First brake pump is soft, second is normal

[s13q]

So I've had this issue for a while, but I never thought of seeking a fix for it cause I knew I was going to upgrade my brakes anyways.

On the first pump the brake pedal is spongy then on the 2nd it's responsive and stiff like it should be.

Its an it's an odd issue, as it changes with the revs/speed of the car.

If I'm stationary at idle it'll be soft no matter how many times I pump it, at 40kph/60kph itll be soft then hard then soft again as if its gaining then loosing pressure. At 100kph I'll pump the brakes repeatedly and it'll be soft the first time then hard every other time until it comes to a slower speed where it goes soft again.

I just upgraded to R33 GTR Brembo brakes all round with a new BMC and I still have the same issue. Me and my friend bled the system 5 times in his workshop and nothing changed.

Im thinking it may be a boost leak somewhere or the booster itself is faulty.

Car is a 97 180sx Type X

[Cash]

Sounds like break booster issues to me. I had a booster go out on me. The brake pedal was inconsistent, and eventually locked up the brakes fully, and pedal was rock hard.

Also check vacuum line to the brake booster.

[brndck]

+1 for brake booster. It may be an issue with the 1-way check valve (its typically in the fat vacuum line from the inlet manifold to the booster)

[Sleepy_Steve]

+1 for booster.

If it only happened once, check your pads. That's what it felt like one time when a brake pad ejected itself from the caliper on me.

[EnemyS15]

Had this exact problem in my s14. Brake booster all the way!

[Matej]

Just skip the first pump and go straight to the second.

[s13q]

Ill be doing a vacuum test tomorrow which should show if I have any leaks and/or the brake booster is at fault.

I will report back with the results! fingers crossed I find the issue.