I just finished the install of the 300zx calipers, cobra 13" rotors and SS lines on the front only.

The brake pedal seems to need more travel to get it to stop. When the car is idle or off, the brake pedal is rock solid and the travel is normal distance like stock as it supposed to be but when driving around, the pedal sinks halfway down until it finally gets hard and the car stops great at that point. I want to know what the problem is with the pedal sinking? Theres no leaks and we bled the car several times and there seems to be no more air bubbles in the system.

did u do a good job bleeding the brakes? sometimes it takes like 3-4 times to get all the air out

We did it about 3 times manually following the sequence and there was no visible air bubbles.

And the squishy sinking pedal only happens when braking when the car is moving. It feels perfectly firm and all that when the car is at idle at a stop

Ok, I think I might know what happened. When I disconnected the left front brake line to replace it with the SS line, the resovoir all drained out empty. Will that cause my problem eventhough I properly bleed the brakes several times and didnt show any more bubbles?

how much did the whole thing cost u, if i may ask?

I bought it all the parts in a 2 year span so a rough estimate would be probably $600-700

Sounds like you still have air in the system. Id bleed it some more. Did you go from the rear to the front, starting from right rear, left front, left rear, right front?

if he did fronts only he should only have to bleed the fronts...there are check valves that separate F & R lines....but it wouldnt hurt to blee the rears to make sure....any way try to bleed them more and always make sure that the master cylinder has plenty of fluid if u run low u could just be putting more air into the system

We did all 4 corners in the correct order. I think I just need to keep bleeding them. But if there is air, why does the pedal feel normal when the car is at a stop but gets softer when im braking while moving?

its a whole pressure thing....when ur stopped the pressure can build back up but when ur slowing down ur using all that pressure....trry bleeding them some more...it can take a while depending on how much air actually got in

You might want to bleed the master cylinder if you ran it dry. 1/2 down is WAY too much. I have just a smiggen more travel ie..1/4" maybe?

kwik sort of off topic question i can never remeber if u need put the master cylinder cap on befroe bleeding.....or as long as its full past the check valve can leave it off??

It drained well over 1/2 down so I guess your right. I have much more travel than 1/4" more like a couple inches

any pics? does your brake pad sit flush against the rotor? i mean that are you using all of your pad?

The pads are flush on the rotors and are breaking in against the rotors evenly. Sorry no pics yet. Ive done a Z/cobra install before and it came out good but I think its when I accidentally let the resovoir drain out is the problem and I just didnt bleed it enough

my wilwood kit does the same thing. when im moving the top softens up. When i stop its still soft, but when i pump the brake peddle once it becomes hard again.

How do I go about bleeding the master cyl? Is there a bleeder valve on the MC itself?