Brake fluid is low but there are no leaks

Kenneth G Zinis

Kenneth G Zinis

TJ Enthusiast
Joined
Nov 6, 2018
Messages
682
Location
Bethlehem, PA
This is a first for me, in any vehicle. TJ brake fluid was very low , no sign of leaks at any calipers, lines, booster, nor brake or clutch slaves. Brakes have felt normal, just happened to do a routine under hood check when I noticed this. I did flush and change fluid last year. Who has answer?
 
No clue, I'd just top it off with some good synthetic DOT 3/4 brake fluid and then keep an eye on the brake fittings afterward. Or DOT 5.1, just don't use DOT 5 which is not compatible.
 
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Artsifrtsi said:
MC could be leaking into the booster. Happened to mine, started losing brake fluid a few years ago. Changed out the MC, Booster, and both front brakes... the booster had about a pint of fluid in it.
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Interesting, I guess none of lost fluid was visible until you removed booster and looked inside?
 
I'll second the leaking-into-the-booster possibility. You wouldn't see any external evidence of it until you remove the master cylinder from the booster.
 
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Kenneth G Zinis said:
This is a first for me, in any vehicle. TJ brake fluid was very low , no sign of leaks at any calipers, lines, booster, nor brake or clutch slaves. Brakes have felt normal, just happened to do a routine under hood check when I noticed this. I did flush and change fluid last year. Who has answer?
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prob.shoes or pads expanded as they wear........
 
Kenneth G Zinis said:
Would brake feel/pressure give any clues?
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Depends on how badly / how it's leaking. I had one fail this way on an old Volvo and in that case, the first sign was that the master cylinder would bleed down a bit so the pedal would go soft while sitting with my foot on the brakes.

But it's also possible that it's still holding pressure fine and it's leaking on the return stroke, in which case you'd only feel a change in braking behavior once the level gets low enough to introduce air into the system.
 
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IOwnCalculus said:
Depends on how badly / how it's leaking. I had one fail this way on an old Volvo and in that case, the first sign was that the master cylinder would bleed down a bit so the pedal would go soft while sitting with my foot on the brakes.

But it's also possible that it's still holding pressure fine and it's leaking on the return stroke, in which case you'd only feel a change in braking behavior once the level gets low enough to introduce air into the system.
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So it's likely that the MC is leaking and it's just ending up in the booster? So I'll want to replace both, correct?
 
IOwnCalculus said:
Depends on how badly / how it's leaking. I had one fail this way on an old Volvo and in that case, the first sign was that the master cylinder would bleed down a bit so the pedal would go soft while sitting with my foot on the brakes.
Click to expand...

This is what my TJ was doing. Brakes were firm when initially pressed, but would bleed slowly to the floor eventually if held that long. When I pulled the booster, there was about a pint of fluid in it.

I don't remember the brand booster I went with, it was one that was not painted, and i was in a hurry to get it back together, and didn't paint it... now is covered with surface rust.
 
Artsifrtsi said:
This is what my TJ was doing. Brakes were firm when initially pressed, but would bleed slowly to the floor eventually if held that long. When I pulled the booster, there was about a pint of fluid in it.

I don't remember the brand booster I went with, it was one that was not painted, and i was in a hurry to get it back together, and didn't paint it... now is covered with surface rust.
Click to expand...

Thanks
 
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