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Leaking Brake Master Cylinder, is Vacuum Booster ok?

Dricky

NAXJA Forum User
Location
NH
1993 XJ Sport. Master cylinder leaking at vacuum booster. How can I figure out if the vacuum booster got brake fluid in it?

Been sitting awhile after blowing the main rear brake line a few years back, besides needing plenty of other work. Ran a new line, replaced the front brakes. 1 front caliper wasn't releasing after braking so replaced that caliper. Flushed new fluid through the lines before installing the new caliper because the old stuff was nice and rusted.

Now that the front calipers work, the master cylinder decided to go. There was already rust on the vacuum booster below the MC, so it mustve leaked at some point before. Id guess between getting some brake fluid spilled out onto where they connect and washing all the rust out of the lines the seal/rust was removed.

Long story short, besides the dragging caliper the MC and VB were working great before flushing new fluid through. Im just going to replace the MC, but when the MCs removed will I be able to see if fluid got into the VB?

* I don't think much couldve gotten in. When the MC failed, the fluid leaked down onto the ground. And locating the leak only took a few pumps.
 
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You should be just fine. Replace master and run like you know what you're doing. If booster is bad you will have a really high, hard pedal with lots of stopping effort.
 
Yea I figured. Just seeing the price, and reading posts of VBs filled with fluid made me wonder. Though now I wonder how it could leak that much into the booster and you not notice a master cylinder issue, loss of fluid, etc.
 
I have had this issue on a few vehicles over the years, but the only way to get it is if the rear seal of the MC is bad, and that you should be able to see. If it's just leaking internally (pedal to floor, etc.) this will not send fluid into the booster. The other thing you'll usually notice when this happens is that you get a good cloud of smoke in the exhaust when you apply the brakes, since it's sucking in fluid. If you did not notice a wet pushrod on the old MC, and if it all seems to work, I'd go ahead and use the booster. If there's a problem it will show by itself.
 
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