pressure bleeding the brakes

[rwilson]

I have read the tech forum procedure for pressure bleeding 996 brakes. Can I assume that the air contained in the 3 ft. of tubing connected to the bleeder reservoir will pass through the brake reservoir, brake lines and out the caliper? Is there a way to remove old fluid from the brake reservoir and replace it with new fluid prior to the bleeding process? I noticed upon removing the black cap from the brake reservoir that another inverted clear cap is attached to the reservoir and turns but does not lift out. Is this removable? If not how is fluid removed? As a first timer I don't want to screw this up! Thanks for any help.

[Rrrockhound]

There's no need to remove the old fluid from the reservoir before you start. You'll be flushing it all through anyway, and besides, you want to minimize how much you handle the fluid since you don't want to splash or spill it.

Most Porsche guys use a different color brake fluid than the old fluid they are changing out. That way you can tell when all the old fluid is flushed through. That is, if the fluid in the reservoir is amber, use new blue fluid, or vice versa. I use clear tubing and flush into a clear jar to make it easier to tell.

And no, the air in the pressure bleeder won't enter the lines, unless you start with too little fluid and end up running out while you're bleeding. If you do, you have to start over. Bad. More flushing. More handling brake fluid. Once you have flushed all the old fluid and air bubbles from all the lines, you're done. You open the pump bottle and the vacuum disappears. Watch for spillage. BTW: I think 3 feet of tubing from the bottle to the reservoir is way too much.

One other tip: I also keep a bucket of warm, soapy water and a sponge on hand in case any brake fluid spills onto the paint or my painted garage floor. If it does, I flood it quick, to hell with the mess. You don't want that stuff on any painted surface.

[jwetering]

The problem is that you don't want to mix the new fluid with the old fluid. You have already figured out that removing the old fluid is difficult, but it's not impossible.

1) Option 1 is to get tubing with diameter small enough to fit through the gaps in the "inverted cup" as you call it. You still need to figure out how to get suction on the end of this small diameter tubing though. It's tricky. You can try a well rinsed liquid soap dispenser pump..that has worked in a similar application for me in the past.

2) Option 2 is easier - that is to push the old fluid out through any one of your bleed screws using your pressure bleeder. You don't say what system you are using but if it's a Motive power bleeder then of course you would do this without putting any new fluid in the reservoir of the Motive. I built my own power bleeder using a pesticide sprayer - basically the same as the Motive but without the pressure gauge.

Here's the trick though. You have to stop pressurizing just before the master cylinder reservoir runs dry or you may push air into your ABS valves. LFMF here and do not do this. Unbeknownst to me (and probably you) is that the brake fluid reservoir is split into two compartments front to back. I was pushing out my old fluid watching the level from the front of the car and then heard air blowing through my front left side bleed screw even though the fluid level looked very high.

Well, I looked from the side and lo and behold the back half of the reservoir was totally empty. Much pain and suffering followed. I deduced that the back half of the reservoir fed the front brakes and the front half the back brakes.

Another tip...procedure is to bleed the inside screw first, then the outside screw, of course still starting with the caliper farthest away from the reservoir.

Another tip - don't bother bleeding the clutch. The procedure is a bear. Do not worry about dropping the fluid level in the master reservoir below the large diameter tube coming out the side. That tube does feed the clutch but air will not get into the clutch hydraulics even if a bit of air gets in that inlet tube.

Need more ? Post away.

[racer]

I don't recall having such a block on my boxster. I did take the time to remove fluid from the reservoir using a thin turkey baster to suck up the old fluid. I also used fluids of different color to be able to note when the "old" fluid was out and the new was being worked thru.

[Pinarelloman]

[Quote]. I built my own power bleeder using a pesticide sprayer - basically the same as the Motive but without the pressure gauge.[Quote]

Any chance of posting pictures of your pesticide sprayer based bleeder? Failing pics then just how you made it would be fine.

I was thinking of doing the same by just getting another brake fluid reservoir cap and installing an air fitting. Is there an easier way. Would a large rubber bung or bath plug work, or will it blow out when pressurised.

[jwetering]

[QUOTE=Pinarelloman;5689204][Quote]. I built my own power bleeder using a pesticide sprayer - basically the same as the Motive but without the pressure gauge.

Any chance of posting pictures of your pesticide sprayer based bleeder? Failing pics then just how you made it would be fine.

I was thinking of doing the same by just getting another brake fluid reservoir cap and installing an air fitting. Is there an easier way. Would a large rubber bung or bath plug work, or will it blow out when pressurised.

Sorry for the delay - I didn't get a thread update notification for some reason.

Instead of a photo, just call up an image of a Motive Power Bleeder. My contraption is the same, except without the pressure gauge and it only cost me $15 instead of $80. OK I found a picture of one. Note that I don't use the wand...I attach a brake fluid reservoir cap on the end of the flexy hose.



There's a club member in our area who uses compressed air instead of a hand pumped system like mine. It works a treat but you have to rig up something to cap the pressure at 10 psi or you will be "made love to" if you know what I mean. A bung will probably pop off at 10 psi, so that isn't worth the effort.

In either case you need to get an old brake fluid reservoir cap, drill a hole in it, insert some kind of barbed fitting, and then seal it all up. I got a cap for free from a wrecker.

As you know brake fluid reservoir caps are designed to bleed air in as the brake pads wear and the fluid level drops and for that same reason I expect that air would bleed off as pressurize the reservoir.

So, I went to the effort of sealing the cap completely but since then I overheard a conversation suggesting that the size of the channels that let air in are too small to interfere with the pressurizing at 10 psi. I dunno, you could try it.

In the case of the Porsche caps the bleeding is by a labyrinth pattern in the bottom of the cap. Take one apart and you'll see what I mean. I filled this labyrinth with epoxy, and then reassembled it all together.

Good luck

[Pinarelloman]

Thanks for the reply. That is exactly the way I thought of making one. I also use the garden pressure sprayer for gearbox and diff refills.