Article 1010 - Door Latch and Door Latch System Problem Diagnosis

TSB #61 - March 10, 1967
(All Car Lines)


This article is a diagnostic procedure to assist in the efficient correction of a problem within the mechanical portion of the door latch system.

To properly review and diagnose a latch system malfunction, the door trim panel and associated trim parts should be removed. In the event that the latch system is inoperative and the door cannot be opened from either inside or outside of the vehicle, the following procedure must be employed to open the door.

DOOR OPENING PROCEDURE - All Car Lines Except As Noted
Fabricate a latch actuating tool from 1/8 inch diameter welding rod or equivalent as shown in Illus. S1190.

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ROD INSERTION DEPTH CHART (INCHES)
Car LineFront DoorRear Door
Ford - All Models (as applicable)1610.5
Thunderbird - All Models (as applicable)1411
Mustang - All Models14-
Fairlane - Falcon - 2-Door Sedan Models13-
Fairlane - Falcon - Comet - 4-Door Models1313 (at 45° angle)
see Illus. S1192
Fairlane -2-Door Hardtop Models13-


Enter the vehicle through the opposite door and lower the side glass of the inoperative door to the full "down" position. From outside the vehicle, insert the fabricated tool through the glass opening at the latch end of the door and engage the door latch pawl lever as shown in Illus. S1191. A slight downward pressure will then unlatch the door. The chart below Illus. S1190 will assist in determining for each car line the approximate depth the rod should be inserted to engage the latch.
NOTE: Because of the stationary vent window design used on the Fairlane and Falcon sedan and station wagon rear doors, it will be necessary to approach the latch on these units with the rod at an angle of approximately 45 degrees as shown in Illus. S1192. A slight pressure on the latch pawl lever will unlatch the door.

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Illus. 1191
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Illus. 1192
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Illus. 1193
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Illus. 1194


After opening the door and removing the trim panel, inspect all rod attachments in the latch system to insure proper connections. In each case, the rod should be inserted in the nylon bushing and the metal clip engaged around the rod (see Illus. S1191 - View A). The following actuating rods should be inspected to assure proper attachment at both ends of each rod.

Front Doors
    • Door Latch Actuating Rod (adjustable)
    • Inside Release Handle To Latch Rod
    • Door Latch To Cylinder Rod
    • Door Inside Lock Push Button Rod

Rear Doors
    • Inside Release Handle To Latch Rod
    • Door Inside Lock Push Button Rod

If, after determining that all rods in the latch system are properly and securely connected, the latch system continues to malfunction, the following problem diagnosis and correction procedure must be used to resolve specific problems:

A. Front Door Cannot Be Opened (unlatched) From Either Inside Or Outside The Vehicle.
POSSIBLE CAUSE AND REPAIR All Car Lines
If no distinct free is evident when a slight pressure is applied to the door handle outside push button, the door latch actuating rod (Illus. S1193) has been adjusted too short. This condition pre-loads the latch such that when the door is closed and then locked (inside lock push button depressed), the latch locking lever will travel past the latch pawl and restrict the necessary upward movement of the locking lever to unlock the door. (Illus. S1194 - View A).

Disengage the latch actuating rod at the latch (see Illus. S1193). After the latch locking lever and latch actuating rod lever have returned to their normal 'free" positions, adjust the latch actuating rod (the lower end of the rod is adjustable) so that the gap between the door outside handle bell crank and push button pin is set to the appropriate dimension shown in Illus. S1193.

Ford and Thunderbird Only - Inspect the latch to determine if the latch actuating rod lever has by-passed the lower edge of its guide slot in the latch plate while the latch was in a "locked" condition.

This condition causes the latch actuating rod lever to remain in an actuated position and prevents the locking lever from returning to its normal "free" position (Illus. S1194 illustrates this condition). If this problem occurs, latch assembly replacement is necessary.

B. Door cannot be opened (unlatched) from outside the vehicle when the door is unlocked and the outside push button is fully depressed. (Front door - all car lines.)
Possible Cause and Repair
• All Car Lines - The door latch actuating rod (Illus. S1193) is adjusted too long and will not operate the latch actuating lever sufficiently to unlatch the door.
Disengage the latch actuating rod at the latch (Illus. S1193) and adjust the length of the rod so that the gap between the door handle bell crank and push button pin is set to the appropriate dimension shown in Illus. S1193.

C. Door cannot be opened from inside the vehicle.
Possible Cause and Repair
• Ford and Thunderbird only — Inspect the latch to determine if the release lever has by-passed the latch actuating rod lever. This condition (shown in Illus. S1194) prevents the release lever from returning to its normal position and latch assembly replacement is necessary for problem correction.

D. Door rebounds (will not latch) upon closing.
Possible Cause and Repair
• Ford and Thunderbird only — Inspect the latch to determine if the latch actuating rod lever has by-passed the lower edge of its guide slot in the latch plate while the latch was in an "unlocked" condition. This condition (shown in Illus. S1194) prevents the latch pawl from returning to its normal operating position. Replacement of the latch is necessary for problem correction.

E. A loud noise resembling that of a tuning fork from the vicinity of the door latch as the door is closed.
Possible Cause and Repair

• Ford and Thunderbird only — A plastic strip which functions as a sound deadener is inserted in the door latch pawl spring during latch assembly. If the pawl spring dampener is missing, the spring will transmit an objectionable tuning fork type noise as the door is closed.

If the door latch spring dampener (Illus. S1191, View C) is missing procure a service released dampener (C7AZ-62219-A37-A, Class "C") or fabricate one as shown in Illus. S1195 from mylar or similar soft plastic material. Insert the dampener into the spring as shown in Illus. S1191, View C.

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F. The front door accidentally locks when the door is closed with the inside lock push button in an "unlocked" (up) position.
Possible Cause and Repair

• All Car Lines — Review the door latch and determine if the door latch locking lever toggle spring is missing (see Illus. S1194). This is evident if the inside lock push button can be moved up and down freely. Also, by inspecting the latch with the door inside lock push button in the "unlocked" (up) position, it can be readily determined if the toggle spring is missing.

If the toggle spring is missing, remove the latch from the door and procure one of the following service replacement toggle springs noted below:

C7AZ-6221872-A (Class "C") - Right Door
C7AZ-6221873-A (Class "C") - Left Door

To install, insert one leg of the toggle spring in the slot in the lock actuating lever, while the lever is in a "locked" position. Apply pressure to the other leg of the toggle spring while guiding the leg into the hole provided in the latch plate (see Illus. S1194). Prior to reinstalling the latch in the door, operate the latch to assure proper installation of the spring.

G. The door latch will not "lock" or "unlock" when the vacuum system is activated.
Possible Cause and Repair
• Ford and Thunderbird only — Operation of the vacuum system can be restricted by the inside lock push button binding on the door trim panel, the push button rod binding on the door sheet metal; or burrs on the door latch locking lever, where the latch pawl contacts the lever.

Prior to removing the door trim panel, a bind condition can be readily determined by removing the inside lock push button and activating the vacuum system. If the latch operates satisfactorily, loosen the trim panel and adjust as required to remove any bind that may exist between the push button and trim panel.

If the latch continues to malfunction with the push button removed, manually cycle the push button rod 10 to 15 times to remove any minor burrs that may exist in the latch. If cycling the latch manually does not improve the vacuum operation of the latch, remove the trim panel. Place a piece of emery cloth between the flange on the latch locking lever and the latch pawl (Illus. S1191 - View D). and with the emery cloth in place, cycle the lock button rod manually 10 to 15 times to remove any major burrs on the latch locking lever.

If none of the above conditions exist or the latch continues to malfunction after employing the above procedures, the problem is not caused by the mechanical portion of the door latch system. Refer to previously published information regarding door vacuum system operation to achieve problem correction.

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