88 civic brakes

i have a problem with my brakes.

They failed the other day. They're soft and spongy.

The pedal, whel the engine is off, is quite firm, but sinks to the
floor. With the engine on, its got very little resistance before it
drops. At the moment, with the engine idle, and n drive, the brakes
barely hold it with the pedal to the floor.

i've heard variously that this is the master cylinder, OR the power
brake boster.

Which is it?

 

Master cylinder. The brake booster can make the brakes feel very hard if it
fails, but it can't make the pedal sink.

I recommend a full rebuilt master cylinder. The price difference compared to
a rebuild kit is usually very small - sometimes the kit is actually more -
and it removes some unknowns from the picture.

When you remove the master cylinder, also thoroughly clean up any brake
fluid that has entered the brake booster. It can attack the diaphragm in the
booster, and then you will be in the market for a booster as well (wrecking
yards are a good source). If you haven't done a master cylinder before, you
may want to find somebody who has done it to help or advise. (If you are
going to have it done, never mind!) There are a few by-the-ways...
*The nuts that hold the brake lines onto the cylinder are usually very
tight, and they are made of brass. Every effort should be made to avoid
rounding them. I favor starting out by applying penetrant to the exposed
threads at least an hour before trying to loosen them. Use quality wrenches.
Special "flare wrenches" are made for the purpose, but I have had those
round the nuts off anyway. Pros will recoil in horror, but I've had best
results with vise-grips and tapping them in the loosen direction with a
light hammer.
*When brake fluid spills, clean it off painted surfaces quickly. It will
lift most paint in a few hours to a few days. Water and detergent should do
the job.
*The cylinder needs to be bled when you are done. There are several ways to
do it - all the common ones require you to keep fluid in the reservoir as
you pump the brakes. Most of the time, with a master cylinder job, you can
cheat by loosening those brass brake line nuts a bit so fluid or air oozes
out as the brakes are pressed. (Keep a catcher bowl under the fittings.)
When it's only fluid, tighten the nut. However, I still recommend a real
brake bleed (at all wheels) to flush the old, darkened fluid out.

Mike

 

never rains but pours, - starter motor mount just broke too - how the
hell do you get those bottom bolts out, or in, without a flexible
shaft?

 

Master cylinder. The brake booster can make the brakes feel very hard

In addition to the great advice given above, always try a flare nut wrench
first! As far as bleeding is concerned, it's usually best to bench bleed
the master cylinder first unless you have a pressure bleeder available. To
bench bleed the master cylinder, hold the master cylinder over a drain pan
on a shop bench, fill the reservoir with brake fluid, hold your fingers over
the two brake fluid outlet holes (where the lines connect), use a screw
driver to slowly depress the plunger in the center of the master cylinder, a
mix of brake fluid air will come out of the holes, before releasing the
screw driver make sure that you tightly cover the holes so that no air is
drawn into the master cylinder, repeat the process several times making sure
that the reservoir does not go empty during the process, now install the
master cylinder and bleed the brakes as you normally would making sure that
you get clean fluid out of each wheel cylinder before proceeding onto the
next one.

Eric

 

<snip>

2:15am, and finally finished. its 27f outsifde and i've never been so
glad to be done in my life


thank you both