Install instructions

How to install your MamiyaPan Pro kit.

Read this whole page once before you start. The conversion is fully reversible, but rushing through any single step is the difference between a working kit and a stuck mechanism. Plan on an evening at the bench.

Before you begin

What's in the box

What you'll need from your bench

Compatibility

This kit is designed and supported for the Mamiya 645 Pro film back. The 645 Super back uses the same dividing-device assembly and the kit will physically work on it, but the gate mask alignment relies on injection-molded registration features that are slightly different on Super backs. If you're installing on a Super, expect to center the vinyl mask by eye rather than letting the molding do it for you. No support is offered for the Super beyond what's on this page.

Phase 1 - Remove the back from the camera and open it up

  1. Photograph the back assembled, all sides. Before any screws come out. If something goes wrong later, these photos are the reference for what the cover, plates, and dials are supposed to look like.
  2. Detach the film back from the camera body. Standard Mamiya 645 Pro back release.
  3. Remove the right side plate. Service manual screws (4), (5), (6). With those out, push the back's release knob gently in the direction of its arrow to clear the plate.
  4. Remove the top cover. Service manual screws (7) and (8). Push the cover up to peel it off the adhesive holding the ISO/ASA leadwires. Slacken the leadwires carefully so you don't strain them - they're delicate.
  5. Photograph the internal layout before touching anything inside. This is your reference for how the dividing-device assembly sits in the frame counter stack.

Don't touch the F-clutch. The dividing-device assembly is independent of the film-advance clutch. The clutch contains friction plates and tensioned springs that need special tools (Mamiya SLA-05 / SLA-06) to reassemble correctly. If you're poking around in there, stop - you've gone too far.

Phase 2 - Disassemble the spacer stack (the part most likely to scare you)

The frame spacing assembly is three layers stacked on a brass bushing: a small black gear underneath (Part A), the OEM 9-notch disc in the middle (Part B - the part you're replacing), and a white plastic gear on top (Part C, gear 12 in the service manual). A thin wire spring (e) couples Part C to Part B.

The brass bushing has a small retaining flange at one end that locks Part C onto the stack. You cannot pull Part C off the bushing without removing this flange first - and pulling harder is exactly how Part C breaks. It's plastic, it's pressed against a brass shoulder, and it has cracked three separate times during testing on this very project. Don't be the fourth.

The fix is to remove the flange, not fight it. Two methods, in order of recommendation:

Method A - Cutting broach (recommended for first-timers)

Slower but very forgiving. A watchmaker's cutting broach is a tapered steel reamer with cutting flutes. You insert it into the bushing bore from the flange end and twist gently. It enlarges the bore wall by wall until the flange thickness goes to zero and Part C slides off freely. A 6-piece broach set with sizes around 0.6 - 2.0 mm covers the size you need (FindingKing or any watchmaker supplier).

  1. Lift the entire dividing-device stack out of the back. The E-ring on the shaft retains it from above; pop the E-ring off (cup your hand or work over a tray - they ping across the room) and lift the stack out as a unit.
  2. Hold the stack so the brass flange faces up. Insert the smallest broach into the bushing bore, twist it
    a quarter turn, withdraw, advance to the next size up, twist again. Work up in steps.
  3. Stop when Part C lifts off freely. The flange is now thinned to zero. The bushing itself is fine - it just lost the lip that held everything together for handling.
  4. Set Part C and Part A aside in your tray. Spring (e) goes with them. Part B is the OEM disc - save it, it's how you revert later.

Method B - Dremel with sanding bit (faster, higher skill ceiling)

If you've used a Dremel for precision work and you trust your hands, this is faster - a minute of grinding instead of five minutes of broaching. The risk is that you're freehand-grinding millimeters away from a precision bushing that retains the entire mechanism's axial alignment.

  1. Lift the dividing-device stack out of the back as in Method A.
  2. Hold the assembly between your fingers, flange end out. Use a small sanding bit (the cylindrical drum kind, fine grit) at low to medium speed. Touch the bit to the brass flange only - keep it off the plastic of Part C.
  3. Grind in light passes. Stop every few seconds, wipe the brass dust away, check whether Part C has freed up. The flange is small; this should take well under a minute. Once Part C lifts off, you're done.
  4. Wipe the bushing clean of brass dust before reassembly so nothing migrates onto the disc faces.

Either method removes the flange permanently. The flange's only job is handling-time retention - keeping the stack together when it's out of the back. Once installed in the back, the housing post and E-ring are what hold everything axially anyway. You don't lose anything functional by removing the flange. You just need to handle the stack carefully during the swap because it'll fall apart in your hand if you're not over a tray.

Phase 3 - Swap the disc and reassemble

  1. Confirm orientation. The new 18-notch disc orients the same way as the OEM 9-notch disc - small drive hole and arc slot on the same side, notch profile facing the same way. Compare them flat on your bench before stacking.
  2. Restack A → B (new) → C onto the brass bushing. Re-seat spring (e) so it couples Part C to Part B - the spring tail engages the small hole on Part B and pin (d) on Part C.
  3. Lower the stack into the back in the same orientation it came out. Without the flange, the stack is loose - keep it together with a fingertip until it seats on the housing post.
  4. Reinstall the E-ring onto the shaft above the stack. This is now your sole axial retainer; make sure it's fully seated in its groove. Reinstall the frame counter wheel and its return spring on top.
  5. Verify the counter springs back to zero when you would normally open the back. If it doesn't, the return spring isn't hooked correctly - take it off and re-seat it.

Optional belt-and-suspenders move: if the stack feels too loose to handle confidently during install, a single drop of gel cyanoacrylate at the Part C / bushing junction will lock the two together. Parts A and C rotate as a unit anyway, so locking C to the bushing changes nothing functionally. Only Part B needs rotational compliance against A/C, and that compliance lives in the arc slot. Acetone is the undo button if you need to reverse it.

Phase 4 - Test before you reassemble the cover

With the cover still off, run a 30-cycle dry test before putting the back back together. This is the single cheapest way to catch a problem before you've committed film to it.

  1. Wind the advance lever 30 times in a row. No film, no backing paper. Watch the dividing-device assembly through the open cover.
  2. Look for two specific things:
    • Catching: the mechanism hangs up partway through an advance. The lever bottoms in a notch and won't release. This is the failure mode that ends rolls early in the field.
    • Slipping: Parts B and C rotate in unison instead of Part C rotating first to load the spring. Spring (e) never compresses. The advance happens but indexing is unreliable.
  3. If everything cycles cleanly 30 times in a row, you're done with the mechanism. Move to Phase 6 (gate mask).
  4. If a tooth catches, mark that exact tooth with a pen as you feel it stick. Don't worry about which frame number - frame numbering shifts after reassembly. Mark the physical tooth.
  5. If parts B and C move together (slipping), the catch walls of the notches are too smooth for the lever to grip. This is rare on production parts but possible.

Phase 5 - Troubleshooting (only if Phase 4 found something)

Skip this section if your 30-cycle test was clean. If you saw catching or slipping, here's the playbook.

For a catching tooth

Catching is the priority failure to fix. Left uncorrected, it can prematurely end a roll mid-shoot. The fix is targeted: sand only the marked tooth, not the whole disc.

  1. Remove the assembly again (Phase 3 in reverse).
  2. Use the X-Acto blade as a scraper first - hold the blade perpendicular to the tooth and shear off the high spot. Scraping removes proud burrs without rounding the cam profile. This works most of the time and is preferred over sanding.
  3. If scraping isn't enough, use the included sandpaper. Sand the tooth tip parallel to the tooth profile. Make small passes and re-test after each one. Don't grind.
  4. Reassemble and re-run the 30-cycle dry test. Repeat if needed.

Don't over-sand. If you grind too much off, you swap a catching tooth for a slipping tooth - the lever no longer grips reliably and you'll get inconsistent indexing instead of catching. The mechanism has a real Goldilocks zone. Make small passes. Test. Repeat.

For a slipping tooth

Slip mode is recoverable. You can usually live with it - the result is occasional overlapping frames rather than a lost roll. If you want to fix it anyway:

  1. Mark the offending tooth.
  2. Sand the catch wall (the steeper, near-radial side of the notch) perpendicular to the direction of travel. The goal is micro-grooves running across the lever's path, giving it a textured surface to grip on.
  3. Reassemble and re-run the dry test.

If cold catches it but room temperature doesn't

Cold dramatically amplifies any borderline interference (lubricant viscosity changes, tiny clearance shifts). If you suspect a marginal install, briefly chill the back in a fridge for 10-15 minutes and re-run the dry test. If it then catches, treat the catching teeth as Phase 5 problems even though they passed at room temperature. This screening is honestly more revealing than any number of room-temp cycles.

Phase 6 - Install the gate mask

The gate mask reshapes the film gate from the full 56×41.5 mm frame to the 56×20.5 mm half-frame format. It's a two-material hybrid: a self-adhesive vinyl base does the bulk masking, and two rigid ABS strips define the precision frame edges.

  1. Remove the front panel (the lens-side panel of the back). Watch for a small loose peg on the bottom-right of the panel as it comes off - it's easy to lose. (Pro back only; Super backs don't have it.)
  2. Apply the vinyl mask to the film-facing side of the panel, adhesive down. The window edges of the mask should line up with the raised plastic features from the panel's injection molding. Note the two thin vertical plastic strips connecting the masking strips - the narrower one goes on the darkslide side (left).
  3. Smooth out the seams thoroughly on the darkslide side. Any crease here will catch the darkslide on insertion and may eventually tear the vinyl. Spend an extra minute making this side perfectly flat.
  4. Reinstall the front panel onto the back. Adhesive side of the vinyl is now exposed on the lens side. Secure with a few screws (don't tighten everything yet).
  5. Insert the darkslide. It acts as a rigid base for applying the ABS strips.
  6. Apply the ABS masking strips onto the exposed adhesive. The rounded corners go into the corners of the original gate, not the masked window. The vinyl window is intentionally oversized; the strips are the precision layer that defines the actual frame edges.
  7. Smooth everything out. Verify the result looks symmetrical. Both strips should be parallel, the gap between them should be consistent end to end.
  8. Tighten all panel screws and remove the darkslide. Test that the darkslide goes in and out smoothly without catching. If it catches, the vinyl seam on the darkslide side is the culprit - remove the panel and re-smooth that edge.

If a strip seems slightly too wide and bows when installed, lightly sand the long edge until it sits flat. A few passes on fine-grit paper. This is normal manufacturing tolerance, not a defect.

Phase 7 - Install the viewfinder overlay

The overlay sits on top of the focusing screen and shows you the half-frame composition through the viewfinder. It's a clear transparency with two thin black lines at 9.05 mm from each edge, defining a 20.5 mm window that matches the gate mask.

  1. Detach the prism / viewfinder from the camera body, following the standard Mamiya 645 Pro procedure.
  2. Place the overlay on top of the focusing screen, transparency side up. The overlay is non-adhesive - the weight of the prism holds it in place.
  3. Verify the overlay sits flat and is centered. The black lines should be parallel to the long axis of the gate.
  4. Reinstall the prism. Look through the viewfinder. You should see a 2.73:1 panoramic frame defined by the two black lines.

Phase 8 - First roll

  1. Use cheap film for your first roll. A roll of Kentmere or a cheap color stock. If something is going to go wrong, you don't want it to be on a roll of Provia.
  2. Wind slowly. Fast, aggressive winding can cause the lever to skip a notch in marginal installs. Smooth, deliberate strokes give the spring its full dwell time.
  3. Count your frames. A correctly installed kit gives you 30 exposures. If the frame counter rolls past 15 and stops at 30, you're golden. If it stops short, the dividing disc is skipping somewhere in the cycle - go back to Phase 3.
  4. Develop and inspect. Look at the negative strip flat on a light table. Frames should be evenly spaced with consistent gaps. A few frames of overlap is acceptable on a $50 experimental kit and won't ruin the roll - the gate mask keeps the image boundaries clean inside the masked area. Repeated overlap or completely missed frames means a Phase 5 visit.

Reverting to standard 645

The conversion is fully reversible. To go back to standard 15-frame 645:

  1. Remove the gate mask (peel off the vinyl, detach the ABS strips).
  2. Lift out the viewfinder overlay.
  3. Open the back cover, extract the dividing-device assembly, swap the 18-notch disc back to the OEM 9-notch disc.
  4. Reinstall the assembly, E-ring, frame counter wheel, cover.

Save the OEM disc. The kit doesn't include a spare for it.

Help

Stuck on a step or seeing a failure mode that isn't covered here? Email support@mamiyapanpro.com with photos of the back, the assembly, and a description of what's happening. The more detail the better. The launch video on No Grain No Gain walks through the install with footage if reading isn't enough.