Overflow Tube on brake fluid reservior

[porscheguy47]

Can anyone tell me where that overflow tube on the brake fluid reservior is supposed to empty? Is there a hole or to which it needs to be placed? I assume that it is an overflow tube? Is it for another purpose? Thanks for any input. Bob

[redridge]

it empties on the ground by the driver inside front wheel.

[redranger]

On my 86, it empties toward the front of the car, driver side.

[EC900]

The braided line from the reservoir transitions to a flexible hard line that runs along L fender, behind fuse panel and bends down into a hole with rubber grommet, exits downward about 3 inches. The “hard” line is flexible but can kink, if using this it’s best to warm it up a bit (heat gun or sun) to make the bend into the grommeted hole. This line is not like the very flexible vinyl windshield washer hose but I think it would work so long as it isn’t kinked up.

[fintstone]

A related question...Does anyone have a good source for that braided line?

[EC900]

Pelican has cloth braided vacuum line., search under the fuel injector section. The overflow line isn’t subject to pressure or constant fluid so vac hose would suffice. Reservoir overflow line appears to be 5mm but not exactly sure.

https://www.pelicanparts.com/cgi-bin/supertech/catalog.cgi?action=frameset&return-url=/cgi-bin/supertech/catalog.cgi%3Faction%3Dframeback%26page%3D2429&catalog-url=https%3A%2F%2Fwww.pelicanparts.com%2Fcatalog%2 FSuperCat%2F0787%2FPOR_0787_FULINJ_pg2_fuel-injectors.htm


Stoddard is another.

https://www.*************/catalogsearch/result/?q=Cloth+braided+hose

[fintstone]

Thanks. Looks like it was 4mm ID. I could not find any that was an exact match, but I found some that matched perfectly (visually) that was 3.5mm ID/7.5mm OD. Just had to stretch the opening a bit with some needle nose inside of it before putting sliding it on. Thanks!

[Walt Fricke]

If you autocross or track the car, it is a good idea, and pretty simple, to run this overflow line into a catch bottle. I favor running the line from the reservoir up into the space under the cowl, then down to a bottle secured somewhere nearby. I use a plastic water bottle or something similar I had on hand. Held on with a bungee. Easy to check to see how much has sloshed in there. Since this fluid will never drain back into the reservoir, it only needs a breather hole in the cap through which you insert the drain line. Easy to design a more aesthetic catch bottle etc. if desired.

Running the line up before down increases the Gs needed to force fluid up over this hump.

No brake fluid on the track, or dribbling out in front of your LF tire perhaps.

[Schulisco]

Originally Posted by fintstone

A related question...Does anyone have a good source for that braided line?

All I know it's available only at Porsche itself. It's a special rubber hose which is definitely resistant againt brake fluids. It tried to find such hoses on local car part dealerships with no success. Therefore I had to order it at Porsche itself.

Quite expensive, Porsche sells them only by the metre, I paid almost 50€ some years ago.

This is how it looks:


Thomas

[chrisbalich]

I capped off the reservoir overflow and changed the cap to a vented cap. I have the vent facing forward and have yet to get any brake fluid to come out of it. (No shortage of hard corners and hard braking)
No brake fluid in my trunk or on my tires. It also looks much tidier than having that little hose draped across the trunk.


An excerpt from my build thread back in February of this year.

Originally Posted by chrisbalich

...I started small with a part I picked up this week as an experiment.
A little backstory first.
Two years ago when I first got my car on the road, I removed the rotten brake reservoir vent hose and promptly chucked it in the bin. #byegurl
Not wanting the res ejecting brake fluid all over my trunk, I installed a vac cap. NBD, right?
Fast forward to last year.
About halfway through the year, I occasionally got a bit more pedal travel on the first pump than I was expecting. It was super rare, and I generally give it a pre-pump anyway, so I didn't think much of it. I made a note to check it over winter and continued driving the car.
Fast forward to this winter.
I'm looking at the brakes while I have the fronts all disconnected to install the RSR swaybar. It occurs to me that by capping the vent, it gradually creates a vacuum preventing the pistons from moving out as the pads wear. #derp
So I put "vent MC" on my pre-April list and moved on.
Fast forward to last week.
A tech came to the parts counter needing a new MC reservoir cap for a chevy something or other. The cap has a very clever vent built in. So I keep the old cap after getting him a new unit.
Sunday
Check out this super slick vent.


I marked the location of the vent/slot with a silver dot and screwed it on. NGL, I was surprised it fit.


So once this hog is back on the road, I'm going to jerk the steering wheel around and see if I need a rubber seal. Once that's sorted, I'll do a 100-0 hard brake (closed course with professional pilot of course) and see if the vent vents fluid in addition to air. I expect it'll work a-ok as-is. But I've been wrong before...

[EC900]

Nice job Chris, I’ll be looking for your project post! but…..The good thing with the overflow hose is that it allows any accidental spillage from the reservoir bowl to flow into the trough and then to the hose rather than allow it get onto the painted surface of the trunk when pushing in the calipers during a pad change or spillage overfill. In your case Chris…What-If the cap somehow fails? When I removed my washer lines, they were running along the L fender with the brake fluid overflow hose, it actually routes under the cowl, behind the L hinge and down to the chassis. Well, when I did the removal, very old brake fluid was still trapped in the hose and came out on the garage floor overnight, slow drip, it was dark as molasses probably trapped in a loop. When I changed the position of the hose it caused the old fluid to finally purge. Nasty stuff but the old hose is still flexible after 45 yrs could use a new replacement and with the exception of previous owner or past services, the overflow line doesn’t get much use if care is taken when routinely changing brake fluid.

[chrisbalich]

Originally Posted by EC900

Nice job Chris, I’ll be looking for your project post! but…..The good thing with the overflow hose is that it allows any accidental spillage from the reservoir bowl to flow into the trough and then to the hose rather than allow it get onto the painted surface of the trunk when pushing in the calipers during a pad change or spillage overfill. In your case Chris…What-If the cap somehow fails? When I removed my washer lines, they were running along the L fender with the brake fluid overflow hose, it actually routes under the cowl, behind the L hinge and down to the chassis. Well, when I did the removal, very old brake fluid was still trapped in the hose and came out on the garage floor overnight, slow drip, it was dark as molasses probably trapped in a loop. When I changed the position of the hose it caused the old fluid to finally purge. Nasty stuff but the old hose is still flexible after 45 yrs could use a new replacement and with the exception of previous owner or past services, the overflow line doesn’t get much use if care is taken when routinely changing brake fluid.

The only mode of failure for the cap would be a crack. Should that happen, the fluid will still be contained in the top (reservoir tip?) of the MC reservoir. If that becomes a regular occurrence, I'll devise a new plan...or go back to Porsche's original plan.
But considering the condition of the original cap, I don't expect a problem. I've had zero brake fluid escape the reservoir thus far.

With regards to brake fluid escape at pad change: I don't typically add fluid between pad services. If I have to, there's something else wrong. And if the brake fluid ages out before the pads wear out, I need to drive more.

[Brian Cameron]

I am in the middle of a fairly extensive restoration and this thread was super helpful, thank you Pelican brain trust! Had the happy experience of both the braided hose AND the plastic extension breaking during a brake bleed and spilling fluid in various places where I hadn't placed cloths to catch overflow, spills etc. I guess those hoses are 40+ years old so it's time.

Special shoutout to EC900 for the excellent pics showing the routing of the overflow hose. Also to Walt Fricke for the idea for an overflow catch bottle, I feel like this could have the added benefit of reducing airflow and humidity into the brake fluid reservoir vs running the drain externally.

Our host used to carry this hose, I bought some in 2018 to replace the fuel evap line from the tank in the front left wheel well, back to the carbon canister in the right side of the engine compartment. I had just enough left over from that to do the braided first section of the brake overflow line. Unfortunately it looks like they no longer carry it, not sure why.

[7783911]

here is one option since the oem line is very expensive..

https://www.newegg.ca/p/2YK-005K-01F55

[wprater]

The new part no. is PAF-101-965, but still quite expensive. I cannot seem to find a part no. for the hard line that exits the tunnel.

I had nothing attached to mine and got fluid everywhere while driving in the canyons this weekend.

[H-viken]

The overflow is also there in case you accidentally boil the fluid, it needs to go somewhere

[EC900]

wprater - so you say no hose whatsoever is connected to your brake fluid reservoir or to the hard (rigid) line?

Any proper sized auto parts store BF (or fuel hose, but not vac hose) hose will do, 1.5mm ID…..even for such a short run, washer hose will suffice as it can fit snugly over the reservoir barb. just get a length to conform (and not pinch/collapse) into the shape you need to route it around toward fender to the rigid lin, which is only a transition section, gasoline line may suffice from the reservoir to the hard line as well. Looser I.D. will require a small clamp.

The hard or rigid extension might still be hidden along your fender, maybe the section of reservoir hose was the only one misplaced(?). At first glance the hard rigid line looks like a washer line. So maybe check again. See my earlier comment photos for hose route.
If you don’t find the original rigid line you’ll need to improvise….by the way the washer line is the same rigid style too - just shorter (999.181.183.49 but NLA also).

Any rigid or semi-rigid hose can be used instead like polyethylene, pvc, nylon etc. - it’s just a drain hose and there’s no pressure psi requirement and a simple friction fit. Since BF really doesn’t settle or hold in this line there’s not much degradation concern.

The rigidity is needed only so any overflow/excess BF doesn’t settle or belly in loops or valleys if the line was too flimsy. If washer hose fits, it would only be a matter of keeping it straight along the fender until it can turn down into the exit point. Should that happen, disconnect at the reservoir and blow out any overflow and reconnect.

A simple solution is readily available 1/4” poly tubing at the Home Depot brand. It has a rigidity and doesn’t crush. It’s just a matter of getting this inside the rubber hose from reservoir. Muscle it by heating and stretching.
Air hose line like from air shocks comes to mind as an alternative for semi-rigidity tubing that would work. Another may be hiss line from Tygothane which has fuel tubing for lawn equipment.

Comment by H-viken on boiling brake fluid is worthy of checking the condition of the brake fluid and temperature rating of what’s been used, maybe a need to replace as well as adding a overflow drain line.

Possibly alternatives for rigid line

[wprater]

@EC900 , that's very informative, thank you. One of these cars had nothing at all connected to it!

I found the hard line on my 71 911, but it's not present in my 73 at all, so it must have been removed from PO, or never replaced during a past repair. I may fabricate a catch, or re-route it, but the exits I see are for fuel vabor and I dont see one for the overflow of BF.

I was trying to find a compatible line, and the information you have shared is quite valuable to help me understand, which is fine since this will rarely see fluid and is not under pressure; that all makes perfect sense.

[EC900]

I can’t speak or the ‘73 fuel evap. system configuration - but I know they do not or shouldn’t exit or vent to the atmosphere (i.e. lingering fumes is garage and cabin).
I’m wondering if what you found may be the brake fluid drain hose exit and that’s the fuel tank line for the expansion tank (previously modified?) and has one hose disconnected(?). Two hoses are go into the exp. tank one incoming from the gas tank, the other draws fumes by vacuum to the charcoal canister.

The only hoses that exit at the left wheel well are the 1/4” BF hose and the washer fluid/gasoline overflow from the filler neck…larger OD hose, maybe 1/2”