Troubleshooting Brakes - odd situation

[rogerwilcos]

Since it is the winter in Missouri I decided to work on a couple of things with my 1983 280zx while the car is in the garage. I replaced all the fuel injectors and the fuel injector wiring. I also removed the valve cover and cleaned it up, and replaced the gasket. Finally, I ordered one of those silicone hose kit and replaced a bunch of the vacuum tubes that were old and crumbling. I put a new fuel filter in while I was messing with the fuel system.

I went to test drive it yesterday and it started up just fine and runs well. I backed it out  in to the driveway and the brake pedal dropped down to the floor. I think the brakes work, but just barely. I checked the brake fluid and it wasn't even up to the minimum line so I added some dot 3. I tried starting the car and pumping the brakes and the pedal still wants to sink to the floor. I checked the vac hoses to the master vac unit by the master cylinder and they are on there tight.

What is blowing my mind is that when I pulled the car in the garage back in November, the brakes worked great. I can't find brake fluid anywhere that would indicate there is a leak. Is there anything I could of touched in the above process that could be causing this issue?

I read through my chilton and I don't see anything. Other forums talk about bleeding the brakes, bad master cylinder, etc....but I find it hard to believe it would suddenly just fail. I could be wrong and it could be completely unrelated to what I did - but I am hoping someone reads this and has a solid idea of what I could have changed that caused the issue.  

Thanks!

Edited February 14, 2021 by rogerwilcos

[siteunseen]

Try leaving the cap off and pumping the pedal while running.

It kinda sounds like you may need a new slave cylinder. No big deal changing those out. Good luck with your issue, easy fix hopefully.

[Zed Head]

Is it cold there?  I'll bet the seals in the MC hardened up and shrank in the cold.  There are two seals to create pressure and and a seal at the back to keep the fluid in the MC.  Your pressure seals have failed, I think.  A heat gun might bring them back, who knows.  That would be a sign.

https://forecast.weather.gov/MapClick.php?lat=38.63839000000007&lon=-92.11855999999995#.YCm31WhKiM8

Edited February 14, 2021 by Zed Head

[rogerwilcos]

I just tried pumping the brakes with the cap unscrewed on the master cylinder. It didn't make a difference. When I turned the car off I could hear air bubbling right around the master cylinder area. I also noticed some sludge between it and the master vac. Does this mean anything to anyone?

[Zed Head]

2 hours ago, rogerwilcos said:

I checked the brake fluid and it wasn't even up to the minimum line so I added some dot 3.

I missed this part.  Site was right, but I think he meant master cylinder.  The missing fluid is probably in your brake booster.  Your master cylinder has failed, maybe due to cold or just high miles or both.  Easy fix.

You should take the booster off too, and drain it and clean it out before the brake fluid ruins the diaphragm.  Don't drip the fluid on your paint it will leave a stain.

[dutchzcarguy]

14 hours ago, rogerwilcos said:

so I added some dot 3. I

Why not dot4.0 ?  it's better i always presumed..

And yes zedhead is right, your mastercylinder needs a overhaul..  clean out the mastervac, put after emptying some washing detergent in it and that will soften up the rubbers in it and clean it. Rinse and dry in the sun.. or.. another warm place. 😉

[rogerwilcos]

I guess it's time to tackle this. It has been unusually cold here. Right now we are -5 degrees and it's been around 0 for over a week. I suspect that gurgling sound from the master cylinder that I hear after shutting the car off is air escaping? 

Thanks everyone for the help. 

[Zed Head]

Are there bubbles actually in the reservoirs?  There are other things that can make bubbly noises.  The windshield washer reservoir is there.  Not clear where exactly the noise is coming from.  Might be coming from inside the booster if the booster has brake fluid inside.  Vacuum releasing through a fluid puddle.  That is bad, the booster is supposed to hold vacuum for a while.

 

[dutchzcarguy]

16 hours ago, rogerwilcos said:

gurgling sound from the master cylinder that I hear after shutting the car off is air escaping? 

Not from the MC, it;s from a leaky booster, you prob. hear it at best from inside the car near the brakepedal..

Revise your headcyl. and the brake booster..