Brake pedal low after changing Rear Pads

[jsxr14s]

I just changed my rear brake pads last night.
Now when i depress on the brake pedal, it goes too far down.
After depressing it several times it becomes firmer as i do so.
My initial thought was that air got into the brake lines. I thought this because when i reset the caliper piston i left the master cylinder open, but i read instructions to do so. so i did. i did not drain or bleed the fluid after so this was my conclusion. And the master cylinder is still full.
But this morning i asked the guy from the auto shop that neighbors my house, and they're telling me it's the brake booster.
I have my doubts about their diagnosis because the brake pedal was not depressing too low before i changed the pads. I am capable though of having messed up the entire procedure.
I can be wrong too. I am a NEWB. I just have my reservations against this auto shop i guess.
So i come here because there are a lot of helpful and knowledgeable folks here. And i respect this community. so please help!

[n240sxfnatic]

Re-bleed everything

[rhd180]

does the brake pedal stay firm after not doing anything after an hour? or does it go soft again and have to get pumped up? if it stays firm then all it was is the pistons in the calipers reseting for the new brake pads. if it goes soft after a while and needs to be pumped up, then you have air in the lines and needs to be bled out.

[Sileighty_85]

Bad Brake Booster= Stiff ass brake pedal
your neighboring mechainc fails.

As stated bleed lines
Master cylinder might be goin bad
is your Master cylinder leaking where it connects to the brake booster?
You'll be able to tell from where the paint is stripped and it rusting below it

[g6civcx]

Bad Brake Booster= Stiff ass brake pedal
your neighboring mechainc fails.

Air in the lines would cause a spongy pedal. This would mask a bad booster so the booster could be bad on top of the air in the lines, although I think that this would be unlikely.

As stated bleed lines
Master cylinder might be goin bad
is your Master cylinder leaking where it connects to the brake booster?
You'll be able to tell from where the paint is stripped and it rusting below it

I agree. Check everything for leaks. Everything from the master cylinder to the caliper should be checked.

[jsxr14s]

Bad Brake Booster= Stiff ass brake pedal
your neighboring mechainc fails.

As stated bleed lines
Master cylinder might be goin bad
is your Master cylinder leaking where it connects to the brake booster?
You'll be able to tell from where the paint is stripped and it rusting below it

esp a fail because he has his own shop.
I'll check for leaks tomorrow as i attempt to bleed the brakes.


I agree. Check everything for leaks. Everything from the master cylinder to the caliper should be checked.

What should i check for on the caliper?

[g6civcx]

What should i check for on the caliper?

Look for signs of fluid leak. If the caliper is leaking it'll dump out fluid every time you stroke the pedal.

Also check the bleeder screw for leakage. Most likely the bleeder screw is leaking. Loosen and tighten very carefully, or replace the screw.

Worst case, replace the caliper.

[palmdale_mob]

Is this your first time changing brakes?
Usually when you push in the piston you will have to pump the brakes to bring it back to where it use to be, then you should be alright
Having the bmc open wont let air into the lines unless it goes empty and then you press the pedal
Did you open the bleeder at all on the caliper?
If you did you will have to bleed it to bring it back to normal
If not just check for leaks

[jsxr14s]

Is this your first time changing brakes?
Usually when you push in the piston you will have to pump the brakes to bring it back to where it use to be, then you should be alright
Having the bmc open wont let air into the lines unless it goes empty and then you press the pedal
Did you open the bleeder at all on the caliper?
If you did you will have to bleed it to bring it back to normal
If not just check for leaks

Honestly i haven't done this since sophomore year in high school auto mechanics. I didn't open the bleeder at all. How else could air have gotten in? it does feel soft and sponge like. but get's firmer. then after stopping completely, and starting back again with the pumping gets stiff. then soft again.

[Sileighty_85]

sounds like the Master Cylinder

[jsxr14s]

In cases where the problem would either be the master cylinder or the booster, what could i have done wrong during changing my rear pads for either of the two possibilities to be the issue now? My breaks didn't feel like that prior to rear pads changed.