Soft pedal, nothing seems to fix it

"New to me" 2007 Tundra w/ 5.7L and 193K miles on it. All is great except for the brakes which have consistently had a soft pedal no matter what I have done. Things I have tried include:

• Replaced all pads and rotors
• Pressure bleed of brakes numerous times, including with pumping pedal, truck on
• Used techstream to do an ABS bleed and also activated ABS numerous times on slippery roads; systems operates properly
• Replaced master cylinder twice now
• Replaced front calipers
• Replace brake booster with a used unit off Ebay (no change so suspect original one was good)
• Checked all lines, etc. for leaks several times, even tried UV dye but still observe no leaks
• Check parking brake to make sure if it is free / not seized up (but haven't done any adjusting on the actual back brakes)

Any other ideas? I feel like I've looked at all the old threads but haven't had anything jump out that I haven't tried. Otherwise feels like last resort is a dealer to see if they can make heads or tails.

 

Did you rigidly observe the manufacturers break in instructions for the new pads?
I noticed when I had to break in my new Powerstops recently that little note was given to stopping during the break in process and that the number of slow brake procedures was far more than I ever remember. It had been a while since I've had to do a break in procedure but I did remember that coming to a halt while breaking in used to be a big no-no, apparently the heat from the discs would cause the pads to glaze up and give exactly the symptom you are experiencing. Pad glaze was easily sorted by dressing the pad. Can't imagine why it would be much different nowadays.

When you replaced the pads did you go with the same type of construction? If you are used to the feel of semi-metallics and have gone for organics you will notice a difference if you are a hard braking fool.

 

Ditto on breaking in the pads, especially with new rotors, otherwise you get what feels like glazed rotors. Have you driven another Tundra to make sure you’re just not used to how Tundra’s break.

 

Be sure to replace the rubber brake lines at each wheel with braided stainless ones. The older lines will expand under braking pressure, and create a softer pedal.

I put all new front and rear Powerstop "towing" brakes on my 2008 (rotors, calipers, hardware, pads), replaced the lines with braided stainless, seated the pads properly, and she now has a rock-hard brake pedal and stops like a boss.

I use a Motive Products power brake bleeder (looks like a garden sprayer), these work better than the vacuum bleeding systems.

Make sure when bleeding you don't run the master cylinder low on fluid, else you can get air in the ABS module which can be near-impossible to get out.

Also bleed from the farthest wheel to the closest. And keep bleeding! As soon as you think you have all the bubbles out, more can come. The MP power bleeder makes it EASY.

Remember to unseal your power bleeder from the master cylinder and add fluid as required. I would top off the master cylinder after doing each wheel, as each wheel used about half the cylinder's fluid to bleed!

Good luck with it,

ToolCat

 

All good suggestions, thanks! The pads being glazed is an idea I definitely should look at. I have steel braided lines in the front, but neglected to do the rear, so that is worth a shot! Guess I know what I am spending my weekend doing

 

This^^^^. Old brake lines will expand. Only thing not replaced.

 

Traditionally, the rear brakes is where you get your pedal feel.

 

Honestly would have thought the opposite, so that is really helpful, as my other attempts have yet to fix things! Wondering if I should take rear pads out and scuff those up as I haven't done anything there yet. Also note that my parking brake doesn't work at all...not sure if adjustment of that on the rear would impact the pedal feel.

To re-cap what I have tried since posting in case it generates any other ideas:

• Pedal feel: remains soft, and double pumping the pedal appears to firm up the pedal for that specific braking moment. If I put any kind of force on the pedal it will sink easily to the ground
• Leaks: no sign of leaks after inspecting the entire engine bay and underbody of the car
• Recent steps:
  • Prior to any work trigger ABS while driving just in case that helped release any air (have previously done techstream bleeds which accurate this, but figured worth a try)
  • Sanded front and rear rotors with 150 & 220 grit sandpaper (rotors left on car), then cleaned using brake fluid
  • Scuffed up the front brake pads only as I was running short on time (maybe try rear today??)
  • Bled brakes using pressure bleeder (connected to master cylinder reservoir) set at ~20-25 psi, and observed good amount of air from the front drivers side caliper, otherwise no air from any of the other three calipers

In terms of hardware, only things I have yet to replace are the ABS, and rear calipers. But nothing I have seen so far seems to indicate either of those is faulty.

 

I'd try rear lines now. Rubber lines can get a "flapper" in them, or fail in some way internally and you'd never know.

 

There are only two things in a braking system that cause that, neither is bulging worn out rubber lines. You have air in the system to bleed out or a master cylinder that needs new seals.

 

The fact that you have replaced the master points to bleeding errors. I've never bled a system with ABS but I understand that it can be tricky getting all the air out.

 

Sounds to me like you need a new master cylinder. Don't forget to bench bleed it before you install.

Reread your post and it seems you have replaced the master cylinder. Did you bench bleed it before you put it on the truck. If this is not the case pull it bench bleed it and start over bleeding the whole system.

 

Looking at the parts the OP has thrown money he has already replaced the master. Is it likely that not bench bleeding will trash seals or could he just remove the one currently installed, bench bleed it, re=install and then bleed the whole system through. I haven't done a car since the 80's but some motorbikes can be a right swine to bleed and they only have a couple of feet to get air out, a four wheeled vehicle has far more pipework and makes sense that some of them could be a complete bastard to get air out.

 

Did you bed in the brake pads to the new rotors. It makes a world of difference

 

While that was my first thought, as I posted most recently, the only thing that makes soft brakes operate when you pump them is air in the system, it cannot physically be anything else. That air is either residual from a poor bleed (most likely) or from air passing the master seals. Air getting in anywhere else means that fluid gets out and then shit really hits the fan.

 

I have the same issue on my 2016. I did install stainless steel brake lines and power vacuum bleed the system a few times. I did a search online and I found a video that said it was because the slide pins where not packed with enough grease? He also said to check if the pads were freely moving in the caliper. Now I have not replaced my calipers yet like you. I am in the northeast and rust is an issue so I can see this happening, especially if the slide pin boot has ripped. I am currently away on business but will try this when I get back. This is cheap to try and I don’t know if it will work, but fingers crossed!

 

I don't this is the case because I live in Socal (Inland Empire) and my truck's rust-free. I rarely drive it in the rain let alone through puddles.

I honestly believe it's the ABS module but I don't have the funds (right now) nor would I want to spend thousands trying to repair it. I've read in other forums the speed and slam-on brakes may fix the ABS issue. A few people have claimed this resolved the issue. I have yet to try it. Sounds a bit scary.

 

If you are in SoCal then ya probably not your issue. But since all it costs is a little brake cleaner and new grease I am going to try it. Will let everyone know how it works out for me. Good luck with yours and hope you fix the problem soon!

 

Chris,

Try the speed & slam-on brakes method. You've tried everything but this so what do you have to lose? Some owners in the same boat as you and I swear that method worked.

 

All, thanks for all the great advice. Not fixed yet, but I tried what Nemesis suggested and something did change - pedal is now noticeably softer, which is odd to me. Also, to further explain the feel - if I double/triple pump the pedal appears to get considerably better. The brakes seem to apply with only slight pedal pressure, but the pedal is soft. Could it be either air trapped in ABS is now free, or the ABS is somehow introducing air? Or...do I just bit the bullet and replace the ABS?? Looks like about 300-500 for a used unit, so not terrible.

Anyway, I will plan to try the following based on all the good advice so far:

• Bleed the brakes to see if any air comes out (may help narrow down the issue I guess)
• I have new rear brake tubes (from rear diff. to driver & passenger side) I can try after simple bleed
• Also, my slide pin boots are pretty much destroyed on the rear brakes so that is a great suggestion
• Look around at places to get an ABS module in case that is it.

 

I think the speed/slam method that Nemesis mentions is used in conjunction with a bleed regime, not just on it's own.

Bleed brakes, find a place to wind her up and hit them hard enough to engage ABS, go bleed again.
Repeat until happy.

 

Quote from member from another forum:

"It was ABS Braking systems. For almost a week when I was above 35 MPH I would not stop but jam on the brakes as fast as I could, this would engage the ABS system and after 3-4 times they tightened right up. The first few times I wasn't doing it right.... You have to hit the brake like you see a kid on a bike and the trucks makes some noise like an old man getting up from a chair."

It's really hard to find a deserted stretch road where I live to test this. I may have to try this 4 in the morning on a weekend. Shoot...should have tried it this morning.

 

Subbed, been fighting the same issue for years.

 

Hey guys, just wanted to give you an update on my truck. So in the rear the slide pins definitely needed grease. The front brake pads both had one pad that was rusty and stuck and not moving freely. Damn Northeast rust! Got the stuck pad out and ground some material off the pad and cleaned up the caliper with a wire brush. Took it for a ride and 100% better. Good luck to everyone struggling with this issue!

 

Thanks for your update.

Will have to take a good look at the pads and pins.

 

Check the slide pins on the rear calipers,I have seen them stick causing a soft brake pedal. I have also seen them bent when removing. Clean the slide pins and use caliper grease when installing them. I worked in a Toyota dealership for 7 years. Good luck.

 

Just to be devil's advocate here... you should go test drive another tundra and compare the brake feel. I have a 2007 and previously a 2014 and both feel the exact same, which is way softer than any other car I own. I've always thought they feel spongy, but I'm pretty sure that is Tundra life.

 

I'm pretty sure the soft spongy feel is more than what it sounds like. You can feel the pedal hydraulically depresses to a point then it sinks even further after that point. It's literally inches away from touching the floor.

That's not Tundra life.

 

I have an 07 bought used in 08, low miles. Had a similar issue as yours after a few years. At a stop, with the brake pedal pushed, there was what sounded like an air leak(hiss) and the pedal would slowly go towards the floor. After changing the pads, which were not the problem for me, I kept listening for where the hiss was coming from. Was the booster for me. And at that time, the part number had changed, was crazy expensive, out of warranty, but it solved the problem. I see you replaced the booster, but it can possibly be the problem, since you bought used off ebay. My oem booster is 44610-0C071.

 

These thoughts come to mind and I speak to the items not mentioned so far.

MC Install:
Swapping the booster and/or MC, can lead to issues from the length of the boosters push rod into the MC. Under normal circumstances, pedal up, the MC's reservoir is open to the MC pistons filling it making it ready for activation with maximum fluid capacity to the calipers. If that rod from the booster is too long, the pistons partially block the feed port, essentially starving the calipers of fluid charge. To short and you loose pedal travel.

One trick to us is a blob of playdoh, place it in the MC and push the MC on to the booster and remove it. If the rod smashes the playdoh out of the way leaving bare metal at the piston cup, the rod is too long. Shorten it. It needs some freeplay for the MC to work right but not a lot.

Rotor run out:
Tighten some washers and nuts in place of the wheels and verify each rotor has no runout. Runout means you have to seat the pads again before pressure builds making a low pedal. Rust on the hub can easily cause this.

Pressure differential valve:
Edit - for / aft brake bias...
I think the abs unit does this, but I had a none abs truck behave poorly for a failed PDV. Replacing it, solved the poor stopping, low pedal.

Pressure Bleeding:
A trick I use is this. After you've flushed the MC lines and calipers, I do a manual 2 person bleed.
Helper holds the pedal down with good force and brake man takes a block of hardwood and taps the caliper from the bottom hitting it upwards. Doing this, frees the trapped air in the calipers and being under pressure, the small bubbles come together forming larger ones that come out of the bleeder when opened. Do this 4x to 7x per caliper. Don't let MC run dry!

Obviously never let the MC run out of fluid. Always use fluid from a new unopened container. Do this on low humidity days if possible.

Edits for clarity.