Another point: It seems that the Cup cars vent their reservoir through a hole in the top of the cap. To keep the top of the reservoir clean, the owners wrap that area with a paper towel (usually the blue kind) held on with a rubber band. This keeps the small amount of fluid from leaving the immediate vicinity.

And on my track only car, with dual MCs mounted low and aftermarket reservoirs mounted high, I never loose any fluid. Pulls even more Gs than the SC. Those reservoirs are the kind with a black rubber bellows inside, so basically the fluid is never exposed to air, or at least has a lot lower exposed surface. They vent from the inside (dry side) of the bellows to the atmosphere. These would solve the power brake overflow issues if they could be made to fit, I think. But these are round and taller. I can run for several years with this setup without having to touch anything beyond changing pads.

I never did understand why on earth Porsche vented the brake reservoir to the atmosphere, when US manufacturers had been using the rubber bellows method since the 60's, and possibly earlier. Makes zero sense, except that Germans always know best, even when they don't.

Based on comments on the prior page - that drilling a hole in the top of the cap works - I'd think some small diameter copper tubing pushed through the plastic nipple so the vent point ends up in the center of the reservoir should work.

There is appropriately sized copper tubing available at FLAPS - the nipple on my reservoir broke off, and I used such tubing to splice it all together again. It was just a light press fit, holds pressure for power bleeder and otherwise works dandy. Even spills quarts of brake fluid when I forget to clamp the vent line.

I pulled an old reservoir, from my pre-power assist days, from my storage clutter. The kind which mounted on the left inner fender well chassis. Lo and behold, its overflow/air admittance orfice faces the rear of the car!

Can I mount this one where the power assist goes? No, it would stick up too high, things point the wrong way, maybe if I changed out the short hoses and fabricated a bracket it could. Besides, it was getting brittle, and the overflow nipple had broken off so it would need repair. One of the pictures shows how it is configured, though. I think it would be possible to use the old reservoir and mounting, and use longer hoses to connect to the master cylinder.

How about just turning the stock power assist reservoir 90 degrees? Well, that runs into the same general issues about bumping into the vacuum pan and hose lengths and hood clearance. But with enough effort and modification I suppose it could be made to work with a modified bracket and hoses. Though the angle of the hose outlets on the non-power reservoir could make this tricky..

How about I use my pressure bleeder cap, which is a stock cap with a tire nipple coming out the top - just pull the Schraeder valve and attach a hose? Well, the issue here is clearance from the hood. There isn't enough. And I didn't have anything to make a right angle screw-on cap with. With something like that and using a super short tire nipple, perhaps this would work.

Ok, off to the junk box (actually a bunch of those plastic drawers where I try to keep nuts and bolts and smallish parts in some semblance of order). What't this - a nice 90 degree sort of fitting. Don't know where it came from, but at one time its function for me was to spray water onto the top of the engine oil cooler - a Mazda oil cooler mounted in the center of the front valance did away with the need for this.

As an added bonus, the cap has a sort of disk like cover inside over the center of the cap, which snaps on. It has a couple of small holes in it. When removed, there is a dimple in the exact center of the cap, which is under a center protrusion on the top outside of the cap. The dimple is ideal for centering the hole to be drilled. And the little cover forms a small space, with the little holes restricting what comes into or goes out of this - perhaps it will reject slosh, but allow air in and out as needed.

To make absolutely sure I didn't have clearance issues, I sank the reservoir down into its mounting. Bend the metal strap some and rebend, and use a longer bolt. Might not have been necessary, but I didn't want to try to get in the trunk and close the lid on myself to see, and couldn't figure out how to use my boresccope.

So here is the result.

http://forums.pelicanparts.com/uploa...1345577313.jpg
http://forums.pelicanparts.com/uploa...1345577347.jpg
http://forums.pelicanparts.com/uploa...1345577384.jpg
http://forums.pelicanparts.com/uploa...1345577416.jpg

At some point I may bestir myself to create a more elegant method of holding the catch bottle. But I know this works, so that may be quite a while as such things go.

It will be mid-September before we get the car back on the track to see how well or poorly this works. Given that these problems never happened with the car and driver in pre-power assist mode, and at one point I used slicks on the car, I am inclined to think that it is the position of the air inlet/overflow which causes this to be a problem for those of us who track or autocross the cars.

Fact is, our cars will brake just fine with no fluid in the reservoir, as long as there is still some in the line. No reserve for pad wear there, or to deal with a little leakage from a wheel piston seal, etc. But in the short term you don't need a full reservoir. So at some point you can reduce the level to the point where eveh high G cornering isn't going to lead to fluid being pushed out.

But I just feel better with a full, or nearly full, reservoir while on the track or at an autocross.

Very nice Walt. I don't face the issue you do. But you've made me wonder if I should move my catch bottle up much closer to the reservoir from its present position below next to the fuel cell. Hmmm..

I used a fuel tank for an RC airplane. I attached the small tank to the booster by taping a hard drive magnet to the plastic tank and just sticking it to the booster. But now for the fun part. I had this arrangment on two cars an 84 and 85 both would throw fluid when driven very hard at the track or autocross. They were fine when driven on the street. Replaced master cylinder and surprise no more loss of brake fluid. I too thought it was my astounding g-forces causing the issue but it appears the master cylinder was the true cause. If the master cylinder is the original the cups inside are likely getting hard and under severe braking are allowing pressure to bleed back into the res tank. Mine did not leak out of the master cylinder which would obviously indicate a problem. Side effect brakes are much better with the new master cylinder less front lockup. The way the master cylinder is designed there are two cups up front and one for the rear. The front has two cups to separate the front from the rear. The double cups appear to hold pressure better and again under severe braking the rear appears to bleed off internally.

Anyhow there ya go........

Here is my set-up two AP reservoirs without issues:

http://forums.pelicanparts.com/uploa...1345619250.jpg

Unrelated to this thread but always brings a smile - how often have you heard:

ONLY USE BRAKE FLUID FROM A SEALED or UNOPENED CONTAINER!!!!!!

yet the brake fluid resevoir is vented to the atmosphere :-)

Chuck.H
'89 TurboLookTarga, 338k miles

On most cars the brake system is sealed with an expanding bellows sealing the top of the resevoir. I would assume that Porsche has compensated for this by either increasing the frequency of recommended fluid changes or there just isn't enough of an opening to let in that much moisture.
If you don't believe that brake fluid will absorb moisture from the air fill a bottle to the top and let it sit. In a short time it will be overflowing.

This brake bleeder jar from HF fits right onto the factory overflow tube. However, the built-in magnet is a little wimpy - might dislodge at 1 G. :-)
http://forums.pelicanparts.com/uploa...1345659541.jpg

Add a stronger magnet
http://forums.pelicanparts.com/uploa...1345660848.jpg

Sherwood

I'll say it again ---

When you are tracking your Porsche take out some brake fluid
so it doesn't overflow.

We race a 1978 Porsche and use the overflow bottle -- but we also
only run with a half filled reservoir when cold - this reduces the overflow
significantly. When the brake fluid heats up and expands it then has about a full
reservoir.

Other results may vary...

Regards,http://forums.pelicanparts.com/suppo...s/beerchug.gif

I'll believe the "fluid expands when hot and causes overflows" theory when someone does the calculations. Somewhere there must be a coefficient of thermal expansion for generic brake fluids. Which is not to say that keeping the fluid level down to half or so may not help control overflow no matter how caused. Would help with expansion, and should help with reverse flows from the MC - what gets pushed up when it shouldn't has to drain back down to refil the MC when brakes are released.

For me, the key fact is that with my fender side reservoir mount and non-power MC I never had any such issues. See how Sherwood's reservoir vents to the rear?

The failing MC seal effect is certainly real. In my case, the MC is but five or so years old, so that is not at the top of my list. However, if the rerouting of the overflow does not stop overflowing (and keeping the level lower as a next step) doesn't solve this, I guess it is MC rebuild time. Maybe the ATE MCs of today are not like those of the '70s?

Many race cars have setups that vent to a tube that eventually dumps out the bottom of the car. Mine does. I never see any fluid in the tube though....

Scott

And I think that is the way it ought to be. But when it isn't, the question is why and what to do.

Better to contain any waste fluids within the chassis, yes? The guy with the nice paint in back of you might appreciate you not sharing extra BF.

Sherwood

Next time you are at the track, take a look at all the cars that vent out the bottom of the car. Let me know how it goes when you tell them to change their setup.

Scott

No problem Scott. I'll just have the NASA scrutineer do it for me! Thanks for the heads up.

-Andy

Andy,

I don't see anything in the NASA CCR or tech inspection documents that says you have to vent the brake fluid reservoir or, if you do vent it, where it can or cannot vent to. I couldn't find anything about in the PCA documents either. Would you please point me to where this is documented by NASA or PCA?

Mat built my car this way and Rich thoroughly tech'ed it and it passed just fine.

You do realize that many of the street and race cars you might encounter at a track day or DE event vent the brake fluid reservoir out under the car too, don't you?

I just think a small amount of brake fluid venting to the ground is a non issue.

Scott

Yeah, I'm going to do that. That's up to the race stewards and track rules. Whether they do so or not or whether the rules allow it, it's still not ideal. Do they allow coolant to vent to the ground too? How about oil leaks or venting crankcase pressure? Is this the James Bond car chase series?

FWIW, BF is corrosive and an excellent paint remover.

Sherwood

i fashioned a bracket out of thin alloy sheeting that uses the same bolts as the reservoir. stuck a brake fluid bottle in it for the overflow.
no way am i letting it dribble onto the track, would get reamed..
http://i.imgur.com/cgIIF.jpg?1

saw this pic... could of sworn that my 996 was not vented, but maybe it is. Hard to tell from all that covering over the reservoir...


http://forums.rennlist.com/rennforum...r-img_2810.jpg