Brake pressure issue

[73 smurf 620]

So i have replaced the booster, master cylinder, rebuilt all the wheel cylinders, bled all the way around, bench bled the master, and shoes all the way around. The problem is I have no pressure when the truck is running, the pedal goes to the floor. When it is off, an when the vacuum line on the booster is removed is removed there is tons of pressure but the brakes still don't work. Any advice or suggestions.

[I'm BLUE]

*booster check valve replacement

 

*master cylinder to booster rod adjustment ( what did you set it at? )

 

*all shoes adjusted correctly 100% and double checked?

 

* leaky line/bad rubber line?

 

( hope wheel cylinders were honed )

 

*** lastly ... sometimes re manufactured products come "bad" ... if all else fails ... after double checks keep this in mind.

 

Could you clarify last sentence please?

[73 smurf 620]

When the truck is not running, it has a lot of pedal pressure. As well as when the vacuum line is pulled off of the booster and plugged, there is a lot of pedal pressure. But if the truck is running, and the vacuum line is on, it has no pedal pressure.

[datzenmike]

Adjust the shoes closer to the drums. Raise each wheel and spin tire by hand while tightening the start wheel. When you can't turn the wheel pump the brake to center the shoes in the drum and check and adjust some more if needed. It's considered adjusted when you can feel resistance to turning by hand. Move to the next wheels.

 

Did you bleed the NLSV? It's on the inside of the frame under the pass side seat.

[73 smurf 620]

NLSV? No I did no, never saw it. I will try that today.

[datzenmike]

Nissan Load Sensing Valve. I think there are 3 bleeder valves there.

 

Bleed in this order...

 

MC front

MC rear

NLSV front

front wheels

rear wheels (left first)

NLSV rear

NLSV center

[metalmonkey47]

Mike, were all 620 equipped with the NLSV?

[73 smurf 620]

Well, everything bled fine. But still no stop, I'm convinced it need new wheel cylinders.

[datzenmike]

Mike, were all 620 equipped with the NLSV?

 

I always assumed so but looks like '76 and on had them.

[Viico04]

Im also having the same issue with my truck. Any one got a picture on the nlsv?

 

[metalmonkey47]

Mike it appears the '76 wasn't equipped. I checked every inch of brake line and didn't find anything other then brake line unions. Nothing with a single bleed screw.

[datzenmike]

It may have just been the earliest one. There were long and short beds and KC.... maybe only on the KC?

[620Soldier]

Great thread. My brakes are a bit on the soft side myself, but I'm pretty sure I just to get those new shoes on there.

 

Lots of good things to know in this thread, thanks a bunch.