C30 brakes not working on cold start

computski

C30 T5, 2009. I find that the brakes are ineffective after a cold start. You have to stand on the pedal and they barely overcome the engine idling in drive. After about a minute they work properly, full sensitivity and full effectiveness.

Thoughts? Vacuum leak?

ramrod

If there was a vacuum leak inside the booster, the pedal would lose feel, firm up and braking effectiveness would disappear. It only takes a tiny crack to cause a vacuum leak.

Now, heat can affect things that leak. Usually heat will open a crack larger as things expand, and shrink once cool. However, you are having the opposite experience.

Is the engine sounding and running the same at the times the brakes are working and not working?

timbo

The C30/P1 cars run a brake vacuum pump, to supplement engine vacuum for brake booster.

The pump setup is pretty reliable, but the hoses are plastic and brittle and the pressure sensor can fail.

The pump is located just in front of the battery.

If you turn the ignition on, you should normally hear the pump run until the booster fills up. If it's not running investigate the plastic piping.

nh2868

Because the engine is turbocharged, when the turbo is operating there is no vacuum in the manifold - just pressure. The electric vacuum pump should produce vacuum for a cold start, but doesn't seem to be doing that. When you start the car and idle, the engine should produce vacuum like a N/A car. Because they come good after starting, I suspect that the pipework is "good enough" but the vacuum pump may have faulty wiring or a blown fuse - or be full of water or something.

GreenGL

What happens if after going for a drive, and parking (but leaving the engine running), you were to hit the brake pedal multiple times?

If the pedal firms up, could be an issue with the electric vaccuum booster.

From a cold start, and driving a bit this probably gives enough time for the main booster to build vaccuum.

Can you hear the vac pump running at all? (I have no idea if they are audible on a C30, I had one fitted to a previous project car and it was fairly loud when in operation)