620 pickup, brakes aren't working properly

[datzenmike]

Here I find my self agreeing with Bill.

 

The NLSV is affected by the downward tilt of the frame in response to a heavy load placed in the bed. When the frame lowers in the rear more braking pressure is allowed to the rear tires because of the increase in traction the added affords. Removing the NSLV would apply full rear braking pressure at all times and you will have premature rear wheel lock up when braking .

[datsunaholic]

The brakes cannot be "good" with the engine off and bad with it running.  They'll feel different though.  What happens is they're always spongy, but with no vacuum assist they feel a lot harder, even though they're still just as spongy at the wheels.

 

One thing I found that causes this is using drums that have been turned close to the max tolerance, no matter how much you adjust them the top part of the shoes still has too much travel.  So, you're just feeling the spring tension.  With the engine off that feels like good brake pressure but it isn't.  Once the shoes start to wear in it gets worse.  The solution is new drums.

 

However, this isn't nearly as common of an issue as having the brakes not bled properly, or having the shoes on backwards.  The shoes on backwards will usually cause it to "brake" better in reverse than forward, or cause very touchy, easy to lock brakes.

[Eagle_Adam]

Here I find my self agreeing with Bill.

 

The NLSV is affected by the downward tilt of the frame in response to a heavy load placed in the bed. When the frame lowers in the rear more braking pressure is allowed to the rear tires because of the increase in traction the added affords. Removing the NSLV would apply full rear braking pressure at all times and you will have premature rear wheel lock up when braking .

 

my truck feels no different after removing the NLSV.....

[Z-train]

my truck feels no different after removing the NLSV.....

"Feel" is a moot point.You just haven't found the "right" stopping circumstances yet.Your truck is just waiting to "swap ends" on you with a hard application and the right conditions.

[Z-train]

Here I find my self agreeing with Bill.

Does it hurt that bad?

[Eagle_Adam]

what are the "right" circumstances?

 

 

based on my experiences from my 74 620 that came without a NLSV stock id say they are the same. 

[Z-train]

Wet road.Road with a crown.You get cut off at freeway speeds.Any reduced traction environment. Datsun didn't put them on the trucks just for shits & giggles.This is almost the same theory as when you put discs on the front of a car that was originally 4 wheel drum.You HAVE to install a proportioning valve or the drums will lock under light pedal pressure.

[Eagle_Adam]

well, guess ill be testing your theories some more 

 

Wet road

cut off at freeway speeds

reduced traction environment(if gravel/mud counts)

 

cus all of those have already happened and ive had no issues yet. 

[datzenmike]

Lowered and grippier tires can compensate for this. The 620 came with 6.00 X 14 nylon tries. Pretty sad.

[Eagle_Adam]

so my 8in wide titans might have saved my ass........

 

 

 

 

prob wont be the last time  :rofl:

[Kulper620]

So if I have little to no braking while in reverse and all brakes have been adjusted and bled properly at least as far as I know what would you say about that, and with still having the same issues I've been talking about, also any of you that "know Datsun brakes" gonna be at the meet in Monroe Saturday, I'd love for one of you to take it for a test drive and see in person what it actually is doing because I know it's better to feel than just have someone tell you

[datzenmike]

To test power brake operation....

 

Pump brake several times to vent any stored vacuum.

Press down on brake pedal in a normal manner and hole.

Start engine.

 

If working properly the pedal should drop toward the floor slightly.

... I haven't done the test you have posted yet, I will be trying that when I get home after work

So is this checked yet??? If not working you will have firm pedal and very little brake. Costs nothing, no tools needed and takes about 10 seconds.

 

 

 

 

Pedal play? Lightly push the pedal down with your thumb. There should be about 1/16" of free play before you feel the push rod begin to bear against the master cylinder piston.

 

When the truck is off the break pedal is quite firm and after I adjusted the rod in the booster out a little bit there is only about an inch of free play before the pedal becomes firm.

 

Free play is about 1/16" not an inch. Just push pedal pad lightly with your thumb. There should be a slight jiggle of play.

[Kulper620]

After I adjusted the rod in the power booster I know only have very little play, when I did the test with my foot on the brake with the truck off and then started it it drops, not to the floor but there is no firm feeling to it until it gets to the point where it is solid, but my braking happens in the area that has no pressure and is very jerky when it brakes but yet I I have my foot planted on the brakes it still won't stop me completely for about 50 feet at about thirty five mph

[datzenmike]

Under ideal conditions 35mph to 0 takes over 70 feet...http://www.csgnetwork.com/stopdistcalc.html

[KlassicMotion]

I'm still having a similar issue (I haven't addressed it yet).  Let me put the issue in my words and see if it is the same as to what your feeling when you hit your pedal:

 

I hit my pedal, there is a lot of travel, during that travel, the brakes jerk a couple times (like they are trying to grab), and after a good amount of pedal travel, the pedal gets firm, but the brakes still don't grip like they should....

 

Does that sound similar to your issue?  If so, then yes something is still wrong.....

[Kulper620]

Yes that sounds pretty much what's happening. And I was just estimating the distance I don't know how far I actually traveled

[KlassicMotion]

Hopefully you've fixed your issue by now. I just got around to fixing mine:

 

All I did was replace the master cylinder and checked to make sure the pedal was adjusted as per the FSM specs, which it's close, but it has a little slop. The adjuster nut is at the end of its travel, so I just left it alone. That doesnt seem to be an issue though, because my problem was solved with the new master cylinder.

 

What's your outcome?