PC-85-928S

After removing, cleaning, and re-installing my throttle body, in my attempt to solve a vacuum leak & surging idle mystery on my 85 US auto, now my brakes are very firm but have significantly less stopping power. I am stepping hard on them but the car is not stopping immediately. How does the throttle body effect the brake system? I assume it is vacuum pressure.

bradartigue

What you are describing is a brake booster that is not building up any pressure; your foot is therefore applying pressure unassisted to the master cylinder. Check that the line running to it is connected to the plenum (not the throttle body) and that it will hold pressure. If it will not hold pressure at the booster then either the booster diaphragm is bad (unlikely) or the seal around the hose connection has given up the ghost (after 20 or 30 years, quite likely).

PC-85-928S

I know it comes off the throttle body and then goes to that metal tube, then the plastic splitter one going to the intake plenum and the other to that plastic valve in the brake booster. Could I have caused air to get into the system requiring bleeding?
I think my connections are all secure.

GlenL

You have a vacuum leak between the intake manifold and the brake booster. Re-check all connections.

bradartigue

It would not require bleeding of any sort. The configurations Porsche used over the years differ, but testing the booster line is fairly easy. Use only the line between the booster and the plastic venturi and draw air using a mitivac or similar device. It should hold pressure. If so then move on, it isn't the booster or the hose connected immediately to it.

My seal had failed and did the same thing, I think it is a $2.00 part.

PC-85-928S

By seal, is that a rubber part that the brake booster check valve goes into on the booster?
Does that come out easily?
Part # 911 355 921 00 ?

bradartigue

Yep, that's the part. Takes about 30 seconds to change out. Okay, okay, 1 minute.

PC-85-928S

Any special tips or tricks for removing old rubber grommet, and installing the new?