Spongy Breaks / Full Master Cylinder

Howdy Folks,
I first noticed the issue about a week ago - prior to that I can't say that I had any issues braking in my taco.
It feels like I can't build pressure in my brakes. I've looked at the Master Cylinder and while it for sure looks old, doesn't seem like there are any leaks coming from the cylinder itself. I was thinking that maybe the cap got too old and the rubber wont hold a seal any longer.
When driving it feels like my brake pedal goes almost all the way down before I actually start to brake the vehicle and even then it doesn't feel smooth like when I first got into the vehicle a few months ago.
When taking a corner the Parking-Brake light turns on and turns off when the vehicle makes it past the corner, that made me think the check the cylinder but its still at the max line.

Ideas? I'm going to check the brake pads in the front over the weekend and I'm going to try to bleed the lines over the weekend also. Any other ideas on what I should try?

 

Brake fluid should be clear, if it's dark, foggy or yellow it's time for a brake fluid flush.

 

I can't believe I didn't think of that. Its definitely dark. Do you think that would cause this severe of a change?

 

Dark/old fluid by itself will not cause spongy brakes.

Spongy brakes is from air getting into your lines.

The fix however, is still a brake bleed, either way.

I'd go ahead and bleed them, but there is a reason air got into the lines and you need to address that. Start by inspecting all of the brake lines, from the master cylinder back to each caliper/drum, and don't forget your rear proportioning valve. Looks for signs of a leak.

 

You'll never get a rock hard brake pedal with dirty brake fluid. I would use a turkey baster to empty the reservoir and fill with fresh Dot 3-4 before bleeding/flushing.

 

Dot 3-4 brake fluid is hygroscopic.
It absorbs water.
Water lowers the boiling point.
Water boiling in dirty brake fluid creates air bubbles in brake system.
Air in brake system causes spongy brake pedal and reduced stopping power.
@jbrandt
Contaminated brake fluid absolutely does cause spongy brakes.

 

@BrainTaste @jbrandt
https://www.hagerty.com/articles-videos/articles/2019/06/12/5-ways-to-bleed-your-brakes

 

Thanks for all the help guys. I'll update after this weekend.

 

New fluid and a comprehensive brake bleed (including the BPV) and you should be in business. Inspect your brake lines make sure that aren't bulging anywhere. Stainless steel brake lines are a solid upgrade. If none of that changes anything I'd suspect the master

 

Possibly brake booster issue? Check that all vacuum lines are attached and not cracked or leaking. Another possibility is a failing rubber brake line that swells when pressure is applied. This will definitely make your pedal feel soft.

 

If you pump the brakes 3-4 times does the pedal firm up? If so, odds are on the master. Internal bypass leaks don't show externally or create fluid loss.

 

I have a 1st gen Taco with 266K miles on it. I had a o shit moment a few weeks ago. As I accelerate and then went to try and stop. The brakes seemed not to bite. I also noticed my check engine light came on. The code read P0171 lean fuel bank 1. This is what I learned.
To correct the code it could be a MAF Sensor, 02 sensor or a vacuum leak. Bare with me I'm getting to the point. I decided to upgrade my brakes with the Power Stop Z36 TRUCK & TOW BRAKE UPGRADE KIT WITH POWDER COATED CALIPERS. I also replaced the the brake master cylinder. To correct the code I replaced the MAF & 02 sensor. After test driving brakes still would not bite properly and check engine light came back on with same code. Now I have narrowed it down to a vacuum leak. I researched how to test the brake booster to see if it was bad. To do this you start car and let run for a few minutes. Next press down brake and turn off car. If the brake pushes up against your foot pressure than its a bad booster. I found a company that sell rebuilt boosters on AMAZON, company name Cardone at a fraction of the cost. I installed it in under an hour. Tested truck and it stopped on a dime. Check engine light was off and no codes were found. It turns out the computer is really sensitive and caught and detected a vacuum leak. Which was coming from a bad booster. I hoped this shed some light on a trouble shooting. Danny with HOLD ON! DESERT RACING TEAM

 

One thing not mentioned was out of Adjustment rear brakes.

If the parking brake is not used to keep the shoes adjusted or the adjusters have failed in some way.

You end up with long pedal travel add dirty fluid into the mix makes it worse .

 

The rear brakes out of adjustment (i have never seen auto adjusters on drum brakes work properly) is a big factor. When I went to do my timing belt, I had a helper hold the brakes on while in gear to loosen the balancer bolt. It would not hold until I tightened up the back brakes. I think the rear drums out of adjustment on these trucks is a very often overlooked factor.

 

I agree 100% with Actionjackson. When I adjust the rear drums there is a noticeable difference in braking for the better.

 

We ended up bleeding the lines until we got clear fluid and adjusting the rear drums.
Everything seems to be good to go now.

 

Good to hear you got it fixed
Thank you for reporting back to us
Sux when people don't share the fix