[Chrysler300] Lessons learned about '57-'58 manifold vacuum safety switch

["rob kern" <robkern@xxxxxxxxxxxxx>]

Hello 300'ly to all!
    I want to pass on what I learned recently about the function of the manifold mounted vacuum safety switch of the '57 and '58 Chryslers. I had a newly rebuilt heater core installed in my C's Model 900 factory heat A/C system since the original sprang a leak (fortunately draining coolant on the engine side of the firewall where the heater core is located and not in the interior compartment). As part of the installation the Model 900 black cover had to be removed(which of course shattered beyond repair, fortunately I procured a replacement which I refurbished from Desert Valley Auto Parts a few years back) along with the  rear carb. and distributor cap. This was performed by the mechanic that removed and reinstalled the engine and transmission and did all the front and rear A/C work on the car over the past 4 years, who is located about 40 miles away. On the way back I noticed the car to run a little rough but didn't really get concerned.  Since the job was completed I drove the C about 75 miles.  The last few weeks I just backed the car out of the storage garage to sequentially remove the rear and front seats to ship to Legendary to have their new seat covers installed.  Mopsy sat for about  2 weeks and this past Saturday I decided to start her up to just idle since I didn't feel safe driving her while sitting on a foot stool albeit wearing a lap-type seat belt. Upon starting her up she ran real rough, was skipping, and the idle was choppy at best.  Upon giving more gas she revved but was still quite choppy. I called my mechanic and he said to strap in and take her for a drive that most likely from sitting for two weeks a plug may have fouled.  OK....this never happened in 4.5 years but with an old car I suppose anything can be expected to occur.  I restarted the car and halfway out the garage she stalled and it took me about 5 minutes of cranking to get her to catch. The charcoal-gas fired army hack that Humphrey Bogart drove to escape the Japanese on a Pacific Island WW II movie with a bunch of orphans and a pretty heroine was smoother than my 300! I decided that there was no way that I would take her out on the road to blow out a fouled plug.  I managed to coax her back into the garage chopping away with one foot on the gas, the other on the brake while sitting on a foot stool.  When I shifted from drive to neutral the starter motor tried to engage. Voila! I turned off the engine and looked at the manifold vacuum safety switch and behold...the prong connected to the brown wire was bent 90 degrees to the right! I figured that this had been inadvertently bent during the heater core installation and after disconnecting the battery I straightened the connector and it felt as loose as a 6 year old's front tooth waiting to be parked for the tooth fairy. After a call to George Riehl, John Lazenby and Jeff Carter I realized that there was most likely a vacuum leak created and the first place to start was with the damaged manifold vacuum safety switch. I removed the switch and consulted the tech section of the Club's website for Mr. Cloer's NAPA 300C part list and a replacement switch NAPA part #NS-6306 was listed.  There not being a NAPA store within 30 miles of Lawton (go figure) I called O'Reilly's and they cross referenced the part and said it had to be ordered and would arrive on Tuesday (today). Meantime a number of scenarios plagued me over the next few days while waiting for the new switch as to what else could be the problem should the switch not be the culprit.  Calls went out a second time to John Lazenby and Jeff Carter and also to Greg Leggatt, Jim Krausmann, and George McKovich as well as my mechanics in town. I threw the old switch in my brief case and while waiting for a patient in labor to deliver last night devised a test to see if my old switch was defective.  I noticed in bright light that the bakelite was cracked around the prong which had been bent.  I dissasembled a blood pressure cuff and my stethoscope and took the stehoscope tubing and connected it to the threaded end of the vacuum safety switch and took the pump bulb of the blood pressure cuff and attached it to the end of the tubing.  Holding the pronged end of the switch close to my ear I began squeezing the bulb and felt the air rushing through the cracked bakelite. Hold the laughs about weird _ _ _ _ jobs! This confirmed to me that there definitely was a vacuum leak from the broken switch and that there was a very high likelihood that this was the source of the engine missing (probably the cylinder closest to where the switch was mounted on the intake manifold was getting a very lean non-metered fuel/air mixture and missing) and the vacuum safety switch was not having the connection broken to prevent the starter from engaging when shifting to neutral from drive or reverse. I checked that the carb. screws were tight and the hose connections from the vacuum reserve tank and the intake manifold were secure and also the carb. to distributor diaphragm hose was properly connected.  Also I checked to make sure the distributor wires were tightly connected to the distributor cap and that the cap was snapped on tightly. This afternoon I replaced the vacuum safety switch and started the engine. It ran crappy for about 45 seconds when I shut it off.  I called my mechanic and he asked if I had shifted from neutral to reverse or drive and back to neutral to see if that starter engaging problem was rectified and perhaps there was a vacuum leak concomittantly elsewhere. (visions of propane torches, WD-40 spraying, and carb cleaner testing were coming to mind). I restarted the car and PRESTO!! smooth as silk, no skipping, firm power brake peddle and shifting from reverse and drive to neutral with no starter engagement!  It then dawned on me that I hadn't allowed the car to replenish the vacuum resrve tank since I had opened the system upon removal of the vacuum safety switch.  The car ran perfect choke high idle and smooth regular idle for 20 minutes while I called John Lazenby for him to hear the engine and my mechanic.  Several calls later to the rest of the club members and mechanics locally that gave me advise and I am ONE VERY HAPPY CAMPER AS WELL AS CLUB MEMBER! So if a scenario develops with a '57 or '58 with a manifold vacuum safety switch look at replacing the switch first in your search for all the causes of the engine to perform the way mine did. $9.75 (tax included) part with 5 minutes installation time and 4 days of thinking it out and crossing fingers, obsessive-compulsive rituals and prayer later, I pass on this 300 pearl.  ROB KERN

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