87 Brat brake pedal to the floor, except when hand brake engaged

[jor2daje]

As the title says, just replaced front pads (used prroper tool to depress piston), brakes were a little spongy before changing but I had assumed that was just rear adjustment (adjusted now). I thought I'd messed up the MC by depressing too far while bleeding so I replaced it (bench bled as best I could) but still having the same issue. Brakes go basically to the floor, the can be pumped up but go back to floor if the pedal is reset. Completely firm if the handbrake is engaged. I'm assuming this might mean bad piston on one of the front calipers, since engaging the handbrake might shift it in such as to cause a better seal, but there no sign of a leak (even within the rubber boot). 

Open to any suggestions of what to look for next, I keep hoping it just needs more bleeding, but the fact it goes firm with the handbrake has me stumped.

Thanks

[Crazyeights]

The parking brake is integrated in to the front calipers on those. Exactly how did you compress the pistons back in to the calipers? If you forced them straight in then the calipers may be damaged. I use a tool to wind them in.

[jor2daje]

I wound them in using a tool, but it's possible I messed something up, do you think the damage would present as a leak or...?

[Crazyeights]

It's probably air in the system then. Usually if they are damaged either they leak or the parking brake fails. It sounds like you did everything right. Do you have access to a vacuum bleeder? I couldn't imagine living without mine.

Edited January 26, 2019 by Crazyeights

[jor2daje]

Yes I've been using a vacuum bleeder, but can't hurt to try again haha. 

[Crazyeights]

I would bleed the system really well. You don't need a helper or too pump the pedal. Once you are sure the air is out if you still don't have any pedal the gently pinch off both front brake hoses and see if your pedal comes back. If it still doesn't then the master cylinder has to be junk. Good Luck, you are almost there.

Edited January 26, 2019 by Crazyeights

[jor2daje]

thanks, great idea pinching off hoses

[Dee2]

I had a similar problem.  Even though I found no problems in my brake system and bleeding did not help solve the problem, I got improvement by re-bleeding the master cylinder.  I did it while it was on the car.   

1. make sure the car is adjusted by lift so the MC is level, (important!)

2. crack open a brake line connection

3. depress pedal and hold it down

4. close the brake line connection

5. check fluid level in reservoir.

6. repeat for other brake line

7. check brake pedal response.

Repeat a few times if necessary.  If you have 4 line connections on the MC you only need to do the two side connections because air rises.

Also if your brake cylinders have the notches for turning them back in make sure the notches are aligned correctly to the brake pads.

 

 

 

[jor2daje]

Welp I feel like an idiot haha, but for any future readers I'll share what the problem was: I went to pinch off the front lines per crazyeights recommendation to narrow down between MC and front calipers and noticed the inner pads were sitting at a slight angle relative to the disc, on closer inspection I hadn't fully seated them in the notches, so the pad was sitting on the caliper brackets on the top side meaning the piston was flexing the pad when the brakes were pressed. Pulling the handbrake would pre-flex the pads thereby stiffening up my brakes. Pads took a slight curve from all this flexing so I replaced and everything's good now.

 

Thanks everyone for the help. 

[rdweninger]

Good for you, owning up to the mistake.   Several of us could have lost many nights of sleep for NOT knowing.

Glad you got it fixed.