Air problem in front brakes

Bought a new to me 91 XJ last month to add to the fleet of them I have.

The pedal was spongy so I bled the fronts. The drivers side was fine but the passengers side let out quite a bit of air. All was well and I had great brakes.

Over the past week the pedal has gotten spongy and the brakes again suck.

There are no visable leaks but when I bled the system the front resivour was low when I first opened it.

No ABS on the rig.

My thought is throw a set of new calipers on it (or at least just the one first to see if it cures it). Acts to me like it is sucking in air at the piston. Anbody else got an idea?

Andy

ususaly when that happens its a bad master cyl

If you're losing fluid, it has to go somewhere. First of all, make sure you have identified which part of the reservoir is going down first. The bigger, deeper section is for fronts and the little one for rears. The part for the front brakes toward the rear of the reservoir. There is a slot in the divider between them so that they will initially equalize. Eventually, one will drop below the other. The lower one is the one with the leak. It's possible that you have a little leak in a caliper piston. Those don't always show if you don't take the pads out. Similarly, a little leak in a rear slave cylinder will often go unnoticed until you look at it with the boots off. Wherever it is, you need to look for it, and fix that first. When master cylinders fail, they usually don't lose fluid, but just go soft, or intermittently drop to the floor. The only place a master cylinder will leak is back into the booster. Usually when that happens, you'll get smoke from the exhaust when you hit the brake.

Matthew:
I don't know for sure it is leaking since I have only owned it two weeks. I know the front is the larger res and it is the one that was low when I checked it.

I have had plenty of rear cylinders with very slight leaks suck in air, but just had never come across it in the front before.

I need to replace a rough unit hub on the same side so I will most likely just throw a caliper on there since I will already have it off and they are cheap.
Glad this rig spent most of its time in colorado and the southwest. So nice not to have to fight all the rust when working on it!

have you examined the front brake soft lines. you could have a very small leak in that. also examine the brake lines and connections when someone is pressing on the brake and look for any leaks.

hth