The Joys of Troubleshooting a Vacuum Leak
I can still remember frantically wiping a tattered cloth across my windshield in a driving rainstorm when I first learned that my 1960 Thunderbird’s vacuum tube to the wiper motor had fallen out. I can also still remember what I said about the Ford engineers who had designed that system. Suffice to say, I shall not repeat it here.
The first widespread use of engine vacuum to power or support other systems that I am aware of was the use of vacuum assist brakes. The brake booster was apparently invented in 1903, but didn’t become common in most North American cars until the 1950s. Lincoln and Mercury equipped their cars with vacuum assisted brakes in 1953 and Ford advertised “Swift Sure” power brakes in 1954. From what I can find, it appears Chevrolet pickup trucks had Hydrovac brake boosters as early as 1950 and 1954 was the first year for the Bendix Treadle-Vac power brake unit.
It was in the mid-to-late 1950’s that vacuum assist was added to a multitude of car systems and Ford was especially fond of this technology, employing it into the late 1980s on everything from parking brakes to HVAC units, which brings me to our current topic.
I have been slowly restoring a 1985 Mercury Grand Marquis LS 4-door sedan. Well, restoring is actually a bit of an exaggeration. Let’s just say I am trying to keep it together as an assembly of functioning parts. Overall, I found it in very good condition but with a few weird quirks one might expect from a low mileage, generally neglected 40-year-old car. After replacing the missing door light cover and finding my old cassettes for the factory installed stereo, I felt I had done my duty and could enjoy my “granny car”, as some have dubbed it, without any need for further expense. Of course that was just foolish thinking.
The Grand Marquis is an old friend. I had a 1980 2-door model when my children were newborns (we had twins – thus the need for something larger than a compact) and it was the family cruiser and my daily commuter for many happy years. When I transitioned to a Country Squire station wagon upon our return to British Columbia, I didn’t miss it that much because I had basically switched over to an even bigger version of the same vehicle. But I digress. My newfound friend was snatched off the lot of a nearby shop that was considering pulling out its perfectly fine 351W V-8 engine for a transplant. The rest of the car was in very nice condition and I immediately made an offer to save the majestic sedan from an otherwise ignominious end at the scrapyard. Not for the first time, I suddenly found myself in possession of a not-so-desirable (by conventional standards) older car with older car issues. After dealing with some minor cleanup, making sure the brakes were good, doing an oil change and putting in a battery, I was quite content to hit the road and cruise the Island Highway in comfort. That’s when I noticed the unusual whine coming from the dash whenever I hit a stop light. As soon as I accelerated, the noise would diminish, but it would come back with a flourish every time I slowed the vehicle to a stop. Aha! I knew it had to be a vacuum leak, because I have endured a lifetime of vacuum leaks! (I’ve had a lot of old Fords). But it seemed to be coming from behind the steering wheel. Why would there be a vacuum line behind the gauge cluster? I wasn’t sure I wanted to know the answer to that question. I had attributed the somewhat bumpy idle to the variable venturi carburetor (a story for another day) but could it be due to a serious vacuum leak?
In any event, with the aid of the trusty folks at my local repair shop, we traced it to the parking brake. The parking brake? Yep, turns out Ford could even use vacuum for that. In the “higher end” cars in the Mercury and Lincoln lineups, a vacuum switch was used to automatically release the parking brake when the car is put into gear. I never really thought about how they might have done that before, but now I know. Here is what a vacuum parking brake switch for a 1985 Mercury Grand Marquis looks like. I started to search for one online. Silly me, I assumed all the mid-sized Fords from that era would use the same switch, right? Couldn’t be that hard to find, right? After all, so many of them shared the same bumpers, grills, or even fenders (do we still call them that?) Why not have the same switch? Well, after looking at over 30 different switches from similar cars from similar years I finally found one on eBay. Fortunately, the price was not as outrageous as some of the others I came across, but it was still more than you might expect. While most of the switches I found are similar in design and size, it’s the placement that appears to differ, with the mounting holes for the fasteners appearing in different spots. And, of course, fastening this to the assembly with screws would have been too easy, so it is riveted in place. I have no idea why, but in the arcane world of mid-1980s automotive technology, why not.
To get to the point, finally, as I await the long-distance delivery of this not-so-essential piece of automotive low-tech, we have simply capped off the hose that runs to it to avoid the consequences of a vacuum leak. The little hand lever that will release the parking brake will do just fine for now. To the larger context of why so many systems were powered by vacuum on these older cars, I can only surmise that like so many other things under the hood, this was the cheapest and easiest way they could think of at the time. For those of use committed to keeping these icons of the malaise-era alive, I view it as a double-edged sword. On the one hand, it will keep me ever-watchful and scouring the old lady to ensure that I catch the leaks as they burst, but on the other hand, at least it is technology I can understand and still work on in my own garage.
