Brakes fade after driving a distance

[Topdis]

I am perplexed with my friend's 2002 Protege sedan. She said her brakes start going to the floor. I replaced the rear drum shoes as they were half worn. The front disc pads are almost like new. I bled the brake fluid thinking after a distance the moisture could start to boil causing air bubbles. The brakes felt fine after doing this. She calls me a few days later and said the brakes always feel good in the morning but after the stop and go commute of 15 miles, the brakes start to go to the floor. Pumping the brakes doesn't help. After her 8 hour job the brakes still feel low. The next day in the morning it repeats with the brake high and starts to get lower after driving and stays that way the rest of the day.
I tried the brakes with the engined turned off and they feel high without any loss of height. When I turn on the car the pedel goes down a little as expected with the booster kicking in.
Does anybody have an idea what could cause this?

 

[tweety2300]

When you bled them was there air in the line? Only a few things can cause this

Brake booster
Seals in master cylinder
Fluid leak

 

[concept]

I suspect the master cylinder is in need or replacement. One thing that can kill the MC's seals is the often-used brake bleeding method of having someone sit in the car and push the pedal to the floor while someone else opens and closes each brake bleeder. The problem with this is that the master cylinder's piston extends well beyond its normal range of travel, resulting in the piston seal getting damaged by the ridge in the cylinder. If someone had bled your friend's brakes this way, the master cylinder seals may be gone.

 

[Topdis]

When I bled the brakes, I got at first what looked like a few inches of small bubbles almost like foam. That is why at first I thought it was the moisture that steamed up.

When you bled them was there air in the line? Only a few things can cause this

Brake booster
Seals in master cylinder
Fluid leak

 

[Topdis]

Well you are the second that did include the master cylinder as the culpret. I will change it this coming weekend. I am curious though, I thought the pumping of the brakes to bleed them was a standard practice. If it causes harm why is it even suggested?

 

[concept]

There are a couple of correct ways to bleed brake fluid. The most often used by dealerships is something like this:

Another looks like this:

The first one uses positive pressure and the lower one uses vacuum pressure. Neither requires pumping the brake pedal. If you MUST pump the brake pedal, position a block of wood under the brake pedal to limit travel to that which the pedal nornally moves but no more than that.

 

[DeeJayP]

Interesting that this is a current discussion. I just replaced the rear brake shoes on my 2000 Protege 1.6 DX non ABS. Found the RR wheel cylinder leaking so I replaced it. I tried to bleed that wheel cylinder, using the old world method of having someone pump the brakes. Had to perform several cycles of pumping/open bleed screw to get even a little fluid. There is very little pressure. It's been a long time since a did a brake system bleed but shouldn't there be a strong powerful flow of fluid when I open the bleed screw?

As of Wednesday night I was suspecting a Master Cylinder failure. After internet research and this forum I suspect the same even more so.
The protege is a manual. I believe the the clutch resevoir is connected to the master cylinder by a hose. Is there any special bleeding requirements for a manual car when replacing the master cylinder.

Also, is the bleeding sequence still RR, LR, RF then LF. I read something about FWD vehicles having a different bleeding sequence but don't no if it applies to my vehicle.

Slotted Rotors and Hawk brake pads on the front. Stainless Brake Lines, Eibach Coil Springs, Custom built Front End Links & better struts(can't remember the brand right now) make my protege handle and stop way better than stock.....when the master cylinder works. LOL.

Any input would be appreciated.

 

[concept]

1. R rear wheel
2. L rear wheel
3. R front wheel
4. L front wheel.
If you replace your master cylinder, you will need to "bench bleed" it, first. Instructions for doing this are typically included with the MC.

 

[Topdis]

Advanced Auto gave me a free loaner bleeder kit (about a $75 deposit required). It has the vacuum pressure pistol mechanism.

Concept; thanks for your advice.