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First things first. This was done on a 1980 733i, which means it's not 100% the same as the later model cars. However, most of it will still apply. Also, it worked for me but that doesn't mean it will work for you. I TAKE NO RESPONSIBILITY IF IT DOESN'T WORK FOR YOU, OR IF ANYTHING BREAKS, YOUR WIFE OR HUSBAND LEAVES YOU AFTER DISCOVERING YOUR NEW VOCABULARY DURING THIS PROCESS, OR ANY OTHER REASON. You can however e-mail me with any questions at kd7olf@xmission.com and I will answer as best and as quickly as I can. I'll also try to post items others discover doing this to help people with other cars newer than mine.
This project ended up being an all day job, but that was due more to lack of an air compressor and having to borrow rides into town to get to one. That took a lot of the time.
Tools Required:
You need a 17mm wrench (or socket, preferably
with breaker bar) to remove the calipers, 11mm wrench for the brake line,
a small drift to knock the pins out of the caliper (and small hammer, or
a big rock would work too if you're desperate), access to an air compressor
with a blower attachment with rubber nozzle end, a big pair of channel
lock pliers (vice grips could also be used), needle nose pliers, a sturdy
plastic awl or needle, a couple c-clamps, PB Blaster, and a lot of
patience.
Parts Required:
2 seal kits, one for each side.
Step 1:
Disconnect the mount on the strut tower that
holds the brake line. This gives you more flex to get the line out
of the way as needed. Disconnect the brake line from the caliper
with the 11mm wrench. I take a small piece of plastic wrap
and a rubber band, wrap the plastic wrap over the end of the brake line
and secure with the rubber band. This keeps any crud from getting
in the brake line, as well as traps any leakage of brake fluid from getting
on the ground, or in your face at the wrong time.
Step 2:
Unbolt the caliper. This is held on by
two 17mm bolts from the BACK side of the caliper (facing towards the engine).
DO NOT UNDO the four smaller bolts on the front. This will separate
the caliper halves and cause a mess. Plus, most seal kits DO NOT
include the seals for the caliper halves. You have been warned.
Step 3:
Now that you have the caliper out, knock out
the pins holding the pads in place with the drift (or a nail with the point
filed off, etc.). You will also be able to remove the anti rattle
spring now as well. Now it's time to remove the existing outer seals.
First, there is a small metal rind around the outside of each seal.
It has a split in it, and is held on by spring pressure from spreading
this split apart. Since you're replacing the outer seals anyway,
you can also grab the seal with a pair of needle nose pliers and pull it
up, pulling the ring with it.If some of the seal sticks to the piston and
rips away from the rest, don't worry about it too much, you can get it
off later.
Step 4:
This is where you need the air compressor.
Put a block of wood or other suitable material (I used the existing brake
pads since they were going to be replaced anyway, about 50% worn out, much
more and you need extra space from a wood block anyway. You want
about 1" or so of material between the pistons). Place the caliper
upside down on a table or sturdy surface, and place the air nozzle from
the compressor in the fitting for the brake line. COVER
THE WHOLE THING WITH A RAG! I learned
the hard way that the rag was needed, as you WILL get some spray back from
the hole, as well as possibly from the pistons if one comes out past the
inner seal. If you're lucky, all four pistons will come out equally,
wedging your pads or wood between them. if this is the case, skip
to removing the pistons. If not, you've got a stuck piston.
Step 5, the fun begins (one or more
stuck pistons):
First thing to try is using a c-clamp and pads
(or small wood blocks) to hold back the pistons that do move, and hit it
with air again. Another note, when you push the pistons back in,
COVER
THE BRAKE LINE FITTING HOLE WITH A RAG!
This fitting, which is most likely facing at you, can jet out a good deal
of fluid when you push the piston back in. And I can now say, brake
fluid does NOT taste very good! If you're lucky, the stuck piston
will now come out, and you can then push it part way back in, put the regular
block or pads back in, and hit it one more time to get all 4 pistons most
of the way out.
Step 6, the !(*@#$!!! piston is
still stuck!
If the piston is refusing to move with shop air,
it's time to get more drastic. In my case, the pistons were stuck
because of crud and contaminated fluid that were most likely caused by
the outer seal on the stuck pistons having gone bad and letting water and
other crud into the area. Also, the pistons were out far enough to
allow me to grab the top of each with channel lock pliers. If they're
in all the way, it's going to be a major PITA to get it out used PC Blaster
to help free the piston (it will eat the inner seal, which is OK since
it's being replaced, but make sure to keep
it out of any open bores!) Let the stuff
work for a while, then carefully grip the top of the piston (the part that
the seal slips over, NOT THE MACHINED SURFACE
THAT RIDES IN THE BORE!. Twist back
and forth, careful not to damage the metal and see if you can break it
loose. Of my two stuck pistons, one started moving easily after the
PB Blaster application, and came out (with a serious coat of varnish on
it). The other was a huge pain. It took four or five applications
of PB Blaster (just on the piston/bore mating area), and a lot of twisting
to get it to finally move. Once it started moving, it took a couple
more applications of PB-Blaster, a lot of twisting, and some choice words
to get it out, but it DID come out!
Step 7, Removing the pistons:
Since they're most of the way out at this point,
gently use the channel locks (or vice grips) and rotate the piston while
pulling it out of the bore completely (once again using the upper part
of the piston and NOT the machined surface). Once all four are out,
check the condition. If all you have is varnish or VERY slight corrosion,
the hard part is all done and you're ready to continue. If there
is bad corrosion, time to get new calipers. You can't machine or
hone the bores in these and not have them leak (or at least so I've been
told).
Step 8:
Remove the inner seal ring with the plastic awl
or plastic needle. Don't use metal tools for this, it's too easy
to scratch the bore. Mine were almost glued in to the groove cut
in the bore, and took some wiggling with the plastic awl to get them to
start coming out, but it's fairly easy. Now you're ready for cleanup.
Step 9:
I used acetone to clean the pistons, and just
good clean brake fluid to clean the bore. I found, at least on mine,
that the varnish was 99% on the piston ad not the bore, so the bore cleaned
up very easily. Once I had soaked the pistons in acetone for a while
(helps loosen the varnish up, and removed the rest of the outer seals that
had glued themselves on), I wiped them as clean as I could, and used medium
Scotch-Brite to clean the rest of the varnish off. Use it gently,
you're just trying to get rid of the rest of the varnish and/or corrosion
without scratching up the metal. If the pistons were corroded, check
them again at this point to verify their condition. If they're pitted
or have any real problems from it, replace the caliper. Clean the
bores with good brake fluid, and flush them out a little with fluid as
well if you used PB-Blaster to get it all out. You want these as
sparking clean as you can get them.
Step 10:
Take your seal kit and layout the parts.
You did also clean your hands well before this step, correct? :)
Take a small CLEAN container and pour some fresh, clean brake fluid into
it. You're going to use it to lubricate the parts as you reassemble
them. Start by putting the inner seal in place. Lubricate it
well (so it's pretty much dripping and completely wet) with brake fluid.
Make sure that it's flat to the inner recess, and has no twists in it.
At least on mine they wanted to twist and took some fiddling with them
to make sure they were completely flat. Get all four of them in before
continuing (they'll stay in place nicely once it's in, so they aren't going
to fall out on you while you turn the caliper around.)
Step 11, reinstalling the pistons
and outer seals:
Use the brake fluid and lubricate the bore (wet,
wet wet!) and the piston. Carefully slide the piston into the bore,
making sure to keep it COMPLETELY FLAT. If it's flat, it will drop
down to the inner seal with just finger pressure. If it won't drop,
it either isn't completely clean, or it's crooked. Pull it back out
and start over. Once you get it to drop to the seal cleanly, you'll
have to put more pressure on it to get it past the seal. A small
block of wood and a small hammer will do this nicely. One trick I
did also, was to put the outer seal on the piston BEFORE knocking it down
into the bore. It's a LOT easier to get the outer seal on now rather
than after the piston is past the seal (and most likely all the way in).
Make sure the piston is ALL THE WAY DOWN TO THE SEAL before you whack it
with anything. The new seals will most likely be a bit larger since
they are fresh and haven't shrunk, and will be much tighter than the old
ones. Once it's pressed into the bore, put the metal ring into the
groove ( I put the opening of the ring towards to middle of the caliper,
between the pistons) and stretch it out so that it falls into the groove
all the way around. I used the tip of the needle nose pliers to gently
press the ring all the way down into the groove. Repeat the process
for the rest of the pistons. And now, you're done with the hard part!
Step 12:
Put your new pads (or old if you're not wanting
new pads) into the caliper, making sure to clean and lube the pins and
spring (or replace with new). Make sure to get the spring under the
pins properly, as well as replace the brake pad wear sensor (thick side
facing the pad, inner pad of left front caliper). The calipers are
now ready to reinstall into the car.
Step 13:
Reinstall the calipers. I find that it's
easier to reconnect the brake line with the caliper NOT bolted firmly in
place, since you can wiggle the caliper as well to get everything to line
up and thread properly. Use a bit of anti-sieze on the bolts to make
removal easier later. Once it's all bolted back together, time to
bleed the brakes!
Step 14, bleeding the brakes:
Bleed your brakes as you normally would.
I would also bleed it more than you normally would, just to make sure that
everything is flushed out well, especially if you used PB Blaster to remove
a stuck piston. I also noticed during the bleeding process (using
the pump and hold method, I don't have a pressure bleeder :(
that the pistons were extending and retracting nice and evenly. That's
a good sign!
Step 15:
Enjoy your new brakes!