Funky brake issue need help!

[Soulprogression108]

So my 94 22re t4r is acting up in the brake department. It did this once then stopped then we had heavy rain and huge puddles and it has been bad ever since.

Problem is the pedal can feel fine/ firm but then depressing it and holding it can go to the floor. I actually almost rolled i to a cop the other morning and thankfully had the emergency brake to save me!

I replaced the brake booster because that went out this year causing very hard to press brakes. After that maybe 6months I did a full overhaul on the front brakes. Full new calipers, pads, rotors, and soft lines. Bled and refilled with new fluid.

I’ve read that it could be the master cylinder because I can’t find any leaks anywhere and the fluid level looks good.

 

[Soulprogression108]

Ok I'm 90% sure I've got it figured out. I believe it's the master cylinder failing. I bled the brakes this morning and flushed out some nasty looking fluid, dark brown! The brakes are maybe a tiny bit better but still the pedal goes to floor especially when holding it at a light. Also the idle drops really low. This confused me for a bit because I know that the booster can affect the idle, but since that is new, and since these are power brakes I think it's just drawing down current and pulling on the idle. I did check the valve inline from the manifold to the booster and it's working properly. Also the hose is fine too.

Since I literally just did the brakes and booster a couple months ago I can only imagine it's the master cylinder failing. I remember reading that when you do the booster you should change the master, but since it seemed to be working fine I left it alone. Since there's no leaks appearing anywhere in the system including around the master cylinder I've deduced after reading around the internet that it's probably leaking internally. i.e. fluid is moving past inner seal and just moving back and forth inside the cylinder instead of out to the calipers.

Gonna pick one up as well as some new brake fluid and hopefully get the rig safe again.

I thought it was a water related thing, but maybe that just pushed it over the edge? I'm not sure, but hoping this is the trick...

 

[Soulprogression108]

Yup brake master cylinder. Swapped it out and bled and thing brakes on a dime. Wow like a new truck. I somehow got lucky as it was going out in stages. Thought it was gone a month ago then started working fine. Went on a wheeling trip and 2/3 up a steep climb got stuck. So thankful the brakes held then because rolling backwards would have been a disaster. My buddy pulled me the rest of the way up. I reckon if I had dropped tps from stock down 15 or so coulda made it. That or just if this model had a freaking rear locker. I dunno how they could badge it 4x4 with no rear locker and an e in the front….

Anyway thankful the bmc when out close to home. Man with all these parts this truck is driving more and more like a new truck every month hahaha. 222,450 tho! Let’s go 300k