Solex 32DIDTA carburetor can be nearly impossible to tune properly. Most Opel GT's have a Weber 32/36 DGEV carb installed, for more reliable performance and better mileage. Install with a thick-style carb base gasket, sealed on all both surfaces with Permatex High-Tack to prevent vacuum leaks. (Weber carb adjustment is in the 12/1995 & July 2000 OMC Blitz).

Keeping a GT in tune means maintaining correct .018" point gap (50 degrees dwell) at zero TDC of the distributor. Check distributor operation when a tune doesn't last, or consider an upgrade to an electronic ignition to ensure accurate ignition timing. Any vacuum leaks at, or to, gaskets or hoses connected to the intake manifold also affects timing, so test and seal all junctions for leaks.

The GT Tune Up Procedure & Vacuum System are discussed here: GT Tune Up #1, GT Tune Up #2.

Transmission fluid leaks quickly cause transmission failure on GT's. Always wipe then refill the transmission, then park over a cardboard or paper surface to check for drip sources. Replace seals & gaskets immediately when leaks occur, to avoid costly repair & replacement. (Clutch and Transmission Tech Tips are in the March 1995 Blitz).

Carry a selection of critical Opel parts in the car: Fan Belt, Water Pump, Fuel Pump, Ignition Points & Condensor, Lower Radiator Hose, Hose Clamps, and Gaskets. (Good place is in rim of a spare). Tools to carry include metric 8, 10, 11, 13, 15, 17 & 19mm wrenches, with "special" 8, 10 & 12mm serrated bits, feeler gauges, 13mm stubby wrench and 11, 13 & 15mm obstruction wrenches. Supplies to carry: Tire & gasket sealers, starter spray and flashlight. Another safety tip is installing a third brake light for greater visibility at the rear.

weber
tach_dwell
bad_mechanic2

9) Seasonal Operation Tips:

Summer GT Operation: Clean the radiator, install a 160-degree thermostat, check the water pump & coolant hoses, & insulate fuel lines to prevent vapor lock. Additional Summer Tips are in the May 1995 OMC Blitz newsletter.

Winter GT Operation: Clean the heater valve, install a 180-degree thermostat, upgrade the alternator, lube headlight cable and locks with WD-40, inspect rubber weather-stripping, floor plugs and shift boot, and consider use of Rain-X on windows for visibility. Additional Winter Tips are in the Jan 1995 OMC Blitz newsletter.

temp_gauge

10) Consider Upgrades: Join OMC!

Once your GT is reliable running, Join the OMC and read our newsletters for additional ideas for more performance and restoration of your GT.

GT upgrade projects are best done component group-by-component group, which is how the OMC tech tip index is laid out: Body, brakes, clutch, engine, interior, suspension, etc. Start with projects for safety, then performance, and finish with cosmetics. Always do your technical research and purchase Opel parts in advance.

Build your own ready-reference OMC newsletter collection. When you have OMC's peer-reviewed tech tips in hand, the job is much easier going -- because it's already been done, by the Opel experts!
"Tech Tip Index"

"Little Shop of Horrors" Opel Mechanic Cartoon Credit: Tina S./NAOGTC Issue #55


Copyright 2008: Opel Motorsport Club