78 Jimmy has spongy breaks

[chevy4x4power]

Quick backstory ya'll. Paid 475 bucks for my jimmy from a guy who let it sit for 5-6 years.

Got it running and took it for a quick spin and it stops but barely. Brake pedal goes all the way to the floor.

What do i need to do to fix this?

New master cylinder, bleed the brakes?

 

[diesel4me]

Any GM that sits that long is likely to need some brake lines or wheel cylinders,calipers,master cyl,etc...if your in a dry climate the lines might have survived,but chances are good some fluid escaped from the wheel cylinders and air got in the system...bleeding out the air might be all it needs,but you'll be lucky to get the bleeder screws to open without snapping them off...

The good thing about the old square bodies is brake parts are cheap--I got a new master cyl for my 82 GMC at Autozone for 13.99,the rear wheel cylinders were 10 bucks each,and calipers were about 15 bucks with the core exchange..hoses will run about 20 each for the front ones...rotors are about 35 bucks and up...its best to just plan on ditching all the old hydraulic parts unless some were replaced recently,to avoid further hassles when you get it on the road..I'd look the lines over very closely,chances are at least one or two of them is rusted enough to pop if they haven't already..

 

[Fordum]

Definitely check the brake tubing. Once you get the air out, you will be applying more pressure to 36 year old steel brake lines.
If they are rusty, one may blow at a bad time.

If you need to replace one, don't cheap out. Go ahead and replace them all since its fairly easy.
This place, http://www.inlinetube.com/ or others like it have complete replacement tubing sets already formed, bent, and with the correct fittings to make it easy.

Plus, you can go stock coated steel, or stainless.