Opel GT: 1969-1973 Opel Factory Service Manuals
These are considered the "bibles" of Opel, but you can't rely exclusively on them as they have their errors too. They can be pricey; usually $35-$49 in good condition from Ebay or the Opel retailers. Supposedly the 1970 is hardest to get (more GT's were produced in 1970 than any other year) but I've found the 1973 manual (probably the best manual) hardest to find myself. All of them emphasize photo reproductions which help you in person, but don't Xerox or fax clearly. All have an index in back and there are "component groups" rather than numbered pages in sequence.
Keep in mind that these refer to 1969-1973 situations in terms of presuming availability of every part in new condition, and they are also annoyingly repetitive in referring to non-existing "Kent-Moore Co." special tools in many situations. Good luck finding these tools; you'll have to improvise for a front suspension "spring compressor" or a steering wheel puller tool, for example. (This is why clubs like OMC became necessary. According to these books, you also have to build your own engine removal tool from 2" x 4"s. I've yet to see one in person, ever).
All are inadequate on tuning Solex carburetors (none say the CO setting, or what to do when it dumps gas -- Buick issued a special Solex training manual in October 1970 that still won't fix them).
All instruct to over torque the clutch pressure plate -to- flywheel bolts (should be 15 ft. lbs; the 33 ft. lb. factory setting breaks the bolts). All are too brief on tune-ups (about 5 pages each), clutch installation, distributor installation and engine timing, and sometimes it seems, whatever repairs you have to do. They all spend too much space on rebuilds no one should ever try themselves, like rear axles and automatic transmissions. Small wonder so many Buick mechanics gave up on repairs. Nonetheless, it is good to have at least one copy around when you're stuck on a repair job late at night; at least with the pictures of another Opel (in new condition) to look at, you won't feel as if anything is necessarily impossible.
In these manuals, the main pattern is repeating instructions from prior years unless major component changes have taken place. Sometimes, the manuals miss those changes -- I've tried to indicate these by year. (See also, the "What Year Is It" OMC article, about identifying year-to-year part changes on the Opel GT).
1969: The "Kadett & GT Service Manual" (red cover) covers those 2 models, including a lot of space on the relatively rare 1.1 Liter engine and drive train. Surprisingly, it does not include the 1.1 Liter automatic transmission (which was an option that year on the Kadett -- flex plate was smaller than a Frisbee!). But for GT's, which about 90% were 1.9 liter engines, this is wasted space.
Advantages are illustration of the A.I.R. air-pump "smog" system (still a requirement in some states), the passenger-compartment located early 1969 heater valve (also shown in '70 book), and some of the other curious 1969-only parts installed in GT's.
Disadvantages are the mistaken illustration of of the non-US parts: starter with engine stud mount, 1-barrel carburetor and intake manifold (from the European 1.7 liter engine), rear axle with anti-sway bar mounts. Also a problem is identifying a now non-existing "notch" in lower ball joints, suggestion of removing the large nut off the yoke flange in order to replace the torque tube "donut" bushing, and the method of separating the inner and outer tie rods by first removing them from the car. Worst aspects are the necessity of constantly rechecking whether you are looking at 1.1 or 1.9 liter specifications in small print and components and certainly the wiring diagrams which are in black and white only and are given one page per car. Since some of the wiring (steering column, headlights) is exclusive to the '69 model year, I say: Good Luck!
1970: The "Kadett & GT Service Manual" (black cover) title is still used. Basically repeats the 1969 manual, as most of the 1970 component changes occured in the middle of this model year. Advantage: Illustration of the evaporative cannister "smog" vapor control system, in limited detail (and is doesn't picture the California-version's extra gas tank vent hose fitting).
Disadvantages are many, and some are critical: doesn't picture the mid-year changes in the manual transmission (speedometer gear, linkage bracket, larger 3rd & 4th gear synchros), doesn't picture the later model rear axle (no internal snap rings to hold the axle shafts, different wheel bearing and retainer structure) and the relocation of the heater system water-valve to the engine compartment. It also neglects the vehicle identification sticker on the left door. Other parts changes missed are the largely cosmetic, so the photos will be wrong: such as rubber steering wheel, steering column high-beam control on turn-signal lever, driver's door window crank, parking brake tray, ignition lock cylinder, and other items known primarily by GT enthusiasts.
It does add at least one interesting Europe-only item; page 120-28 shows the GT A-L headlight switch on the instrument panel (a blank switch on US GT's). The 1970 still has the one-page only black and white wiring guide. Ironic that the highest demand manual could cause its owner the most grief. Nice section on removing interior stains though.
1971: Now the "1971 Opel Service Manual" (green cover), it includes the newly introduced "1900" series line offered that year (Manta, Ascona, Wagon, etc). A thick book, it also carries over the Kadett and 1.1 liter information as well. The sections are reconfigured from the 1969 and 1970 sequences, and component groups are moved around. Many improvements are here, mostly in the expansion on the earlier coverage of various operating systems. Biggest improvement: Colored fold-out wiring guide and individual circuit illustrations of electrical system. Almost worth the cost of the book alone, but not necessarily useful for 1969 & 1970 GT's as some wire colors were changed.
Disadvantages: It does show the internal changes in the rear axle and manual transmission, but unfortunately, the only rear axle design shown is in a Manta rear axle housing! This quirk in illustration makes it hard to explain to the unknowledgeable mechanic. (The quick ID is if the center of the bolts on the rear brake backing plates measure exactly 2 3/4" from each other in a square pattern; earlier axles' bolts are slightly closer than 2 3/4" at the center and are not square to each other).
Instruction in adjusting the hydraulic valves tells you to adjust the rocker nuts one full turn in from zero-clearance; this is too tight (later Buick Service Bulletin corrected it to 3/4 turn in from zero clearance).
It ignores the newly-available dealer-installed GM air-conditioning system (see 1973 manual), and the change in GT body insignia to "GT" in the rear. Interestingly it still shows the '69 dash panel, and the prototype's stitched vinyl covered dash with a vinyl headlight lever knob (pg. 120-53). Overall, an acceptable book.
1972: The "1972 Opel Service Manual" (orange cover) this includes the last of the original Kadett models, and only the 1.9 liter engines. Except for the cover color, it's basically the same as the 1971 book with content changes so minor as to mostly escape my attention.
In late 1972, the end of the parking brake cable where it meets the rear brake shoe was changed from a "ball" to a hollow-rectangular "hook" style and this isn't pictured; but then again, it isn't in the 1973 book either. So, see the 1971 manual description for any parts inaccuracies. Some of the layout within the various component groups is improved, making it at least one manual I bought for my first GT (also a '72) and it did me well. Only 1972 GT owners with GM air conditioning should consider the '73 alternative, and there is a thin (and rare) a/c supplement that was issued separately that year.
1973: The "1973 Opel Service Manual" (purple cover) for the last year of the GT's was the only manual without the Kadettes. Again a reconfigured layout book, this time a major change in structure and location of the "component groups." Wiring diagrams are now in front, for example. More improvements within the component groups also, generally more writing in detail on various procedures.
Major change in cylinder head design included addition of two 6mm allen-head bolts in front, here it it interestingly shown as an option rather than the standard feature it is. This also includes the 1973 EGR smog-control system (required in some states), and the only section on the GM air-condition system on the GT included in a service manual. The a/c system is comprehensive and is by itself 104 pages long! An essential book for 1973 (and most other) GT's.
"Opel GT Owner's Workshop Manual" (green):
Described by an Opel retailer as "a good supplement to the factory service manual." It is precisely that, primarily because it is from a source very different from these manuals. It is a larger-scale reprint of the earlier Autobook manual on the GT, which was written in England rather than Germany or the US. This makes it a separate view on the same car, which is necessary to cover the oversights of the factory manuals. This view is in outline form, making it the best choice for xeroxing, faxing, or illustrating technical articles, as outline reprint more clearly than old photos. Advantages also include a good section on engine and distributor timing, good tune-up specifications, a "bonus" reprint of an original Road & Track report circa 1969, and its current availability in new condition. Disadvantages include curious British tern that pop up, such as "gudgeon pins" (wrist pins), "generator" (alternator), "gearbox" (transmission) and the like. A handy glossary of terms is in the back. It also shows the non-US one barrel carburetor, intake manifold, and the starter stud mount. Sections on trouble diagnosis are very condensed and don't indicate how to test for possibly faulty components.
Possible problems for late 1970 through 1973 GT owners: It only lists the early model solid-valve lifter adjustments (the US-only 1971-1973 hydraulic lifters aren't mentioned), and the only rear axle described is the early type with the snap-rings on the axle shafts. ALL USERS of this manual need to be aware of these discrepancies! Also, using a "spring compressor" for work on the front suspension is in the instructions, and the wiring guide is one-page black and white, with non-US options like foglamps mixed in. By itself it's good (better than most others), a book to get new while you still can.
Chilton "Opel 1971-75":
Like its title, this book delivers at best a partial view on the GT, in skimpy proportions. Cheapest, most common out-of-print Opel book, here you get about what you pay for. Combines all Opel models, so there's no room for anything but scant commands. Photos are a rip-off of factory manuals; far fewer and it seems never from the angle you need to see. Has the drawbacks of the early factory manuals regarding non-US parts shown. Advantage: The generic sections on troubleshooting a non-starting car and the fuel economy section give you general tips to consider. Not Opel-specific though. O.K. when the factory manual is adequate: Clutch job, brakes. The main advantage over all other manuals, is explanation of disassembly of the front suspension without use of spring compressor, and it emphasizes safety! (Diamond in a coal mine). Wiring diagram for GT is a joke -- with this much spaghetti, there should be a meatball. Good only if you get this cheap.
Clymer "Opel GT, Kadett, 1900, Manta 1966 - 1975":
Another inexpensive, highly condensed, commonly available out-of-print Opel guide. All the disadvantages of the Chilton; in a pinch it says "consult a professional" to do the job. A few differences though, advantages include: A tune-up specifications sheet right in front, some simplified and labeled component photographs from Buick (carburetor, brakes), and a "bonus" 18 page high-performance section in the later editions. Some of the performance information is interesting, such as their tips on specific manufacturer's anti-sway bard (addco -- yeech!), heavy duty springs, shocks (Koni, Bilstein - yea!), high-performance ignition coils (Mallory - OK) and headers (only available on Ebay, often in a version that doesn't curve enough to fit the GT).
The "Stage" number system of rating Opel performance improvements looks to have originated here; According to Clymer a "Stage II" means improvements of an oil cooler, oil sump, lightened flywheel, and a heavy-duty clutch, while a "Stage III" Opel is defined as a Weber Carb, camshaft, big-valve cylinder head, forged pistons, lightweight rods, and a machined crankshaft with heavy-duty bearings. I found the writing here interesting as it contrasts some of the wildly inaccurate sales claims I've read elsewhere. These 18 pages somewhat redeem this book. If it cheap, grab it (at least the 1983 edition that I saw).
If you own an Opel GT, decide what it is you want and either order it from an Opel retailer, automotive literature retailer (like faxon.com) or wait for it to come up on Ebay. Check you local book stores, and always ask for a book when buying an Opel, as the owner will typically have no use for it anymore. Place a want ad on online Opel sites, if other tactics don't work. Like with hard-to-find Opel parts, here, patience combined with persistence is the best money-saving approach.
Also, don't believe everything you read, and rely on your own best judgment, particularly when someone is trying to sell you something (and their general reputation isn't good). Best to consult multiple sources before taking on any individual job. Do always consult the experts: Opel retailers, OMC members, and technical articles in the back issues of the OMC Blitz newsletter. (EZ reference is in the "Tech Tip" index). Best sources of all are the OMC members who have already done the project(s) you want to do. You can see their Opel and talk to them in person, at OMC activities like the big OMC Annual Meeting gatherings scheduled each Summer in California - See you there!