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Old 11-05-2004, 05:51 PM   #1
65Z01
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Default '88 brake pedal won't pump up to bleed fronts??

I just installed new front calipers and now have no leaks but the brake pedal won't pump up and no fluid (nor air) comes from an open bleeder and the "BRAKE" light stays lit?

I'm really stumped here; never had any problem bleeding brakes on a car before.

Could it be an issue with the ABS, booster or maybe even master stuck??
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Old 11-05-2004, 05:59 PM   #2
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I had the same problem on an older car where some crud got sucked back into the brake line right at the caliper. I took the brake line off and slowly pushed on the brake. Pressure finally built up and it blew the junk out and a bunch of brake fluid as well. Made a big mess. This may not be the answer to your problem but if the brake fluid in the caliper was trashy its worth a shot.
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Old 11-05-2004, 07:36 PM   #3
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I just pulled the brake hoses loose from the front calipers and now fluid would come from either even when I pumped the brake pedal.

I'm wondering if I got air into into the master cylinder last night when I was out road testing with that leaking right caliper. The fluid got very low in the front resevoir before I got home.

The shop manual says that, if you change the master cylinder, you need to open the lines at the master cylinder to bleed out air; if you open a line at a wheel to bleed air at that wheel.

So, does that mean that you cannot bleed the master cylinder throught the ABS module???

I don't understand why fluid will not flow from the open front brake lines???
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Old 11-05-2004, 07:48 PM   #4
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You can bleed the MS while it's on the car. Have you tried doing that? Then bleed the lines
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Old 11-05-2004, 07:55 PM   #5
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No, I've been reluctant to bleed the MC but it looks like that will be tomorrow's chore.

If I got air into the lines past the MC can I still bleed the system or must it be pressure bled because of the ABS (thinking I now may have air in the front brake line back to the ABS module??)?

Or is it just air in the MC that is preventing me from getting any pedal pump up?? In this case would cracking the front brake line at the MC be the answer?
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Old 11-05-2004, 08:02 PM   #6
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JIm...in reading your last post....I am assuming that you meant that NO fluid was coming out of the disconnected brake hose when you applied pedal pressure......if that is the case, I agree wiht the above post about bleeding the master cylinder. It may also be that by pressing to hard when pumping the pedal (if you did) ..you may have damaged the seal with in the bore of the master. I'ts happened to a lot of guys. No full brake storkes when bleeding the brakes via pedal pressure. You can run plastic lines from the M/C bleed screws into each fluid resevoir. Pump the brakes to remove the air until the fluid shows no signs of air. The only problem is that you will have introduced air from the M/C into the ABS. That is something I haven't had to tackle...but I see no reason why you couldn't rebleed the system starting from the left rear to remove the air....
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Old 11-05-2004, 08:16 PM   #7
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Well, that too is one of my current concerns as I did apply substantial pedal pressure. Also, the shop manual warns about excessive pressure damaging the booster, but rears seem to work...sort of (hard to tell if there's any boost when only rear brakes are working).

The problem is I don't know if the MS can fail on front brakes only and if it could...what does it feel like (no help from the shop manual on that one).
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Old 11-05-2004, 10:09 PM   #8
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in some cars you have to bleed rear brakes first to achieve a brake pedel, then do fronts
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Old 11-05-2004, 10:15 PM   #9
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On our C4s the front & rear brakes are independant (supposedly), so that a failure in one system still leaves you with the other system.

So, fluid (or air) from the front brakes cannot get to the rear brakes, not even in the MC.
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Old 11-05-2004, 10:20 PM   #10
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I think your problem will be resolved when you bleed the master cylinder.
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Old 11-05-2004, 11:00 PM   #11
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I don't see how air in the front chamber of the MC would not be displaced into the lines by weight of fluid in the resevoir above when I open the hoses at each wheel but I will try bleeding the line at the MC anyway as it's far simpler and cheaper than alternatives.

Maybe brake fluid (not air) is needed in the MC before it can apply pressure to the lines, even when they are open. I don't know the construction of the innards of the MC to know the answer.
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Old 11-05-2004, 11:34 PM   #12
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Well, I couldn't wait till morning, so I just loosened (and removed) the front and then the rear brake line from the MC and pumped the brake pedal. Fluid readily came from the rear MC port but none from the front, not even with repeated attempts.

It looks like, when I pressed heavily on the pedal, I must have damaged the MC front brake piston as I can't come with another explanation.

Any other explanation or ideas??
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Old 11-06-2004, 08:10 AM   #13
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I think you found the problem
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Old 11-06-2004, 05:42 PM   #14
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Chuck I do believe you are right.

I have the MC out and was trying to disassemble it per the Shop Manual only to find that the secondary piston won't budge (it should come out with gentle tapping of the case). It looks like I pressed the pedal so hard as to somehow dampage the secondary valve and lodge it in the bore.

I have a rebuilt MC comming in Mon morning so we'll see what happens....
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Old 11-06-2004, 05:42 PM
 
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