Re: [Amc-list] F('ing)ailing parts 2

[Keleigh Hardie <keleigh3000@xxxxxxxxx>]

One small nit:

"An oil pressure switch closes the contacts as soon as the engine is 
started and the contacts stay closed until the engine is shut off."

Most standard oil pressure switches are the other way around, I think. 
There is power to the light whenever the key is on. If there is no 
pressure, the switch is closed, grounding the light and turning it on. 
When you  start the engine the pressure opens the switch, removes the 
ground and turns the light off. Only if there is a relay or electronics 
involved do they work the other way around...

Keleigh

Swygert, Francis G MSgt 436 CES/CECM wrote:
> >From Tom J (edited)
> It seems to me now that this is an engine-oil sensor, that some
> bean-counter smart-ass "cross checked" in a catalog, noted
> matching mechanical/electrical specs and OK'd the substitution
> and subsequent inventory shrinkage. And overlooked that brakes
> generate 1000PSI where an engine can't generate 100PSI.
>
> The immediate failure was a pitted contact -- there's a phenolic
> block with two brass contacts poking through, radially opposite.
>
> * There was brake fluid (DOT5 silicone) inside. The rubber/crimp
> seal is poor by design. There was ooky black on the electrical
> parts; maybe the rubber isn't silicone compatible? Seems unlikely,
> rubber otherwise OK. Might have simply been carbon from arcing,
> in solution.
> ----------------
>
> I mentioned the pressure in a previous post. Now that you mention the
> immediate failure of the contacts, and that this is really and oil
> pressure switch, brings to light something else! Brakes are used a lot
> -- lots of on/off action. An oil pressure switch closes the contacts as
> soon as the engine is started and the contacts stay closed until the
> engine is shut off. It's just a ground circuit for one small light bulb
> -- not carrying the load for 2 or more (third brake light, trailer?)
> bulbs that are also higher current than the warning light. So the
> contacts aren't made to carry the load NOR is the diaphragm rated for
> the pressure! It seems to me that even though the contacts failed first,
> the seal was evidently starting to fail and would have, though it would
> have lasted a bit longer with heavier electric contacts. Your whole
> findings report needs to go to NAPA, especially the tear-down. That
> along with the pressure and electrical differences might convince them
> to change the part number. They should be able to research the Ron
> Francis part source and get the correct part. Even if they don't, I'd
> rather see them list the switch as "no longer available" than sell a
> component that will fail in 3-6 months of regular use. The only reason
> they get by with it is that most cars old enough to be designed with a
> pressure switch aren't driven regularly. If you drive it only on sunny
> days the switch will last several years.
>
> I overcame the problem by making a bracket for a 1973 or so AMC pedal
> mounted switch. No more pressure switch to fail! I think this is a
> common retrofit for regularly driven vehicles due to the failure rate of
> the standard switches. Retrofit to a pedal switch or spend the $20-$25
> for a Ron Francis switch, which was designed for the load (pressure and
> electric). 
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