NOTE: This instructable describes the disassembly procedure for the older type C backs. However, with a few differences (such as positioning of screws etc) the same procedure also works for the newer A12 and A16 backs.
Some of my Hasselblad film backs don't like cold temperatures. They cause all sorts of problems, overlapping frames, locking up, etc. This is common due to old grease and lubricants gumming up inside, and fixed by cleaning and lubricating the internal film back mechanism. A standard service job, but quite expensive when done by a professional -- so this time I decided to try it myself.
I armed myself with my (expendable) old C16 film back, a service manual (found on Scribd, unfortunately for A12 & A16 backs only, but it still provided me with enough leads to do this on my older C16 back), a few tools... and a fair dose of patience.
Pointy metal tweezers
Q-tips, degreaser, Isopropyl alcohol
For the orthodox: Isoflex Topas L 32 (grease) and Isoflex PDP 48 (oil) -- as recommended by Hasselblad.
For the home tinkerer: use what you have, in my case lithium grease and sewing machine oil. It works.
Time needed: 1-4 h -- but add countless hours if you drop a screw or a spring on the floor...
DISCLAIMER: This worked for me, and it may or may not work for you. I am a tinkerer (if that), not a mechanic -- nor am I a Hasselblad expert. This is not the official Hasselblad procedure for this job, I worked this out for myself. If you decide to try it, great, but I will not be held liable. :)
Start by peeling off the circular leather piece on the back's film advance wheel.
Unscrew the fastening screw that was hidden behind the leather. I used my pointy tweezers as a small spanner for this.
Remove the advance wheel -- you may need to pry it off, it can be a tight fit.
Peel off the leatherette on the sides to gain access to the fastening screws.
NOTE: On the newer A12 and A16 film backs, these screws are located under the leatherette on the side panels instead!
Although not strictly neccessary I decided to remove the leatherette altogether, so as to not have it flapping about during the rest of the procedure.
Step 2: Remove Light Seal, Clips and Spring Rods
Before removing the back cover:
Remove the 9 screws surrounding the film opening. Note that one screw is longer than the others, it is marked blue in the image. Make note of its position.
With the screws removed, carefully lift off the "frame". Use the darkslide as an aid to loosening it if needed.
Under the "frame" you will see the light seal. Remove it. If yours looks worn and old, have a new one ready for the reassembly. Find new (3rd party) seals on eBay, or do as I do and make your own from old exposed film and thin self-adhesive foam, folded and cut to size using an old seal as a template.
Lift out the two black spring rods, and the metallic "clips" (note the position of these).
Step 3: Remove Back Cover
Unscrew two screws (note: these are longer than the other three) on one side and three on the other side. Technically you don't need to do this in order to remove the gear cover. However, in order to actually get the gears out for cleaning it has to be done.
NOTE: Again, on A12 and A16 backs these screws are under the leatherette on the protective side panels.
Remove the middle screw from the inside (marked red).
Lift off the side panel.
Then remove the inner plate from the inside. (This is actually why you removed the side screws on the cover: the cover may need some prying out in order to get this plate out.)
Unscrew the three screws holding the covering plate. The plate is a press fit, and may require a bit of persuasion to come off. Push down (using your screwdriver or similar) on the gear rods at point B, C and D, making sure they come loose. Especially at point A the fit is tight -- you will need to push down hard on the protruding axle as you pull on the plate.
With the cover plate off, the first gear to come off is the big one (marked E). Everything is interlocked at this point, so you'll need to push the rod out in order to remove the gear (see next step).
Working from the inside, push the rod for the big gear (marked E in previous image) out using a pointy object.
With some careful wiggling, the gear should come out.
Try not to pop out the gear in the lower right (E), or you're in for a surprise: the cog is spring loaded underneath. Use a small screwdriver or similar to hold the spring in the gear as you slowly remove the gear. If you don't take great care when removing that gear (F in previous image), the spring will pop out with (SPROINGGG!) and tangle itself. It's no disaster if it does pop out, but it means you have to spend extra time and patience to untangle it and refit it into the gear. It's not difficult: place the spring "hook" into the slot (as seen above), and gently wind the sping back while turning the gear.
Note for reassembly later: (ADD PHOTO)
slide the spring loaded gear on to its washer (black disc thingy in the next photo). Use a gentle rocking motion when sliding it in place, all the way down. The washer has a small stop that the spring will catch once in place, allowing the spring to be tensioned. Once in place, tension the spring by rotating the gear (don't remember the direction, but it's obvious as the spring only tensions one way) and holding it in place while replacing the big gear (the one removed in previous image). There's probably too much tension and too little tension here, and I have no idea what Hasselblad recommends. I tensioned it something like 1.5 to 2 full turns, it worked for me. Too much tension and the nylon stopper will wear out. Too little tension and the big gear (that interconnects to the camera winding) will not spring back into its correct position.
The big gear your removed in previous step is actually two gears sandwiched around two spring loaded stoppers (and a removable rod).
If you separate the gears (and you should if you intend to clean these parts), there's a trick to putting them back together later for reassembly: insert the rod into the lower (bigger) gear, and slide the top gear on to the rod. Then, using a thin screwdriver or similar through one of the holes of the top gear, slide the stoppers outward until the top gear clicks down into place.
Simple, but it took me a good while to figure out... Then again, on some backs these parts just click into place without effort. Your mileage may vary!
Remove the frame counter plate, two screws. Make a note or a photo of the position of the counter plate, for reassebly later.
The white L-shaped part is the infamous nylon stopper, that tends to get worn out in backs that have seen extensive use. It may need replacing, but spare parts are hard to source. It should be possible to replicate one by hand, if suitable material is found. The material looks and feels like HDPE plastic.
Then, basically remove everything else. :)
Uscrew and unhinge the linkage arms, springs, wiggle out gear cogs etc, it's a bit fiddly but pretty intuitive. See attached images.
Yes, there are a couple more parts that could be removed, but I wouldn't bother. For cleaning purposes, this is where I would stop.
Clean and lubricate:
Immerse all gears, springs, linkage arms etc in a degreaser, and let them sit for a good while. Rinse in isopropyl alcohol. Short of Isoflex Topas L 32 (grease) and Isoflex PDP 48 (oil) that Hasselblad recommend, I opted for what was available to me: lithium grease and plain sewing machine oil. I put a minute amount of grease on gear teeth, and sparingly applied oil to other moving parts and joints.
Reassembly is, I'm afraid, simply a reversal of disassembly. ;)