GM Full-Size Trucks 1970-1979 Repair Guide

Breaker Points and Condenser

Print

REMOVAL & INSTALLATION



1970-74 Vehicles

See Figures 1, 2, 3 and 4



Click image to see an enlarged view

Fig. Fig. 1: The points are retained by screws; use a magnetic screwdriver to avoid losing them



Click image to see an enlarged view

Fig. Fig. 2: Proper breaker point alignment



Click image to see an enlarged view

Fig. Fig. 3: The condenser is also retained by a screw



Click image to see an enlarged view

Fig. Fig. 4: The points have a locating tab which fits into a hole in the breaker plate

The usual procedure is to replace the condenser each time the point set is replaced. Although this is not always necessary, it is easy to do at this time and the cost is negligible. Every time you adjust or replace the breaker points, the ignition timing must be checked and, if necessary, adjusted. No special equipment other than a feeler gauge is required for point replacement or adjustment, but a dwell meter is strongly advised. A magnetic screwdriver is handy to prevent the small points and condenser screws from falling down into the distributor.

Point sets using the push-in type wiring terminal should be used on those distributors equipped with a Radio Frequency Interference (RFI) shield (1970-74 vehicles). Points using a lockscrew-type terminal may short out due to contact between the shield and the screw.

  1. Push down on the spring loaded V8 distributor cap retaining screws and give them a half turn to release. Unscrew the 6-cylinder cap retaining screws. Remove the cap. You might have to unclip or detach some or all of the plug wires to remove the cap. If so, number the wires and the cap before removal.
  2.  
  3. Clean the cap inside and out with a clean rag. Check for cracks and carbon paths. A carbon path shows up as a dark line, usually from one of the cap sockets or inside terminals to a ground. Check the condition of the carbon button inside the center of the cap and the inside terminals. Replace the cap as necessary. Carbon paths usually cannot be successfully scraped off. It is better to replace the cap.
  4.  
  5. Pull the 6-cylinder rotor up and off the shaft. Remove the two screws and lift the round V8 rotor off. There is less danger of losing the screws if you just back them out all the way and lift them off with the rotor. Clean off the metal outer tip if it is burned or corroded. Don't file it. Replace the rotor as necessary or if one came with your tune-up kit.
  6.  
  7. Remove the radio frequency interference shield if your distributor has one. Watch out for those little screws!
  8.  
  9. Pull off the two wire terminals from the point assembly. One wire comes from the condenser and the other comes from within the distributor. The terminals are usually held in place by spring tension only. There might be a clamp screw securing the terminals on some older versions. There is also available a one-piece point/condenser assembly for V8s. The radio frequency interference shield isn't needed with this set. Loosen the point set hold-down screw(s). Be very careful not to drop any of these little screws inside the distributor. If this happens, the distributor will probably have to be removed to get at the screw. If the hold-down screw is lost elsewhere, it must be replaced with one that is no longer than the original to avoid interference with the distributor workings. Remove the point set, even if it is to be reused.
  10.  
  11. If the points are to be reused, clean them with a few strokes of a special point file. This is done with the points removed to prevent tiny metal filings from getting into the distributor. Don't use sandpaper or emery cloth; they will cause rapid point burning.
  12.  
  13. Loosen the condenser hold-down screw and slide the condenser out of the clamp. This will save you a struggle with the clamp, condenser, and screw when you install the new one. If you have the type of clamp that is permanently fastened to the condenser, remove the screw and the condenser. Don't lose the screw.
  14.  
  15. Inspect the distributor cam lubricator. If you have the round king, turn it around on its shaft at the first tune-up and replace it at the second. If you have the long kind, switch ends at the first tune-up and replace it at the second.
  16.  

Don't oil or grease the lubricator. The foam is impregnated with a special lubricant. If you didn't get any lubricator at all, or if it looks like someone took it off, don't worry. You don't really need it. Just rub a matchhead size dab of grease on the cam lobes.

  1. Install the new condenser. If you left the clamp in place, just slide the new condenser into the clamp.
  2.  
  3. Replace the point set and tighten the screws on a V8. Leave the screw slightly loose on a six. Replace the two wire terminals, making sure that the wires don't interfere with anything. Some V8 distributors have a ground wire that must go under one of the screws.
  4.  
  5. Check that the contacts meet squarely. If they don't bend the tab supporting the fixed contact.
  6.  

If you are installing preset points on a V8, go ahead to step 16. If they are preset, it will say so on the package. It would be a good idea to make a quick check on point gap, anyway. Sometimes those preset points aren't.

  1. Turn the engine until a high point on the cam that opens the points contacts the rubbing block on the point arm. You can turn the engine by hand if you can get a wrench on the crankshaft pulley nut, or you can grasp the fan belt and turn the engine with the spark plugs removed.
  2.  


CAUTION
If you try turning the engine by hand, be very careful not to get your fingers pinched in the pulleys.

On a manual transmission you can push it forward in High gear. Another alternative is to bump the starter switch or use a remote starter switch.

  1. On a 6-cylinder, there is a screwdriver slot near the contacts. Insert a screwdriver and lever the points open or closed until they appear to be at about the gap specified in the Tune-Up Specifications. On a V8, simply insert a 1 / 8 in. allen wrench into the adjustment screw and turn. The wrench sometimes comes with a tune-up kit.
  2.  
  3. Insert the correct size feeler gauge and adjust the gap until you can push the gauge in and out between the contacts with a slight drag, but without disturbing the point arm. This operation takes a bit of experience to obtain the correct feel. Check by trying the gauges 0.001-0.002 in. (0.025-0.051mm) larger and smaller than the setting size. The larger one should disturb the point arm, while the smaller one should not drag at all. Tighten the 6-cylinder point set hold-down screw. Recheck the gap, because it often changes when the screw is tightened.
  4.  
  5. After all the point adjustments are complete, pull a white business card through (between) the contacts to remove any traces of oil. Oil will cause rapid contact burning.
  6.  

You can adjust 6-cylinder dwell at this point, if you wish. Refer to Step 18.

  1. Replace the radio frequency interference shield, if any. You don't need it if you are installing the one-piece point/condenser set. Push the rotor firmly down into place. It will only go on one way. Tighten the V8 rotor screws. If the rotor is not installed properly, it will break when the starter is operated.
  2.  
  3. Replace the distributor cap.
  4.  
  5. If a dwell meter is available, check the dwell.
  6.  

Dwell can be checked with the engine running or cranking. Decrease dwell by increasing the point gap; increase by decreasing the gap. Dwell angle is simply the number of degrees of distributor shaft rotation during which the points stay closed. Theoretically, if the point gap is correct, the dwell should also be correct. Adjustment with a dwell meter produces more exact, consistent results since it is a dynamic adjustment. If dwell varies more than 3 degrees from idle speed to 1,750 engine rpm, the distributor is worn.

DWELL ADJUSTMENT



See Figures 5, 6, 7 and 8



Click image to see an enlarged view

Fig. Fig. 5: Setting the dwell on a 1970-74 V8 distributor



Click image to see an enlarged view

Fig. Fig. 6: Adjusting the point gap/dwell on a 6-cylinder distributor



Click image to see an enlarged view

Fig. Fig. 7: The point gap on 6-cylinder engines is adjusted with a screwdriver



Click image to see an enlarged view

Fig. Fig. 8: The point gap on 8-cylinder engines is adjusted with an Allen wrench

1970-74 Vehicles
  1. To adjust dwell on a six, trial and error point adjustments are required. On a V8, simply open the metal window on the distributor and insert a 1 / 8 in. allen wrench. Turn until the meter shows the correct reading. Be sure to snap the window closed.
  2.  
  3. An approximate dwell adjustment can be made without a meter on a V8. Turn the adjusting screw clockwise until the engine begins to misfire, they turn it out 1 / 2 turn.
  4.  
  5. If the engine won't start, check the following:
    1. That all the spark plug wires are in place.
    2.  
    3. That the rotor has been installed.
    4.  
    5. That the two (or three) wires inside the distributor are connected.
    6.  
    7. That the points open and close when the engine turns.
    8.  
    9. That the gap is correct and the hold-down screw (on a six) is tight.
    10.  

  6.  
  7. After the first 200 miles (320 km) or so on a new set of points, the point gap often closes up due to initial rubbing block wear. For best performance, recheck the dwell (or gap) at this time. This quick initial wear is the reason why the factory recommends 0.003 in. (0.076mm) more gap on new points.
  8.  
  9. Since changing the gap affects the ignition timing, the timing should be checked and adjusted as necessary after each point replacement or adjustment.
  10.  

1975-79 Vehicles

These engines use the breakerless High Energy Ignition (HEI) system. Since there is no mechanical contact, there is no wear or need for periodic service. There is an item in the distributor that resembles a condenser; it is a radio interference suppression capacitor whi