Calling any brake system experts

Greetings,

I’ve been having brake issues for quite some time, with nothing seeming to fix it. My truck currently has a Tundra front brake upgrade using OEM pads and rotors. The calipers are remanned calipers from advanced auto. Still running original rear brakes, as they are only at 88k miles. They are adjusted properly. I had a sinking pedal for a while, and a replacement master fixed that. It is an aftermarket master cylinder, as Toyota has discontinued new ones. I also have SS brake lines from Wheelers off-road, and a rear extension bracket due to lift.

My current issue is I get a small soft portion of the pedal, maybe 1/4 press, where there’s a decent initial bite, and then it’s like I hit a hard wall where there’s not much braking power. I can press hard into the wall until my wheels totally lock up, but there’s almost no brake power until I slide due to lockup. I recently just had a new booster installed thinking I may have a lack of vacuum, and there’s now a very small improvement, but I still have that hard wall with little brake power. Every once in a while the pedal will change feeling and the braking will be fantastic, and that hard wall will go away, but it is very rare.

I have been wondering for a while if the proportioning valve underneath the bed could cause this issue. My rear brakes will lock up with the front and slide in the rain. I ended up sideways once trying to stop in rain quickly. Contemplating deleting the valve for a manual one. If anyone has ideas or suggestions, I’m looking for advice and ideas.

This issue is enough to make me want a different truck. I just got a boat to tow, and braking is sketchy enough without a load behind me to make it a nail biting experience while towing. This truck is rated to tow enough stock that there shouldn’t be an issue towing my size boat, especially with the Tundra brakes, but the brakes are far worse than any other vehicle I’ve driven. The pedal just doesn’t feel correct.

Thanks for any help you can provide.

 

Just a Guess it sounds like your booster is on the way out

Mine has been not working for 2 years or so Have the new one just never enough time.

All brakes were like this in my youth before power brakes

 

I'm only raising the question, I have no knowledge of this model. Is that a load sensing proportioning valve? I read or heard somewhere that these adjusted the proportioning via some kind of lever based on the rake of the bed with or without load. Some trucks had them,I'm not sure which gen. I could be totally off base.

 

Just replaced it. Same pedal feel.

 

Yes, 1st gens have them. Toyota stopped using them after the 1st gen because they aren’t necessary. LSPV’s are an overengineering feature that isn’t needed to have good brakes.

 

First question why the Tundra brakes? You call this an upgrade but is it?

I bring this up because years ago I swapped a Ford Explorer rear axle into my Jeep. The disks were SUPPOSED to be an upgrade over the stock drums. I had nothing but issues since the swap. I will explain my situation so you can think about your UPGRADE. Stock the Jeep has disk front and drum rear with the tiny wheel cylinders vs disk calipers. I say tiny because the amount of fluid required for wheel cylinders is just that tiny vs the massive amount of fluid needed to achieve the same amount of braking from disk brake calipers. So yes I now had superior disk brakes but I didn’t have the fluid required to move the pistons so I actually had less braking force at the rear disk. The fix was to modify a Dakota master cylinder to replace the stock one. This was supposed to move more fluid and was designed for 4 wheel disk. The Jeep was sold before I ever did that mod.

Without knowing all the details of the UPGRADE you have done (or was done by others) you might have part of the solution to upgraded brakes but not all of it. This could result in all or part of your current issues. If your calipers are larger and require more fluid than your stock calipers to move the same amount you will have less force for the same pedal travel. I would start with examining the details of the upgrade. Short of comparing it to others that have the exact same mods as you you won’t know if the mod was done along with all of the other nessecary requirements to make this an actual upgrade. I would even consider going back to stock.

 

This is my guess too. sometimes you get unlucky and get a brand new one that is bad. also check the vacuum hose coming from the motor.

 

Needs a bigger master cylinder to move the bigger pads in those calipers againts the bigger rotors.
I think I saw some where on Finnegan's Garage where he was testing out some Wilwood Big Brake kits on his el Camino. He had a couple of different sized diameter brake rotor's and pads. The first kit had everything matched, m/c, calipers and rotors, the car stopped great. He switched up to the bigger set of rotors, calipers and pads but kept the same m/c and the car stopped a little better but not as good as he thought it would so he called Wilwood up and they said he needed a bigger master cylinder for the larger brakes and when he got it, there was a big difference in stopping power and feel.

 

If the brake system has been changed (Tundra front brakes) and still has stock rear drums, the proportioning valve cannot behave the same way as designed. It's purpose is to balance front and rear brake force so that locking is minimized as I understand it. I don't know if that valve is adjustable via some lever arm or other load sensor or is bad. Maybe there is an adjustment or test procedure in the service manual. O/p complains about soft pedal feel too. There is no guarantee that a rebuilt aftermarket master cylinder is good now,or was out of the box ,when installed. This sounds like a dangerous situation for the O/P, something is obviously not right.

 

So the Tundra upgrade is quite a common upgrade to do. The stock Tacoma rotors and calipers are inadequate, especially for heavier vehicles running bigger tires and armor. The calipers are a bit larger, as they accommodate a larger pad and use a bigger rotor. The upgrade is very common. I’ve read my 1999 model has the larger size master cylinder and the dual diaphragm booster. 01-04 it was changed to a smaller bore size master.

My hard pedal issue occurred before putting on tundra brakes. It also isn’t the entire pedal. When this occurs, there’s a soft portion where there’s a good initial bite, maybe 1/4 push, and then it’s like I hit a hard wall where braking sucks and the pedal is hard. This problem is also intermittent. Yesterday I started with it, and after driving a bit it changed feeling and braking was good.

I’m leaning towards the proportioning valve as the valve does not stop my rear from locking up. I am wondering if it’s getting stuck.

 

As far as the new booster, I felt a definite improvement in braking after install, but there’s still a wall in the brake pedal. I’ve checked the vacuum line to the brake booster. It’s fine. Without the booster, the brake pedal has no soft spot in it at all.

 

I would also suggest another long shot. Have someone push the brake pedal hard while you check ALL rubber lines under pressure. They can get soft and expand without bursting (yet!!) We replaced soft lines on a BMW with some aftermarket flex lines and the pedal was noticeably firmer. We couldn't pass NYS inspection with the old lines, cracked and deteriorated.

 

I don’t have any rubber lines. What isn’t hard lines is now stainless.

 

Do you have ABS?

 

No

 

Are you running a lift? The BPV needs to be moved if your axle to mounting point distance is from stock. The load sensing spring can also get bent. That could change the amount the valve is open for a given height. I also second checking and probably just replacing the vacuum lines. It can be difficult to find leaks. My '03 sometimes does like you describe, where it feels like there are no brakes until you get close to lockup. Also have the tundra calipers and SS lines.

 

It’s been relocated after lift