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Vacuum Pump Corrects Low Vacuum Power Brake Problems

    If your camshaft is more than 280° duration (230° @ .050" lift), your idle vacuum is probably less than 15" hg (mercury). Really big cams bring it down to 5-7". This is not enough to evacuate (re-charge) the power brake vacuum boost cannister. The result is that, at idle or in traffic, you have no power assist - the pedal feels like there's a brick under it, and nothing happens! From cruising conditions (higher vacuum), the cannister retains enough vacuum for 1-2 pedal depressions, then nothing. Embarrassing and dangerous - has this happened to you (yet)? There are two methods of dealing with this.

    Click here Band-Aids for Low Vacuum to see the usual methods of dealing with this problem, none of which really works.

    If you've already tried these, or decided they're not practical, as alternative #1 I suggest an electric (12 volt) vacuum pump. The GM original equipment pump made by AC-Delco (#215-119, shown in the illustration) is discontinued, but a replacement is available: Standard Motor Products part # VCP-103. The cost: $ 140.68.

New alternative: Audi/VW pump, read about it here: Audi vacuum pump

Please: do NOT e-mail me about this pump. I do NOT sell them, I do NOT have a source, I do NOT have any more information. I will NOT respond to e-mails. Do your own search using the part numbers I have provided here.



High-quality product from major American industrial manufacturer

AC Delco Vacuum Pump

DOT-safe, 100,000 mile life expectancy


Proven reliable in the under-hood environment (heat, fumes, vibration, voltage changes)


Safe to install in the passenger compartment - under the dash, or in the glove box (no oil leaks or fumes)


Fully automatic operation when the vehicle is in use


Hot with the ignition key on only (or armed with a master toggle switch - your choice)


Low 3 amp current draw


Senses existing vacuum in the power brake cannister


Evacuates (pumps out) the cannister if the existing vacuum is less than 11" hg


Cannister is always charged for full power-assist, even at idle in traffic, even if the motor stalls!


Automatically stops pumping when vacuum reaches 20" (perfectly safe)


Fairly small (7½" x 4" x 5") & light weight (4½ lbs.)


Simple installation: only 2 hoses & 3 wire connections


Has 3 mounting ears for bracket attachment (bracket not supplied)


Mounting ears are rubber-grommetted for vibration and noise control

Click here to read my installation comments PBA-Kit Instructions

Potential Cures

Install a much smaller (210 - 220°) cam (or one with more lobe separation, or less overlap) [major power loss]


Add .002" - .004" to valve lash to shorten the overlap a bit (up to the maximum of manufacturer's suggested range) [increased valve train wear & noise]


Advance the cam 2 - 4°; same overlap, but the early intake closing will increase cylinder pressure a bit [reduced peak power]


Add 2 - 4° initial spark advance (deducted from the mechanical advance) [more knock sensitive]


Widen the spark plug gap .002" - .004" (may help)


Increase the idle speed slightly


Open the secondary throttle ¼ - ½ turn, and close the primary throttle a bit (may help)


Looser torque converter [expensive, reduces mileage]


Single-plane manifold: reduce the plenum volume (plenum divider, "turtle", stuffing block, etc.), or go to a dual-plane [reduced peak power]


Dual-plane manifold: reduce the divider notch height (separate the left & right sides more completely) [reduced peak power]


Install a vacuum reservoir holding tank

    All of these methods are expensive, time consuming, complex, and not completely effective. The 12 volt pump is the best way to restore your braking power. Click here  to return to the product description.

Vacuum Pump Installation

Pump Orientation:
    The pump should be mounted with the rubber mount bracket on the top (4 screws secure it to the pump body). There are drain holes in the bottom of the pump that remove any moisture that might have collected inside the pump. If the pump is mounted at another angle, it will have a shorter life.

Mounting Bracket:
    No mounting bracket is supplied with this pump. The pump was designed to be secured by a 3-dimensional bracket which bolted to the firewall or inner fender, etc. Since no 2 installations are similar, I can't help you with hints as to bracket shape or size. Try to determine the best place to put the pump before you start making the bracket. Remember that most brackets are strong in tension, but flexible in compression - if mounting the pump from below, the bracket must be stronger than if suspended (hanging) from a top-mounted bracket.

    The rubber grommets (provided in the pump's mounting ears) reduce noise and vibration, and should be used. Use all 3 mounting holes if possible. Do not over-tighten the mounting bolts - the grommets are not effective if fully compressed. To keep the hoses short, the pump is usually placed close to the power brake booster cannister (driver's side fender or firewall). Look for existing bolts, brackets, threaded holes etc. in this area as potential points of attachment.

    The bracket can be made of sheet metal (16 ga. & up preferred), aluminum flat stock, angle iron, wood, masonite, etc. as long as it will stand up to under-hood conditions and will support about 5 lbs. It may be easier to start with 90° corner brackets (common hardware store item) to attach to the pump's grommets; then the fabricated piece that ties them together can be a simpler shape. You could use 3 pairs of corner brackets: arrange #1 to align with a pump grommet, #2 is bolted to it in mirror position to form a "U". Do the other 2 pairs the same way. Now you have 3 tabs parallel to each other and above (or below) the pump body, so a single flat piece of material can tie them all together.

    The final tie-in should be to substantial sheet metal or an existing bracket. Look for a fender brace, wiper motor bolt, etc. and replace it with a longer bolt if necessary. Try to keep bending force to a minimum by making the highest point of attachment to the car centered above the pump body as much as possible, or attach a strap between the top mount and the overhanging grommet.

Hose Connections:
    To connect the pump to the existing vacuum hose, remove the hose from the booster (leave it attached to the intake manifold). Connect the free end of this hose to the pump exhaust (gold-colored metal can on the side, with a hose fitting protruding). In the original installation there's a small (carbon) filter just before the pump (Vacuum Filter #675-5136, retail $10.60, net $7.99 from NAPA, or GM). This is a good idea - if you're going to use this, the hose goes from the manifold to the filter, then to the pump exhaust.

    A new hose goes from the suction side of the pump (black rubber "T" fitting mid-way on the pump body) to the booster. This way the pump is installed between the motor and the brake booster. The pump has a pressure switch so it will not turn on unless the pressure gets below about 5 pounds. Idling around in town the pump often comes on. If the engine stalls (manifold vacuum rises to ambient air pressure), and the key is still on, the pump provides all the vacuum. Some owners install a switch to disable the pump until they need it. A side benefit of the pump is that if your booster has developed a leak, the pump will run continuously to make you aware of a problem before an emergency occurs.

    Some owners "T" the pump into the vacuum hose between the manifold and the booster. Installed this way, the engine sucks through the pump, to the booster. This would require a check valve in the booster hose ahead of the pressure switch to keep the engine from drawing down the pump vacuum if the motor stops. The pump will not be able to draw a vacuum in this configuration if the engine stops because the engine will bring the booster up to ambient air pressure. The only time the pump comes on is when the vacuum is too low and then it helps the engine vacuum.

Electical Connections:
    Try your local auto store (or GM, wrecking yard, etc.) for the electrical plug that goes to the pump. From left to right on the lugs, the first lug (A) is 12 volt (+) constant. The second one from the left (B) is 12 volt (+) from the ignition switch and/or toggle switch. The fourth one (D) is 12 volt (-) negative ground.
  • Connection A (Red wire, in the original harness) to the battery positive (12 volts +), heavy (10 gauge) wire through a fuse.
  • Connection B (Black with white stripe) to the ignition positive (12 volts +), light (18 gauge) wire
  • Connection C (plugged) not used (not used in factory system either)
  • Connection D (Black wire) negative ground (12 volts -), heavy (10 gauge) wire
    The pump is powered via the A connection, but will only run if it receives power from the ignition switch on the B connection. If you wish, a manual over-ride switch (with the key "off" or on "accessory") can be used as a second source of 12 volts to the B connection to power the pump on demand. This may be useful for towing with the motor off, so that you still have power assist. For safety, a relay can be placed in between the fuse and the pump to control power to the A terminal, with the control wire patched into the B connection to the ignition. This will keep power from reaching the pump at all until the ignition is on.
    Other useful parts to assist you with your installation:
    »   10 gauge wire, black
    »   10 gauge wire, red
    »   18 gauge wire, red
    »   Scotch connectors
    »   toggle switch (single pole, single throw OK)
    »   fuse or circuit breaker (10 amp)
    »   10 amp relay for main 12 volt source

Diagram by Jeffrey Diamond

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