My problem is that the brakes feel spongy and I have done all of the usual checks. I have bleed the lines and flushed all of the old fluid out while I was at it. The brakes will pump up and be firm with the motor off but when it's running they feel very soft and spongy. I'm assuming that the master cylinder is leaking pressure internally just wondering if anyone can confirm my suspicion.

 

Maybe. Have you ever adjusted your rear brakes?

 

Forgot to mention that I'm running an 8.8 in the rear so disk brakes. Brakes were firm after the swap it's been about a year and now they are soft. Less than 3k on new pads and rotors on all 4 corners so I know that the pads are good

 

Probably the master cylinder, but what happens if you pump them up and hold the pedal for a bit of time with the engine off?

 

Not sure I'll try when I get home in about a half hour

 

The peddle doesn't move no matter how long I hold it with the motor off

 

I wonder if some nice stainless steel brake lines would crisp up that brake pedal for you.

I'd definitely not rule out cruiser's idea first.

 

I love those braided lines. Serious Off Road has them quite reasonable.

Master cylinder are cheap. Do that and the braided lines all at once and bleed fresh fluid through the whole system. Also be sure to get your booster pushrod to master cylinder clearance set correctly.

 

I'll have to look into setting that clearance. I'll swap to stainless lines after the fourth of July weekend it's just got to last for one last wheeling trip then the tons are going under it.