Vacuum source for Brake Booster
 

Hey guys. Have a S4 T2. Just swapped out to a S5 upper intake manifold. On the S4 mani there were 4 ports on the back, the biggest whicj went to the brake booster. On the S5 there are only 2 ports, 1 small and the other just a tad bigger (not as big as the port on the S4). I used the bigger port for the booster, but just took the car for a drive and the pedal is hard and the car barely wants to stop. Is there somewhere else I should use for the vacuum source? And does the hose material that I am using matter? (Using 3/8" heater hose). Thanks.

-Sheldon.

The largest port on the back of the intake manifold is the one you need to use for the brake booster. By any chance did you discard the original stock hose without saving the plastic 1-way check valve that was inside it for reuse in the new hose? You'll need that for proper brake booster operation. On the S5T2, that check valve is located inside the stock hose on the brake booster end, probably the same location on the S4.

Yeah, the check valve is still there.

Were the brakes working fine before the booster hose was changed? If so, another possibility is that the check valve was reinstalled backwards, which would prevent the booster from holding a vacuum.

I believe the largest fitting of the fittings inline on the back side (facing the firewall) of the upper intake manifold is for the oil injectors?
If so, this fitting is sourced BEFORE the throttle body, which means it will NEVER see vacuum.
This explains why your brakes are not working properly.

The brake booster needs to source vacuum AFTER the throttle body.
I believe this fitting to be at least 10mm?


-Ted

I just checked my Zenki FC turbo...
The brake booster fitting is on the surge tank of the upper intake manifold.
It's offset towards the passenger side of the car facing the firewall.
This is for US-spec engines.
It's basically the lowest fitting back there.

For J-spec upper intake manifolds, there's a short banjo to pipe fitting that comes off the lower intake manifold right over the turbo.
This is to compensate for the RHD design which locates the brake booster on the opposite side of the firewall.


-Ted

Damn, I wonder if I ended up getting a JDM manifold. I'll take some pics and post later. Thanks guys.

Sorry for the late pics. I am using the nipple at the top of the intake manifold for the vacuum source. The nipple where the little formed hose comes off and goes to the IC. So far everything is good.