Brake Riddle

#1
I have Gen 2.5, It's has spongy brakes, I have literally changed 95% of the brake system

- New Master Cylinder, did bench bleeding
- All new calipers
- Pads are newish
- Bled per the manual farthest side first and so on. Bled the proportioning valve too
- Made sure there are no leaks

Still have spongy brakes, brake travels almost halfway before it engages. I'm clue less, what else can i do?

Thanks
 
#3
I'm fighting the same thing. All pads, rotors, calipers, and master cylinder have been replaced. I've used easily over a gallon flushing and bleeding the setup.

Worst feeling pedal i've ever experienced. Feels somewhat like a bad booster, i get better pedal if i pump once every stop. Unfortunately, it doesnt show any of the other signs of a bad booster. And a booster isn't something you just throw at a truck.

Utterly maddening.
 
#6
I used Akebono pads all around.
It doesn't matter for your symptoms. Brake pads used do not affect the point at which the pedal "engages," no matter what you might read on the internet.

You have a hydraulic/pedal issue, as do i. Salonika's idea might be worth checking. Doesn't apply to mine unfortunately. Wish it did. My lines are nice and not noticeably expanding or ballooning at all with my wife standing on them with me under the truck. :(
 

Salonika

Monterror Pilot
#8
I'd have it power bled before I did anything else. I've never experienced a failed booster, but I was just reading that they shouldn't create spongyness. The booster does its thing between your foot and the master cylinder, so if it fails, it should just make a stiffer pedal sort of like pushing the brakes with engine off (that simulates a total booster failure, right?). I've also always wondered about bleeding with ABS. I've never replaced a master cylinder on a car with ABS, but I worry about the day I need to. There are a lot of passages in that unit that I can see air getting trapped in. Funny thing is, the FSM doesn't call out anything special for it, so maybe it's no big deal.
 
#9
I'd have it power bled before I did anything else. I've never experienced a failed booster, but I was just reading that they shouldn't create spongyness. The booster does its thing between your foot and the master cylinder, so if it fails, it should just make a stiffer pedal sort of like pushing the brakes with engine off (that simulates a total booster failure, right?). I've also always wondered about bleeding with ABS. I've never replaced a master cylinder on a car with ABS, but I worry about the day I need to. There are a lot of passages in that unit that I can see air getting trapped in. Funny thing is, the FSM doesn't call out anything special for it, so maybe it's no big deal.
ABS is another thing i was thinking of. On a lot of vehicles, there's a way to cycle the system in order to bleed it, otherwise you'll never get all the bubbles out.

The only reason i was thinking the booster was that the pedal sinks based on RPM, and the booster is the only part linked to the engine in the entire setup. I have a "higher" pedal in cold mornings when the truck idles at 1500rpm than i do when it's dog days of summer and it's idling around 600-750rpm.

I'm a bit annoyed because i did the entire overhaul because it felt like crap to begin with. And it feels like crap after. Interesting tidbit: Reading threads on FJ80s with bad brake pedal, it sounds like in their world, the load bias adjuster causes a lot of problems for them once their trucks are lifted. My truck is fairly high, and the front is sagging a bit, so assuming it's serving the same function on the Gen2.5 as the FJ80, i could definitely see that causing issues.
 
#10
If you replaced the master cylinder, you need to make sure the depth of the Piston in the master cylinder and the length of the brake booster rod are within specs. I belive the gap between them is only a couple millimiters, check the factory manual. Too big a gap makes the pedal feel spongy. I had a booster fail before and the symptoms were the opposite of yours, the brake pedal was really hard.
 
#11
Is that spec something that would change over time? Or only something that needs to be checked when installing a new master? I replaced the original OEM master and pedal didn't get better or worse.
 
#12
That is something that needs to be checked any time you replace the brake booster or the master cylinder since it sets the relationship between the brake booster rod and the master cylinder piston.
 
#13
That is something that needs to be checked any time you replace the brake booster or the master cylinder since it sets the relationship between the brake booster rod and the master cylinder piston.
Ok, so if no change in feel whatsoever between old oem original master and new master, somewhat safe to ASSume i could move that to the back of the list of things to check, since the master cylinder is a huge pain in the *** on this truck?
 
#14
I had mine power bled by a mechanic yesterday, the brake is better but still not as good. Even though it was power bled, it still feels a lil spongy but if i tap it cycle the brake pedal, the stopping power is better the second time i press it in quick succession.

That tells me there is still air in system or not? even though It was power bled.
 

Salonika

Monterror Pilot
#15
I’d replace the flex lines. If you have no history on them, don’t risk it. And even if they aren’t visibly worn, over the length of them and x4, a little bit of expansion could contribute to your problem. You’ve replaced everything else. Plus it’s a safety issue.