Re: V8 vacuum routing diagram?
Posted by HH56 On 2016/8/2 16:36:12
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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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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(80.25 KB)
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