77 620 no brakes

[dat620_77]

Hello, it's been a long time since I posted here, and the previous advice I received helped me greatly! So I recently got this 77 620 5 speed that was sitting for decades. I replaced the m/c, booster, and all the w/c's. I bench bled the m/c. gravity bled, vacuum bled, slow pump 3x and hold bled the w/c's, and the pedal still goes to the floor with no resistance and very little if any fluid from bleeders. My previous 73 620 would shoot fluid across the shop. 

So I started loosening fittings from the three way block on the firewall. 1st on the m/c in (not the top one) push the pedal and fluid cam out of the line not gushing but there was fluid. Then I loosened the opposite side pushed the pedal and no fluid. The was no fluid when I broke it loose either. So I figured there must be a blockage in that 3way. And in taking it apart I destroyed it so there is no way to test my theory. Then I read on here about a load sensing valve? 

My questions are could I have a faulty m/c, if the 3way is blocked would that cause the pedal to go to the floor, and can I bypass this load sending valve thingy? Oh and where can I get a new 3way, are they universal or is it specific to the vehicle?

Sorry for the novel but I want you to have as much info as I have 

[datzenmike]

If there was a blockage and fluid can't pass then pressure would build and the pedal would not travel to the floor. There would be resistance. 

 

Did you bench bleed the master cylinder????? Find a short length of brake line with a fitting. Disconnect one of the master outlets and fit the small brake line to it. Bend the other end so any fluid is directed back into the reservoir. Give it several pumps to expel all air bubbles. Remove the fitting and hold thumb over the outlet. Have someone slowly depress the brake pedal. If the master is working fluid should easily push your finger out of the way and across the room. Do the other one. 

 

If you get these results try bleeding the brakes again. Be sure to loosen the emergency brake cable and adjust all four sets of brake shoes before bleeding. 

 

The master is bled, next is the NLSV (Nissan load sensing valve) located inside the right frame rail below the passenger seat. There are 3 bleeders. Bleed the front one, now bleed the front brakes, any order. Now bleed the rear wheels starting with the left one. Last is the NLSV rear bleeder and the NLSV center bleeder.

 

If brakes are now properly working, don't forget to adjust the emergency brake.

[bilzbobaggins]

Is the brake pedal adjusted correctly?

[dat620_77]

I did bench bleed the master, I got it from rockauto. it's an a1 cardone reman. I was suspicious about it when I got it ( a few years ago ) I think it didn't bench bleed well or something, I can't remember I'm old. Anyhow now I've destroyed the 2 lines going into the brass distribution block. I had to cut them, they seem to have welded themselves to the distribution block! Is that block specific to Datsun, or will any 3 way block work? Then I'll bleed this fandangled nldv! As far as pedal adjustment I don't remember messing with that. But the pedal will bottom out and barley actuate the w/c's.

[datzenmike]

Any 3 way will do.

 

Make sure you adjust the wheel cylinders.

 

Lightly push down on the pedal with your thumb. There should be 1/16" or a couple of mm pedal travel before there is firm resistance. I doubt this is a problem.

 

 

[dat620_77]

2 hours ago, datzenmike said:

Any 3 way will do.

 

Make sure you adjust the wheel cylinders.

 

Lightly push down on the pedal with your thumb. There should be 1/16" or a couple of mm pedal travel before there is firm resistance. I doubt this is a problem.

 

 

Thank you, you have helped me keep these Datsuns on the road! I don't think my 73 620 had a load sensing valve, is it relatively simple to bypass it?

[datzenmike]

The NLSV was  added in '77. Bleed it and leave it alone. 

 

The NLSV has a slight upward tilt to the front. Inside there is a steel ball that is free to roll forward and block the flow of brake fluid to the rear wheel cylinders. As weight is added to the truck box, it sags lower, increasing the ramp angle and making it harder for the ball to roll up hill and block the valve. This allows bore brake fluid pressure to the rear cylinders increasing the braking. The added weight increases rear wheel traction preventing lock up even with more fluid pressure added. Your truck will stop faster with a load than without the NLSV.. 

[dat620_77]

2 hours ago, datzenmike said:

The NLSV was  added in '77. Bleed it and leave it alone. 

 

The NLSV has a slight upward tilt to the front. Inside there is a steel ball that is free to roll forward and block the flow of brake fluid to the rear wheel cylinders. As weight is added to the truck box, it sags lower, increasing the ramp angle and making it harder for the ball to roll up hill and block the valve. This allows bore brake fluid pressure to the rear cylinders increasing the braking. The added weight increases rear wheel traction preventing lock up even with more fluid pressure added. Your truck will stop faster with a load than without the NLSV.. 

I wish I would've known or asked you two years ago, when I gave up and just let it sit in the shop. Or destroy that 3way block and lines. Speaking of which, is there anything special about the steel lines coming from the master into the 3way, or should my local parts house have them.

[datzenmike]

Dealer is only place the correctly bent brake lines would be... and they are almost certain to be out of stock. Take the old one and measure the length with a piece of string then measure the string length. Take it with you so you can compare the fittings to pre-made lengths of brake line and bend them yourself. Get the same length or just slightly longer. Bend around a baseball bat. 

[dat620_77]

10 minutes ago, datzenmike said:

Dealer is only place the correctly bent brake lines would be... and they are almost certain to be out of stock. Take the old one and measure the length with a piece of string then measure the string length. Take it with you so you can compare the fittings to pre-made lengths of brake line and bend them yourself. Get the same length or just slightly longer. Bend around a baseball bat. 

Cool, I was able to save that 3way. Kinda genius if I do say so myself. My vise grips rounded the hex head of the steel line. Even with heat and WD-40 it wouldn't budge. I drilled a hole through the rounded nub and drove a nail through it. Now my vice grips had something to grip on, and the nub came out!!! Id show a picture but I don't know how.