Don’t let your diagnostic blind spots bite you in the rear


When it comes to cars (and life too, I suppose), things aren’t always as they seem. Two weeks ago, in a story about “Points vs. Pertronix,” I mentioned installing a brand-new condenser that turned out to be bad. The slightly longer story is this: I’d just had the distributor in my 1972 BMW 2002tii rebuilt. I outfitted it with a new cap, rotor, points, and condenser purchased at the dealership—e.g., presumably high-quality parts in BMW boxes with BMW part numbers. I test-drove the car, and after about five miles, it began to run horribly. I barely made it home.

This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2019/02/04/avoid-diagnostic-blind-spots


Great article, I had a similar situation with brake rotors. I had recently installed front rotors and pads on a BMW X5 and a little more than 10k miles later I was getting severe steering shudder when braking from high speeds. I assumed the brakes had to be fine since they were relatively new and focused on worn suspension components. Sure enough though, after inspecting all suspension components and finding no issues, one of the relatively new rotors turned out to be warped (and just out of warranty) so another new brake service it was!


Great article. This is along the line of K I S S, which I subscribe to.


Good article - wished I had friends like yours to rush over and help out.


I’ve had the same blind spot in the past… nice to have company! Could be the clutch parts you installed two years ago had been on the BMW shelf for over ten years… I had a one year old Tilton clutch master fail on my race car with fluid going past the seal, allowing for ever so slow engagement with the pedal still on the floor.


With my 71 VW Super Beetle, I also have had to the problem of a new, out of the box condenser being bad. While condenders do wear out, I found it best to not change it out when replacing the points and keep a known working one in the glove box.


A lesson I learned a long time ago about life in general and particularly true with condensers is, “if it ain’t broke don’t fix it.” I learned a long time ago from a mechanic I was working under when I was serving a 3yr apprenticeship that you are more likely to have problems by replacing the condenser when doing a tune-up that you are by leaving it alone. Unless somehow damaged a good one just does not go bad.


Having sold auto parts for 32 years, I heard stories like this quite often, especially on older vehicles where the customer purchased repair parts that might have been sitting for a long time. Brake wheel cylinders, masters, really any hydraulic component, will end up with dried out seals and leak within days, hours or minutes of installation. And conversely, I have had situations of brand new modern electrical components simply dead on install. Stuff happens. Goes back to Rule #1: DIAGNOSIS!! Anyone who has ever picked up a wrench has been burned by not doing just that. Sucks when it happens as you just shelled out dough to obtain “known good” product and wham! you get bit.


I learned the condenser trick in my first car, a '67 T-Bird with a 428. With the first tune up I replaced the condenser along with the points, since they came as a kit. Ten miles later, I found myself limping home. Luckily I had already learned to stop with one foot on the brake and the other on the gas to keep it running. After checking everything else, I dug through the trash to find the old condenser. Problem solved, and it stayed int he car for the next several years. Each time I replaced the points I’d toss the new one in the spare parts box.
Also, NOS is good for hard parts, but not soft parts. Anything with rubber I’ll only use new, and I don’t stock up on parts with rubber, that may not be used for a decade. They are bound to fail. You wouldn’t drive on the interstate or racetrack with tires over ten years old. The same goes for those other soft parts that stand in the way of you and death. Cars that are 100% authentic down to the wiper blades belong in a museum. If you want to drive it, keep it maintained with fresher parts.


About 50 years ago, an old mechanic told me never swap out a working condenser but always carry a spare in the glovebox.


I learned that there was a subtle but distinct difference between “known good” and “thought good” when it comes to used parts.



I had new distributor cap that, being foreign manufactured now, proved to be out of round on the inside. This resulted in the rotor grounding out where it shouldn’t. Car ran, but no end of problems at higher RPM. Took me weeks and unnecessary dollars to diagnose, all because I had already changed the cap and points, so of course no problem there. Dummy.


Good article…good points (no pun intended). In my 49 years of working on cars, I’ve had the occasional bad part right out of the box. But, more often, a failure after a few days or weeks, especially w/ electical components. So I often begin troubleshooting with the most recently replaced part of a system, based on symtoms of course.