After 8 months of watching the oil pressure gauge on my 1974 Pontiac Trans AM Super Duty 455 sit on the peg without moving (even with the ignition off) I decided to dive into the issue yesterday. I've always liked having an oil pressure gauge versus an idiot light because it can give you advance notice to avoid serious internal damage, even though catastrophic oil pressure drops are quite rare.
Over the last few weeks I'd checked with the local NAPA to confirm they had (or at least could quickly acquire) an oil pressure sending unit for a '74 Pontiac 455. I'd researched where the oil pressure sending unit was located (still learning my way around a GM engine compartment after 25 years of working on mostly Mopars) and I was ready to start working early in the day so I'd have plenty of time to deal with the inevitable, unexpected problems that crop up on these types of seemingly simple repairs.
Of course all my advance prep work was a complete waste of time.
After opening the hood and angling my head around the passenger side of the engine compartment I managed to spot the oil filter. According to the various sources I asked, the oil pressure sending unit was supposed to be right next to it.
And there it was. I could see a domed piece of metal about the size of small lightbulb. And on the end of the dome was a metal tab that...wasn't plugged into anything. Near the sending unit I could also see a wire, but I couldn't see where the wire ended. It almost looked like it was plugged into something else near the oil pump, but I couldn't actually see the plug.
I took another look from underneath the Firebird, just behind the passenger-side front wheel. Yup, there's the wire, ending in a dangling plug (it was originally hanging near the engine block but I moved it over for this photo). After some body contortions in that cramped space I had the wire plugged back in without even jacking up the car. Of course the problem could run deeper than an unplugged sending unit. Maybe the gauge failed and somebody was monkeying with the wire to diagnose the problem before I purchased the car?
Nope. Start the car and the gauge works great. And in perfect irony, where does the gauge sit now that it's working? Just below peg, which is where these cars' oil pressure gauge should sit, at least when cold. I actually turned the engine off but left the ignition on just to watch the gauge sink through it's entire range of travel. I'll probably never know why the wire came off, though I slightly rerouted it to ensure additional slack between the sending unit and the wiring harness. Maybe the engine moved around enough to yank the plug.
Total repair time: 20 minutes (including shooting photos for this post). Total cost: $0
But what I really learned, or re-affirmed, from this experience is why original, unaltered classic cars are almost always more desirable than modified -- or even restored -- versions. When I've dealt with problems on modified cars the diagnostic and repair process is always more complex. You still start with the simplest causes and work your way to the more advanced possibilities, but it seems like there usually is some weird/annoying/difficult issue when you finally figure out the problem.
So far on this Trans Am I've dealt with several mechanical issues, and every one of them was caused by essentially the easiest/simplest problem possible.
Problem: Inconsistent brake pedal Solution: Bleed the brakes.
Problem: Power windows not working Solution: WD-40 the switches (clean the dirty contacts)
Problem: Heater-A/C Fan not working Solution: Replace fan fuse
Even when the car's engine wasn't running right, which kept me from driving it across the country after I bought it, the primary cause was the ignition points. And it wasn't even bad ignition points, just points that needed adjusting. The carb also needed some adjustments and the EGR valve was messing with things a bit, but neither would have kept the car from making the drive. Unforntunately, I didn't know how to diagnose and adjust points back then.
You always want it to be an Occam's Razor situation when something doesn't work on an old car. And if you've got an original, unmodified version it usually is. It's yet another reason original cars are worth more than either modified or restored versions.
powell_jr says:
03:54 AM, 01/18/11
Great post. I'd like to see more of these.
throwback says:
05:36 AM, 01/18/11
I would love to see a performance test of this car with modern tires. I remember my buddie's T/A (not a SD) being a pretty good handler, for the '70s anyway.
adamb1 says:
05:56 AM, 01/18/11
Would like to see a picture of the entire car.
elvinjijo says:
06:03 AM, 01/18/11
Nice post Thanks for sharing. www.onlinetruckbuy.com
ed124c says:
07:26 AM, 01/18/11
This post should give those readers, who have been hesitant to purchase an "older" vehicle, a bit more courage.
Thanks, Karl.
My fixing up of cars ended after my experience with my '67 Sunbeam Alpine. I disassembled the engine 'til I got the head off, and brought it in to a shop that ground the valve seats and installed new valve stems. Then I put it back together. It worked fine until, on a trip to Montreal, one of the valve seats blew out. We didn't drive it in Montreal (friends driving in another car), but we drove it back to Rochester. It averaged about 36 MPG for the trip, My wife (for some reason) found a used cylinder head and I brought it into the same shop (after disassembling the engine again) and spiffed up the "new" head, reinstalled the valve stems, and charged my nothing-- as well they should have. Then, of course, I put it back together and drove it until, well... that's another story for another time, children.
felonious says:
08:35 AM, 01/18/11
I had a 65 Mustang as a daily driver for eight years. She was beautiful, but treated me like dirt. I finally dumped her and never looked back.
Classic cars are okay, but not as daily drivers. The ease of maintenance is more than offset by the frequency that it is required. Now that I'm a husband and father, I'm also concerned with the lack of safety features as well. Do you guys remember seeing that crash test comparison between the old car and the new car a while back?
ed124c says:
08:47 AM, 01/18/11
@felonious: Good points. But, for a lot of buyers of old and classic cars, the fun is in the putting- it- back- together work. They might not drive it much at all. Just looking at it, and showing it off to friends, is sometimes enough to justify the work.
juggernaut929 says:
09:06 AM, 01/18/11
Nice Write up,
Gotta love the easy fixes, its where it (sometimes) saves you a lot of money than to going to a shop, at least compared to major problems. My buddy and I both had the same problem once, fan blower only worked on high setting. He took his Stratus in and had it repaired for a mere $150. A google search, a trip to the junk yard, and -$10, got me a new fan resister board, 15min later, works great.
@Karl, I remember the write up before, you'd said the car was stalling and lurching? and the oil gauge broke the same time, maybe it was from that? That's a sweet ride you got there, Any chance you might give the Trans America journey another try? Need a co-pilot?
@Felonious, I completely agree. Another reason not to drive a nice classic in bad weather. Better for when you want to drive for fun and not for the need to get anywhere. And, that article has been good ammo for me anytime anyone says "they don't make them like they used to", or "They were built like tanks back then", *cough* more like a empty beer can.
7driver says:
10:42 AM, 01/18/11
Although it works well in a pinch, there are better products out there than WD-40 for cleaning electrical contacts.
roadburner says:
12:35 PM, 01/18/11
"Classic cars are okay, but not as daily drivers. "
I love driving my 1975 2002 on a daily basis. A capacitive discharge ignition box cuts down on fiddling with the points and valve adjustment is an annual chore that takes all of an hour. Other than that it doesn't need any more maintenance than my modern cars.
roadburner says:
12:38 PM, 01/18/11
"Although it works well in a pinch, there are better products out there than WD-40 for cleaning electrical contacts."
True. I use DeoxIT.