Brake Pressure Loss, Many Parts Replaced, No FIX...

Hey OP, just sharing my recent experience, I had just replaced front pads and rotors and ended up with this same issue. Super spongy and the braking power just wasn't there. After bleeding several times with no change, I opened up the rear drums. The auto adjusters were not working as they should. Adjusted the shoes outward and VIOLA! Fixed! I am by no means a mechanic.. this may not help you, but its an idea! Seems like you are exhausting all other options! Good luck!

 

Rear shoes being dirty wont affect how the pedal wont hold pressure.. the rear shoes being out of adjustment will affect where the pedal starts to engage I don't think this is your issue being you said the park brake feels to tight.. The park brake feel changes also when rear shoes are adjusted.. Front caliper pistons being seized could be an issue however if that was the case you can usually see signs of this either in the uneven pad wear or by turning the wheel when vehicle is in neutral in the air. If one tire wont spin or is harder to rotate then you may possibly have a seized piston on the caliper.. I don't believe its a vacuum issue since lack of vacuum to the booster usually results in a hard pedal not soft.. I don't think the dealer has actually evacuated all air from system or as others have mentioned it could be a factory defect on the Master cylinder.

 

Right, and new parts can also be bad out of the box too, I have seen it before in aviation where parts are insanely expensive..

 

https://media.giphy.com/media/XuBJvrKHutnkQ/giphy.gif

 

They have to be missing something, if you had a normal solid pedal for 2 years and then all of a sudden have this problem it is obviously not normal.

 

When did this issue start occurring.. have you added any fluid to the system prior to work? did you over heat your brake? something that hasn't been mentioned yet, I work in a brake and alignment shop I've had one similar issue.. car came in with low pedal engagement and it wouldn't hold pressure, the master cylinder was leaking so I replaced it but after pressure bleeding the brakes multiple times the pedal was still not holding pressure.. went through the works couldn't figure it out, long story short have them put a line clamp on the 1 rubber brake line at a time.. what they are checking for is if a brake line has collapsed internally. fluid will still flow through when bleeding.. but once you drive the fluid pressure will feel as though its there however it will slowly bleed off as more

 

fluid starts to compress against the pistons. if they check 1 hose at a time they need to see if clamping any 1 hose is making a difference. the hose that solves the pedal feel when clamped will be the one with the problem.. hopes this helps may not be your issue but worth checking being that they seem to be just throwing parts at it

 

Sounds like the OP had normal brakes and pedal feel for 2 years and then it went to hell during a trip.

 

just wondering if he got fluid hot enough to boiling point.. I see it at work every summer mainly with RV's since we are in a valley and they drive down a MT pass to where I'm at. once fluid boils it gets lots of air in the system. usually we can just flush the old fluid out and bleed the system and there good. the other question I had was due to the fact that most times I've had where brakes are having strange non common issues. its because at some point someone introduced a petroleum based product into the system. oil in the brake system will usually cause similar issue followed by eventually the opposite the pedal will be to stiff, due to all the rubber components swelling and cutting circulation off

 

I wonder if 1) the dealer is really not competent enough to fix the issue ( why replace the brake booster, or pads and rotors) 2) they've been the only ones servicing and a lube guy put oil based product in brake reservoir.. my dealer wont even replace shit that's actually wrong with my truck always cant replicate issue.. this guys dealer seems to just be throwing parts at it, as far as my experiences go with dealers the dealer has to provide Toyota with a actual reason for replacement under warranty either they could visually see the part was bad or after diagnosing they determined a issue.. doesn't seem to be the case here other wise they wouldn't have replaced this many parts already. just my 2 cents

 

Damn pic. Thought smitty was back

 

Me too. And while I was navigating to see, I couldn't help but wonder it he was offering insightful help -or- some clever smartass comment.

 

I'm gonna go with the latter. It was good though, made me look. Haven't seen smitty around here in a while.

 

Sounds to me like your HCU (hydraulic control unit) which is attached to the ABS module, is internally bypassing. One or more of the valves could be sticking allowing pressure to bleed off until the end of the pedal travel. I've replaced several on fords and I'm sure other brands could suffer the same fate. Just my $0.02

 

Agree with prior poster.

Check your rubber brake lines. Failing line(s) might be causing this. Cheap fix, too.

JL

 

Same same.

He still banned. Probably perma but they never specified in the banned memorials thread.

 

The internal line in the soft brake lines could have ruptured. Fluid will bleed out when the pedal is pressed but be contained between the outer cover and inner lines.

 

@blackohio-- Exactly. That is what I/we are referring to. Not always obvious, nor necessarily easy to diagnose.
Quick, cheap and easy to fix though.
JL

 

Alright, another quick update. Got my truck back Monday morning, drove to/from work Monday and Tuesday. Stopped at the dealer on way home last night to have them a) adjust the brake fluid to correct level (was over filled) and b) correcty torque all the lug nuts. While there, I told the manager I still wasn't satisfied with the spongy brake feel, and drove an almost new 2017 TRD Sport DC, same as mine. Wouldn't you know, that pedal felt exactly the same as mine - as near as makes no difference. The strangest thing to me is, and I swear, before the actual brake pressure loss issue, my pedal felt way stiffer than it does now and the 2017 I drove. 2 weeks ago while diagnosing, I drove a 2016 4 cylinder (same brake system as mine since the sport doesnt have the crawl control/MTS) and that trucks pedal was stiff like mine used to be. Here's what I wonder... Did Toyota switch/update one of the brake components that was replaced on my truck between the 2016 and 2017+ model years? That's the only thing I can think of that matches up with my experience. Maybe they knew of an issue and remedied during 2017+ production?

Anyway, the dealer has done what they can do at this point. I may try the brake line test mentioned above on my own to see if that does anything (thanks for the idea). I also tested the abs system on wet grass/dirt on my way home last night, and it works. It's also true what someone said in another thread about the abs not engaging under 5mph, only faster than 5mph. I experienced that as well.

 

yeah,
Used to see it alot on mountain bikes when people bought cheap hydro lines or the lines failed. They'd bleed the system endlessly and have decent lever feel but once they really got on the brakes they'd loose pressure and the lever would drop to the bar or be inconsistently spongy since up to a certain pressure the fluid would still move the pistons and when pressure got high enough it began to bleed out.