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V8 vacuum routing diagram?
#1
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Dave Brownell
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I have gone through both my 1955 and 56 factory service manuals to no avail. Is there a diagram or schematic for the vacuum lines? I was able to find the picture of the windshield washer in the Accessories section, but I need a picture or diagram of the Easamatic system, including the in fender reservoir. My 56 has a leak and the new TredleVac booster is getting no vacuum. Is the Rochester big rear port where brake vacuum originates?

Posted on: 2016/8/2 15:54
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Re: V8 vacuum routing diagram?
#2
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HH56
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There is no brake vacuum factory diagram that I am aware of other than this one published in a 52 service counselor instructing dealers on how to field install units.

Aside from an external breather on early units the rest of the plumbing is virtually identical. The external breather was changed to one built into the unit in 53. Other than one extra hose on early units which I erased from this diagram, 55-6 layout is as shown. The vacuum source on V8s is thru a check valve coming off the base of the carb instead of the intake manifold.

From the checkvalve it goes across the firewall to a tee fitting above the brake unit. A hose off one port of the tee drops down to the unit fitting and the other port goes on to the reservoir. I believe the V8 placement is somewhat lower on the firewall than this diagram.

There have been reports of the check valve sticking so one suggestion would be to check vacuum right at the hose connection at end of checkvalve. Another known issue is a hose inside the unit coming loose. The hose is not clamped so age and gravity can let it come loose at the fitting denoted by arrow. To check for that possibility you might be able to hear a hissing sound if your ear is near the pedal. The only thing left would be a hole in reservoir or a crack where the fitting is soldered onto the reservoir.

If you have old or cracked supply hose you can get heavy walled 11/32 power brake vacuum hose in 3 foot lengths at most parts stores. The V8 route coming off the carb is slightly shorter than this 52 drawing so it will require two lengths to change all of the hose. If the hose inside the unit has fallen off the fitting it is a special formed hose so nothing for easy replacement is available. You can use a small clamp or maybe even a tie wrap on the hose but be sure to orient the clamp so there is no interference with the piston.

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Posted on: 2016/8/2 16:36
Howard
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Re: V8 vacuum routing diagram?
#3
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Dave Brownell
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Many thanks for your prompt and clarifying response. The vac line routing and hose dimensions are most appreciated.

I recently rebuilt the Rochester carb using a specially ordered NAPA/Echlin kit. This was a multi-application kit for mid-Fifties cars that used this GM carb, including Cadillacs and Buicks, as well as senior Packards. Now some self-doubt is creeping in; did I use the proper lower and base gaskets to insure a proper vacuum path? I think I did, but when I get back to the car, that check valve port will be the first place I use my finger to check for both suck and sound. Luckily, the unused rebuild gaskets should still be boxed together and stored in the trunk of that car.

Dave

Posted on: 2016/8/3 7:42
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