Anyone know about class A brakes?

On my P32 chassis. There was a little slide door under ther drivers side floor.
Had to pull carpet back than open to check brake fluid.
Still was a PITA.

Check the master cyl. there was a period where they had a lot of problems with master cyl. leaking. Easiest way to check is if you have level system raise the front a few inches and turn the steering wheel all the way to the right. This will give you enough room to get in and check the brake fluid also a small mirror helps. There was also a problem with the rubber fluid lines to the front Calipers that would deteriorate internally and block the fluid. Lastly you want to completely change all brake fluid and should be done at least every 5 years!

Try to locate the VIN number. It should be on the dash. There could be a sheet hanging in a closet or cabinet with it on it. Should be on the registration and title.
Most Chev work off the powering steering pump to operate the brakes. It is a Hydro boost system.
There is normally two belts that operate the power steering pump.
Without the hydro boost the brakes will feel like there isn't any.
Next, flush the brake fluid completely out.
Look to see if you have drums or discs on both the front and rear.

I had the same problem on a Chevy Class A. It was a 1986 I bought in 2001. The dealer I bought it from had just replaced the master cylinder at the Chevrolet dealer. It was fixed with no further problems. The fleet mechanic where I worked told me it was probably due to the hydraulic system NOT bled properly. The system must be POWER BLED. RJsfishin is correct. The P 30 chassis has the master cylinder under the floor on the drivers side. I checked the master cylinder fluid level using a mirror and sitting on the ground by the left front wheel.

My '84 Taska P-30,...the MC was under the floor drivers side .Don't know about no chain. Seems like the PB and PS was all one unit on the fire wall. I remember those units gave trouble. Maybe the system has air, just needs bleeding out.
Disc brakes on rear ?? I doubt it

The brakes are probably not responding to pushing pedal due to calipers are stuck due to the caliper pistons being rusted and can't move. They will get stuck out and more stuck in as you push pedal. This is quite common on these units due to them not being driven enough. You probably need a complete brake job around $800. That's because when the calipers hold pads out they stick and drag on the rotors and cause burn spots that can't be milled out. The tag axle, if it has one, is drum brakes that may be fine, just have them checked for wear and lube. The system is set up so the tag brakes work first then the rest which are ABS and disc brakes. If the rear disc brake rotors need replacement they probably are attached to the axle shaft as one unit each side of the transaxle. If they can be turned and resurfaced, it's best as they are pricy to replace. They have to be turned on the vehicle by a special turning unit. Note : This information is based on my 1997 P32 older models may be different.

I believe that would be a P-32 Chassis. The brake fluid reservoir is in the frame rail on the drivers side, just behind the front wheel.
You might want to try the Workhorse and Chevrolet chassis forum at irv2.com

Never seen a brake system operated with a chain, are you sure that chain isn't the pull down for the cruise control? Could the master cylinder be underneath the floor? I've seen that on some older trucks.