Last update: May 16 2015

Power Brake Vacuum System


Vacuum for the power brakes is supplied by a Hella UP30 electric vacuum pump, part number 8TG 009.286-001 purchased from Summit Racing.

Hella UP30

Many auto manufacturers use Hella electric vacuum pumps in gasoline cars. They are found in the Subaru Tribeca and 2015 Impreza WRX.

Subaru Hella Vacuum Pump

The UP28 augments the vacuum from an internal combustion engine and is not powerful enough to work alone. The larger UP30 works without any vacuum from an engine.

Hella UP28 vs. UP30

The connector on the UP30 sold by Summit Racing mates with the Yazaki 7283-5575-10. The connector terminals and seals for 18-16 AWG wire are 7114-4151-02 and 7158-3113-40, respectively. This connector is difficult to obtain. The parts can be purchased from Nexus Electronics LLC, however they have a $50 minimum order.


The original brake vacuum hose connects the pump to the master cylinder. The hose is first cut in the center to insert a tee fitting that goes to the vacuum switch. This cut also allows changing the angle of the hose. Then the ends are cut off to fit. The hose already contains a check valve to keep air out of the master cylinder when no vacuum is applied. You can see the valve where there is a slight bulge.

Hose Hose Hose Hose

Vacuum Switch

The service manual specification for the brake booster vacuum is 500mmHg / 19.7inHg (10psi). An adjustable vacuum switch turns the pump on and off to keep the vacuum level near the spec. The switch is a DesignFlex World Magnetics PSF109S 81-330 (20623) purchased from MCM Electronics. The switch is mounted to a small bracket with a hole for the port, and held in place by the hose clamped onto the port.

Vacuum switch


The pump is mounted in the space vacated by the secondary air pump, between the brake master cylinder and the fuse box.

Pump installed Pump installed