Friday, December 7, 2018

Replacing the Fuel Filter on the Rochester Quadrajet

Where is the Fuel Filter Hiding?

In plain sight, that's where.

And even though that may sound like a dumb question once you know the answer, I know I was left scratching my head many years ago when someone told me that it would be a good idea to replace my Corvette's fuel filter on another '76 Vette I owned back in the early 1980s.

Anyway, the fuel filter resides inside the fuel inlet housing right on the carburetor itself.


GM engineers even added the word FILTER along with an arrow showing the location.

But as it's often the case with older vehicles, getting the old filter out without damaging the fuel line, flare nut, or housing, can be a battle all in itself.

And even though my QuadraJet carb was professionally rebuilt a couple of years ago and the line and flare nut are clean and corrosion-free, at some point in the past, someone managed to round off the flare nut enough to make filter removal challenging.

I guess I failed to buy a new fuel line with fresh flare nuts so that will be material for a future project. In the meantime, I had to do what I needed to do in order to get the old filter out.


From the Beginning

First, let me say that these filters are inexpensive enough so there's no good reason not to change them on a regular basis.

Second, my '76 Stingray has—as far as I know—the original fuel tank as well as the original fuel lines, so chances are plenty of tiny trash particles flow from the tank to the carburetor which, one hopes, are being trapped by the little fuel filter before they find their way into the QuadraJet itself.

And third, replacing the fuel filter really is a simple procedure provided you have the right tools and correct replacement filter element at hand. Also, having some penetrating fluid to help remove bits that have "welded" themselves together, may not be a bad idea.


Start with a Cold Engine

The chances of starting a fire pale in comparison with your chances of burning your hands while working on a hot engine. But either way, I prefer to work on a cold engine.


Yes, my engine and engine bay are clean. Almost spotless, some will say, and that makes working on my car that much easier.

And as a side note, one of the best things I ever did—while the L-48 was in the process of being rebuilt—was to have the exhaust manifolds ceramic coated. I really hate rusted exhaust manifolds, but mine look brand new, even after almost two years and thousands of miles.


Let's Do This!


First things first. I start by removing the air cleaner lid.


Then, I disconnect the air-cleaner-to-valve-cover vent tube.


Followed by disconnecting the front air duct hose.


I set the air cleaner assembly on the workbench, out of harm's way, and I get my parts and tools ready.

By the way, even though you can find ACDelco fuel filters, any new aftermarket unit will do the job, but keep reading as there are a few significant details to keep in mind.


Tools of the Trade


You will need a 1-inch open end wrench. In my case (since I don't have one), I use an adjustable wrench which works just fine.

And since we're dealing with a flare nut, a 5/8" flare nut wrench is required... almost in all cases. I'll explain in a bit.

Also, a 5/8" open end wrench can be handy in order to speed up the flare nut removal process once you loosen it with the flare nut wrench.


As they say, parts is parts, but I always favor brand names for whatever reason. But regardless, you have to get the right size filter for your application. In the case of QuadraJet carburetors, there are two size filters available. A short filter (1-inch) and a long one (2-inches). My '76 uses the long filter and I installed one made by FRAM, Part. No. CG3389.

Also, worth mentioning, is the fact that these filters have an open end (shown) and a closed end. How you install them matters, and the right way is to point the open end toward the fuel line. In other words, the fuel must flow into the open end (the one with the hole). Many DIY mechanics have installed these filters backward, and the car won't run. Of course, I've never done that. Ahem!


A Flare Nut Can Make You Nuts!

At some point in my Corvette's life, someone replaced the fuel filter and, most-likely used a regular open end wrench. This resulted in a rounded off flare nut.

Not good!

So, when I tried loosening the flare nut with the 5/8" flare nut wrench, it would not make proper contact. And had I continued, that approach would've done more damage than good. Unfortunately, there's not enough room in that area to beat the flare nut into submission with a big hammer (I'm kidding!), so my solution was to dig in my toolbox for the next best alternative...


Sometimes ya gotta do what ya gotta do —Bubba


I consider myself intelligent enough to know how to use a set of locking pliers to loosen a flare nut without aggravating the whole situation. So I did, and it worked

Once the nut started turning, I used the flare nut wrench, as well as the open end wrench to disconnect the fuel line from the fuel filter housing, which must be held in place by the 1" (or an adjustable) wrench, so you loosen just the flare nut.


The photo above shows the damage a previous mechanic or DIY'er did to the flare nut. Oftentimes, the small investment required to buy the right tool for the job is tiny in comparison to buying new replacement parts.


Once the flare nut was off, I used the adjustable wrench to remove the fuel filter housing.


There is a small spring at the end of the filter. I reached in the housing with a finger to make sure it was there. The job of the spring is to put the proper pressure on the filter so it can do its job, which is to filter the fuel. If you install a new filter without this spring, dirt particles are going to get by it and end up inside the carburetor. So that small spring plays a very important role. Do not leave it out!


This is the closed end of the fuel filter, which rests on the spring shown above. The open end faces the fuel inlet. This is important to remember so the car will run after all the parts have been reinstalled.


And Speaking of Fuel Filters...


The one I purchased at the local AutoZone came with a fuel check valve. This valve keeps fuel in the carburetor when you turn the engine off.

From this point on, you can trace back the steps and install the new filter (pointing in the correct direction, of course), tightening the housing first, then the fuel line.

If the flare on the fuel line is seated properly on the mating surface of the fuel filter housing, your car should be leak-free. But, if you detect a fuel leak, use Permatex 56521 High-Performance Thread Sealant. Better safe than sorry.

Another area prone to fuel leaks is the end of the fuel inlet housing where it mates with the carb. There should be a plastic gasket there. It's a good idea to replace it when installing a new fuel filter. Dorman offers a pack of five gaskets.

I hope this article is of assistance in case you decide to tackle replacing your 1976 Corvette's QuadraJet fuel filter, which—again—I think is something that should be done on a regular basis as part of a classic car's maintenance program.

1 comment:

  1. Great job. This is something I learned back in auto shop class years ago. This is a great reminder of how to do it properly. I like the check valve. Mine is due in the spring and I will use those same filters. Thanks.

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