Why Won’t My New Parts Fit My Old Car?

We’ve all had that one friend that could go into any clothing store and pull something off the rack, and it fit them perfectly – almost as if it was custom-tailored specifically for them. The rest of us, we look like we just pulled something off the rack but it doesn’t fit very well at all – it looked better on the mannequin. That’s not a far stretch from what we find out when we install a part onto our vehicles – sometimes the part we buy for our own car or truck seems like it was made for another vehicle altogether. Welcome to the world of “hot rodding.”

The real problem with parts not fitting often has little to do with the part and more to do with the vehicle itself. Back in the era of the classic muscle car, we didn’t have the robotic precision that today’s vehicles have. It’s an old joke to not buy a car built on a Monday or a Friday afternoon for fear of having someone a little moody building the car, or someone who partook in a liquid lunch build it. Body panels weren’t always perfect, and then there were the engine options: small blocks, big blocks, inline 6 cylinder engines – and the varying displacements – all made parts fit better on one car, not so well on another.

When someone buys a custom part that is listed for their car and it doesn’t fit perfectly, the initial reaction is that the part was not made properly. But that’s not exactly the case because the part likely will fit with a little modification. Smitty Smith, Technical Sales Coordinator at Edelbrock told us, “We all know the real reason some parts do not fit is because the manufacturers do not want to have more than one item per application. Like the Tri-5 Chevy’s, sure some parts will fit the ’55 and ’56 , but not the ’57 Chevy. So you have to modify what you are installing to fit, in this case, for the ’57.”

There’s also the off chance that the car was involved in an accident at some time and not repaired back to specs. “When a part doesn’t bolt-on directly, the customer tends to think something is wrong with the purchased item,” Smitty continued, “when they truly do not know about what they are installing, nor do they know the history of the vehicle.” Core supports and front ends on classic vehicles can be notorious for fitment and alignment problems of parts like radiators or grilles. One bad frame pull and the vehicle is not square, and modifications might be required.

This steering box was a tight fit, and required a small amount of grinding on the housing to clear a brace on the K-member. Two other K-members didn’t require any grinding at all while using this same steering box. Blame that on the build, not the part.

Another example is when I installed a Borgeson steering box into my car. The part is made to fit 1962-1982 Mopar vehicles, but when we installed in on my car we had to do a little grinding on the housing. Again, some vehicle owners immediately blame it on the part, not the vehicle. When we mounted that steering box to three other K-members, we realized that it was the way they built the K-members that was the problem, not the part. The steering box fit all four K-members differently. One required even more grinding, two required none at all.

Borgeson Universal’s Sales Manager, Jeff Grantmeyer, explained it a little more. “Product development takes many aspects into play. Ease of manufacture, ease of distribution, and overall ease of installation for the end user,” he said. “Take, for instance, our power steering box for the 1962-1982 Mopar cars. We developed a product to fit all of the Mopar body styles throughout this year range.”

For that year span, the steering boxes were virtually identical, while the K-members were different, depending on whether you had a big block, small block, or a slant 6 – or a Hemi. To get each car into the shop and build a specific box for all of them would have driven the price up much higher to cover development costs. What this really narrows down to is a limitation of part numbers, or SKUs. If a part will fit one particular model perfectly, and nine others with a slight modification, there’s no need to have 10 different part numbers.

Jeff continued, “There are about 10 different variations of K-members used on these cars. For us to develop a product for each specific vehicle and K-member combination would have created shopping/distribution nightmares. Instead we took the widest range of variation and developed a product that would fit all with nothing but some very minor modifications. Perfection in this case would have created more problems in the sale and distribution of the product line resulting in a product that would have been priced out of the market.”

It’s a tight fit, and this time no pounding and reshaping metal was needed. But this header was made specifically for this application.

What we can learn from this is that by expanding application coverage for a part it helps to keep production costs down, which is then passed onto the consumer. This is one reason why engine gasket sets include gaskets you might not even need: it’s easier to have one kit with a few extra gaskets for other applications than to have several kits that each fit a specific application. If you have a popular muscle car with a popular engine but things aren’t going together as easily as planned, it’s always good to step back, gather your thoughts, and regroup. It simply might need some modification to either part or vehicle in order to fit. Anyone who has installed a set of headers on a big block knows that often times it was necessary to use a little ball-peen persuasion to get the headers to fit.

We run into a similar thing here at Champion Cooling Systems from time to time, and sometimes the radiator we sell might not line up perfectly with the holes in the core support. We promise you won’t need to use the same kind of persuasion used on those headers, but as we said, it’s not the end of the world. Simply drill new holes and mount the radiator accordingly. This is the world of hot rodding and if it was too easy it would take a lot of the fun out of it.

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