M4 light leak around the back door

[rosshj]

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Hello. I have a light leak around the back door of my M4. It took me a while to realize it was coming from the back door, but I narrowed it down when I taped off the back door and had zero light leaks. 
 

I’m wondering if it’s my light seal at the top under the back door. If so, is this a big job to fix it? Any DIY solutions (not involving tape), or should send it out? 
 

Cheers! 

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[Al Brown]

Back door leaks are nasty. Some forum members who have them can vouch.
(If you search the forum you will find a solution to every light leakage problem. Make sure you select "all content" from the search sub menu.)

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[rosshj]

This is actually a better representation of the light leak. 

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[dpitt]

It looks to be one of the sides of the back door, both top and bottom. Maybe start by inspecting the backdoor sides and see if one side does not fit as it is supposed to.

[250swb]

It looks like the light is coming from the rebate for the sliding catch of the rear door, is there any damage around there? It's hard to imagine damage or is there something stopping the catch from closing properly? The top seal is really as much a dust seal, the whole door relying on the baffles to stop any light leakage.

[rosshj]

Thank you all for the replies. The back door seems to be totally fine. No damage from what I can see. I'm going to run another roll through there (I've burned about 5 so far) to see what else I can figure out. 

[Michael Geschlecht]

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Hello Ross,

Welcome to the Forum.

It would appear that the felt lite seal on the side of the film chamber under the range/viewfinder window is missing.

That felt lite seal should look like the 1 on the other side of the film chamber.

It should go top to bottom & be thin.

Best Regards,

Michael

Edited February 28 by Michael Geschlecht

[TomB_tx]

10 hours ago, Michael Geschlecht said:

Hello Ross,

Welcome to the Forum.

It would appear that the felt lite seal on the side of the film chamber under the range/viewfinder window is missing.

That felt lite seal should look like the 1 on the other side of the film chamber.

It should go top to bottom & be thin.

Best Regards,

Michael

M models did not originally have felt seals at the sides of the back door, but relied on the labyrinth path around the body/door joint. My M3s & 2s do not have the seals, It was common for Techs to add the seals when cameras were serviced. Possibly repeated flexing / wear of the door made them a good idea. Sherry added them to my M4 when she serviced it.

[Michael Geschlecht]

Hello Tom,

I think that some M3's came originally with felt strips on both sides of the film gate.

It was the felt strip NOT being on the left side that I noticed.

Best Regards,

Michael

 

Edited February 29 by Michael Geschlecht

[250swb]

Foam light sealing is often added in the search for a light leak but it doesn't mean it should be there by design. I see my MP came with a very thin sealing strip either side of the film gate (and the top of course) but I don't think any camera up to that point ever had them from the factory. In the case of my MP it may simply be there to stop a clatter or damage to the paint if the door slams shut? My M4-P for example doesn't need extra sealing and has never had it, and I think the difference is in the depth of the light baffle and the paint coating which on the older cameras was a thick heavy textured crackle finish. The OP could add some foam seal around the edge (you can buy it in sheets to cut to size, 1mm or 1.5mm thick) and see if it stops the leak and life could go on, except it's probably a sign of trouble elsewhere. I'm also sure camera techies add foam because it saves searching for a leak around the door and many of their customers believe it's missing if there isn't any. 

Edited February 29 by 250swb

[williamj]

You have a functional reason to add tape to the outside of your camera, not just an aesthetic reason. I’d grab the opportunity with both hands. 

[Michael Geschlecht]

On 2/28/2024 at 9:06 PM, Michael Geschlecht said:

Hello Tom,

I think that some M3's came originally with felt strips on both sides of the film gate.

It was the felt strip NOT being on the left side that I noticed.

Best Regards,

Michael

 

 

19 hours ago, 250swb said:

Foam light sealing is often added in the search for a light leak but it doesn't mean it should be there by design. I see my MP came with a very thin sealing strip either side of the film gate (and the top of course) but I don't think any camera up to that point ever had them from the factory. In the case of my MP it may simply be there to stop a clatter or damage to the paint if the door slams shut? My M4-P for example doesn't need extra sealing and has never had it, and I think the difference is in the depth of the light baffle and the paint coating which on the older cameras was a thick heavy textured crackle finish. The OP could add some foam seal around the edge (you can buy it in sheets to cut to size, 1mm or 1.5mm thick) and see if it stops the leak and life could go on, except it's probably a sign of trouble elsewhere. I'm also sure camera techies add foam because it saves searching for a leak around the door and many of their customers believe it's missing if there isn't any. 

Hello Everybody,   

just to clarify things:

When I bough my M3 at the Leica dealer, years before the M4 was introduced, it had a felt light seal on both sides of the film gate.

Best Regards,

Michael

[rosshj]

I’ve had a few M bodies and never seen light seals on the sides, but I’m sure it wouldn’t hurt. Maybe I’ll try that if I can’t figure out another solution.

For now I’m running another roll through it and taping just half the back to see if I can narrow things down. 

[Michael Geschlecht]

Hello Ross,

Welcome to the Forum.

You have an "M" body with a light seal right now.

Please look to the right of the winding spool in your Post #1 above.

It is that approximately 4 cm/1.6 inch long.

Thin, vertical thing.

Sticking up a little bit.

A little to the right of the winding spool.

Best Regards,

Michael

Edited March 1 by Michael Geschlecht

[George Collier]

I had leaks on an M4-2 and an M4, but higher up the film, to the left of the aperture right along the frame edge and into the frame  - with your pic as a reference. I was in Massachusetts and took it to Youxin Ye (he had worked on both cameras before). He looked at it and said that the back door was defective. He offered to replace it for I think $150 (I could return the door if it didn't work), and he put in a small amount of think black padding material in the light traps above and below the aperture. I didn't take him up on the back door, but tried the seal. Still leaked. Closer examination when I got home revealed that the back door hinge pin, far left at the top of the door was loose. This pin sits tightly in a hole, withdrawn by a spring loaded pull to remove the door (as you seem to have done for your picture above). If the pin becomes loose, it allows the door to not seat properly and leak. Youxin didn't say, but I think that was his conclusion. I don't see any material sealing mine and I eventually removed what Youxin put in, but my final solution is to cover the three edges of the door edge with a black graphic arts paper (but opaque) tape, low tack and replaced every 2 or 3 months.