89 740: brake pedal goes to the floor....

TO stop, you have to push the pedal ALL the way to the floor. The
brake fluid reservoir is topped off. In spite of this the brake
warning light doees not turn on. I don't get any light for brake wear
(if there is one), and the brakes are not making any tell-tale squeals
indicating they are worn out. What should I check first?

 

If I had to choose a "first" it would be the front brake calipers, since you
don't indicate anything has been done with the brakes that would cause this.
In addition, if the car pulls to one side when you brake, be especially
suspicious of the opposite side caliper. A quick check would be to raise the
front wheels, either both together or one at a time, and have somebody step
on the brake gradually until it goes all the way down. If either or both
wheels turn freely, continue to remove the wheel and caliper. (The following
may vary with brake manufacturer.) You will probably find the pads rattling
loose rather than being held against the rotor when you remove the caliper.
Remove the bolt that holds the two parts, then remove the sleeve that goes
over the bolt. You may have to drive it out of the caliper housing with a
soft faced mallet... that is what goes wrong. Clean and lubricate that
sleeve and the housing where it fits with disk brake grease, then reassemble
and make sure the sleeve isn't binding. Put it together and check the other
side. Unless the wheel becomes very difficult to turn when your assistant
begins to press on the brakes (like it should), I recommend you do the clean
and lubricate thing. It is an easy alternative to frustrating brake
problems.

The rear brakes (at least on my car - I think it applies to all variations)
don't have a floating caliper so are not susceptible to this problem.

If that doesn't fix the brakes and it has been 100K miles or more since the
last master cylinder overhaul, I recommend going ahead with that. Same
philosophy - a moderate cost for a likely suspect that needs periodic
attention anyway.

Between those and bleeding if you overhaul or replace the master cylinder I
think you will be on the road again.

Mike

 

You need to bleed the air out of the Brake system

Harold

 

Will try those things. Was wondering if it could possibly be the
booster that has failed. When I step on the brake, I hear the sound of
air...a "woooosh" sound. Like air coming out..or I suppose it could be
vacuum---air coming in. I did pull the vacuum line off the booster
with engine running, and there was a strong vacuum there. I am going
to see also why the brake switch doesn't activate with (seemingly)
full pedal travel. Thanks for the help.

 

The brake light switch (stop lights in UK) is mechanically operated and sits
at the top of the brake pedal bracket. The "whoosh" from the booster is what
you would expect as the air rushes into the booster to assist the braking
effort.

 

Bleed the air out of the system.

 

If the booster failed, the brake pedal would be stiff as heck, you'd have to
put your weight on it to stop the car.