Thursday, May 4, 2017

Door Latch Removal & Repair

More Than You Wanted to Know About Door Latch Removal, Workings & Repair
My truck door latch would lock, but wouldn't always unlock. When I tested the latch outside of the truck it worked perfectly. I finally figured out the problem.

When the temperature was less than forty degrees, the latch would not unlock. It locked fine, but wouldn't unlock. If the temperature was more than forty degrees it worked.
This latch is from a GMT-400 Chevrolet C1500, but nearly all GM door latches from the '80s and '90s work very similarly.

It turns out the issue was with the latch that releases the door pin. When the assembly was latched, the latch was dropping too low and preventing the striker that lifts the latch from lifting it and opening the door.

To remove the latch, the door panel must first be removed.

Door Panel Removal:
  • Remove the triangular shaped piece of plastic near the A pillar. Pry up an edge and pull on it hard.
  • Remove the door handle trim, their are (3) tabs that can be depressed with a flat head screwdriver (gently)
  • Remove the power window/lock/mirror panel. Pull up at the rear, then slide the assembly backwards. Then remove the electrical connections with pliers.
  • Remove (2) phillips head screws on the arm rest. 
  • Pry up one corner of the door panel. I typically start at the bottom, back corner. All that's left are plastic clips, pull along the perimeter, then lift the panel up and over the top door panel edge against the window.
Pull this piece off.

Three plastic tabs hold this in place.
 
Pry the back up, then slide it backwards.
Door Latch Removal:
  • (2) 10 mm bolts holding the handle in place. One in the jamb, and one directly behind the handle. There is a hole in the inner metal door panel for wrench access. You will need an extension.
  • Three torx T-25 screws hold the actual latch in place.
  • Remove the (3) door jamb vent screws to access the latch/rods. They are 7mm.
  • Pull/push the latch up, so that the door handle can be pushed up and the lock cylinder and tab can clear the bottom of the exterior door handle opening, then pull the handle down and out. Remove the rod from the lock cylinder with a flat head screw driver. I would pry one side of the clip up, then the other while using the flat head to push the rod out of the clip. The handle rod just sits in place.
  • Remove the rods from the interior latch and lock clips with a flat head screw driver.
(3) 7mm bolts for the vent
Inner door panel
(2) 10mm bolts for the exterior handle
(3) T-25 screws for the latch
How the Latch Operates:
Latch open
Latch closed
Interior latch release
Interior lock connection unlocked
Interior lock connection locked
Exterior latch release
Exterior lock connection unlocked
Exterior lock connection locked
Striker that extends when unlocked and retracts when locked
Striker that extends when unlocked and retracts when locked
Latch that lifts to release and opens the door. The striker was hitting the
back side of this plate instead of extending under it.
Latch that lifts to release and open door. The striker was hitting the
back side of this plate instead of extending under it.
The plate that stops the latch and the culprit of my problems.
I had a gap between the yellow plastic and latch. This caused the
latch to drop too far down.
I cleaned the latch by soaking it in gasoline, then greased it with white lithium grease. I tested the latch mechanism, and everything worked fine. I re-installed it. This didn't seem to help. I had the same symptoms after re-installing it.

It's incredibly difficult to see the latch in action inside the door. I removed it again, checked it again, and discovered nothing new. I would latch and check the door without shutting it, so that I could still access the latch. When I checked it, everything seemed to work.

It got to the point that the latch wouldn't open at all. I removed the exterior door handle and left the door unlocked just so I could access it. I left the door panel off, because if the door were to lock with the panel on I'd have to either cut a hole in the inside or outside of the door and I'd prefer not to do that.

I removed all the rods just to ensure it wasn't a rod problem, and that the rods were fully engaging the latch. Even engaging the lock by hand, the same symptoms occurred.

Determined to either fix the latch or sell the truck, I jammed multiple flashlights and two mirrors inside the door.

The issue was that the striker (for lack of a better term) was hitting the actual latch upon unlock. It should be extending under the latch and then the handle release pulls the striker up, engaging the latch and opening the door. Instead the striker was hitting the back side of the latch. The latch was dropping too far down.

Being very familiar with how the latch assembly worked at this point, this had to be a problem with the latch. There is a plate that stops the latch from rotating. It has a piece of plastic so that metal isn't hitting metal.
In its resting position there was a gap between the actual latch and this plastic encased plate. When I would lock and then engage the latch, somehow it was dropping the actual latch lower than it should go because the plate wasn't stopping it in the correct position. When the latch dropped lower, it was lower than the striker, the striker couldn't extend underneath the latch. What temperature had to do with this, I still don't know.
By bending that plate, which stopped the latch from dropping too far down, my latch assembly has been fixed and works correctly. I used a hammer and screwdriver to bend the plate and close the gap, after first removing the piece of plastic and then putting it back after.

I gave it a week to check and even when the temperature dropped to below forty degrees, it still worked. Problem solved! If you've got a latch that won't unlock and it is driving you crazy, this may be it.
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