Squishy brake pedal on 85 eta.

[StealthiE30]

Ok so i got my 85 eta about 3 months ago.
When i bought it the previous owner had told me he replaced the master cylinder and also had the calipers rebuilt.
Brakes were a little squishy on the ride home but i figured maybe thats how
a non ABS 27 year old cars brakes should feel.
Well after a couple weeks of driving they got worse and worse,
to the point where i had to engine brake just to get her to stop.
So i take it to a local shop and have it checked out, they bled the lines and
said there was some air in them, with no obvious leaks anywhere.
So i get it back and the brakes felt like a completely different set!
The pedal was very firm and responsive, i actually locked them up
because i was not used to non abs and the new firmness.
Well after a bit of driving, i started to hear some squeaking coming occasionally from what seemed like the passenger rear side.
I also started noticing grooving on the rear rotors.
The pads seem to have a lot of life left on them from what i can tell.
As i noticed the squeaking to be more frequent, i also noticed the pedal losing its firmness.
So this is leading me to believe that the calipers might need a another rebuild?
If that is the case, would this be the time to upgrade
my braking system to something more "current"? Im not looking for crazy
performance, but i would like something that is sporty and maybe something
with abs. What are my options fellow R3V members?

[E30_fiend]

It's probably your brake booster. 90% of master cylinder failures happen on the plunger dude of the MC. When this happens, it leaks into the booster which fouls the booster. When the previous owner changed the master, he should have changed the booster along with it.

Good rule of thumb is to replace the master cylinder and booster at the same time. I'd bet money that the booster is your issue.


Taylor

[StealthiE30]

It's probably your brake booster. 90% of master cylinder failures happen on the plunger dude of the MC. When this happens, it leaks into the booster which fouls the booster. When the previous owner changed the master, he should have changed the booster along with it.

Good rule of thumb is to replace the master cylinder and booster at the same time. I'd bet money that the booster is your issue.


Taylor

Thanks ill try that before i do a full caliper replacement.

[WhyNot]

So i take it to a local shop and have it checked out, they bled the lines and
said there was some air in them, with no obvious leaks anywhere.
So i get it back and the brakes felt like a completely different set!
The pedal was very firm and responsive

air is no good but fluid goes bad just from being in the car and dot 4 [what i think you should be using] absorbs water so it needs to be changed regularly.

Well after a bit of driving, i started to hear some squeaking coming occasionally from what seemed like the passenger rear side.
I also started noticing grooving on the rear rotors.
The pads seem to have a lot of life left on them from what i can tell.
As i noticed the squeaking to be more frequent, i also noticed the pedal losing its firmness.
So this is leading me to believe that the calipers might need a another rebuild?

the squeaking is probably because the surfaces have a hard glaze on them.
its hard for brakes to stop when this starts to happen
the pedal might really not be losing firmness but it is really requiring more pressure to stop because the pads and rotors are hard glazed.
the grooving on the rotors [assuming its not metal to metal] is kinda proof that the pads and rotors arent working right.

So this is leading me to believe that the calipers might need a another rebuild?
If that is the case, would this be the time to upgrade
my braking system to something more "current"? Im not looking for crazy
performance, but i would like something that is sporty and maybe something
with abs. What are my options fellow R3V members?

the calipers usually get rebuilt when the puck isnt moving in and out of the bore smoothly or if they leak.
although abs is an upgrade [static coeffecient of friction vs kinetic cof]
some might argue that it is less sporty since you cant lock up the brakes to steer/throw the car round. also i think abs is really used in a small percentage of real world stops.
imho and speaking from years of experience...i would suggest you do a complete brake job.
that is pads [like hawk brand in usa cars but not sure about bmw] and new rotors. replace any lines or calipers that are leaking and replace the rubber lines if you want to go crazy, but these can be a pia.
clean the rotors and install pads then do the critical break in process-bip
bip is 3 moderate stops from 25-30mph then do 3 hard stops from 45mph then park the car and let it cool down, or overnight.
now your done and they stop great.
also i think the brake squel is actually the caliper piston ringinging in the bore much the same way you can make a crystal glass sing by rubbing a wet finger around the edge.

[TurboJake]

I don't know what E30fiend is talking about, but a bad booster can and will only cause a hard pedal, not a squishy one.

The loss of the vacuum aiding the brakes causes a hard pedal. There's nothing more the booster does. It's a single diaphragm with atmospheric pressure on one side, vacuum on another, and a connection in the middle between the pedal and the MC that runs through that diaphragm.

But he's absolutely on the money about the MC failure, what it causes, and that they should be replaced together if brake fluid got into the booster.

[jlevie]

A soft brake pedal results from air in the system, a bad master cylinder, or leaks at the lines or calipers. Squeaking from the brakes can be as a result of sticking calipers or the pad choice. Low dust pads can be bad about this.

To find out if you have a sticking caliper drive the car for a couple of miles without using the brakes and coast to a stop. Then check to see if any of the rotors are hot. A hot rotor would mean that the pads are dragging on the rotors, which in turn means the caliper is sticking.

As mentioned, a bad master cylinder that has leaked fluid into the booster means that the booster must be replaced along with the master cylinder. Brake fluid will kill the diaphragm in the booster rather quickly.