Brake Fluid Leak, mystery source: 97 Civic

[HeX]

I've had a seemingly mysterious brake fluid leak in my '97 Civic HX for a while, only to realize today that my Brake Booster is leaking into the foot well. I hadn't noticed it before because the fluid is being leaked into the floor matting and not showing up above it on the plastic layer. Understanding that brake fluid can eat into many materials, should I consider removing that soaked padding, possibly replacing it, or can it be sopped up?

I considered upgrading the Brake Booster to one that would perform better but after much research it seems I'd have to upgrade some combination of parts (such as the master cylinder, calipers, rear drums to discs, etc.) along with it to have more than just a stiffer pedal with the same braking capacity. It seems that no master cylinder & booster just bolt on without some sort of mod, and I don't want to mod anything for this fuel sipping daily driver unless its considerably worth it while keeping the rear drums. If I am mistaken, by all means do correct me.

O'Reilly's currently has a reman.'d OEM brake booster for $78 & change after the $20 core charge., which includes lifetime warranty. I personally prefer re-manufactured OEM parts over aftermarket parts in instances such as this. Any added suggestions?

I also noticed the vacuum line to the brake booster was loose at the engine to where I could pull it off after a few decent twists. I tightened it up but haven't driven it around yet. Would that loose hose allow enough of a leak to affect braking?

 

[dancam]

I agree with your thoughts on reman OEM parts being better than aftermarket, but myself i would get one from a wrecker. As for the vac line- is the hose soft or hard? If soft vaccume will very easily seal itself. If its hard you should replace the hose. No harm in clamping any hose though


Sent from my iPhone using Tapatalk

 

[HeX]

I agree with your thoughts on reman OEM parts being better than aftermarket, but myself i would get one from a wrecker.

The only reason I wont buy a junkyard booster is because I'll have no idea how close it could be to leaking as well. Thus, the lifetime warranty is a nice bonus for a sub-$100 purchase.

As for the vac line- is the hose soft or hard? If soft, vacuum will very easily seal itself. If its hard you should replace the hose. No harm in clamping any hose though

It is hard to the point where there is no flexion upon squeezing, but there are no observable leaks either. I'll add it to the list of parts to replace.

 

[dancam]

The only reason I wont buy a junkyard booster is because I'll have no idea how close it could be to leaking as well. Thus, the lifetime warranty is a nice bonus for a sub-$100 purchase.

It is hard to the point where there is no flexion upon squeezing, but there are no observable leaks either. I'll add it to the list of parts to replace.

Ok, probably time for a new one then. They are supposed to be stiffer than rad hoses because they have to be able to handle the vaccum without collapsing but they shouldnt feel brittle/hardened. The only vac lines ive ever seen that were supposed to be stiff/hard had special clamps.
The leaking brake fluid wont damage metal, justpaint and plastic unless you leave it long enough to let the metal rust. The problem with it is that it doesnt evaporate. So after you get your carpet pulled back use a quickly evaporating solvent to clean off the brake fluid. Like gunwash, 99% isopropyl alcohol or something similar. What to do to your carpet depends on how bad it is. How soaked is it? I dont know if a steam cleaner/carpet cleaner would do much. To get engine oil out of vehicle carpets we would remove the carpet, put it on the shop floor and use a hotsy and a lot of soap/shampoo on it. (Hotsy is a pressure washer that uses nearly boiling water basically).


Sent from my iPhone using Tapatalk

 

[HeX]

Ok, probably time for a new one then. They are supposed to be stiffer than rad hoses because they have to be able to handle the vaccum without collapsing but they shouldnt feel brittle/hardened. The only vac lines ive ever seen that were supposed to be stiff/hard had special clamps.

It made sense to me to expect a vacuum hose to be stiffer but I'm not sure how much stiffer. It definitely has virtually no flex to it when manual squeezed. I'm not concerned with it though since there is no current leak.

The leaking brake fluid wont damage metal, just paint and plastic unless you leave it long enough to let the metal rust. The problem with it is that it doesnt evaporate. So after you get your carpet pulled back use a quickly evaporating solvent to clean off the brake fluid. Like gunwash, 99% isopropyl alcohol or something similar. What to do to your carpet depends on how bad it is. How soaked is it? I dont know if a steam cleaner/carpet cleaner would do much. To get engine oil out of vehicle carpets we would remove the carpet, put it on the shop floor and use a hotsy and a lot of soap/shampoo on it. (Hotsy is a pressure washer that uses nearly boiling water basically).

I'll definitely keep the solvents in mind. I have no idea how bad it may be as I didn't yet pull back the carpet. However, its been leaking for at least 2.5 years so I rather prepare for the worse as I doubt there's any reasonable way I have available to remove such fluid from thick matting. I may just squeeze in a towel underneath the matting and press the matting onto it in the hopes of draining out as much absorbed brake fluid as possible.

Backtracking for a moment though, I'm also considering replacing the Brake Master Cylinder as I'm not entirely certain I can rule it out as the leak culprit. I wiped clean the leak area in order to inspect it after a day or two of driving. I did some further research and I'm not understanding how the Booster can leak when in theory only the Master Cylinder holds fluid. I've read so many threads citing "brake booster leaks" so I may have assumed too quickly. My brake feels seems the same as far as I recall, but that doesn't mean that my leak couldn't have coincidentally started right around a brake change and I incorrectly associated some of the symptoms. Some clarity from the experts will be greatly appreciated. I may end up replacing it anyways being that I can get an Exedy BMC for $20, but I should still understand exactly how this all works together.

 

[dancam]

Can the fluid leak out of the the master cylinder and run onto/in the 'linkage' o the booster? Your right, there is no fluid in the booster.


Sent from my iPhone using Tapatalk

 

[HeX]

Can the fluid leak out of the the master cylinder and run onto/in the 'linkage' o the booster?

That's exactly my current concern.

 

[mc360]

i wouldnt change anything just replace with oe replacement.

 

[HeX]

i wouldnt change anything just replace with oe replacement.

Your comment doesnt help at all with the questions at hand.

 

[mc360]

the question at hand was should i upgrade since i have a leak, correct? unless you have a bunch of money to waste an upgrade is not needed and will not really help to much. you could go boosterless and install a wilwood booster delete, you could upgrade to rear disk and upgrade the master cylinder to a 1" but why?

 

[HeX]

Now it makes more sense being that I had previously asked multiple questions and didnt know what you were specifically commenting on.

So we both agree that its not worth the extra effort to swap any system parts for a daily driver.

 

[mc360]

It might be worth it if you had more power than stock but we both know your all about sipping fuel so ya it's not worth it, plenty of people dd 300hp+ civics that might want upgraded brakes though.

 

[HeX]

It might be worth it if you had more power than stock but we both know your all about sipping fuel so ya it's not worth it, plenty of people dd 300hp+ civics that might want upgraded brakes though.

Ha! Yup. This one isnt worth the upgrade.

 

[HeX]

After further research and observation, I've Identified the Brake Master Cylinder as the culprit, as its leaking at the piston arm in the footwell. After wiping it clean 2 days ago, I inspected it today and clearly see a black grease-like leak all around it. This obviously changes the purpose of this post a bit. As a result, I change the title as it shows now from the original "Brake Booster leak, possible upgrades, etc.". In addition to the original comments (copied below)....

I've had a seemingly mysterious brake fluid leak in my '97 Civic HX for a while, only to realize today that my Brake Booster is leaking into the foot well. I hadn't noticed it before because the fluid is being leaked into the floor matting and not showing up above it on the plastic layer. Understanding that brake fluid can eat into many materials, should I consider removing that soaked padding, possibly replacing it, or can it be sopped up?

I considered upgrading the Brake Booster to one that would perform better but after much research it seems I'd have to upgrade some combination of parts (such as the master cylinder, calipers, rear drums to discs, etc.) along with it to have more than just a stiffer pedal with the same braking capacity. It seems that no master cylinder & booster just bolt on without some sort of mod, and I don't want to mod anything for this fuel sipping daily driver unless its considerably worth it while keeping the rear drums. If I am mistaken, by all means do correct me.

O'Reilly's currently has a reman.'d OEM brake booster for $78 & change after the $20 core charge., which includes lifetime warranty. I personally prefer re-manufactured OEM parts over aftermarket parts in instances such as this. Any added suggestions?

I also noticed the vacuum line to the brake booster was loose at the engine to where I could pull it off after a few decent twists. I tightened it up but haven't driven it around yet. Would that loose hose allow enough of a leak to affect braking?

... I also need to further evaluate if there be any benefit to changing the Brake Booster while I'm already removing the Brake Master Cylinder. With everything we've covered so far in this thread, I'm now heavily convinced that the main symptom of a faulty Brake Booster would be a suddenly stiffer pedal with a longer brake catch feel. The only other reason I can fathom now is the leaking of fluid into the booster that would slowly damage the internals and seals. Again, I'm speaking in theory as I'm not an expert on these parts. I'd like to confirm how brake fluid seeps into the Brake Booster from the BMC. From the general diagrams I've viewed, it seems it would be from a single faulty seal, yet I've read of no such instance where the seal itself is even replaceable. Please share your knowledgeable input.

In my situation, I know this leak has gone on for over 2 years so if fluid has gotten in the Brake Booster within that time then something must be damaged or on the verge of failure. I rather change it to be on the safe side than wait for a sudden failure while driving.

Thanks for all the responses so far. I apologize for the bouncing back and forth, but this is clearly a learning experience for me right now.

 

[dancam]

Lol, i need to read more carefully. The entire time i read and commented on this i presumed you were talking about the master cylinder :p it is the only thing with oil.
Anyhow, i believe the reason its getting past the seal on your booster is that its meant to be a dust seal and not an oil seal.
Also where the master cylinder attaches to the booster its quite a tight seal with the metal on metal tere right? So oil leaks out of your master cylinder under pressure, fills whatever cavity is in between the booster and MC and then the path of least resistance is by that dust seal.


Sent from my iPhone using Tapatalk

 

[HeX]

LQTM. Thats what it seems like you were thinking. Your explanation sounds like it makes sense. So being that brake fluid is clear yet its leaking black gunk, could the back gunk be eaten away gasket or sealant of some kind?

 

[HeX]

For those wondering...

Laughing
Quietly
To
Myself

Thank you, Demitri Martin. It really does make more sense to use that regularly, so now I am in this modern world of acronyms.

 

[HeX]

I picked up a reman.'d OEM (Findlex) Brake Master Cylinder at O'Reillys for $67.99 (they price matched AutoZone and I prefer O'Reillys service) and installed it today. It was actually very easy. After plenty of brake bleeding at all 4 wheels in order to pump in all new DOT3 synthetic brake fluid, the brakes are feeling very good.

Here's the nasty old brake fluid I drained out (with help) from the BMC. The BMC was filthy inside.

Here's the cleaned Brake Fluid Reservoir, with new DOT3 synthetic fluid, as I primed the BMC.

 

[HeX]

I inspected the old Brake Master Cylinder and it definitely seemed like it was leaking fluid through the piston. The old piston feel wasn't nearly as smooth as the new one. I also inspected the Brake Booster petal engaging pin (if that's the proper term) and seal. It looks to me like the brake fluid is able to leak from the BMC piston, onto the Booster's pin, through the seal and down to the petal linkage because the Booster's seals purpose is to protect its internals and not cabin leakage. It doesn't seem like the leak damaged the Booster as I tested it without the vacuum line and it creates vacuum sound through the open hole every time the brake petal is pressed. I'll continue to monitor everything for a few weeks, but I'm feeling optimistic that my leak issues are solved and the Booster is fine. I'll eventually make time to remove the carpeting and inspect the padding for absorbed brake fluid.

Here are some reference pictures I hope help others understand my conclusions:

This is the Brake Booster pin at neutral. Notice the surrounding black seal.

This is the Brake Booster pin extended (brake petal pressed down). Notice the seal doesn't bulge at all. Seeing it up close, its clear that there's enough seal to fit snug but not enough to obstruct brake fluid.

Prior to a wipe down, the Booster pin bad some black grease for the assumed purpose of lube. I don't really see the purpose as both the Booster pin and BMC piston are rigid. I believe the leaking brake fluid blended enough with the grease to also leak through and create the black sludge accumulation that I've seen to be common in these leak issues on other forums.


So here's my current synopsis...

Only the Brake Master Cylinder can leak fluid and will do so either where it seals at the Brake Booster or by trickling through on the Brake Booster petal engaging pin, thus leaking into the driver's foot well.
The Brake Booster can only be damaged by leaking brake fluid (via the Brake Master Cylinder piston) if the Brake Booster seal around the petal engaging pin becomes damaged and allows fluid to begin accumulating inside the Brake Booster, thus allowing the internals to slowly deteriorate.

As always, do correct me if needed or add any helpful opinions. I'm hoping this leads to making a Sticky to clarify all the confusion I had that many other have experienced.

 

[HeX]

UPDATE: THE LEAK CONTINUES!
​

I cannot find the source to the brake fluid leak now. Since installing the rebuilt Master Cylinder, the leak began again not long after. Since then I simply check and top off the fluid every two weeks or so, but its time I find the mysterious culprit.

Suspecting it was the installed rebuilt Master Cylinder, I swapped it for another rebuilt one (lifetime guarantee) a few months ago and yet the leak continues. There are no observable leaks at the master cylinder, inside at the pedal or underneath it, at any wheel, the proportioning valve, the stainless steel braided brake lines, the rear drum internals, none of the joints in the system, and not from the brake line piping at least from around the exhaust resonator on back. I doubt it could be leaking inside the car and be underneath the matting because after all this time it would be an obvious pool through the carpeting by now. I haven't gotten the car high enough to safely inspect the brake line piping from the resonator area up to where the lines bend upward towards the prop valve. If its not there, then what else have I not inspected or considered yet? I may just try to sit in my car pumping the brakes for 20-30 minutes to see if any pooling occurs anywhere underneath the car.