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Old 11-29-2003, 08:21 PM   #1
SLeepr
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Default Booster or Master Cylinder?

I just inspected my wife's brakes and the front and rear pads are all in great shape. There are no leaks or any reason to believe air entered the system. However, her pedal travels close to the floor board before it engages the brakes. When I pump the brakes with the car off, they build the expected resistance. But, once you turn the key to the run position, the pedal travels downward (does not sink slowly like a bad master cylinder). I'm wondering if this is a booster or master cylinder issue? Any other possibilities?
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Old 11-29-2003, 09:26 PM   #2
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Check the rear brake adjustment, assuming they're drums, notwithstanding your calling them pads.
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Old 11-29-2003, 09:35 PM   #3
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Sorry, I should have referred to them as shoes. They are adjusted appropriately, as they seem to have the expected resistance when you turn the cylinder.
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Old 11-29-2003, 09:40 PM   #4
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I'm uncertain what you mean by "expected resistance" or "turn the cylinder". To me, the expected resistance is zero, whether there's .0001 inch clearance between the shoes (good adjustment) and drum, or .5 inch clearance (impossibly far off). By cylinder, I can only assume you mean the brake drum, not the wheel cylinder...otherwise, I have no idea waht you're talking about!
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Old 11-29-2003, 10:43 PM   #5
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Sorry, I guess it's a little harder to word on the internet. The shoes give slight resistance to the shoes but still turn as you normally would expect them to. When the brake pedal is engaged, they do bite down. I don't think that it's an adjustment issue with the rear brakes, as they haven't been touched for quite sometime......up until today. Also, the rear brakes are only doing a small portion of the braking anyhow. I'm guessing that there's a hydraulic issue in the booster or master cylinder. Even looking around the master cylinder and all four corners, there is no evidence of a fluid leak.
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Old 11-29-2003, 10:51 PM   #6
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If the pedal travel is normal with the engine off, I would suspect some kind of booster problem..
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Old 11-29-2003, 11:18 PM   #7
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I don't see a booster problem increasing travel.

I will note that the 96 Saturn FSM does list internal MC seal leaks as one possible cause of excessive pedal travel.

While I would expect that to be true across brands, what year and make is the vehicle you're talking about?
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Old 11-29-2003, 11:26 PM   #8
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Come to think of it, the pedal would be harder to depress if the booster was shot. My experience with bad master cylinders usually involves a slow increasing pedal travel when depressed. However, you should still be able to pump and get initial bite from the brakes. It would take quite a leak to have it initially travel down to the floor. Is there anyway for air to enter the system, short of a bleeder screw or running extremely low on brake fluid? It's not making sense.

The car is a 91 Ford Escort 1.9 Sohc.
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Old 11-29-2003, 11:28 PM   #9
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Pedal travel and "felt" firmness WILL NORMALLY increase when you pump the pedal with the "engine off" as you described. The vacuum brake booster STORES vacuum with the engine OFF that gets gradually used up if you repeatedly pump the pedal with the engine OFF. Once it's all gone, you "feel" the resistance in the system that is ALWAYS there, except now you have no vacuum booster helping you to depress the pedal. On the other hand, if pedal travel gets "firmer" or "varies" when you pump the brake pedal with the engine RUNNING, it strongly suggests a problem with the MASTER CYLINDER'S hydraulics.
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Old 11-29-2003, 11:33 PM   #10
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With the car running, I can pump repeatedly and get no change in brake travel. It consistently falls to the same place, close to the floor. I plan to bleed the brakes tomorrow, although I can't see how air could have gotten into the system (except through the MS?).
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Old 11-30-2003, 12:20 AM   #11
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Quote:
Originally posted by SLeepr
Sorry, I guess it's a little harder to word on the internet. The shoes give slight resistance to the shoes but still turn as you normally would expect them to. When the brake pedal is engaged, they do bite down. I don't think that it's an adjustment issue with the rear brakes, as they haven't been touched for quite sometime......up until today. Also, the rear brakes are only doing a small portion of the braking anyhow. I'm guessing that there's a hydraulic issue in the booster or master cylinder. Even looking around the master cylinder and all four corners, there is no evidence of a fluid leak.
I think that you are still not getting the terminology right. Rear brakes have drums? Then you will have two brake shoes on the inside of each drum. They are activated by the wheel cylinder pushing pistons out against the shoes that then push out against the drums to provide the friction to slow the car. The proper adjustment of the shoes is so that the shoes should almost be touching the drum. Best way to do get this is to adjust the shoes out using the the adjuster so that the shoes are just touching the drums. Easy done by adjusting and then putting the drum on the car and spinning the drum. with the drum on the hub square you should be able to hear the shoes scraping on the drum very lightly and still be able to spin the drum with little to no resistance. Now back the adjuster off a few teeth so the shoes are moved away from the drums. Do this on both sides. If the rear brake adjustment was the problem then you should have just fixed it. You said that the rear brakes haven't been touched in a long time which gives good reason to believe that the rear shoes are out of adjustment. As for the rear brakes doing a small portion of the brake work well they likely do about 40% of it. But if they are out of adjustment then they can do even less and the brake pedal will have to travel more than normal because the master will need to push more fluid to the rear to get them to start biting and let pressure build in the hydralic system. The fronts will not begin to work until there is pressure in the hydralic system.
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Old 11-30-2003, 12:51 AM   #12
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Quote:
Originally posted by ssicarman
I think that you are still not getting the terminology right. Rear brakes have drums? Then you will have two brake shoes on the inside of each drum. They are activated by the wheel cylinder pushing pistons out against the shoes that then push out against the drums to provide the friction to slow the car. The proper adjustment of the shoes is so that the shoes should almost be touching the drum. Best way to do get this is to adjust the shoes out using the the adjuster so that the shoes are just touching the drums. Easy done by adjusting and then putting the drum on the car and spinning the drum. with the drum on the hub square you should be able to hear the shoes scraping on the drum very lightly and still be able to spin the drum with little to no resistance. Now back the adjuster off a few teeth so the shoes are moved away from the drums. Do this on both sides. If the rear brake adjustment was the problem then you should have just fixed it. You said that the rear brakes haven't been touched in a long time which gives good reason to believe that the rear shoes are out of adjustment. As for the rear brakes doing a small portion of the brake work well they likely do about 40% of it. But if they are out of adjustment then they can do even less and the brake pedal will have to travel more than normal because the master will need to push more fluid to the rear to get them to start biting and let pressure build in the hydralic system. The fronts will not begin to work until there is pressure in the hydralic system.
Yes, I botched the terminology. Again, I've been in and out of the garage, trying to type and work at the same time. I apologize for not collecting my thoughts and typing them appropriately. I do understand your explaination and to tell you the truth, that's pretty much what I was trying to outline with my earlier post. The shoes are and have been slightly toughing the drum but still allowing it to spin freely. This would be proper adjustment would it not? I am almost certain that this is not a rear shoe adjustment issue.
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Old 11-30-2003, 01:38 AM   #13
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This may or may not help...

I had the same thing going for me until I changed the rear brake cylinders. They were seeping and thus loosing pressure. This ultimately led to increased pedal travel. Look at the cylinders and see if they are seeping.
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Old 11-30-2003, 12:57 PM   #14
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They are completely dry. Also, the master cylinder fluid level is still at the full mark, unchanged whatsoever. If anything, the fluid is looking a little brown and needs to be changed.
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Old 12-02-2003, 12:49 AM   #15
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My guess is master cylinder. I had the seal fail between the front and rear "ports" on a master cylinder once. The pedal would fall to the floor easily while driving. Don't remember if pumping helped or not.

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Old 12-02-2003, 02:29 AM   #16
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Yeah, I'm going to work in that direction. It seems to be the only logical thing at this point. Bleeding the brakes didn't make any difference. All four corners were dry and everything seems to be adjusted appropriately. Braking is even and balanced when the pedal finally engages. My guess is, either my wife didn't notice the sinking when/if it was happening. Or, it just crapped out all at once.

I'll let you guys know.
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Old 12-02-2003, 08:29 AM   #17
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Yeah, sometimes the one driving the car daily won't notice a gradual change, but when a "new" driver tries it, the difference is obvious.
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Old 12-02-2003, 09:48 AM   #18
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Why not get her a Saturn? Theataris has a great deal in the classifieds.
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Old 12-02-2003, 11:36 AM   #19
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Oh you don't know how long I've been trying!!

It would make things SO much easier. The only bright side is, I've gotten TOO much practice working on an Escort. Don't ask me how many times I've changed the alternator (you think Saturns are tough to get out).

If she were open to it, I would have bought David93SL2m's SC2 and let her use it. Oh well, maybe I'll talk her into a Vue one of these days.
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Old 04-13-2004, 03:03 PM   #20
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Sleeper what happened? i need some closure.

i had crappy pedal feel for a while, and i replaced pads and shoes. it was almost worse. still a lot of travel.

so bleed the whole system and we are at the same point.

so i think the master cylinder is my next stop.

let me know if you guys have any suggestions
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