Restore Project almost done, Got an issue with BRAKE PEDAL PRESSURE! (Help)

[mini_aaron]

Hi all,


I am working for a motorsport/car restoring company in Korea,
our team have been working on 91' NSX restore project since June 2014.
The job is almost done, but got a weird brake pressure issue from her first testdrive after the restoration.


Since it is "Restoration" job, we've replaced/serviced brake lines, calipers, hoses, and even completely cleaned ABS solenoid(they were full of gunk)
To clear up the air bubbles in hard-to-reach-ABS system, she've gone through brake flushing with more than 6 liters of fluid.


The picture shows how dirty ABS solenoid was...
(The car was having intermittent ABS engaging issue before)
ABS engaging issue has been solved after the cleaning job, but...

After all that, now the car got this symtom with Brake pedal(pressure)


*When pressed with enough force, braking system works, pressure is being delivered well, car stops ok.
*When pressed very softly, brake pedal just falls down with ease, no pressure to the floor, with weird(buzzing? leaking?)sound from Engine bay.

We know it wasn't like this before we started...

Could this be brake master cylinder related? (Are they going bad from long-term storage situation?)
Or... any idea? experienced?


Any comments will be appreciated.


Help us to give her a new life!



Added: For now,, the amount of brake fluid in the reservoir is staying at the same level.. looks like there is no leak in the system..(looks like...)
But will double check with carpet... for any leak.

 

[B2FiNiTY]

Yup. You might as well change the master cylinder come you're doing a "restoration". It could have blown due to the way you bled the brakes.

 

[warrenw]

*When pressed with enough force, braking system works, pressure is being delivered well, car stops ok.
*When pressed very softly, brake pedal just falls down with ease, no pressure to the floor, with weird(buzzing? leaking?)sound from Engine bay.

This is a classic master cylinder issue. When bleeding the brakes, did you use the brake pedal? If you did, and the pedal went to the floor during bleeding, your master cylinder just tore the piston rubber. The NSX is famous for it. Replace the master cylinder. Bleed the brakes with a MityVac to avoid this problem: http://www.mityvac.com/

 

[Jinks]

+1, all my brakes were bled via a hand pump.

 

[Larry Bastanza]

What is mileage on the car?
What bleed method did you use?

You mention about a buzzing sound in engine bay. The hose that feeds the power brake booster is located by the coolant tank. (actually there is a clamp on the coolant tank to hold it). I am not suggesting this is the problem, but since you hear something it is worth the look. I would probably agree the master needs replacing.

Regards,
LarryB

 

[mr envy]

I know it might sound silly but if the peddle is over adjusted at the linkage then not all the air can leave the m/c keeping it spongy

 

[mini_aaron]

for the record, problem solved with new master cylinder.
Car performs beautifully, just need a oem spare tire to finish the entire project up!
Pictures are to come!