1976 Cadillac commercial chassis fuel system

I would appreciate some advice on replacing fuel filter on 1976 Cadillac - commercial chassis - appears to be Rochester quadrajet M4ME according to Cadillac shop manual - Superior Regal landau combination. Email direct at gmkubancsek@comcast.net- shop manual shows it at base of carburetor. I have replacement filter. Thank you. Gary K
 
Use two wrenches. Do not try to remove the fuel line from the inlet nut without holding the inlet nut. You will most likely twist the fuel line.

When removing the inlet nut watch for pieces of threads while removing the nut. These threads are really easy to strip out. Tomco used to make a repair kit for these.

When reinstalling turn the fuel filter nut in by hand. If ANY binding, remove and try to determine why. There should be a thin nylon flat washer that fits on the end of the nut that would butt up against the float bowl when tightened. Without this washer fuel will probably seep past the threads but I have seen people install this nut without using a washer and getting no leaks. Probably dumb luck or just tightening the nut in so far it crushed against the bowl.

Don't overtighten the inlet nut either.
 
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I would appreciate some advice on replacing fuel filter on 1976 Cadillac - commercial chassis - appears to be Rochester quadrajet M4ME according to Cadillac shop manual - Superior Regal landau combination. Email direct at gmkubancsek@comcast.net- shop manual shows it at base of carburetor. I have replacement filter. Thank you. Gary K

You might also check the outlet at the fuel pump. If it has a large nut it has a filter here also. I have seen some with the just the filter in the pump and some with the filter in the carb and some in the carb and fuel pump.
 
like they said. standard q jet filter, most likely a paper one. emailing you direct doesn't help any one else who may have the same question.
 
I would suggest that you take the line off the fuel pump first, and leave it in the threaded hole. You must first clamp off the rubber hose that goes from the metal line along the frame to the inlet of the fuel pump. Now would be a good time to also replace this hose, because it is in all probability old and cracking. Then, holding the large nut, with the proper size wrench, and using a tubing wrench on the fuel line where it enters the large carburetor nut, loosen this next. You will now have both ends of the metal fuel line loose, and will be able to move it to the side, to take the large nut out of the carburetor. Once you have the large nut off, you can remove the fuel filter. Usually, there is a spring located at the back side of the fuel filter, and it is important to make sure that you don't loose this, and put it back in with the new fuel filter. The next step is exceedingly important. Before you start turning the nut into the carburetor, place the nut into the threaded hole, and turn it backwards, until you feel it "jump" over the last thread. Then gently turning it to the right, and continue to screw it into the carburetor by hand. If there is the slightest bit of resistance, stop and turn it clockwise, and give it another try. If you ruin the threads of the carburetor, the carburetor will in essence, become instant junk, and a new carburetor will be in your immediate future. I have seen even experienced and seasoned mechanics ruin Quadrajet carburetors by cross threading this nut.
Also, as Dan has said, there might be a filter in the fuel pump, and now would be the time to change that also. From memory, it is a 1 1/4" wrench to loosen it. The filter is a long paper filter, also with a spring behind it. The reason for the springs, is that should the filter get clogged, it will allow gas to flow into the carburetor, so the car will keep running. Usually, by the time that you have a filter bypassing, you will also need a carburetor rebuild.
Now that you have the large nut reinstalled, and gently have tightened it, it is time to reinstall the fuel line. Start by screwing the fuel line into the large nut, but don't tighten it. Go to the fuel line nut that goes into the fuel pump, and install that finger tight. Then give it just enough tightening to secure it. Go back up to the carburetor nut, and while holding the large nut securely with a proper sized wrench, finish tightening the fuel line. Then go back to the fuel line at the fuel pump, and finish tightening it. Reconnect or unclamp the rubber hose, and you are done.

One of our members called me with a leaking fuel problem at the carburetor, and it was a Quadrajet. The shop that worked on the car last, cross threaded the fuel filter nut, and it cost him hundreds of dollars to source the correct remanufactured carburetor for his car.

If you feel that your carburetor needs to be rebuilt, there are a few recommended rebuilders listed in the "Recommended Vendors" forum, or I can give you my recommendation via private message.

Paul
 
Pic

Pic of the carb from my 72 Olds that I rebuilt ,basically the same carb.
 

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I am hording one of the aftermarket over sized self theading replacements for that problem on the q jet. Stumbled on it in one that we had to junk.
 
I am hording one of the aftermarket over sized self theading replacements for that problem on the q jet. Stumbled on it in one that we had to junk.

Keep hoarding it, because they don't solve the problem, but make it worse. Problem is that rarely do they cut new threads that are perfectly parallel to the original, and when you tighten it to the carburetor top housing, it doesn't fit flat against the casting, so it will continue to leak. You can then try Teflon tape, however, that is just a Band-Aid fix, and it will start leaking down the road. The best thing is to not strip out the threads, and follow the instructions for proper removing and replacing the nut.
 
One thing I have used over the years for things like this is Bakery String (you know the kind they tie up your box of donuts with) it fine and you wrap it tight around the fitting screw it in and no leaks on a stripped fitting. Just the junkmans way of making it work. Problem with teflon tape is todays gas it seems to be able to work its way through the tape. Just remember the Government is always making things better for us.
 
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Eat a lot of Dominos Pizza, do ya Dan?? Lol

Not really had a van come in one day , that had a box of these.They changed the # and were tossing these out. I had the plates restored on the wagon and ever year you get a new sticker for renewal. Rather than stack them on or try and peel them off each year I take one of the Dominos magnets put the sticker on it and attache it to the plate ,easy on easy off.:)
 

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