Brake fluid reservoir/cap
Thread Starter
Race Director
Joined: Dec 2000
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From: San Diego CA
Brake fluid reservoir/cap
Here's a thought-provoker for you guys:
The brake fluid reservoir cap in my 68 was held onto the reservoir very tightly with a metal strap. When the fluid level dropped, the rubber bellows inside the cap would be pulled down to take up air space in the reservoir.
The C5 cap, while having a type of rubber bellows inside its cap, does not seal tightly against the reservoir neck and therefore vents brake fluid onto the outside of the reservoir, over time. If left alone, the buildup of fluid could spill down and eat whatever lies underneath.
Now, is the reservoir designed to vent air that expands in it, say, when engine bay temperatures rise? This is my guess, but if so, why would GM engineers knowingly allow brake fluid to leak down into the engine bay?
This has been bothering me for some time because if the cap is really supposed to be leak-tight, a fix is very simple. Should this be a vented cap, preventing fluid leaks is not so easy.
Thoughts?
The brake fluid reservoir cap in my 68 was held onto the reservoir very tightly with a metal strap. When the fluid level dropped, the rubber bellows inside the cap would be pulled down to take up air space in the reservoir.
The C5 cap, while having a type of rubber bellows inside its cap, does not seal tightly against the reservoir neck and therefore vents brake fluid onto the outside of the reservoir, over time. If left alone, the buildup of fluid could spill down and eat whatever lies underneath.
Now, is the reservoir designed to vent air that expands in it, say, when engine bay temperatures rise? This is my guess, but if so, why would GM engineers knowingly allow brake fluid to leak down into the engine bay?
This has been bothering me for some time because if the cap is really supposed to be leak-tight, a fix is very simple. Should this be a vented cap, preventing fluid leaks is not so easy.
Thoughts?
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Here's a thought-provoker for you guys:
The brake fluid reservoir cap in my 68 was held onto the reservoir very tightly with a metal strap. When the fluid level dropped, the rubber bellows inside the cap would be pulled down to take up air space in the reservoir.
The C5 cap, while having a type of rubber bellows inside its cap, does not seal tightly against the reservoir neck and therefore vents brake fluid onto the outside of the reservoir, over time. If left alone, the buildup of fluid could spill down and eat whatever lies underneath.
Now, is the reservoir designed to vent air that expands in it, say, when engine bay temperatures rise? This is my guess, but if so, why would GM engineers knowingly allow brake fluid to leak down into the engine bay?
This has been bothering me for some time because if the cap is really supposed to be leak-tight, a fix is very simple. Should this be a vented cap, preventing fluid leaks is not so easy.
Thoughts?
The brake fluid reservoir cap in my 68 was held onto the reservoir very tightly with a metal strap. When the fluid level dropped, the rubber bellows inside the cap would be pulled down to take up air space in the reservoir.
The C5 cap, while having a type of rubber bellows inside its cap, does not seal tightly against the reservoir neck and therefore vents brake fluid onto the outside of the reservoir, over time. If left alone, the buildup of fluid could spill down and eat whatever lies underneath.
Now, is the reservoir designed to vent air that expands in it, say, when engine bay temperatures rise? This is my guess, but if so, why would GM engineers knowingly allow brake fluid to leak down into the engine bay?
This has been bothering me for some time because if the cap is really supposed to be leak-tight, a fix is very simple. Should this be a vented cap, preventing fluid leaks is not so easy.
Thoughts?
From a few other posts I have seen on this I think it just seems to be a case of an ill fitting cap/seal. Try a new cap w/seal, it may fit better (tighter), or as some have suggested, maybe the seal can be "shimmed" so-to-speak as to fit tighter. If I were "shimming", I would try to use something brake fluid resistant and bear in mind that the "shim" would still have to allow air to come in on top of the diaphragm so it can move downwards with vacuum.
Le Mans Master
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From: DuBois PA
St. Jude Donor '11-'12-'13-'14-'15
Team Owner
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From: Raleigh / Rolesville NC
One thing that may also help, is dont fill the MC to the full line. Fill the MC to about 3/4 tank, you will be just fine.
Thread Starter
Race Director
Joined: Dec 2000
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From: San Diego CA
Thanks for your thoughts; I actually did select, cut and install an elastomer material that is highly brake fluid-resistant to use a shim as Lonestar suggested. It is approx. 1.9" in diameter and 1/6" thick. I bought 1/32" think material as well, not knowing what thickness would be adequate. I tried the 1/16" disc, first and the cap seems to seal much better.
However, right after I installed it, I started thinking that perhaps the cap needs to vent, just as gas caps do. I agree with Lonestar that allowing moist air to get "pulled" in is potentially damaging to the fluid, but I also know that this is a common issue, so why would GM make such a silly design error?
However, right after I installed it, I started thinking that perhaps the cap needs to vent, just as gas caps do. I agree with Lonestar that allowing moist air to get "pulled" in is potentially damaging to the fluid, but I also know that this is a common issue, so why would GM make such a silly design error?
Team Owner
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Thanks for your thoughts; I actually did select, cut and install an elastomer material that is highly brake fluid-resistant to use a shim as Lonestar suggested. It is approx. 1.9" in diameter and 1/6" thick. I bought 1/32" think material as well, not knowing what thickness would be adequate. I tried the 1/16" disc, first and the cap seems to seal much better.
However, right after I installed it, I started thinking that perhaps the cap needs to vent, just as gas caps do. I agree with Lonestar that allowing moist air to get "pulled" in is potentially damaging to the fluid, but I also know that this is a common issue, so why would GM make such a silly design error?
However, right after I installed it, I started thinking that perhaps the cap needs to vent, just as gas caps do. I agree with Lonestar that allowing moist air to get "pulled" in is potentially damaging to the fluid, but I also know that this is a common issue, so why would GM make such a silly design error?
FWIW, when I replaced my cap with a new one (the newer design has the graphics printed directly on the plastic cap as opposed to a "sticker), it seems to fit more snugly.
Thread Starter
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From: San Diego CA
Mmmmm, maybe I'll leave my shim disc in to see what happens. I do need to have the fluid flushed and replaced, soon, so I'll run our thoughts by the tech guy at the dealership. I stopped flushing brake fluid (myself) after selling my silicone fluid-equipped 68, year ago. My painted floors don't like the non-silicone stuff!
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Le Mans Master
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From: Longview Texas
There should be no brake fluid leakage to the outside. If your cap is leaking, the gasket needs to be replaced. Also, it is not uncommon for the reservoirs to develop cracks and leak. If you are getting fluid at the seam of the reservoir constantly, you may need to replace the reservoir.
The corregations in the cap seal should let it move up or down to compensate for normal fluctuations in the fluid level. I have not actually looked at the gasket on the C5, but most other GM gaskets have a tiny slit in the center section of the gasket to balance the pressure if the gasket runs out of travel in the corregations.
The corregations in the cap seal should let it move up or down to compensate for normal fluctuations in the fluid level. I have not actually looked at the gasket on the C5, but most other GM gaskets have a tiny slit in the center section of the gasket to balance the pressure if the gasket runs out of travel in the corregations.
Team Owner
Joined: May 2001
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
There should be no brake fluid leakage to the outside. If your cap is leaking, the gasket needs to be replaced. Also, it is not uncommon for the reservoirs to develop cracks and leak. If you are getting fluid at the seam of the reservoir constantly, you may need to replace the reservoir.
The corregations in the cap seal should let it move up or down to compensate for normal fluctuations in the fluid level. I have not actually looked at the gasket on the C5, but most other GM gaskets have a tiny slit in the center section of the gasket to balance the pressure if the gasket runs out of travel in the corregations.
The corregations in the cap seal should let it move up or down to compensate for normal fluctuations in the fluid level. I have not actually looked at the gasket on the C5, but most other GM gaskets have a tiny slit in the center section of the gasket to balance the pressure if the gasket runs out of travel in the corregations.
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Tech Contributor
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From: Charlotte, NC (formerly Endicott, NY)
It is also not a big deal. The little bit that I have seen show up on the reservoir never makes it any lower than the reservoir and usually dries up quickly. Other than the paint on the frame there really isn't anything below that brake fluid dripping from the reservoir can damage.
Bill
Bill
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From: San Diego CA
Well, my painted garage floor wouldn't like it, that's for sure.
Seriously, the "seeping" has been going on since a few months after I bought my car (with 3 miles on the odometer). If I don't sop it up with a paper towel, it will drip down.
I remember years ago when I first posted about this issue, many told me that it is normal. It may be normal, but it "aint right"!
Seriously, the "seeping" has been going on since a few months after I bought my car (with 3 miles on the odometer). If I don't sop it up with a paper towel, it will drip down.
I remember years ago when I first posted about this issue, many told me that it is normal. It may be normal, but it "aint right"!
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 244
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Well, my painted garage floor wouldn't like it, that's for sure.
Seriously, the "seeping" has been going on since a few months after I bought my car (with 3 miles on the odometer). If I don't sop it up with a paper towel, it will drip down.
I remember years ago when I first posted about this issue, many told me that it is normal. It may be normal, but it "aint right"!
Seriously, the "seeping" has been going on since a few months after I bought my car (with 3 miles on the odometer). If I don't sop it up with a paper towel, it will drip down.
I remember years ago when I first posted about this issue, many told me that it is normal. It may be normal, but it "aint right"!
Le Mans Master
Joined: Dec 2003
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From: Atlanta metro Ga.
Absolutely should be an air tight seal. Mine had / has the same issue - I shimmed it a few years ago, seems to be holding up so far - The price for new cap seemed outrageous - $30 or something, so I'll continue on with the shimming method until it doesn't work any longer.
Le Mans Master
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From: DuBois PA
St. Jude Donor '11-'12-'13-'14-'15
I'm going to trade mine out with my parent's Cadillac cap... 
I bet their the same anyway!
Hmmm Maybe we oughta go the junkyard route and see what other models will fit and NOT leak? $30 for a damn cap, that's nuts!!!!
Tim
I bet their the same anyway!Hmmm Maybe we oughta go the junkyard route and see what other models will fit and NOT leak? $30 for a damn cap, that's nuts!!!!
Tim
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Race Director
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From: San Diego CA
Tim,
I have what is very likely to be an effective fix. I bought a strip of EPDM rubber (2-inches wide) for a few dollars and cut out a 1.9" diameter disc. Slip it in underneath the cap's rubber gasket and you're good to go!
I have what is very likely to be an effective fix. I bought a strip of EPDM rubber (2-inches wide) for a few dollars and cut out a 1.9" diameter disc. Slip it in underneath the cap's rubber gasket and you're good to go!
Le Mans Master
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From: Longview Texas
I agree. I thought mine was defective until I noticed new gaskets also had the small slit. You have to be looking closely to find it.
Safety Car
Joined: Sep 2002
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From: San Diego CA
I've looked under the hood of many a C5 and I would say they all have a bit of brake fluid residue around the top rim of the cap. If I wipe mine off about every 6mo or so, it's not a problem.