Speed Control - Diagnosis
83chrysler7 ModelsAll Domestic Passenger Cars & Trucks Equipped with Speed Control
Subject
Speed Control Diagnosis
Index
FUEL
Date
April 25, 1983
No..
14-20-83
P-1192-C
This Technical service Bulletin will assist you in diagnosing possible causes of automatic speed control malfunction complaints before arbitrary replacement of the speed control servo.
Information to assist you in diagnosing such complaints is compiled in the following sections. Do not replace the speed control servo before doing the simple, quick tests described in this bulletin.
A. SYMPTOM/CONDITION
Sags on hills, grade, or trailer towing.
DIAGNOSIS
If poor control occurs under these conditions but is good on level road with normal loads, the problem is a low vacuum condition caused by a low power-to-weight ratio. This is especially true on four and six-cylinder cars and some speed drop off is to be expected.
REPAIR PROCEDURE
The engine should be set at peak performance and the customer should be instructed to "assist" the speed control by manually pressing on accelerator.
B. SYMPTOM/CONDITION
Minor hunting surge or speed variation at speeds below 40 mph.
DIAGNOSIS
With the introduction of lock-up torque converters, leaner carburetors, and intermittent cyclic A/C clutch engagement there is a tendency for speed variations, even with normal throttle control. Speed control operation may amplify the speed variations thus making the condition more noticeable during speed control engagement.
REPAIR PROCEDURE
The engine should be checked and set to proper specifications. The servo should only be replaced for this problem after establishing the car is normally smooth running.
C. SYMPTOM/CONDITION
Speed control does not work at all.
REPAIR PROCEDURE
1. Check brake switch adjustment visually, brake switch button should extend out 1/8" inches. This can be verified by observing brake lights which should come on with 1/4" to 3/4" pedal travel. Manual transmission cars must also be checked for the similar clutch switch adjustment.
2. Check throttle control connections and adjustment at the carburetor or throttle body which must be 1/32" to 3/32" inches slack (see page 4 for front wheel drive adjustment procedure).
3. Check to be sure the speedometer is working properly. A broken or disconnect speedometer cable will prevent the system from operating.
4. Check vacuum hose connection for tight connections at nipples and no sharp bends or kinks.
5. Check electrical circuit at speed control servo using a 12 volt test lamp. Attach one end to good ground and the other end to the connectors and turn ignition switch and speed control switch to "ON" position.
The terminal diagram and test lamp responses can be found on Page 5. Only after the correct lamp response has been obtained with the indicated action at each test lamp position should the servo be replaced.
D. SYMPTOM/CONDITION
Speed setting after lock-in is erratic, sometimes high and sometimes low.
DIAGNOSIS
This condition can be caused by:
1. Vacuum leaks.
2. Throttle cable misadjustment.
3. A "bouncy" speedometer cable drive - a bouncing, fluttering or noisy speedometer will be noted.
4. Servo lock-in misadjustment.
REPAIR PROCEDURE
1. Eliminate any vacuum leaks.
2. Adjust the throttle cable per earlier directions.
3. Correct speedometer cables per the service manual.
4. After the above solutions fail, then adjust the servo lock-in screw.
REMEMBER: To increase speed one mph turn screw counterclockwise 1/4 turn. To decrease speed one mph turn screw clockwise 1/4 turn.
E. SYMPTOM/CONDITION
Tap up too high or too low.
REPAIR PROCEDURE
This condition can be improved by adjusting the servo lockin screw (after checking throttle cable adjustment) in the same way as correcting for a high or low lock-in speed setting. Remember, this will affect lock-in accuracy.
NOTE: USE NO LUBRICATION WHEN ASSEMBLING THE VACUUM SUPPLY HOSE TO THE SERVO NIPPLE AS CONTAMINATION OF THE INTERNAL VACUUM ORIFICE MAY OCCUR.
POLICY: Information only
SPEED CONTROL CABLE ADJUSTMENT FOR DOMESTIC FRONT WHEEL DRIVE VEHICLES.
FIGURE 1 - CABLE RETAINING CLAMP:
Speed Control Cable Adjustment The speed control cable is supported by a cable clamp located approximately seven inches from the throttle lever stud (Fig. 1).
FIGURE 2 - CABLE CLEVIS TO STUD CLEARANCE:
(1) Start engine and let run until it reaches operating temperature.
(2) Remove snap ring (Fig. 2).
(3) Clearance between the throttle stud and the cable clevis should be 1/16 inch (1.66 mm) (Fig. 2).
FIGURE 1 - CABLE RETAINING CLAMP:
(4) To adjust cable loosen cable retaining clamp nut (Fig. 1).
FIGURE 3 - CABLE CLEVIS TO STUD GAUGE SURFACE:
(5) Pull all slack out of cable, using the head of the throttle stud as a gauge (Fig. 3). Do not pull cable so tight that it moves throttle away from curb idle position.
(6) Tighten retaining clamp nut to 45 in.lbs. (5 N-m) and move cable clevis back on round portion of stud.
(7) Install snap ring.
SERVO WIRING TERMINALS:
SERVO WIRING TERMINALS