Busted Brake Master Cylinder?

Having some erratic braking problems. I took apart and cleaned my caliper pistons. Reinstalled and bled the brakes with a vacuum bleeder. I thought I bled everything properly but still having an at times spongy pedal. Sometimes very stiff, other times a lot more play. So I went to engage the ABS, haven’t bled it since then but now my pedal is really soft. Brakes are barely there. I know I should probably bleed the lines again, I plan to. But don’t have the time right now. Just to check, I opened up each brake fluid line at the master cylinder and the one closer to the front of the vehicle (opened in the picture) isn’t draining any fluid. Got a drip or two but nothing after that. Anyone know if that is a red flag or no?

 

What caused you to take apart your calipers in the first place?

I would follow the FSM, but did you bleed the master manually with partial presses of the brake pedal following a process like in this video (connecting a nipple to the master with a tube back into the reservoir and then actuating the piston to prime it)? That could show if fluid is being ejected out of each circuit.

https://www.youtube.com/watch?v=tq6FcjrSrdg

An indication the piston is pushing fluid to each wheel is if getting fluid ejected with a partial press of the pedal at each wheel. This video shows the tube connected to the bleed screws can be submersed to keep air out.

https://www.youtube.com/watch?v=ag-Q_lP0dOk

Also can consider with wheel off ground spinning it by hand and then applying the brakes to see if it stops.

BTW, usually best to post in one not multiple threads.

https://www.tacomaworld.com/threads...t-gen-edition.138573/page-11208#post-30727413

 

It’s hard to tell in the pic, is your brake fluid black, if so, could be the MC seals are shot

 

Is your symptom hard pedal but not good braking, like there is not booster assist?

 

With the age and mileage on these trucks a new MC/booster replace is money well spent

 

On the rear axle there is a load sensing proportional valve, this needs to be bleed too.

With that line out put your finger over the output hole and have a buddy slowly press the brake pedal, fluid should come out. Seal it with your finger and have him release the pedal, if you dont seal the hole the piston will draw air into the master cylinder that you will just have to bleed out. ABS brake bleeding can be challenging to get all of the air out. You might have to find a dirt road and get her up to 20 mph and hit the brakes to acuate the ABS pump. After a few applications you "should" be able to bleed the air out of the system.

 

I’ve been trying to diagnose some brake pulsing. Used a dial indicator on the rotors and they are within spec so I figured I’d rebuild the calipers to make sure they’re operating smoothly. Cleaned things up etc. just trying to rule stuff out.

I asked the specific question about the brake master cylinder because of a video I saw showing that the ports should drain freely, but for whatever reason one of them doesn’t on mine.

After rebuilding the calipers I bled the brake lines. Then I engaged the ABS just cycle out anymore air. Then a couple days later the brakes started acting weird again. So I just bled the brakes again and there was a lot of air at the rear brakes but the braking is now back to normal. Hopefully it stays that way.

 

Having similar brake issues too, following this to see how it goes