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  #1  
Old 02-25-2010, 12:23 PM
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brake bleeding damage?

has anyone not heard of but actually themselves messed up the master cylinder while bleeding.

i exchanged my rear soft lines and did a 4 wheel bleed till the fluid was all blue and no bubbles. the pedal was hard but soon as the booster engaged it went down to the rear circuit.

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  #2  
Old 02-25-2010, 02:06 PM
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Quote:
Originally Posted by r.e.wing_fc3s View Post
the pedal was hard but soon as the booster engaged it went down to the rear circuit.
Could you explain this a bit further?
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  #3  
Old 02-25-2010, 06:31 PM
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the pedal gets harder the farther you push down. the rear brake circuit is at the front of the m.c. when you have air in the front brake circuit the pedal only starts to get firm as you engage the rear brakes.
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  #4  
Old 02-25-2010, 07:14 PM
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So what you're saying is that you bled the brakes and they seemed fully bled and otherwise fine until you started the car, and now you have a soft pedal with the engine running, right?
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  #5  
Old 02-25-2010, 07:27 PM
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The reservoir on the 123's have two chambers. A front chamber and a rear. The majority of the res. is the rear chamber and it has to be completely full to fill the front res. The front res actually feeds the rear brakes. So if you bled the brakes and haven't checked to make sure the front res. is full then you've probably bled them dry. I did this on my 240.
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Old 02-25-2010, 07:30 PM
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Does the pedal slowly (way slow sometimes) go down? I have one doing that after I did the front calipers etc... now its the m/s I believe. I use a pressure bleeder.
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  #7  
Old 02-25-2010, 09:12 PM
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i rebled the master cylinder to be sure. i get consistent large bubbles when pumping out the front lines, same on both sides. i wasted a liter of super blue trying to see if the bubbles would stop. i think what happened is that when i replaced the rear lines and was bleeding the rear circuit there was no pressure at the front of the master cylinder, thereby allowing the piston cups for the front circuit(rear of master cylinder) to go into a possibly rusty area not normally traveled by the cups and become damaged. im so mad. another simple job turned into >$100 dollar repair. i couldn't find a rebuild kit for the 85 300d and ended up ordering one for 98. and the super blue that i could buy anywhere else for 12 is 28 a liter up here in bellingham.
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  #9  
Old 02-25-2010, 10:34 PM
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What is this super blue stuff? Regular DOT 3 works just fine.
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83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
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88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #10  
Old 02-25-2010, 11:12 PM
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i didn't remove the m.c so no i didn't bench bleed per say. though i did have my helper pump then hold the brake pedal while cracking the line on the m.c. no air bubbles or sputters just fluid. i like to use ate super blue brake fluid. im sure dot3 works just fine too. i like to see the color change as i bleed out the old fluid. it also has an extremly high boiling point. not that i have ever stressed the brakes that much (or i'd do the 126 upgrade) but with a heavy car, single piston calipers and solid rotors its nice to have a little extra margin of protection.
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  #11  
Old 02-25-2010, 11:28 PM
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If it needs to be bench bled then you will need to bench bleed it...
I have tried to get around it in the past ....and just wound up having to take it off and bleed it...
might check the instructions on a new one and see if they call for that...
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  #12  
Old 02-26-2010, 12:29 AM
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Any new master cylinder will need to be bench bled. If you're just refilling, then no it doesn't need it.
I don't get why you ordered parts for a 98- You can get a new/rebuilt master cylinder for $65 from CSK auto. You don't give your location, but they are switching over to O'Reillys right now, some stuff is a little harder to get but if you talk with the guys chances are you can find what you are looking for. Looking at their website there is a master cylinder for your car sitting at my local Checker auto store for $66.
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  #13  
Old 02-26-2010, 01:29 AM
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to clarify and get back to the original question, im still trying to figure out if people out there have ever had their piston cups torn up while bleeding. this seems to be the case with mine. and if my idea of how it could happen is correct.

i dont yet have the new master cylinder so i haven't bench bled it though i have bench bled many others and would certainly do that. you usually bench bleed until no sputtering, just solid fluid comes out, which is how mine is on the car now.

i spent that much because i wanted to go with an oem trw master cylinder. i dont understand why rebuild kits arent available that i could find for the 85 300d. they have them for the older cars for like 10$
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  #14  
Old 02-26-2010, 03:24 AM
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Quote:
Originally Posted by r.e.wing_fc3s View Post
to clarify and get back to the original question, im still trying to figure out if people out there have ever had their piston cups torn up while bleeding. this seems to be the case with mine. and if my idea of how it could happen is correct.

i dont yet have the new master cylinder so i haven't bench bled it though i have bench bled many others and would certainly do that. you usually bench bleed until no sputtering, just solid fluid comes out, which is how mine is on the car now.

i spent that much because i wanted to go with an oem trw master cylinder. i dont understand why rebuild kits arent available that i could find for the 85 300d. they have them for the older cars for like 10$
There was another thread a few months ago debating how to bleed brakes. No resolution. I use the two person method with the helper putting pressure on the pedal while I crack the bleeder screw. However, I do a short open close on the screw so the helper's foot never goes to the floor. That to prevent the damage that you probably had by pushing the cups to a never used region that had a bad surface. I've never ruined a MC.
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  #15  
Old 02-26-2010, 05:58 AM
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I frankly dont see how you could damage the mc that way. I suppose it is possible but I cannot see it.

It sounds to me like a bleeding error. It is what would happen if you let the bleeder open and just pumped without closing the bleeder.

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