Wednesday, November 22, 2006

VW - St. Muir Revisited

>One thing I have never understood is why this book has so much controversy surrounding it.


Dear Peter (and the Group),

It's largely a matter of competence. Or perspective. To an experienced mechanic the Idiot Book is an hilarious collection of good information and bad, like that bit on pg 85 of the 19th edition (Step 3. Check Sensor) where John tells his Disciples, "be sure to get a six volt [oil pressure] sensor if your car is 6 volt and a 12 volt sensor for a 12 volt system" And if that sensor fails to work, you should take it back and get a replacement... because "You have checked everything else." (emphasis added)

First off, like 99.99% of all low-voltage switches, the VW's oil pressure sensor switch is not voltage-specific. Volkswagen used one sensor from 1949 thru 1981 (go find the microfiche; look for yourself).

Secondly, the switch is the Normally Closed (NC) type. When it's just laying there on the bench smiling up at you, to find out of its good, bad or indifferent, all you gotta do is stick it with your VOM. Or your trouble light (and a source of power). Or a continuity checker. No need to screw it in, screw it out and screw it up running back & forth between your car and the dealer, praying to find that one magical six volt sensor that works... when the problem is somewhere else in the system. (Even though you've checked everything else.)*

To an experienced mechanic, this sort of foolishness is funny as hell, an enjoyable break in a life devoted to detail. And a point completely beyond the ken of people who's lives are not.

Logically, the two branches of this decision tree, as indicated by the state of the lamp [ie, on or off] should be addressed systemically. But they are not. Over on page 87 John finally addresses the second branch of the diagnostic tree -- the lamp staying on for no readily apparent reason (such as overheating) and assumes the fault is in the sensor... which is the same error he makes when the lamp fails to light. Taken as a whole, John's diagnostic procedure is more akin to slap-stick comedy than auto repair.

The sticky bit is when the kiddie, who may be fifty years old, insists you sell him a six volt 'sensor' and starts waving his copy of St. Muir in your face as proof of his certainty and your incompetence.

What to do? When it comes to theology there's no easy answers. Automotive engineering, yes. Retailing, for sure. But not religion and that's really what's involved here -- someone who has taken John's word entirely on faith.

A lot of parts-guys 'discover' a six volt switch lurking in the bin... little '6V' written right there on the corner of the box with ball-point pen... and sell it to the idiot for about five times the price of a "12V" switch. But most will simply head them down the road... Have you tried at...? No? Wellll... have a nice day. And go on to the next customer, because for them it's a business, not a religion.

So John made some errors. Let he who hasn't take the mound. And initially at least, it may not have been an error but merely a misconception. There is a later-model pressure switch for another VW vehicle that is identical in appearance... except for having an M10 thread instead of 1/8NPT. (and a completely different part number)

I've had parts-guys try to sell me this other sensor, saying it was 'Just as good' as that other part number... the one they don't carry any more because no one in town drives an air-cooled VW. When that happens just smile and take your business elsewhere. Because, while M10 will fit the START of an eighth-inch pipe thread, it jams after a few turns and will strip out the case. (Don't ask... but you run into the same thing with brake light switches. Pipe thread early, Metric thread late.) So mebbe that happened to John. VW shifted to 12v in 1967. Perhaps John thought the new part number (indicating the difference in thread) signified a difference in the car's voltage. Just a guess. But if you hold both types in your hand you gotta know your onions to be able to spot the NPT from the Metric thread.


Now, were there a lot of errors? Again, we run into the Point of View. To the novice the errors are invisible and the book is therefore perfect. To someone with a little experience, the errors can be an embarrassment and cost them some time but they can usually work around them. But to the experienced mechanic... if he needs a doorstop he knows where to look.

So where do we draw the line? Again, it depends on who does the drawing. For me, I don't like to see folks using 'repair' procedures that end up doing more harm than good so I've pointed out alternatives for some of John's methods, such as not setting fire to your brake shoes... unless we're talking Model T's. Nor hammering on your axle nuts, trying to balance wheels mounted on the front spindles and a few others. Over the years I've also addressed a couple of safety issues that I felt should be mentioned in certain repair procedures.

But a lot of the 'errors' simply reflect the differences between a professional mechanic and an amateur. The fact Volkswagen taught its mechanics to do a valve adjustment in a way that takes only ten minutes or so (and is the same method advocated by every other car maker) does not mean the method John advocates is wrong. The valves still get adjusted. Eventually. In fact, I've actually had people tell me they enjoy spending an hour adjusting their valves, and make it clear they feel I'm denying myself one of the joys in life by spending so little time on that task.

Personally, I continue to recommend John's book to the newbies as the best way to demystify the mechanical arts. The work is technically flawed but philosophically sound. Were it not for John's untimely death I'm sure the hilarious gaffes, backward images, typos and missing parts would have vanished from the book.

But until then, Proceed With Caution, for no matter your level of technical expertise, you are the Mechanic-in-Charge. Not only of your vehicle, but your life.

-Bob Hoover

* - When you've checked all components in a system and found them functional, yet the system does not work, then the fault is in the system itself and not the components. So stop worrying about the lamp and the sensor and get busy checking the connectors, wiring and the socket. There's a lot of wire between the indicator lamp and the temperature sensor. If the lamp works and the sensor is good then bite the bullet -- you've got a bad wire or -- most probably -- a bad connector. Indeed, given that the indicator lamp only draws about 250mA, and is grounded at the engine, ten feet or more of wire away, you could have a wire that tests good conductivity yet has enough internal corrosion to not allow the lamp to glow brightly enough for you to see it. But that isn't the sort of thing that would happen from one day to the next; over a period of storage, yes.

So what's the answer to 'No Green Light!'? Usually, the connector at the sensor or the wire immediately adjacent to it. Next best bet is that funny little connector on the other end of the green wire, the one on the back of the speedo... that got mashed flat by a six pack of beer about five minutes ago when you whipped it up to beat the train across the tracks.

Life's funny that way :-)

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