Could the diaphragm be the culprit to my brake problem? - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 13 (permalink) Old 07-16-2009, 08:01 AM Thread Starter
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Could the diaphragm be the culprit to my brake problem?

Hi again, guys,

Man, just when you got something fixed, another breaks (pun?). Was driving and brakes went to the floor, then with some pumping restored to the correct/good/normal position. happened 2 times going to work. So I parked, and looked at the fluid level and OK. Also, no apparent leakage under car. Could this indicate a bad/starting to go bad brake booster (diaphragm?)?
Tanks
Joe

Last edited by Joe Papa Sr; 07-16-2009 at 08:08 AM.
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post #2 of 13 (permalink) Old 07-16-2009, 08:31 AM
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A failed brake booster would not cause the pedal to go to the floor. A failed master cylinder would. And a leaky master cylinder can leak into the booster and hasten its demise.

- - Eric
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post #3 of 13 (permalink) Old 07-16-2009, 09:34 AM Thread Starter
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A failed brake booster would not cause the pedal to go to the floor. A failed master cylinder would. And a leaky master cylinder can leak into the booster and hasten its demise.
Thanks, Eric. Master is only low about 1/4" from tippity top. Also, no leakage drips etc under booster, or area.

So, when you say a failed MC, could you have a bad MC and no leak, as the plunger would be in the process of failing by not plunging, and not necessarily leaking?
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post #4 of 13 (permalink) Old 07-16-2009, 11:43 AM
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The seals inside the master cylinder can fail preventing the pedal from building any pressure in the system. It could leak into the booster and, if in small amounts, get sucked into the engine (intake vacuum is what 'powers' the booster) such that you wouldn't really see any evidence. If such a leak is bigger, it will tend to produce white smoke out the exhaust. It could also accumulate inside the booster and also remain unseen (for a while...)

The master can also leak around the seals and the fluid get returned to the reservoir (so you won't see the level drop).

Anyway, brake pedal that goes to floor means 'don't drive until repaired'. Especially - don't drive behind me!

- - Eric
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post #5 of 13 (permalink) Old 07-16-2009, 01:26 PM
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. . . It could leak into the booster and, if in small amounts, get sucked into the engine (intake vacuum is what 'powers' the booster) such that you wouldn't really see any evidence. If such a leak is bigger, it will tend to produce white smoke out the exhaust. . . .

In this case, wouldn't the fluid accumulate only in the non vacuum side of the brake booster (aft chamber)? Wouldn't this only be drawn into the engine if the brake booster diaphragm also leaked?

Thanks.
Gerry

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post #6 of 13 (permalink) Old 07-16-2009, 03:52 PM
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Oh, so now you're expecting me to think and make some sense? When did that rule get implemented!?!

I suspect you are right. But many brake boosters seem to have rubber bits that are intolerant of brake fluid (who's smart idea was that?). So, if some brake fluid does get inside, it often isn't long before the rubber becomes degraded and leaky. And we can all imagine the consequences of degraded rubbers and defective diaphragms...

- - Eric
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post #7 of 13 (permalink) Old 07-16-2009, 04:10 PM
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....And we can all imagine the consequences of degraded rubbers and defective diaphragms...
ROFLMAO!!!
BLAAHAAAHAAHA!!!

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post #8 of 13 (permalink) Old 07-16-2009, 04:38 PM
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In this case, wouldn't the fluid accumulate only in the non vacuum side of the brake booster (aft chamber)? Wouldn't this only be drawn into the engine if the brake booster diaphragm also leaked?
What can happen is that the vacuum in the booster can suck the fluid out of the brake master cylinder (M/C) through a leaking rear seal. So the fluid goes into the forward (M/C side) of the booster. This is the side of the booster that has the vacuum line but it is not the only side of the booster that has vacuum. When the brake pedal is released, the air valve in the booster opens an air passage which connects the front and rear booster chambers together. In this condition, there is equal vacuum on both sides of the diaphram. When the brake pedal is pressed, the air valve closes the vacuum passage and opens the rear chamber (brake pedal side) of the booster to atmospheric pressure. It is this differential pressure, atmospheric pressure on one side of the diaphram and vacuum on the other, that provides the 'power' assist. The 'whoosh' sound you hear when pressing the brake pedal is air entering the rear chamber to fill the vacuum.

Joe Papa,
Your symptoms indicate at least one (of two) failing piston primary seals in the master cylinder.

Jim

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post #9 of 13 (permalink) Old 07-16-2009, 04:46 PM
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Joe:

We could diagnose the exact failure mode of your MC all day long, but the bottom line is that you need to replace it pronto. Having the pedal go to the floor is NOT good. The fact that pumping fixed it the first time doesn't guarantee that it will work the next time.

When you pull off your old MC, you can try using a turkey baster, or other source of suction to see if there is old brake fluid down in the booster. Yea, some of it would have gotten drawn into the engine, but some will remain puddled down there. Use the baster, then stuff in rags / ppr towels to get as much out as possible.

As ghnl says, the booster will eventually die due to exposure to brake fluid (and no, that doesn't make sense to me either). But, it will last for awhile longer - perhaps a few years. And, when the booster does fail, the consequences aren't that dire - it just takes more muscle to stop the car, but unless your petite, 90 pound wife routinely drives it, that's not a big deal.

Jay Mackro
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post #10 of 13 (permalink) Old 07-16-2009, 05:52 PM Thread Starter
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Thanks to everyone here on this, and good advice on safety to attack this asap. Update: drove home from work, and absolutely no problem. Tight brakes. Cant understand it. Now, I just did some work on the car a few days ago (you may have seen the post (s)), removed rad, new ac belt, etc. I cant see how this would have altered the brakes.

Anyway, I need to get a handle on this, and I appreciate your concern. If anything, I am driving only on the right lane, and keeping distance. Also, I have right hand like Black Bart's ready to draw his 6 shooter, fingers twitching, but mine is ready to pull the safety/emergency brake for rear tires.
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post #11 of 13 (permalink) Old 07-16-2009, 05:56 PM Thread Starter
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Thinking ahead, I rebuilt my clutch MC before with a kit. Can the same be done effectively for the brake MC?
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post #12 of 13 (permalink) Old 07-16-2009, 06:33 PM
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Yes, master cylinders can be rebuilt. It the bore is corroded or pitted the rebuild won't last long however. Check prices of rebuilt vs a rebuilding kit. The ready-to-install master cylinder may not be that much more than the D-I-Y kit.

- - Eric
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- -~ 1981 GTV-6 ~
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post #13 of 13 (permalink) Old 07-16-2009, 07:02 PM Thread Starter
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Yes, master cylinders can be rebuilt. It the bore is corroded or pitted the rebuild won't last long however. Check prices of rebuilt vs a rebuilding kit. The ready-to-install master cylinder may not be that much more than the D-I-Y kit.
Good point. I might just go with the new. Now, to see what happens tommorow driving in to work.........
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