Brake Pedal Goes to the Floor

I have been working on my brakes for weeks and can't seem to figure this out. No visible leaks in the system. I replaced the master, bled it before installing, bled all four didnt fix it. Put new brake pads on front and regreased guide pins, top two were seized, inspected my pistons seemed to be fine. Took the rear drums off and inspected the cylinders and shoes and they seem to be fine. I also replaced the front brake lines. I cant seem to figure this out. My booster seems to be working. I have a good pedal with the engine off but when I start it it just goes to the floor. I had to replace one of the rear wheel cylinders too bc i bled the system so many times I ended up chiping a peice out where the bleeder threads in at. The only two parts that I havent replaced are the other wheel cylinder and the booster. What do y'all think?

 

You probably filled your ABS block with air, only way to bleed that is with a scan tool than can pulse/actuate the solenoids.

 

Key-Rei, I don't have ABS

 

Have you bled the proportioning valve above the rear axle?

 

Chances are that you could have a bad brake booster.

 

Styx586, I did not. I was looking at that but didn't know what it was. Could that be my problem?

 

Most definitely could be… theres a bleeder screw on it, if you’ve got air in there it could be your issue

 

Thanks I will go bleed it right now and report back.

 

Another thing I’d be interested to know, did this happen suddenly or is this a new to you truck that has had this issue the whole time you’ve owned it?
Have you adjusted the rear brakes?

 

Brake master cylinder?

 

Do you have the LSPV (load sensing proportioning valve?

 

How are you bleeding the system? Good-ol-fashioned way, Motiv power bleeder, etc.. While I never had an issue with the pedal hitting the floor, I did notice better pedal feel once I upgraded to a Motiv power bleeder.

bleeding order with LSPV: Right rear, left rear, LSPV, front right, front left.

 

I just bled the proportional valve and got a ton of air out there, but I guess I need to go back and bleed the whole system in the correct order bc it didn't fix the problem.

Styx586, yeah its been a problem for a while and yes the rear brakes seem to be fine.

 

Have you inspected the Brake booster? I think it's possible for fluid to get in there, so you may not see it leaking.

 

Andy, i will take a closer look at the booster, tomorrow. As of right now, that and the other wheel cylinder are the only things that I havent replaced.

 

I don't think the booster will let air get into the system, if you mean into the brake tubes. It's only there to help you apply more pressure to the brake pads by creating a vacuum, then using atmospheric pressure to help push against the M/C piston. Sounds like you just need to do more bleeding to make sure all the air is out of the system.

However, if you had a bad seal between the M/C piston and the booster before you replaced it and fluid got into the booster, it will probably fail. Brake fluid vs the internal parts of the booster is not good.

 

^This.
My guess is OP just hasn’t quite gotten all the air out of the lines, replacing a master cylinder and brake lines introduces a lot of air. Sometimes it takes a while to get it all out… worst case scenario he needs to tow it to a shop with a pressure bleeder and have it done right.

 

https://www.youtube.com/embed/rnyK3V-OGn4

 

According to this website, http://www.4x4wire.com/toyota/maintenance/bleedingbrakes/, the LSPV is bled last.

In Tim's video, you can see the last step in the FSM is Bleed LSP and BV, but he didn't mention it : (

 

Another thing to consider is whether or not you got a faulty MC... I'd say it's fairly unlikely but if you really can't get a good pedal and you're certain there's no air in the lines, it could be a bad replacement part.
Did you get a OE part or aftermarket? New or Remanufactured?
Also, (and this is just a shot in the dark) back when I was wrenching I had a customer come in with this exact complaint except he had replaced both front calipers. He just couldn't get a good pedal. Turns out, the caliper's were installed on the wrong side of the vehicle upside down, so the bleeder screws were on the bottom of the caliper, meaning it was impossible to properly bleed the system.
I know you said you replaced the front lines, so just make sure your calipers are right side up. (I don't even know if the Taco's calipers will bolt on upside down, but it's worth double checking)