Master cylinder or brake booster?

[Squishy]

Having a problem with the Escort.  Sometimes the brake pedal will travel almost to the floor, and this problem appears and goes away regardless of being warmed up.  At first I thought it might be the check valve in the booster, but I appear to have full vacuum assist when the pedal is to the floor.  However, braking action is less smooth - where the brakes are usually applied gradually, they become more of an on-off type of deal when this problem happens.  The total braking force to stop the vehicle remains the same.

Do the symptoms sound more like a leaking master cylinder?  Are there some steps I can take to diagnose further?

EDIT: With the engine off, I can't pump out the vacuum and hold the brake pedal up.  I can feel the vacuum going away, but after that the pedal can still be pushed all the way to the ground with medium force.  With the engine on, pumping the brakes does not reduce the pedal travel.

[rrocket]

http://www.tegger.com/hondafaq/mastercylinderreplace/index.html

[blur911]

The master cylinder might be leaking by internally, or you could have an external leak and brake fluid being pumped out.  If your reservoir level isn't going down bet on the master cylinder.

[mar1990]

http://www.tegger.com/hondafaq/mastercylinderreplace/index.html

That was a very good write up...and Canadian to boot!

[barrie1]

Could be the rod in the brake cylinder is slipping past the seal  in there which then allows the pedal to hit the floor. With the engine off you only have vacumn for a few quick stops before it disapears and its gone. I would think a new master cylinder may be in order.  

[articsteve]

How many brake boosters fail relative to the master cylinder?  Not many.

If the brake booster has vacuum like you say I'd put my money on the MC.  Brake pedals with failing MC can act like normal, but just very weak stopping.

[Squishy]

Sounds like the MC then, especially the fact that I can slowly press the pedal to the ground once vacuum is gone.

The Escape has more booster failures (the check-valve) than MC failures, which put me on the wrong track.  Both failures have similar symptoms, but the booster failure results in very weak braking.

[articsteve]

but the booster failure results in very weak braking.

It makes for hard foot pressure plus the weak braking.

The Escape has more booster failures (the check-valve) than MC failures

Well i just consider the check valve more of a failure of the vacuum line more than a bad booster because it's separate part.  When I mean a bad booster I mean one that has sprung a leak in the metal casing due to rust or if the guts no longer work.

There is usually an O ring where the MC fits into the booster.  Maybe that is leaking.  I dunno.  I had weak brakes in a Saab after I pulled it out of storage and never nailed it.  I suspected the MC, but it was more than the car was worth so I didn't bother changing it.

On the Saab to test the booster:  engine off, full pressure on brake pedal, start engine, pedal should then push back against foot pressure.  Doesn't work on every car though.

[Screwbal]

What would cause a hard pedal with hard braking?  I hope this won't be looked at as a thread hijack of the OP.  My car (subaru) has been acting up where when I start off the brake pedal seems normal but over time ~15 miles ~30 minutes the pedal gets harder and harder to the point my pads start to drag and create heat at the rotors.  I'm trying to nail down if it would be the BB or the MC and from what little I know its a 50/50 shot (in my mind)

To ask others who may know more, what would lead to your brake pedal turning into a rock (maybe traveling 1 inch) and applying full braking force?

[Squishy]

A broken master cylinder return spring? 

As the pedal gets harder, do you have to apply more force to stop the car?

[Screwbal]

A broken master cylinder return spring? 

As the pedal gets harder, do you have to apply more force to stop the car?

Once the pedal gets stiff it takes less effort to stop the car.  Less than an inch and your grinding to a halt.  I'm starting to suspect something internal with the MC is broken, or it could be as simple as the brake pedal adjustment.  I found a detailed write up after my post at wwwdotteggerdotcom/hondafaq/mastercylinderreplace/howworks.html where at the bottom it discusses the problems of not having the pedal properly adjusted.

BTW forgive my wwwDOTteggerDOTcom - I dont have enough posts to be able to put in the correct URL

[barrie1]

If the pads are dragging I would suspect the calipurs to be hanging up which will make the pedal stay down as they are not retracting properly. Thats another possibility to have inspected as well. 

[Screwbal]

If the pads are dragging I would suspect the calipurs to be hanging up which will make the pedal stay down as they are not retracting properly. Thats another possibility to have inspected as well. 

I thought about that too.  I'm scheduled to have the MC replaced on Thursday so I'm hoping all is well after that.  Two reasons I'm hoping its the MC.  Its almost 600$ less for the MC vs just 1 caliper being rebuilt.  Its about 1600$ less to replace the MC than replace one caliper (stupid Subaru STI and expensive parts )

The second reason I am thinking the MC is how the rotors are heating up.  I've pulled temps from them multipe times and while the temps vary depending on how far I've been driving the base results are always the same.

Passenger Front - Always the hottest
Driver Front - Warm but cooler than the passenger side
Driver side rear - always hotter than the passenger rear
Passenger side rear - always the coolest.

I found online that my brakes cross between corners for failover sake.  The passenger side front connects to the driver side rear.  The brakes on that circut are always the hottest and end up dragging.  We cracked the bleeder on the driver side rear and it releaved the pressure from the passenger side front and freed up the wheel.  Since cracking the bleader on the rear wheel let the pressure out and freed the dragging I think that should rule out the caliper.  If it was the caliper there wouldn't be any noticable effect from opening the bleeder but that free's it up right away.

Sorry for all the passenger/driver side front/rear over and over - its just the easiest way to describe it but probably makes it confusing to read

I'll keep an eye on this thread for any new suggestions between now and when I get the MC replaced and will also reply back with how the car performs once that peice gets fixed.

**Edit** adding a few more things below.

For some back info I already had to replace my front rotors and pads due to this pressure issue i'm having.  The pressure in the system created a downward spiral on the freeway where I wasn't able to pull over right away.  It caused the pads (all 4) to hang up hard to where I had to downshift to have enough power to not come to a stop on the highway.  When I was able to pull over all 4 rotors were hot as the sun a little blue and even the wheels were hot.  Thats another reason I suspect it isn't a single caliper that is hanging up and more that pressure wasn't able to make it back out of the MC to the resivor.  When that happened and I pulled over the driver side front pads were actually smoking    but now after getting new front pads and rotors its the passenger side front which is buliding the most heat. 

Note to self - never again buy a used car from a private party without having it inspected.  That and people are liars    There were a few other issues the person I bought it from hid or straight up lied about.  But through out the whole process I did learn something... don't be so trusting of people you don't know heh

[barrie1]

Sounds like you have done your research quite well on this brand of vehicle. Its unfortunate that its going to cost you so much for the repairs tho as  many Import parts can be so pricey. Parts can wear out on all brands but its the paying for them later that really counts over the years. 

[Screwbal]

Well as it turned out my research paid off and after replacing the master cylinder everythings been ok horay!!

Anyways just wanted to come back and let anyone know who was watching this thread

[barrie1]

Thank You for the final answer as its good to hear that you are Happy and the car is repaired correctly. 

[moezo]

I know this posting is old but in case someone is searching in this blog. I did think I had a master cylinder problem. I replaced it and found out it was my booster, they say it's rare but it dose happen.