What is this...

[wantone]

On my rear alxe - Looks like a second valve for the rear end

I have a 71 cuda with a bunch of pirated parts from a roadrunner I believe.
Car has Power Brakes - disc front and rear drum
This is on the rear axle ...

I think I have proportioning valve issues potentially and noticed that I needed to rebuild both rear drums ... in yanking the wheels, i found this guy.  Goodness knows if it's adjusted or what it even is if it is an adjuster.

[HP_Cuda]

That is the junction for the rear brakes.

Notice you have one hard line coming down the drivers side, then into a soft line into said junction box. Then over to both wheels.

If you are looking for a proportioning valve that would be in the engine bay near the master cylinder - if you have one(PV).

[acudadude]

Also axle vent bolt?

[HP_Cuda]

Yes the junction slides over the vent.

[wantone]

IS this something that requires maintenance?   The car is still very new to me so I wonder if I need to do anything when addressing the brake bleeding or rebuilding of drums etc...

PS -  Is the rear-end self-venting through that valve?

[TelisSE440]

Yes the valve works both as a vent to the rear axle and as holding for the brake line tee on the rear axle housing. Maybe sometimes you'll see that the area around it after a cruise will be a shade wet from the extra warm gear oil. About maintenance, when I took it off I just blew air in it to remove some sludge like material blocking it. Nothing more, no problems until now.

[azievinger]

I had to replace mine's. Lost power to the rear drum brake, and this was the issue causing to lose power. front continued to work though.

[wantone]

Cool... i'll rebuild my rear brakes and then see if they work.

PS - I have no idea how to tell if my proportioning valve works.  We'll have to see there too I suppose.   I'm not sure if I want to go with an adjustable one vs standard parts replacement.