Braking issues

[FatalTempest]

Hey guys. First time posting here and hoping I can get some advice as to where to look for my problem. I have an 85 720 z24 and cannot figure out the problem with my brakes. I have installed a new set of front calipers and pads, a new master cylinder and bled the system many times, though I still have no brake pressure. As far as i can tell there are no leaks. 

 

This started while driving a couple years back. Came to a red light and slowed down to about 5-7 mph and then the pedal fell to the floor. I replaced the front calipers, pads and bled a week later and still nothing. It then sat for 2 years and I'm now picking the project back up. Did the master cylinder and was thinking about the booster, but i believe a broken booster makes the pedal harder to press.. thoughts? Am going to do a better inspection of the lines and probably order drums and shoes as well

[Ranman72]

if you didnt pre bleed the master it will make it hard to get all the air out 

defiantly check the lines for leaks if you have a leak it may draw air and never bleed out completely 

also try bleeding with a vacuum draw it may produce better results

the booster if bad shouldn't make it where you have no brakes it will just make the pedal harder usually

Edited September 17, 2022 by Ranman72

[datzenmike]

The original pedal to the floor could simply have been low fluid in the master. Pedal to the floor is lack of hydraulics. it won't be pads/shoes or drums. It could be the master but again most likely low fluid in the reservoirs. A leak would be obvious wetness... somewhere. With the poor quality of replacement parts today simply replacing everything risks putting a defective part in making the original problem even harder to solve. Everything will be suspect.

 

When you bled the hydraulics, did you also bleed the NLSV? Nissan load sensing valve? It's roughly under the passenger side seat bolted to the inside of the frame rail. The bleeding procedure is bleed master (if replaced) then the NLSV, the rear brakes, then the fronts.

 

The booster increases the brake line pressure by about 50% so in effect more braking for less effort. If it fails to work the pedal becomes 'firmer' and effort increases with less braking. To test operation, pump brakes several times to exhaust any vacuum in the servo unit. Step on brake pedal and hold. Start engine. What you should experience is the pedal will drop slightly as manifold vacuum rises. If so, it's considered working.