Lost brake pedal pressure after replacing brake parts...

[84seven20]

Hi all,

 

This is my first 720, a 1984 4x4 and my most extensive auto project to date AKA I'm learning a lot but still a newbie.

 

I recently replaced both front axles (CV boots had been torn for a while) and the truck was in good running condition. Started, ran, stopped just fine after this, and the hubs locked properly so I know I did it right! Next, since I live in Portland and have to drive it out of town to get new tags (I don't think it'll pass a smog test, bought the car with the EGR deleted and a Weber 32/36 carb already on it), I figured I go ahead and replace all the brake components preemptively before I hit the highway. Prior to replacing these parts my brakes were working ok, but all of the components looked pretty old and tired. 

 

This was the first brake job that I've done; I replaced the rotors, calipers, pads, and 3 soft brake lines (both banjos for the front and one straight line that heads to the rear I think) in the front as well as both sets of drum brake pads and wheel cylinders in the rear. I adjusted the drum brake tension to where it felt good (just a bit of resistance when turning the rear wheels) and then bled all four brakes going from the passenger rear, driver rear, passenger front, and to driver front. The only component I did not replace was the brake master cylinder. I figured that if it worked fine before then it would probably be fine with the new components. 

 

When I was bleeding the front driver side brakes, I noticed that some brake fluid was leaking from where the banjo line connected with the caliper. I disconnected it but it looked fine, the copper washer between the banjo and caliper was there but didn't seem to be doing it's job. In order to get the connection to stop leaking, added a second copper washer between the banjo and the caliper and that seemed to take care of the issue. This was the only leak I noticed in the whole system, so I bled that brake and thought we were good. When I got in the truck, I noticed that my brake pedal felt loose/not stiff enough. Sure enough, when I tested the brakes (in my driveway), then did not work. I pumped the brake pedal for a minute and the pedal felt a little stiffer, but still not enough to provide any braking power. 

 

The soft brake pedal leads me to believe that the issue lies somewhere in the hydraulic fluid system. In my mind there are two suspects: 1) the brake master cylinder, which was previously working fine but is the only component that I haven't replaced, and whose cylinder seals might have torn as a result of being used with all new brake components, and 2) the two copper washers that I used between the banjo fitting and the caliper might be letting air into the system, though there is no longer any leaking fluid. 

 

Let me know what yall think about this, any suggestions are appreciated!!! Hoping to get this fixed soon so I can go get an alignment and start dailying this thing!

 

[84seven20]

Additional info: No brake fluid has leaked from anywhere since the events I described above.

[datzenmike]

You did not bleed the NLSV. Nissan Load Sensing Valve. It's under the passenger seat on the inside of the frame rail.

 

Bleed it first then the rears then the fronts.

[84seven20]

10 minutes ago, datzenmike said:

You did not bleed the NLSV. Nissan Load Sensing Valve. It's under the passenger seat on the inside of the frame rail.

 

Bleed it first then the rears then the fronts.

 

I absolutely did not do this, just double checked the FSM because I hadn't seen anything about this part and sure enough it says "Bleed air in the following sequence: N.L.S.V -> Rear Wheel -> Front wheel.

 

Thanks again Datzen Mike!!! I'll give this a shot and report back.

[84seven20]

Checking back in with this after spending a while bleeding the brake system! This time, I bled the NLSV, then the rear wheels, and then finally the front wheels. Unfortunately, still no brakes 😞.

 

However, I did notice a few interesting things: when bleeding rear and front driver side brakes I had great pressure; fluid was shooting into my bottle, filling it up quickly and there were no bubbles to be seen. This was pretty much the same for the NLSV after bleeding a lot of air out, though it took quite a while. 

 

The only wheel that gave me trouble was the rear passenger side, which I was unable to bleed all the bubbles from and the brake fluid wasn't moving very quickly (like there wasn't much hydraulic pressure. This was interesting because the wheel cylinder on this wheel was one that I had to frankenstein together with old a new pieces since the new one I got had some machining issues (one of the pistons did not slide in the cylinder correctly).

 

I'm wondering if the reason I was unable to get good pressure/bleed the bubbles from this wheel is because the wheel cylinder that I made with old and new parts has a small leak letting air in. This would explain the bubbles in the fluid even after bleeding it for around 20 minutes. Does this sound like a possibility? I think I'm gonna go ahead an order another new wheel cylinder and give it another shot. 

 

Also, after bleeding the last wheel and feeling decent about the brake pedal pressure, I put my tools up and went to give the brakes a test in my driveway. By the time I got the truck started (maybe a minute or two) my brake pedal felt a lot more soft than when I had just finished bleeding. This seems like it would make sense if pressure was escaping from the system from somewhere, which might support my wheel cylinder theory.

 

As always, thanks in advance for the advice! 

 

[datzenmike]

Put a new cylinder in there.

[thisismatt]

Banjo bolts need a crush washer on both sides of the fitting, so I would double check this everywhere you have that type of connection.

[bottomwatcher]

This is on a slave cylinder but may help you see what is going on when bleeding.