78 620 Brakes will not bleed.

[HRH]

Replaced both rear wheel cylinders and master cylinder, brakes wouldn't bleed. Took it down to Schwabbies as I was getting irritated, they decided the master cylinder (new one) was bad, so I sent them a refurbished one. Same problem, they couldn't get it to bleed.

 

They tried gravity, pressure bleeding, and pretty much ate their ass trying to fix my truck. Got it back with a very small bill and a weak brake pedal that goes to the floor though does provide a small amount of stopping force.

 

Fast forward to today, installed new brake pads on the front. Didn't disconnect anything. Began by bleeding normally, RR,LR,RF,LF.

 

Nothing, still not much of anything for pedal.

 

Then looked in the old manual I had and bled per procedure of 1976-1979 master cylinder front, master cylinder rear, NLSV front, RF,LF,LR,RR, NLSV rear, NLSV center. (Nissan Load Sensing Valve)

 

Skipped the master cylinder step as it had already been bench bled.

 

Here's my question: Has anyone had this happen? I'm thinking maybe the NLSV is bad and trapping air, and I'm about ready to disconnect the lines and hook them up to couplers to bypass that valve.

 

Basically, I can't get the brakes bled fully, and this isn't rocket science. I've done a lot of brake jobs. It's a 78, disc front, any help would be appreciated.

 

-Matt

[slodat]

As said in another thread in the past couple days, my bet is on your "reman" master cylinder. They are shite. You need a good master cylinder. Several of us have had luck with a USED m/c over a reman.

[HRH]

Yeah, but before that one I got a brand new master cylinder and it did the same thing. Still, it makes more sense, so I may try a different brand of master cylinder. But crap, I've already bought two of them.

[slodat]

Are you sure, and I mean damn sure you are bleeding enough volume? Are you sure the wheel cylinders and calipers are actually moving when you put the pedal down? Do the bleeder valves pass a lot of brake fluid when opened? Or just a little? Brakes are simple systems. Keep looking until you find the problem. Either you have air and aren't bleeding enough or you have something restricting the flow - which is holding in the air....

[HRH]

Sometimes it seems it wants to push a lot of volume, other times not as much. Freakin' weird. I guess it does seem to point to the master cylinder. It has power brakes, which as far as I know will push the cylinder all the way in regardless of if it has vacuum or not. If it was bad, I should just get a hard high pedal, right?

[slodat]

I have seen bad rubber brake hoses cause problems bleeding..

[HRH]

Good thought, sadly they were just replaced with new ones. Think I'm going to try the MC, then bypass the NVLS.

[]2eDeYe]

Yeah they can brake down inside and block the line or they can crack, expand and 'steal' pressure from the system.

 

You didn't mention adjustment after new pads...obvious I know, but...

[HRH]

Well, good news and bad news.

 

Good news is I went up to Schucks and got their reman. master cylinder and it was the EXACT same style as what was originally on there. What's more, it bench bled nicely and I now have brakes. Eureka! I might bleed some more out tomorrow but the pedal is firm enough to almost lock up the brakes from 30 mph to dead stop. And that was with the new pads which seemed to be still breaking in, and were a little better with each progressive stop.

 

So yep, shitty master cylinder.

 

The bad news is I'm an assistant manager at NAPA and if I got one BRAND NEW master cylinder from us that was bad, AND a reman that was bad/incorrect, that means our other potential customers might have the same problem unless I just got a fluke of two bad ones right out of the box. Which is completely possible, but you wouldn't think so.

 

Anyway, thoroughly annoyed at this and will probably be calling our manufacturers to find out what the f*** is going on.

 

On top of it, I had to apologize to Josie for thinking about selling her for a newer pickup. :( Not having brakes was beginning to bother me.

[slodat]

I'm glad you got it sorted.

[datzenmike]

You just can't beat OEM Nissan parts. HRH, rip 'em a new one. It's a brake part for god's sake. They should be 100% defect free. Just where are they 'made' anyway???

[HRH]

I tell the people who come in with returns that the poor 8 year old Chinese kid with a stump for an arm missed quality control that day, but only because he got some acid in his eye. He'll be back on the ball next week. :D

[volksmike]

Had same problem. Took old (original) rusty, cruded-up MC apart. Cleaned the steel and rubber parts. Polished the inside of the bore with Mothers aluminum polish. Put it all together and it worked better than the cardone brand replacement.