"When you say 4 pot" slang for four piston caliper

 

The D1 has 4 pot front calipers stock. The D90 fronts are 4 pot as well but they are 46mm diameter vs 41mm. The real improvement of the D90 calipers is that the pads are bigger. The vented aspect of the rotors really doesn't do much. These things aren't race cars. If you're going down steep grades you should be downshifting, not constantly braking.

My '96 brakes just fine, however, on all stock brakes and the absolute dirt cheapest pads I could find. Unless you have a ton of extra weight on your truck, the problem you're experiencing is due to a failure of some part of your braking system.

 

Got you, yeah definitely no race car, and I suppose when off roading I may ride my brakes too much I just wish they wouldn't go to complete nothing

and there is air coming out so i'm not completely crazy.

Don't want to start an opinion war but...what are the best brake pads to deal with brake fade? I don't care about dust, life expectancy or noise really, just the best performer.

 

Call MrBlaine and see if he can help with pad selection.

Black Magic Brakes

Seriously. He knows his ****. It looks like its only Jeep stuff but it isn't.

 

old fashion semi metallic pads always seemed to work

 

I wouldn't worry about fancy pads until you get your problem sorted. And when you do get your problem sorted you won't need fancy pads. Good ole semi-metallic.
Step 1: Go to RockAuto.com
Step 2: Input your make/model/year(use 1998 Discovery to make sure you don't get D2 pads by accident)
Step 3: Buy the cheapest pads they have, usually less than $10/set.

Pads are cheap and easy to replace.

 

The only thing I can think of that would allow air in but not fluid out (at least not out to a noticeable degree) is maybe a failure in the caliper piston seals. Application of the brakes causes them to expand to the point of sealing the system, but on release they are allowing air to be sucked in to the system.
But if that were the case, I would expect the fluid level to rise some until the air made it to the MC reservoir.
This is pure theory of course.

 

if a piston seal was gone, when you applied the brakes I think the thousands of psi would push brake fluid out, long before it could suck air in

 

My brake system slowly leaks fluid, and I have no air in it and a good pedal.

I try not to think about it.

 

Likely.
I was theorizing a seal failure where the pressure differential could cause a leak in one direction and not the other. If the fluid pressure is pressing the seal tightly against the piston and the bore.

I can't think of any other condition that would let air in and not leak fluid, assuming all of the air is really out of the system to start with.