[Sluggo]

I have a few Pentax 35mm bodies that sometimes give trouble when advancing film, especially bulk-rolled film. Only recently did I realize that some models have an extra roller in the film door to hold the film against the teeth of the advance roller, and some don't; and the ones that lack this roller, in particular my MX, are the ones that most often give me overlapping frames.



That's a KM in the middle, showing the film guide roller with grooves cut in it to accommodate the film advance roller's teeth. It looks impossible for film to slip while advancing, with that in place.

The bottom camera is an LX. It doesn't have the roller, but a couple of raised ridges built into the film door probably have the same effect. They line up slightly offset from the advance roller's teeth when the door is closed.

The top camera is the MX. I don't see anything holding the film against the advance roller, except whatever tension is produced by the take-up roller. Looking through my collection, it seems the extra roller is missing from all the M- and A- series bodies. (Most but not all of the K bodies have one; my Spotmatic doesn't.)

Has anyone else had trouble with film slipping during advance in, say, an M body? Is there a tension adjustment for take-up to hold the film tighter against the advance rollers so it won't pop off the gear teeth? I bet that's the real problem - it's lost tension with age. Or might it make sense to modify the door by adding ridges like in the LX?

[seventhdr]

You are quite right. Possibly one of the cost savings in moving from the K series to the M and A series.

The Z series and MZ series does seem to bring back this roller, in some cameras it is moulded into the door with two little rollers top and bottom.

The LX initially did not have a roller. The addition of a roller was one of the first of about 300 modifications made to the LX over its twenty year production life. Most of these modifications being internal. The lack of a roller generally indicates a very early production LX. I say generally, because the door on the LX is removable.

Regards

Chris Stone

[jimH]

I've never had an issue with film advance with either my ME Super or my MX as long as I got the film tucked between the little white pins to capture the film properly. Unlike many 35s you have to actually tuck the film into the white pins. Other model allow you to just lay the film on top of the take-up spool and it would do it's thing. I'm guessing that's why Pentax got shed of the little white pins on the film uptake spools.

[Tom in Delaware]

You may actually be having this problem with your MX:
https://www.pentaxforums.com/forums/pentax-film-slr-discussion/120326-rewind-shaft.html

[Sluggo]

...Unlike many 35s you have to actually tuck the film into the white pins....

Yes, but that's not the issue here. The first few frames are always okay, so I'm sure the leader is threaded properly. But after about a dozen frames the film starts skipping over the teeth, so I think it's a torque problem and the camera needs some time on somebody's repair bench.

I was speculating that the extra roller would have prevented this happening, because the advance roller would reliably feed film to the takeup roller and not much torque would be needed. I don't really know that.

Delaware Tom, thanks for finding that thread. Drag on the supply side might cause this too, though I'm not seeing any torn sprocket holes. I'll see if I can make Eric's tip work.

[Gashog]

I got in the habit years ago, of checking the take-up for slack.
I think the fuzz on the film can has a lot to do with the tension of the film.

[Sluggo]

You may actually be having this problem with your MX:
https://www.pentaxforums.com/forums/pentax-film-slr-discussion/120326-rewind-shaft.html

Late followup: I applied some molytone grease to the rewind shaft with a toothpick, then worked the shaft around for a little while. No body disassembly required.

Took a while to get through that roll of 36 exposures (bulk Fomapan 200), but it was all smooth, no grindy noises, and no overlapped frames on the negatives that are hanging to dry right now. Might have been a fluke, but I'm happy.