Master cylinder

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Re: Master cylinder

Postby 3X00-Modified » Fri Feb 07, 2014 3:32 pm

Depending on the failure a bad booster makes the pedal harder... not softer... The booster is assisting pedal pressure against the master so you get more braking power with less effort... take that away and its like a rock and you have to push really hard to stop. Obviously other failures are possible but in his instance he keeps re-bleeding the system and getting air from it.

When you first move the car can you hear the ABS system click and whatnot? It will not do it when just starting you need to start rolling before it will do like a test cycle. I know the pedal can feel softer until this happens.



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Re: Master cylinder

Postby ifixalot » Mon Feb 10, 2014 9:24 am

Yes, after the car rolls a few feet, I hear the anti-lock test itself.
When the pedal goes soft and has more travel, I notice it even before I start
the car. (I have a habit of stepping on the brake before turning the key.)
So, then I move the car, the anti-lock tests and the pedal stays soft and has
more travel than normal. But this last time, playing around and getting the anti-lock
to kick in, The pedal got better, then I bled it again and I'm waiting to see if it holds.
I checked yesterday and it was still good. We had -7 last night so I'm curious
how it is this AM.
I wonder, if air was sucked in at any wheel cylinders or calipers, could that air travel back up
to the master? I know the rear brakes apply first and then the fronts apply "on top" of the rears.
This feels like the sponginess is in the rears. It all started with the rears, maybe the parts I bought
for the rear were inferior.



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Re: Master cylinder

Postby 3X00-Modified » Mon Feb 10, 2014 9:28 am

I think you'd notice more of a leak before seeing it suck air back in the system... just think your sending like 500-800 PSI to those cylinders.



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Re: Master cylinder

Postby ifixalot » Tue Feb 11, 2014 10:42 am

We had -12 last night. Pedal was spongy and I got air out of it again this morning.
Yesterday it wasn't bad but before I parked it, I bled it just to see
if anything would come out, I got a couple tiny bubbles.
This AM I got lots of big bubbles.
Has anyone ever had the ABS unit apart? Does it have o-rings or seals
inside that might be letting air in?
Maybe my rear cylinders weren't bad, maybe my master was okay too, maybe the problem
has been the ABS unit all along?



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Re: Master cylinder

Postby 3X00-Modified » Tue Feb 11, 2014 11:35 am

This is the best exploded view of the setup I can find online.. I'm sure there are other o-rings in there but there is also the sensors on top that have o-rings on them...

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I can't see how your getting air in the system yet when brakes are applied you don't have an external leak somewhere.



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Re: Master cylinder

Postby ifixalot » Tue Feb 11, 2014 8:58 pm

Thanks for posting the diagram.
I have seen some fluid on the ABS but I thought it was just drips from the bleeding.
I'll have to keep an eye on it. Air molecules are smaller than brake fluid molecules, I would think, perhaps air can get in but not much fluid leaks out. In doing a search for :"ABS unit leaks", it does occur.



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Re: Master cylinder

Postby 3X00-Modified » Wed Feb 12, 2014 8:40 am

Yeah but I always look at the extreme's... You have 14.7 PSI of air pressure and maybe the addition of vac when you apply and release the pedal... BUT you have 800PSI of brake fluid pressure when braking... kinda crazy that the air makes it in there yet the fluid isn't pouring out.



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Re: Master cylinder

Postby woody90gtz » Wed Feb 12, 2014 9:22 am

I have heard of this before while I was researching my brake saga with the Camaro. Air molecules are smaller than brake fluid molecules, so you can get air in without a fluid leak.


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Re: Master cylinder

Postby ifixalot » Thu Feb 20, 2014 9:15 am

Update, after cleaning the ABS, I found no more fluid on it.
So I don't think it is leaking.
I wound up taking the rear cylinders apart and found one cup was
a bit distorted. That one, had fluid residue under the dust cap, the others
were dry. I don't like the springs Autozone uses so I put in my original
springs with washers that force the cup out against the cylinder wall.
I'm thinking this was the source of my problem. Time will tell.




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