1955 Ford Part 107: Solving a Frustrating Vacuum Leak on the 292 Ford
Updated: Oct 6, 2021
There is nothing more frustrating than trying to find a vacuum leak...
Welp, here on the blog we show the best and worst of times. This past week included a flurry of activity, sometimes very late at night or very early in the morning, trying to get things resolved before attending the nationally known Pumpkin Run car show held each year at the Clermont County Fairgrounds in Owensville, Ohio. I do not really attend car shows very much but had been encouraged by several friends to go. Obviously, the oil pan leak in the previous post was resolved but just as soon as I had the engine all buttoned up to check for leaks we went from an oil leak to a serious vacuum leak. What timing...
As is my custom on the blog, I have not only provided a written article with pictures but I also did my best to record video of the action. Anytime I do this, the video portion can make the work time go much longer since it is only me in the garage doing the self-filming; but from what I can tell of our website here at over 1,000 hits a month with over 700 unique visitors in September, there is definitely a need. Subscribers and visitors would not rummage through the content here if it was of no help. I do have a YouTube channel but with the way that Google controls much of what is posted, content, etc, because it is free, I choose to host the videos through an account that I have purchased on Vimeo. And of course I pay for the website hosting by Wix to have the website and the domain name HotRodReverend.com.
The 600 cfm Holley 1850 four barrel carburetor has been a great performer!
I initially believed that the vacuum leak was at the base gasket of the Holley carburetor. There was an obvious whistling sound that was different than the sound rushing air makes as it is sucked into the air cleaner. When I put my fingers around the base of the carb the whistle went faint and almost stopped. When I pulled my fingers away from the carburetor the whistle came back. In the video at the end of the post you will find that the first half concerns the carburetor removal, upgrade with a Thompson Performance plate that improves the performance of your accelerator squirter nozzles, and re-installation. The second half - well, let's just see!
One inch phenolic spacer (taken when the ethanol fuel was wreaking havoc)
Removal of the carburetor, assessment of the gaskets and spacer, installation of the plate from Thompson Performance, and re-installation of the carburetor is all pretty standard fare. There is not too much reason to take time to review such simple tasks in writing - but I did put some of the work on video for those that are interested. Base gaskets for carburetors are pretty simplistic. The only thing pertinent to how I go about the gasket situation at the manifold and carburetor would be that I use white lithium grease. Obviously, it is rare to use any kind of sealer for a carburetor gasket, and I would dare say that most manufacturers do not recommend the that you do so. However, if you use lithium grease it certainly makes removal of the carburetor and the gasket itself much easier! For all practical purposes the gasket will just slide off the surface of the metal and leave very little, if any, residue which will need to be removed before re-installation.
White lithium grease is an excellent way to seal ports at the intake and carb!
Back to the task at hand - this vacuum leak. When I installed the carburetor the whistle was gone but I will have to admit there was still another sound of air being sucked into the engine - I thought this was just because the air cleaner was off the carburetor while I was warming up the 292 Ford to make tuning adjustments to the idle mixture screws. The engine climbed to 190 Fahrenheit and leveled off there so I got out a small flat-bladed screwdriver and started turning the screw on the driver's side. No response after a full rotation in or out. I put the screw back to the recommended settings by Holley to begin adjustments and then walked over to the passenger side fender. Immediately I could tell that the sound of air coming into the engine was a bit louder on that side, but I took my screwdriver and started turning the mixture screw out a whole rotation - nothing. By now I was convinced that the day before I had more going on than the whistle at the base of the carburetor. Although there was no more whistle there, this vacuum leak had to be at the intake manifold and on the passenger side. I whipped out a can of carburetor & choke cleaner and affixed the needle to the nozzle so I could more easily direct the spray. On the first spray at the edge of the intake runner for cylinder #1 the idle seemed to steady out and the sound of air movement changed dramatically. Just for kicks I held the nozzle down for a full count of one thousand one, one thousand two, and the engine started to shutter. BINGO!
I like to use the magnetic trays to hold the hardware... don't want this stuff getting away!
This gasket was not torn by removal but was literally sitting just.like.this on the head!
Even the gasket at the intake runner to cylinder 3 had a small tear!
The pictures above show the problem - no wonder this engine had a vacuum leak! The gasket material came off quite easily since I had used the lithium grease back in 2015 when the intake was last secured to the heads, but there was some slight clean up needed in other places. I prepped all of the surfaces for the installation of new gaskets. From my collection in the basement I dug out these gems I had purchased about a year ago on RockAuto.com...
I keep a large stash of gaskets in one of those Sterilite totes made to go under your bed.
The gaskets have the small ported plate to keep exhaust heat down on your intake...
From there the work was just a reverse of the removal. I do believe the intake is easiest to install if you put the gaskets on the studs (remember they are passenger/driver side specific!), slip the 5/8 heater hose on the thermostat housing, and then simply come in at an angle from the rear to the front while you fit the hose onto the by-pass tube at the water pump. Bring the intake to rest on the gaskets and there you go!
For the torquing sequence, do work from the middle intake washers out to the bolts on the ends. Just don't forget to hook everything back up the way that it was when you removed it. I like to use Napa Syl-Glyde on the fittings where the coolant hoses go - they have a tendency to seal much better and be easier to remove (the product limits corrosion as well) along the way. The video below will show a little more than what I have described above, but for the most part this should be a simple process with hand tools. I do like to use a vacuum gauge for a final tune on the carburetor though. One of these days I may get with the 21st century and install an air/fuel gauge just for kicks. I have heard they are extremely accurate.
Resolving a Vacuum Leak in the 292 Ford
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After the work was through, the 1955 Ford Club Sedan received a quick wash right at dusk.
The 1955 Ford Fairlane stood out in the morning sun at the car show. In addition to the intake manifold work, the repair of the leak at the oil pan, and a quick wash just the night before, she was also sporting the beautiful rocker panel trim! (More on that install and coverage of the Pumpkin Run in an upcoming post - would you believe that I did not have to drill any holes for that trim?)
The Hot Rod Reverend
aka Daniel Jessup