Could be more than several things.
#1. Have you checked the master cylinders for fluid..?? Located under the dash, should be a hand hole on top of the dash cowling. You'll have to check what they used in your particular machine, by serial number. At one point, they went from using DOT3 brake fluid, to hydraulic fluid. Master cylinders may need replaced too. These are now $370.00 ea. through Case Construction. I bought all aftermarket parts through a supplier here in Ohio, for a LOT less. I'll post a link to their page below.
#2. Brake line from master cylinder, to wheel cylinder maybe rusted through. They have some pretty funky bends in them. 10 years ago, OEM lines from Case Construction were $75 ea. At that time, I found it was less expensive to buy a kit from Eastwood, to make the double flare fittings.https://www.eastwood.com/professional-brake-tubing-flaring-tool.html I also bought a 25' roll of NiCopp brake line from Advance Auto.
Advance Auto Parts - Down for Maintenance You'll have to check the size to make sure, but thinking it is 3/16". As luck would have it, at the time I did this repair, it was shortly after Christmas, and everything was marked down to like 35% off, so I bought an extra roll, and one of 1/4". It only took like 10' of line to make both, but I've made several other brake lines for trucks around here, so it's handy item to have around. They also at that time, carried fitting in bulk bags of like 25 on sale, so got several different styles of each. The NiCopp line bends to form very easy, and very resistant to corrosion. I did this 10 years ago, and other than the natural patina, the lines look great.
#3. Short flex brake line, just before the brake cylinder. From memory, this line is around 10" - 12" long. It's a short rubber line, that transitions from the steel line, to a rubber flex line. Mine had blown out, and the other looked like it was on its last leg, so replaced both.
HOSE | #D66741 | H-ASSBLY, OTHER | Hose & Tube Assemblies | Hydraulics | Category | Case CE | MyCNHi US Store This line through Case Construction is now $47.50. At that time, it was 10%less through Case/IH AG., but is not the case now. In fact, it's a couple dollars more. If the need replaced, you maybe able to get them through a local auto parts store.
#4. The brake cylinders were bad on mine, so replaced both. These to were purchased through the aftermarket supplier. 99%sure they were made in China, but seem to be quality parts. It's been 10 years, and everything still functions as it should.
Luckily, the bull pinion shaft seals weren't leaking, like they were on the old 310B I had, and had to replace. Pretty easy to tell if they are leaking, you'll see drops of oil hanging on the bottom side of the brake chamber assembly.
My 480C (same brake system) has a ROPS on it, and not a cab. I found it a lot easier to remove the fender, and floor board on the right side to get to everything a lot easier, than doing it laying on my back. The left side was accessible by just removing the floor board, and center floorboard.
If you don't have an OEM service manual for it, I'd suggest getting one. I got a NOS one on ebay for around $75 at that time, and is worth every penny. They are 4"+ thick, and very descriptive on repairs, and have a lot of actual pictures of a procedure, not a generic drawing.
I got all of my parts through Joseph Industries here in Streetsboro, OH.
Remanufactured Transmissions, Torque Converters, Engines - Joseph Industries I have no idea if the same phone salespeople are still there, but at that time, were very knowledgeable. The key to ordering parts, is to have your part numbers in hand. Being they were within 150 miles of me, if I ordered before 10:00 am, they were here the next afternoon, before 2:00 pm.
If you don't have a parts manual for your machine, you can look your parts up online at Case Construction. Here is a link to the site, and this particular section is for your brakes.
Brakes | Case CE | MyCNHi US Store
For all other parts for the machine, here is a complete parts listing. Just select the function group, then drill down through the menu.
Case construction king loader backhoe | Case CE | MyCNHi US Store Any time you're looking for parts, use this parts manual, and get the OEM part number. Check the price through Case Construction, then use that part number to do a search on line. You can do a search, through a search engine ( I've found Google gets the best results) and most definitely run that part number through ebay. I've found a lot of new old stock parts through there. There are also several vendors who've bought up NOS parts from other OEM dealers. If it's listed on any of their sites, via the internet, using the OEM part number, you'll get a hit. You can just shop, until you drop...
Hope this helps..!!