Courtesy of Unknownroad.
WORK IN PROGRESS!
Additions and corrections are welcome.
(warning, this may be a bit dizzying)
Brief introduction:
In the U.S., the CX/GL series was sold for five years.
In 1978 there was just one model, denoted as a CX500, sometimes referred to as a CX500A.
In 1980, there was a minor facelift, and production was split into two models- the standard was now called the “Deluxe”, and a cruiser-influenced "Custom" was added. They differ primarily in bodywork.
In 1981, Honda added two more models, the GL500 and GL500i Silverwing. While they used the same basic engine as the CX500A/C/D, and appear similar at first glance, they were actually entirely different bikes based on a frame that shared few parts with the CX. They had upgraded brakes, a different intake design, and a new ignition system. The i (Interstate) model featured a standard fairing and luggage for touring.
In 1982 the GL500 and GL500i were basically unchanged. The CX500 got the new ignition system. Another model was added, the CX500 Turbo, different from both the CX/C and the GL!
In 1983, Honda raised the stakes by increasing the displacement of the engine to 650cc. We now had the CX650C, GL650/i, and CX650T for exactly one year before Honda North America pulled the series from the U.S. market.
AIR CLEANER
The same air cleaner element was used for all of the 500cc bikes except for the Turbo. Both Turbos shared the same element, then the CX650C and GL650s each used unique elements. The common one is Honda part # 17220-415-003, which generally retails around $30; however, there is a replacement filter made by Emgo (part # 178679) available for about $10. There is also a K&N filter available.
The air cleaner housing is interchangeable between 78-79 bikes. It does not interchange with GL or Turbo models.
Although Honda lists the same part number as applying to 80-82 CX C and D models, I could swear that the housing on my '80C had a recess on one side for tool kit?
BODYWORK
The tail sections and fuel tanks are interchangeable between 78-79 and 80-81 Deluxe models, but not the Customs.
The Custom models have a smaller cruiser-style fuel tank, which is secured by bolts in the front, while the tank for the A model and Deluxe sit on rubber bushings on steel posts welded to either side of the frame.
I’ve been informed that you can adapt a Deluxe tank to a Custom by inserting short bolts or studs into the frame holes and putting the rubber bushings over them. Presumably you can fit a Custom tank to a Deluxe by cutting off the posts and drilling the frame.
BRAKES, FRONT:
78-81 CX500, CX500C, and CX500Ds all use the same brakes, a single, one-piston caliper on the left side, same bracket, same brake disc. The caliper is used on the 79 GL1000 and CBX as well (couldn't be very confidence-inspiring on the big CBX!). The bracket is unique to the CX series. The disc is also used by the 79-80 CB650A, 80 CB650C
The 81-82 GL500 bikes upgraded to dual-piston calipers on both sides. The calipers were shared by numerous Honda bikes of the era, including the 82 CX500T, 83 GL650, 81-82 CB900F, 82 CB650A, 82 CB750A, CM450A, 83 CB1100F, 85CB650SC, and others. Look up part #s 45101-MA3-006 (L) and 45201-MA3-006 R for a list.
The GL500 brake discs were interchangeable side to side, and were shared with the 82 CX500C. However, the brackets were unique to the 81-82 GL500s.
The 82 CX500 got a single dual-piston caliper as above, sharing the brake disc with the GLs, but had a completely unique caliper mounting bracket.
The 82 CX500T used the same calipers as the GLs, but had unique brake discs, which have different part numbers on each side. The caliper brackets were used again for the 83 CX650T.
The 83 CX650C used a new dual-piston caliper on the left side, shared with the CX650T, 84-86 CB700SC, 83 CX650C, 83GL1100, 83-86 VF1100C. The caliper bracket and brake disc interchanges with the 83-86 VT500C, 84-85 VF500C, 82-83 FT500.
The 83 CX650T used the same left caliper as the 650C, and the right caliper was the same design, shared with 84-86 CB700SC, 83GL1100, 83-86 VF1100C. It used the same brake discs as the 83 GL1100, different side to side. It used the same caliper brackets as the CX500T.
The 83 GL650 used the same calipers as the 81-82 GL500s. The caliper brackets were shared with 81-82 CB900F, 86 CB450SC, 85-86 VT1100A and AC, 81-82 CB750F, 82 GL1100. The discs were shared with 83 CM450A, 83 CB1000C, 83-86 CB450SC, 84-85 VT700C.
The CX650/CX650T calipers are externally identical to the GL500/CX500T calipers, can be mounted on the same brackets, and can use the same brake pads. However, the later calipers have larger-diameter pistons. So, you can put calipers from a CX650 (or V65, or CB700SC) on GL500, and vice-versa, but they must be replaced in pairs.
EXHAUST
You can not take the headers and H-box assembly off a GL500 and put it on a CX500.
You can fit GL500 mufflers onto the end of the H-box from a CX model, however, you will need to fabricate new hanger brackets, and the rubber stopper for the sidestand will not be in the correct place.
FINAL DRIVE
The final drive units are interchangeable from 1978-1982 for CX, CX-C, CX-D models. The GL500 models can use a CX final drive, however, the reverse is not true (there is a hole in the CX version to mount the right side shock absorber)
FRONT FORKS
The 78-80 CXs have 33mm forks. The 81-82 GLs have 35mm forks, except for the Turbo, which has 37mm. The CX650 has 39mm forks. I have not found a size on the GL650. My source says that 81-82 CX models have 35mm forks, but the ’81D I picked up had 33mm.
The steering head bearings are 26 x 48.5 x 15.2 upper (18 balls), and 30 x 50 x 14.4 lower (19 balls) for all CX and GL models except for the Turbos. These use upper 26 x 47 x 15 and lower 30 x 55 x 17.
A dual-disc GL500i front end will mount easily on an earlier CX frame, however, you may encounter issues mounting the gauges and headlight. The top clamp is also not interchangeable, however, you can unscrew the fuse block from the CX top clamp and fit it into the GL top clamp without modifications (the electrical systems are not interchangeable).
Another note on the GL forks- the top of the upper clamp has a ridge around the inside of it, which is meant to fit into the groove about 1” down from the top of the fork tubes. If the fork is clamped with the caps almost even with the upper clamp, it will compress the fork tubes over the caps and make them VERY difficult to remove.
The 78-80 forks (33mm) use 140ccs of oil per leg. The GL500 front end (35mm) uses 210cc of fork oil per leg. Honda recommends Automatic Transmission Fluid (ATF) for fork oil, but the common practice is to use 15- or 20-weight Fork Oil (available from any motorcycle shop) instead, to stiffen up the front end.
IGNITION
All 78-80 CX models, and the 81 C and D models, use a CDI (Capacitive Discharge Ignition) system. This is run by a black or gold-colored “brain box” under the seat, which is a point of failure as these bikes age. There is no modern replacement currently available. The black and gold boxes can be freely interchanged among any of these models, as can the coils.
The 82 CX500, 81-82 GL500 use a transistorized ignition. These are not directly compatible with the older bikes without making changes within the engine. Therefore the coils, ignition circuits, etc., are only interchangeable among these later bikes.
CDI system coils have the plug wire permanently connected to the coil. On transistorized bikes, the plug wires are attached to the coils by a threaded cap.
The plug caps can be removed from the plug wires, and these can be swapped between CX and GL models.
OIL FILTER
ALL CX/GL models use the same oil filter! How about that? The Honda part # is 154A1-413-005. It was also used on a handful of other bikes, most recently the 1990 VTR250. There is also a pattern filter available from Fram, CH6007, which I have found on the shelf at discount auto parts stores. Prefer Purolator? That’s an ML16807. Wix 24938.
REAR SUSPENSION
1978-79 and 1980D-81D models use the same rear shock absorbers. The 81C-82C models have a different part number for the assembly, but the same numbers for the spring and damper units, so they are most likely functionally identical. They are interchangeable side-to-side. Replacements are available from JC Whitney, and Progressive. Harley Sportster and Honda VT1100 Shadow shocks have also been used successfully with little or no modification. Sportster shocks are available in a variety of lengths, so decide what ride height you want before shopping.
The GL500 suspension is completely different, utilizing a monoshock design that was the same for 81-82.
TIRES
The CX500A/C/D and GL500 all use the same front tire, size 100/90-19 (interesting fact- you can get big paddle-type tires in this size in case you want to race in mud or sand). The 78-79 models use a 110-90/18 rear, the GL500 and Custom models use a 130-90/16 rear. Be aware that 130-90/16 FRONT tires are also out there for some Harley models, and you don’t want to get those.
ACCESSORIES
A comprehensive and illustrated guide to engine guards:
http://choppercharles.com/cs/forums/16780/ShowPost.aspx
Because the CX and GL models have different frames, luggage racks, sissy bars, luggage, etc., are generally not interchangeable.
...more later...