master cylinder reservoir

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denny

Master Mechanic
Feb 4, 2017
279
116
43
i think i have an O ring leaking from my NEW.. master cylinder. 81 malibu with the standard mc,nothing special. i think it's from the rear reservoir O ring. i'm pretty sure they just need to be popped off but i have read where some have a pin or bolt that needs to be removed. don't see a pin or bolt on mine. seems to be on pretty tight. i think i removed one years ago and just pried it off without any damage to it. am i on the right track? thanks
 

pontiacgp

blank
Mar 31, 2006
29,270
20,391
113
Kitchener, Ontario
if it is a new defective master cylinder I would be bringing it back to exchange it for a good one
 

malibudave

Greasemonkey
Mar 12, 2010
204
227
43
Houston, TX
I would take it back. It might not be the reservoir seal, but a internal piston seal that is pressurizing the reservoir along with the brake lines, which in turn will leak out of the reservoir cap or the reservoir seal.
 

denny

Master Mechanic
Feb 4, 2017
279
116
43
if it is a new defective master cylinder I would be bringing it back to exchange it for a good one
thanks for the reply pontiacgp. i bought it years ago before retirement. was not very expensive then so i'll probably just chuck it and get another. btw i also still have the original one that worked good but was thinking why not just go new with everything else. have heard some horror stories about todays quality control with master cylinders.
 

denny

Master Mechanic
Feb 4, 2017
279
116
43
I would take it back. It might not be the reservoir seal, but a internal piston seal that is pressurizing the reservoir along with the brake lines, which in turn will leak out of the reservoir cap or the reservoir seal.
thanks for the reply Dave. like i told pontiacgp, i'll just get one from the local parts suppliers and hope for the best. at least i'll have a warranty. was in the garage today inspecting it and was having a hard time with the rear line sealing. kept weeping on me after about a dozen times of on and off. there has to be a problem in that inverted flare port. there are seven inverted flare ports on the master and prop valve and thats the only one that won't seal. i inspected the flare on the line(from inline tube) with a jewelers glass and was not cracked or ill formed. i also lapped the flare with 400 grit then 600. still no seal. when i install these fittings i can see the master port and i push the flare from line on master and hand tighten while holding the flare on the port flare (hope i'm describing that right). the ports on the store bought mc don't look like the ones on the factory ports. factory ports look like they have a very small cross in them. not a very good description but you would have to see them side by side. sorry for the long rant but it pisses me off that a small job like this turns to crap. i'm tempted to get a rebuild kit and just rebuild the original master.
 

pontiacgp

blank
Mar 31, 2006
29,270
20,391
113
Kitchener, Ontario
thanks for the reply pontiacgp. i bought it years ago before retirement. was not very expensive then so i'll probably just chuck it and get another. btw i also still have the original one that worked good but was thinking why not just go new with everything else. have heard some horror stories about todays quality control with master cylinders.

Sounds like me and the manual MC I bought years ago and it turned out to be defective, it took me a few hours to figure that out so I chucked it and bought a new one... :)
 
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