Leak From Brake Master Cylinder Area

Gilly11277

Gilly11277

TJ Enthusiast
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Oct 13, 2021
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Dekalb, IL
Hi all,

Novice here...I had my brake fluid changed late last week, everything was fine - no issues. Yesterday night a buddy & I replaced the front brakes (pads and rotors) along with rear drums (everything except rear brake cylinder). On my way home I noticed no problems with braking, everything seemed fine. About 20 minutes ago after I got home running errands in the family minivan I noticed some fluid on the driveway under the Jeep by the drivers side. I traced the leak back to the brake master cylinder and it looks like there was either a spill from when mechanic changed fluids, or fluid was coming out during my ride home after changing brakes.

Jeep was purchased used with 28,000 miles and is an 05. Everything under the hood looks relatively new and there are no cracks/deterioration on any of the rubber seals or hoses. There is obviously fluid coming out from somewhere, can't really tell where exactly because it was sort of all over the place.

Here is a theory of mine. Could be totally off...

When they changed the brake fluid I'm thinking more went into the reservoir than before because of the extra space in the caliper due to the piston being pushed further out on the factory pads, which were about 60% worn. After installing new pads (and not touching fluid or brake lines), the fluid in the reservoir was closer to the cap because there wasn't enough space in the system to allow it to make it's way into the caliper and get back to the previous levels.

I'm going to keep an eye on it and see if I keep getting leaks. I hope it was just too much fluid in the reservoir and it having no where to go when I was breaking in the pads with harder pedal movement. I really have no idea how these systems work but it seems to be the most logical conclusion if the system is under pressure and it went the path of least resistance.


Thoughts? I'm ready for a school lesson.


*edit*

I suppose it could have also happened when we pushed the pistons back into the caliper using the compression tool. All of that extra fluid in the caliper would have made it's way back and possible put pressure in the system causing the fluid to leak from the cap. Idk, just trying to make sense of it...
 
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i have to ask, why did you have the fluid changed and then changed the brakes yourself ?i normally change the brakes then bleed the system .
 
mrblaine said:
Good way to get sticky or stuck calipers. Flush first enthusiastically before you push the pistons in.
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I suppose I did it the right way? To be honest it was just coincidence that it played out that way. I figured it would make more sense to do brakes and then flush. Like I said, I’m a novice! :)
 
I called the shop it took it to for brake fluid and Bill (the owner) said he’s 99% sure it overflowed because the fluid levels, while perfect at the time, were higher in reservoir after pushing the pistons back. Told me to keep an eye on it but it should be fine now that the excess came out during my drive home.

Today I learned. I’ll touch base if I still see leakage.
 
Gilly11277 said:
I called the shop it took it to for brake fluid and Bill (the owner) said he’s 99% sure it overflowed because the fluid levels, while perfect at the time, were higher in reservoir after pushing the pistons back. Told me to keep an eye on it but it should be fine now that the excess came out during my drive home.

Today I learned. I’ll touch base if I still see leakage.
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To clarify, the add level in the reservoir should be at or close to how far the fluid drops as the pistons extend when the pad wear down. From Full to Add should be fine. The mistake folks make is adding fluid to top it off between pad swaps. The other thing is your shop is dumb. Everyone who works on brakes knows that owners like to top shit off so it will overflow during a pad swap. As such, you lift the hood, suction some fluid out and then top it off to the Full level when the pads are in. Also, you don't want brake fluid on any paint under the hood or on the frame as it will eat that off with a quickness. I'm sad your shop did not take care of that and then didn't tell you when you called.
 
mrblaine said:
To clarify, the add level in the reservoir should be at or close to how far the fluid drops as the pistons extend when the pad wear down. From Full to Add should be fine. The mistake folks make is adding fluid to top it off between pad swaps. The other thing is your shop is dumb. Everyone who works on brakes knows that owners like to top shit off so it will overflow during a pad swap. As such, you lift the hood, suction some fluid out and then top it off to the Full level when the pads are in. Also, you don't want brake fluid on any paint under the hood or on the frame as it will eat that off with a quickness. I'm sad your shop did not take care of that and then didn't tell you when you called.
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My shop only changed my fluid. When they did that the factory brakes were still on the vehicle. They didn’t know I was going to change out the brakes so they really didn’t do anything wrong. They did exactly what I told them to do: Replace old fluid.

Yeah I cleaned that out as best as I could. What is in the fluid that causes it to destroy painted surfaces?
 
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Gilly11277 said:
Yeah I cleaned that out as best as I could. What is in the fluid that causes it to destroy painted surfaces?
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Some people claim google is your friend, or something like that.

It didn't even need the word "brake" be used but if it wanted to be a good friend it would have also told us glycol is there because it has a very high boiling point without needing a second search.
 
JEEPCJTJ said:
Some people claim google is your friend, or something like that.

It didn't even need the word "brake" be used but if it wanted to be a good friend it would have also told us glycol is there because it has a very high boiling point without needing a second search.
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The second one points out that silicone based brake fluid won't hurt the paint and won't corrode brake internals. Sorta true but what they left out is any moisture in the system collects at the lowest point which does corrode and also the main reason normal brake fluids are hygroscopic, so they do absorb moisture and in doing so, heavily dilute its corrosive properties. You also can NOT mix the two.
 
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After a week of monitoring I am happy to announce that there are no other leaks! Guess we can say with confidence that it was too much fluid in the system when the cliper pistons were pushed back to allow for the installation of new pads.

Thanks everyone for the input.
 
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