Double pumping In my 76 620.

[sick620]

On my drum brake 620 I have to double pump to stop. 

 

One push of the pedal slows me down very slowly, but on second push I can brake ok but not the safest. 

 

If I double pump and slam on the brakes at any speed the back tires lock up.

 

Its has been like this for nearly an entire year of driving, symptoms have not changed/gotten any worse.

 

I took the drums off in back today, they looked healthy, lots of pad left, wheel cylinders not leaking by what I could tell. Drum itself looked good.

 

I adjusted them in back they were a decent amount out of adjustment... 

 

Took the driver side off, looked pretty healthy, ok pads, no leaks that I could tell. Tried to adjust but it acted funny spinning the drum it would catch in one spot and spin freely in another... re seated the drum 5 times to make sure It was true to the backing plate.

 

Didnt get to inspect the passenger side didnt get time today. should have time tomorrow. 

 

also it should be noted that I tried replacing my master cylinder a few months ago with a known good used one with no changes...

 

After my rear adjustment and attempt of adjusting driver side front I still have to double pump to stop, tho I can tell I little change in the pedal and it fells slightly more healthy.. 

 

any thoughts? Do you think that front drum could be warped? What usually causes double pump in these old datsuns of ours? 

[izzo]

for me its always been when they are out of adjustment.  You have to pump extra to make the cylinders pop out further to compensate for them being so far out.  in your case, you did adjust them.  I'd bleed the shit out of the system. How's your brake fluid? Clear or dark and nasty?  Do up your passenger side tomorrow and adjust it also.  Then bleed the brakes on all four corners.  I believe its, passenger rear, driver rear, passenger front, driver front. If this has one of those load sensing valves under the bed on the frame bleed that too.

[sick620]

ok ill try this and report back! my fluid is clear as can be and always full...