M Series Door Latch Repair

majortom

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The following information is how to repair the common failure of the door latch mechanism used on M series 2 1/2 , 5 & 10 ton trucks is also applicable to M37 Dodge.

We get many calls for door latches due to internal failure causing the outside handle not to function. The left latch is very hard to find and is not interchangeable with the right hand latch. The latch is the same for all of the above mentioned units except for the length of the arm to the inside handle.
Yesterday the latch failed on my truck. But I couldn't just replace it I had to know why. After disassembling the latch, the failure was obvious. The quick fix was also obvious.
How the latch works: After you rotate the outside handle it rotates a cam, that pushes a lever attached to the striker. What happens with use is the clearances increase enough so that the cam will slide under the lever and the outside handle does nothing. To repair the problem you must remove the latch from the door. With a firm tap on a specific spot with a punch and hammer on the striker lever the latch will work just like new.

Pic 1: Shows Left Hand Latch

Pic 2: Shows The Exploded View From Left To Right Latch, Cam, Cam Retainer & Cover.

Pic 3: Shows a that the cam has slide under the lever (Broke).

Pic 4: Shows the striker held in the open position with a vicegrip to gain access for the bending operation.

Pic 5: Has the cover removed so the part striker lever being bent

Pic 6: Bending the lever using a punch or chisel with a hammer. Give the punch several good raps then insert outside handle in latch checking for proper function, repeat as necessary.

Pic 7: Shows the cam resting against the striker arm in the proper position with the cover removed.

Pic 8: Shows the cam rotated to the open position.

In short you do not have to take the cover off the latch to repair it we did that to give a better understanding of the inner workings of the latch. One of the easiest things I have ever fixed on a Deuce.

Time to complete Procedure: Half Hour
Materials: 0
Beer: 2
 

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Gastrap

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Nice job. Its always a plus when you turn the knob & something actually happens:-D

I just got done with mine too. all the contact surfaces on the cam & hook were so badly worn I had to build them up with weld & grind them back into shape. Then I had to weld an extension on the back of my latch "bolt" to engage what was left of my broken spring. Works great so far & cost nothing.
 

chris10980

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While on the subject of door latches, has any one replaced the door handle with one of the locking versions found in the Grainger or McMaster Carr catalogs? If so which one did you use?
 

M-37Bruce

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Midlothian, VA
Wasn't Sure

While on the subject of door latches, has any one replaced the door handle with one of the locking versions found in the Grainger or McMaster Carr catalogs? If so which one did you use?

Where they came from, but the locking ones I have seen over the years were chrome, I guess they would/could be etched or bead blasted & painted? Unfortunately, they will only slow the @ss's up a little? :evil:

I have always wanted to visit McMaster Carr, I worked @ a hardware store part time after the AF, learned a lot form the owners pappy!
 
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Amer-team

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Centralia/WA
Thank you for the excellent pictures in this thread. The repair did not take long, but I did not anticipate taking the door handle assembly out of the inside too. Once it was figured out that it all came out together, it did not take five minutes to do the repair outlined in the pictures. Liberally lube the whole mechanism up and put it back in place.
I had previously moved the exterior door handle to the horizontal position, that made it easier to grasp, as opposed to the vertical hanging down position. What I wonder is if this did not make the mechanism more susceptible to higher force when being pulled down. This could have aided the problem of the interior piece being bent and not functioning. Anyway, moved the handle back to the vertical position. Thanks again for the help.
 

whatadeuce

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Thought I could remove the 1/4" pins holding the hinges together, rather than remove the entire hinge from the cab fram, well I had a hard time getting some of the 1/4" pins put, out, and after heating the hinge too hot, I bent it all up. Had to use a reverse drill-out device to remove the 4 hinge to door frame tapping bolt which broke the heads off. But I got them al out. I went and purchased a SNAP-ON strike tool to loosen the next hinge to cab frame bolts.
 

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Cape Coastie

CWO4 ENG/MSS, USCG, RET.
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Fixed mine too!

Thanks Majortom for the great write up of fixing the door latches. Took my passenger side off my M923 and did the repair you did. Seemed to work and upon reinstalling after shutting the door several times it failed again. Took the latch back out for a better look. My latch had an additional failure. The actual door latch was coming apart from the slide mechanism. In your photo #7 the 2 rivets just above the yellow colored slide mechanism had failed causing the slide mechanism to separate from the latch. I repaired it by punching out the rivets and putting in 2 brass machine screws as that is what I had laying around. I had to bend up one tab to separate the slide from the latch body. Filed down the heads on the back side (forgot to take a picture of that side). Greased everything up and reassembled. Everything seems to work well now and saved the price of a new latch. Hope this helps someone else.
image.jpgimage.jpgimage.jpg
 

BigSky

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Can Someone help me with how to get the latch mechanism out of the door? I need to replace the spring. It broke off in two parts. One part is still in the mechanism, the other I did find inside the door frame after removing the side panel.
 

Yarz

Member
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Location
Fawn Twp. PA
Can Someone help me with how to get the latch mechanism out of the door? I need to replace the spring. It broke off in two parts. One part is still in the mechanism, the other I did find inside the door frame after removing the side panel.
I don't remember it being difficult, so I just took a look.

It looks like you remove the door handle (1 screw in the center), and the 3 screws surrounding it, and then remove the 3 screws around the latch. 1 on the interior, and 2 on the back edge of the door, above and below the actual latch. Then drop the whole thing down and out the access panel.
Depending on how yours is broken into 2 pieces, the fishing it out the access panel may be even easier than usual.
 
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