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lacombe620

1977 long bed bad brakes

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Picked up a 77 off Craigs list for 450 with out a hood. Had to replace relays,alternator,and a dried out weber to get it going good. Replaced wheel cylinders to get it to stop. Rear brakes kept locking up. Changed out the N.L.S.V. thing, continued to bleed and it continued lock up. Pulled off vacuum assist and master cylinder off my 74" and found the 77's was bad. Separated when it came out. So now it no longer locks up but I cannot get any pedal. Really hate drums but have no funds to update to discs yet. Any ideas out there?

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Have you adjusted them at all? Probably won't help with the lack of pedal but it's worth a shot

 

Also, did you make sure the 74 master cylinder was properly bled?

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Everything adjusted and bled

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Check adjust the pedal free play. Push down on the brake with your thumb. There should be 1/16" of looseness before it begins to push on the master.

 

Loosen off emergency brake. Raise each wheel and turn adjuster in till wheel rubs brake shoe when turned by hand. Pump brake several times to center the shoes within the drum. Check that wheel still turns and add more adjustment if needed, and repeat. Do all 4 wheels and now adjust emergency brakes.

 

If still no pedal it will be in the hydraulics. 

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I've had quite a similar problem as well. 76' with stock 4-way drums. Before Canby I tried to rebleed my entire system and that caused me to have incredibly soft brakes and nearly no pressure. After multiple tries in fixing it, I went ahead and replaced the MC with a 7/8" mc for a Z, and it gave me pressure, but only in the second half of the brake pedal travel. 

 

I raised the entire system, bled it thoroughly in order 

 

Front MC, Rear MC, Front NLSV, Front R, Front L, Rear L, Rear R, Rear NLSV, Center NLSV.

 

Bench Bled MC, and solid fluid when bleeding. Proceeded to Adjust the brakes like Datzenmike states, and I fear that my NLSV still traps air back and forth within itself, or it is bad.

 

After driving the 1200 miles, my braking situation changed from needing a two pump to brake nicely, I had good pressure with one pump, but the front brakes don't feel like theyre grabbing as hard as the rear, and the front brakes squeal and squeak as if there isn't enough pressure in the front. 

 

 

If your situation is similar to mine, my guess is that you have okay brakes, soft in half the pedal, harder in the 2nd half. And if you release and pump again you'll have good pressure hold and braking. My best bet for you is to completely make sure that the NLSV is completely bled, through and through. I think if air is trapped within, or if its bad, it'll act as if your truck is either "loaded in the rear" or on an incline, causing inadequate pressure to the fronts or rear. I've tapped my NLSV with a hammer once to see if that ever did anything, but I never really noticed it. 

 

@datzenmike Do you know if people who owned a 75-77 620 that came equipped with the NLSV and 4-way drums have trouble bleeding the brakes alot? I suspect that the 78-79 with discs in the front have a much easier time in bleeding. 

 

One annoyance with my '76' Datsun Pick up Service Manual by Nissan' is that it does not state the bleeding order of the 620 with the NLSV. IzTWHQs.jpg?1

 

One word of advice in bleeding drum brakes (By my personal experience) Is to make sure that all of your brakes are adjusted correctly before doing a full bleed. If you have one brakes with inadequate grab (as in it's out of adjustment) it can cause weak braking, especially if its the fronts. 

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The first piston in the back of the master is for the front brakes and is the first to begin moving. If the fronts are left adjusted loose or bled last it will travel farther and begin pushing the piston for the rears. You'll get more fluid out the rears this way because of the increased pedal travel. I would do the rears first, then worry about the fronts.

 

The load sensing valve is tilted on an incline and higher to the rear. There is a spring loaded steel ball inside that closes a valve limiting the pressure to the rears. As weight is added to the truck the rear lowers reducing the incline and the weight against the valve. More pressure is allowed to the rear to take advantage of the increased traction from the weight.

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