510 rear drums locking up.

[Marsh510]

For some reason, I'll drive my car around for 10 minutes or so, than my rear brakes lock up and I'm stuck on the road. Have my dime on jackstands trying to figure out the problem, everything is working properly, In their correct place. Could it possibly be the brake adjuster?

[paradime]

Pull the drum and check to see if they have rusted up inside. That would do it for sure. Also check to see if the return spring is still attached.

[banzai510(hainz)]

Does it feel as you apply the brakes its going thru a ck valve where it just keep tighening up?

My 521 did this and is was the master clyinder.

I would have to pull over hit the bleed screw and drive enought to get home. then a few days later it would do it again.

A 521 has only a 1 resvior master so it happen to all the brakes at once.

Ck the length on the master at the pedal. to make sure the master is fully relasing.

 

a 510 is a 2 resvoir so maybe it the same proplem.but with the rear resvoir. if it even works that way.

 

But 1st pull the drum to make sure you just not filling it up with brake fuild and its getting sticky.

 

if a wagoon then ck the rear axle seal for leaks.

[Marsh510]

I have the drums off, they aren't rusted up, the return spring is still attached. It isn't getting filled up with brake fluid or sticky. This is a 2 door btw to clarify if it matters. I believe your right banzai. When i start to brake, the pedal does get very hard.

[ggzilla]

Adjust the pedal rod. The spec is in the repair manual.

[Marsh510]

Which repair manual? Any links? I do not have one unfortunately.

[ggzilla]

Any repair manual for the 510 including chiltons, clymer, haynes, nissan, etc.

[javier302]

mine was doing something similar, on a 521 tho, and after I backed the brake light switch to let the pedal release farther went away... still likes to pull to the right but at least 1 problem taken care of.

[Sealik]

Which repair manual? Any links? I do not have one unfortunately.

 

http://www.nicoclub.com/

[datzenmike]

1/ As long as there is some free play a few mm or 1/16". Push down on the brake pedal with your thumb gently. There should be a tiny amount of movement before the pedal begins to push on the brake master and becomes firmer. If there isn't any clearance you can loosen the lock nut, remove the cotter pin and screw the clevis in on the push rod to get your clearance. For god's sake put the pin and cotter pin back in or you will have no brakes. 

 

If there is no clearance the piston inside the master can't return fully and pressure can't be released back into the reservoir.

 

 

2/ There is one other possible cause and that is that one of the flex line hoses has de-laminated inside and is acting like a one way valve.

[Marsh510]

1/ As long as there is some free play a few mm or 1/16". Push down on the brake pedal with your thumb gently. There should be a tiny amount of movement before the pedal begins to push on the brake master and becomes firmer. If there isn't any clearance you can loosen the lock nut, remove the cotter pin and screw the clevis in on the push rod to get your clearance. For god's sake put the pin and cotter pin back in or you will have no brakes. 

 

If there is no clearance the piston inside the master can't return fully and pressure can't be released back into the reservoir.

 

 

2/ There is one other possible cause and that is that one of the flex line hoses has de-laminated inside and is acting like a one way valve.

I believe the 2nd problem is what i am dealing with currently. Could you explain a little more please? Thank you.

[datzenmike]

The flex line is basically a rubber hose. The inner liner can deteriorate and peel forming a flap that closes when fluid reverses direction to return to the master reservoir. I've only heard of this happening but it's a possibility that shouldn't be ignored when all other causes have been eliminated. 

 

When it has locked it's assumed that some pressure is trapped in the lines. Loosening the fitting at the master will release a spurt of fluid if it's the master causing it. Loosening the wheel cylinder side of any flex line should releases pressure if it's that flex line. I would assume there is one flex line at or near each rear wheel. 

[ggzilla]

Flex lines doing that are very rare. Basically we've heard of it but never seen it.

 

Push rod not adjusted happens to someone here every month. Very common after rebuilding or replacing the master cylinder.

[datzenmike]

Agreed, just mentioning it.

 

As suggested, check brake pedal free play. If good, next time the rears are locked loosen the front fitting on the master (front is for the rear brakes) and see if fluid spurts out. If it does and the pedal play is good then I would suspect the master.