Overflow for brake fluid reservoir?

[175K911]

Originally Posted by sc_rufctr

I'm curious. Do you have a pic of a G50 reservoir?

No actual pic, but .....

From our host:
Pelican Parts - Product Information: 911-355-017-04-M100

[911pcars]

Originally Posted by GaryR

I use one of my Longacre bleed bottles that has a magnet attached and stick it to the steel body in front of my spare, works perfectly and never moves. Even if it fell over it wouldn't leak as it's sealed..

An equivalent is the brake bleeding bottle from HF. The nipple and supplied hose fits the reservoir nicely.




This takes care of fluid expelled by G-forces. If large quantities of BF are expelled, you have other brake system issues (e.g. excessive heat).

MHO,
Sherwood

[fredmeister]

Has anyone ever measured how hot the fluid gets inside the MC reservoir after running hard?
I am surprised that the fluid transmits that much heat all the way up to the reservoir from the caliper.
interested in seeing some temp data for this.

[teenerted1]

Originally Posted by Flieger

I also route mine through a handy hole in the bootom of the smuggler's box. Just the right (small) size for the overflow line.

Not much comes out, just a little drip here and there after sitting after a hard drive where the lateral G's gets it into the overflow tube.

ditto...but i like this catch bottle i see everyone using. i keep running over the pan i have in the garage

[911pcars]

BTW, a friend races his street-prepped car in POC/PCA events and runs his overflow tube into a 35mm film canister. Seems to have enough capacity.

Sherwood

[Mike Metzler]

Here are a couple. Note that the brake and clutch each have their own compartments, but the wall separating them has holes in it to allow sharing fluid. It should also significantly reduce the amount of "slosh" that will get to the overflow.

[burgermeister]

Note that the G50 reservoir vent does not originate at the side of the reservoir. There appears to be an internal passage to somewhere near the center of the reservoir.

On the 915 reservoir, taking the vent line out the driver side, routing it rearward, and then up, might not prevent fluid leakage. A RH turn would fill the line, and subsequent accel might push the fluid in the line over the hump.

A better solution would be to route it straight up and over the top of the reservoir. It would be difficult to get sufficient g-forces to push the fluid over that hump. Another possibility would be to get some very thin copper tubing that fits inside the nipple and push it through to extend the vent line pickup point to somewhere in the middle of the reservoir where brake fluid is least likely to be.

[175K911]

Mike- thanks. That helps a lot. Quite a difference from the 915 reservoir setup.

Burgermeister- I tried routing up over the top but it really didn't make any difference. I agree a tall loop up high would be the solution, but the top of the reservoir cap already is extremely close to the hood itself.

I may just order the G50 reservoir and bracket from our host and give it a shot. Certainly can't hurt.

[JeremyD]

I never had this problem with the G-50 reservoir - But from the looks of these solutions - Number one issue would be heat management. #2 would be fluid management - #3 I'd look for an extra brake bleeding bottle with the magnetic attachment. Seems like the most logical solution.

[175K911]

Originally Posted by JeremyD

I never had this problem with the G-50 reservoir - But from the looks of these solutions - Number one issue would be heat management. #2 would be fluid management - #3 I'd look for an extra brake bleeding bottle with the magnetic attachment. Seems like the most logical solution.

Jeremy I'd agree re the G50 reservoir. I've got #1 covered with both the 993 control arm deflectors blowing air to the calipers and air ducting from the inlets in the Yellowbird valance through Smart Racing manifolds into the eye of the rotors. #2 is covered with either Motul600 or Brembo racing. Never ever boil fluid, just loose the fluid.

[Kemo]

what would happen if you just blocked off the vent line?

[SCOTITUDE]

Originally Posted by Kemo

what would happen if you just blocked off the vent line?

I tried that with a pair of vise grips once while trying to sort out the issue. The brakes worked fine on the first application. the second time i went to the pedal i had to pump it to get any braking. the third time i needed to pump even more. Not the direction i wanted to head so i pulled off the road and removed the clamp and all went back to normal. This is my $.02 non scientific theory. The pistons will extend with the hydraulic pressure but since there is no vent the fluid will retract to its previous position sucking the pistons back in. I assumed it created a vacuum where your pedal created hydraulic force to move the pistons out but it became a closed system so there was no more fluid to fill the void. I am sure someone will chime in with the appropriate terms and proper explanation.

[911pcars]

You're correct.

It's called a "vent" for that purpose - route for atmospheric pressure.

Sherwood

[Eagledriver]

This problem can be minimized by running a lower level in the reservoir. I run mine about 1/2 inch below the top. I only drain about 1 oz out per weekend.

-Andy

[Wilhelm]

Originally Posted by Eagledriver

This problem can be minimized by running a lower level in the reservoir. I run mine about 1/2 inch below the top. I only drain about 1 oz out per weekend.

-Andy

+1 on that. On my car (71 911S) after about 30 or 40 miles of really quick canyon driving , I only get a spot on my garage floor about the size of a quarter. My brake fluid level is normally around 1/2 to 1 in from the top of the resevoir. I have no catch tank. Just a clear tube run through a convenient small hole in the bottom of the pan. I check the fluid every couple weeks. It doesnt seem to be a big issue.

I suppose for full-on track driving, lots of laps, G's, heat, etc. I would need something better.

[Kemo]

anyone make a vented cap? Combine that with lower level of fluid?

[911pcars]

Originally Posted by Kemo

anyone make a vented cap? Combine that with lower level of fluid?

That could be easily accomplished with a small drill (remove cap first).

Can't think of any dire consequences other than the purists wanting to know about the missing plastic.

Sherwood

[GaryR]

Originally Posted by 911pcars

That could be easily accomplished with a small drill (remove cap first).

Can't think of any dire consequences other than the purists wanting to know about the missing plastic.

Sherwood

Not necessary, just use the standard vent with hose routed to the floor for street cars and to a catch tank for track cars. For both run the fluid (cold) down a 1/2" or so. Done.

[mnez]

I just did what Sherwood suggested, drilled a small hole in the cap and clamped the overflow tube. Great brakes and no fluid loss and no catch can to empty. Confirmed over a 3 day DE at Watkins Glen.

[Walt Fricke]

Anyone gotten further in analysis of this issue?

My SC started life as a '77 2.7, with no vacuum assist brakes. I upgraded with SC flares and a 3.0. I DE's and once raced with slicks, now with Hoosiers. I get around a track fairly well, so am pulling whatever Gs are normal in a pretty fully prepped track car of this type.

Then I added the power assist brakes without changing anything else. And I started having this issue. I have to watch the fluid level carefully, and installed a catch bottle to keep from spitting so much out the front.

So my suspicions rest on some difference in operation of the power assist MC. I doubt my MC itself is bad, as it was new and others seem to have this issue. Has anyone with an old style, non-power assist MC had this problem?

Could the fact that the non-power reservoir is so far away and above the MC have an influence on this?

I share the belief that high quality brake fluid does not expand enough to push fluid out of the reservoir. But I don't have the expansion coefficients to hand to quantify this. And if it was expansion which did it, when the fluid reached equilibrium it ought not to expand further, in which case the outflow should stop. Not the case for me.

I wonder if reorienting the reservoir so the breather faced rearward would solve this? When I had some instrumentation 20 years ago, I would see maybe 0.33G accel, but about one G lateral and decel. Anyone tried this?

I run stainless pistons, titanium plates behind the pads (after they have worn a bit so they can fit), have ducting (yes, not always in the best shape) from front spoiler openings, and the right setup at the brakes. None of this has changed in years. And, as to excessive heat, with the right fluid the fluid does not boil because the pedal, while it might get a hair lower, does not go soft or cause operational problems, even after a one hour enduro. Had to do all this stuff when wife and I both drove back to back run groups racing and first had pedal go to floor.

I have changed from Castrol SRF (dry boil about 600F) to Prospeed RS683 (683 dry boil). So I suppose I could be putting more heat into the brakes before boilding. If expansion is a factor, that might make a difference.

But for now I am focusing on what I see as the two variables: distance and location of the reservoir, and possible differences in how power assist MCs work.

I have some trouble thinking that the power assist system leaves a fraction of time in which there is pressure in the brake lines/mc chambers, but one or both orfices to the reservoir are already a bit open. In addition, that does not seem to explain why, after enough has escaped to the catch bottle, more keeps coming.

Any further thoughts on this?