Question Brake Question

[Salty_Dog]

OK. This is not a Tundra brake question, but it is a brake question.

I just finished a rear disk brake conversion on my 2002 Corolla. With the help of a nice fellow in South Carolina who is a Corolla guru and goes by the moniker of "Dr. Tweak", I was able to adapt the rear disk brakes off of a 1996 Celica GTS to replace the drums on my Rolla.

Everything when semi-smoothly with only a few hitches along the way; nothing that creative problem solving couldn't fix.

While I was at it, I decided to install Stainless Steel brake hoses and Speed Bleeders on all 4 corners. I also added EBC rotors on the front and OEM rotors on the rear. The front calipers are still the original stock calipers; the rear calipers are new OEM's. Each corner also got Hawk HPS pads.

So I get the whole system flushed and bled out this morning. I have zero air bubbles coming out of each corner. When I got done, the brake pedal felt nice and firm with the engine not running. But when I started the engine, the pedal got soft on me. (No jokes please about that feeling you get when things go soft on you. )

Now the brakes still work and the car still stops, but I have to push the pedal down about 3/4's of the way to the floor to feel any braking action.

What am I doing wrong? Where did the nice firm pedal go when I started the motor?

[Salty_Dog]

OK. I've had 20 views but no help.

Alright. I'm desperate. I've pumped over a quart of brake fluid through the damn thing and I've still got the same problem. The pedal is nice and firm until I start the motor then suddenly, the pedal goes all the way to the floor.

If I pump the pedal with the motor on, it firms up a little but not as much as when the motor is off. And even then, the firmness doesn't last.

What's the problem here? Anyone?

[fredkolias]

When the car is running, the brake booster takes vacuum from the engine and helps you push the master cylinder piston. It is normal for it to be much harder to press the brake pedal when the car engine is off, that's how power brakes work.

If the pedal is going to the floor with the car running, you have a problem someplace (sorry to state the obvious). Either air is in the lines, or something got messed up when you did the brake job.

I have a Tundra that I recentlly replaced both front and rear brakes, and for some reason I'm having the same problem, no pedal with the truck running. I"ve been bleeding it for weeks with seemingly no bubbles coming out. I've even replaced the master cylinder. No luck.

[Salty_Dog]

Originally Posted by fredkolias

When the car is running, the brake booster takes vacuum from the engine and helps you push the master cylinder piston. It is normal for it to be much harder to press the brake pedal when the car engine is off, that's how power brakes work.

If the pedal is going to the floor with the car running, you have a problem someplace (sorry to state the obvious). Either air is in the lines, or something got messed up when you did the brake job.

I have a Tundra that I recentlly replaced both front and rear brakes, and for some reason I'm having the same problem, no pedal with the truck running. I"ve been bleeding it for weeks with seemingly no bubbles coming out. I've even replaced the master cylinder. No luck.

Thanks.

Last Sunday, I decided to swallow my pride and took it to my local Toyota dealer. I'm a regular customer and they know me. The mechanic power-bled the system but even he could not find the source of why the pedal goes all the way to the floor.

So at this point, I'm going to rule out air in the lines as being the problem and proceed in a different direction. I'm beginning to suspect it be something with the proportioning valve. The existing valve is designed for disks/drums and not disks/disks and maybe I need to replace it with one that is designed for disks at both ends.

A prop valve off of a disk/disk Celica runs about $175. I'm willing to spend that if I was confident it would solve the problem but I want to be sure. So, I guess it is back to the 'net for some more research.

[CharleyTundra]

It is a vacuum hose issue more than likely.

[Salty_Dog]

Update:

I took it on a long (300mi) trip this past weekend and it performed beautifully. It might be my imagination, but the pedal seems firmer now. I put it to the real test when my radar detector went off while I was cruising too fast on the Pennsylvania Turnpike. No lockups or anything.

I think I'm going to call it good.

[Jowett Engineering]

My guess... each rear caliper has a larger piston and thus fluid volume than each drum brake wheel cylinder did... the short answer, you might need the larger master cylinder from the Celica.