Newbie Errors When Bleeding Brakes

[TD in DC]

Hello All:

I have two questions regarding Brakes and brake bleeding:

I have an '02 996 Targa that I use regularly for DEs. I use Castrol SRF Brake Fluid (and yes, it is pricy) and stock brake pads. I also have a Motive bleeder and have read the great bleeding DIY article on this forum. Thanks Loren

First Question: I have been told that you should be able to use the SRF Brake fluid for an entire DE season without any worries. I have also been told, however, that you can simply bleed the calipers to remove old fluid (rather than the entire system) to keep your brakes at an optimum level since the fluid in the calipers goes bad faster than the rest. Is this true?

Second Question: The last time I bled my brakes (I was receiving help from a very experienced Porsche tech guy), I put an air bubble in the system. What a PIA, and dangerous. We did nothing that was obviously wrong, and I still don't know how it happened. My question is about what common newbie errors you can make when bleeding the brakes? In other words, can someone make a top ten list of errors and how to avoid them. Assume I both (1) know nothing and (2) am an idiot. In other words, I will not be insulted by very basic explanations.

Thanks!

TD in DC

Edited May 19, 2005 by TD in DC

[Loren]

First Question: IMHO - I would bleed my brakes after any serious track event. Mind you not replace all the brake fluid - just bleed for bubbles.

Second Question:

1. Make sure that there is plenty of brake fluid in the Motive bleeder.

2. Keep the pressure on the bleeder at 15 to 20 psi - all the time.

3. For the catch tube, find a some clear plastic (aquarium) tubing that fits snug over the bleeder screw.

4. Only open the bleeder screw enough to see the flow start and close it immediately when you see clear brake fluid. In most cases the valve is only open a few seconds.

5. Check the pressure and (new) fluid level before moving on to the next wheel.

6. Don't forget to bleed the clutch slave cylinder as it shares the same fluid path.

That's not 10 items but what I can think of right now...

[ar38070]

You do not need to use 15-20 psi in the bleeder. 5-10 is plenty. You do not want to use more than that because theoretically you are compressing wet air on top of the fluid and forcing more moisture into the fluid.

You want to bleed starting from the valve furthest from the reservoir (right rear). Then move closer (left rear, right front, left front).

If you are just bleeding you do not need to put any fluid in the bleeder, just make sure that the reservoir is at least half full. You do not need to have fluid in the bleeder as the amount bled is small. (If you are paranoid about running out, then top off the reservoir first.)

I do not usually bleed after each event (I do 30-40 a year). I only bleed if I notice a problem.

Once a year complete fluid replacement is plenty unless you are tracking 50+ days/year.

Also there really is no reason to use SRF. ATE blue/gold or at most Motul 500 is good enough.

If you are constantly boiling your fluid then you probably want to reevaluate your braking technique.

[PorschePRH]

a couple of nuggets:

1) Elevate the catch tube and receptacle well above the caliper. Otherwise, the fluid in the down side of the catch tube will draw a vacuum on the line and you may see bubbles in the catch line from suction around the bleed screw when they really aren't any in the brake system.

2) Buy cheaper brake fluid and bleed before and after every event. The life of brake fluid in a caliper on a track is not an easy one... You will get moisture in brake fluid over time no matter what, so you are better off having fresh fluid before every track event. A day on the track cooks that fluid, so get it out of there to be nice to your caliper and it's seals. You should be taking the wheels off anyway to check the pads for wear after a day on the track, and this is the hardest part of bleeding brakes (wheel removal). Also a good time to wash the wheels in the inside and give them some wax, so you don't end up with stained wheels from the heavy brake dust of a track day.

[TD in DC]

I am not boiling my fluid, and I am actually pretty easy on my brakes (from a comparative standpoint). In fact, I am not sure that I would recognize boiled brake fluid when it happened since my brakes have performed fine. What are signs that you are having a problem? Do the brakes start to fade progressively or suddenly? What happens?

[umn]

...

2. Keep the pressure on the bleeder at 15 to 20 psi - all the time.

...

4. Only open the bleeder screw enough to see the flow start and close it immediately when you see clear brake fluid. In most cases the valve is only open a few seconds.

...

I wouldn't close the bleeder screw as soon as I see clean fluid. The Porsche workshop manual recommends that you bleed about 250ml (about half a pint) of brake build per caliper.

Whilst 250ml might be slightly excessive, it would wait until I see at least 50-100ml of clear fluid. The car and brake manufacturers' reasoning behind it is this:

1) We want to sell expensive brake fluid to our customers :clapping:

2) Within the calipers and abs pressure modulator there are quite a few recesses and awkward places where it takes a while for all the old brake fluid to flush out. So if you start seeing clear brake fuild at the calipers, it is good practice to let it run for a little while to make sure that all the old fluid has come out from these awkward spots.

The second point brings me to the recommended pressure of the bleeder. Porsche recommends 1.5 bar (I guess about 20psi). As "ar38070" pointed out, that's not ideal with a Motif bleeder because you are pressing wet air into the brake fluid. That's a design flaw of the low-cost Motif bleeder. Professional bleeders solve this problem by either using an electric pump to pressurise the brake fluid, or in pneumatic systems similar to the Motif bledder they use a membrane to separate the brake fluid from the pressurised air.

However, I probably wouldn't recommend reducing the pressure below 1.5 bar, even with a Motif bleeder. With reduced pressure, you decrease the speed with which you press the fluid through the lines. However, high speed is desirable because again it makes sure that the old brake fluid is flushed our from all the awkward places such as the pressure modulator and calipers. This is particularly important because the old brake fluid containts a significant amount of water which can lead to corrosion problems (apart from a decreased boiling point).

Therefore, I'd probably stick with Porsche's recommendation.

Cheers,

Uwe

[Izzy]

I have found switching between yellow and blue fluid every other bleed helps with a visual check to ensure the "old" fluid is completely gone. It helps foolproof the process.

[ar38070]

I am not boiling my fluid, and I am actually pretty easy on my brakes (from a comparative standpoint).  In fact, I am not sure that I would recognize boiled brake fluid when it happened since my brakes have performed fine.  What are signs that you are having a problem?  Do the brakes start to fade progressively or suddenly?  What happens?

<{POST_SNAPBACK}>

Boiled fluid or having air in the system will be noticed in two ways:

As the system heats up

1) initially the pedal will travel farther for the same brake effect.

2) if it gets really bad then your brake pedal will go to the floor and you will have to pump the pedal if you want to stop in order to build up pressure in the system.

Again if you are not seeing these symptoms then your fluid is okay and you may want to rethink what brand of fluid you are using. The higher $$ fluids have higher boiling points but if you do not need it why waste the money. Also depending on the brand some of the higher $$ fluids are more hygroscopic i.e. they absorb water more easily than the lower priced brands.

I bleed my brakes every 10 or so track days. I have yet to see any bubbles (ATE blue fluid).

[djantlive]

One 1000ml bottle should have plenty left after bleeding all 4 corners. Typically, i use up 750ml.

Keeping the master cyclinder filled with new fluid is important. As soon as it runs low, air get sucked in.

Keeping the bleedning screws undamaged is important as you will bleed often. use an enclosed wrench instead of an open box wrench.

lastly keep the fluid away from painted surface including garage floors. wear double gloves and safety glasses

[C4S Surgeon]

Don't bleed it dry, you'll f up the ABS system.

When your fluid boils, the sensors will melt and set off brake check lights, just pack up and go home at that point.

[dj996]

Be careful with the brake fluid, it can eat the paint down to the bare metal.

Edited May 24, 2005 by dj996

[carrera mike]

Buddy and I replaced his stock brake calipers(997) with big reds. On the 997, big reds need their own front wheel carriers and reservoir, so we had to open a lot of connections and introduce air in the system. After bleeding the whole system with probably 2 gals of fluid, it was still a little bit spongy. I knew that there were still bubbles trapped in the ABS sys even though we were getting solid flow from the calipers.

So what we did was do it the old fashion way, press the pedal 4 times, and while holding the pedal down, release the fluid pressure the normal way thru the caliper bleeder valve. Boy, you wouldn't believe how much bubbles came out. As soon as the pedal bottoms out to the floor, close the caliper valve and pump the pedal again and hold. Repeat until there's no more bubbles coming out.

Edited May 24, 2005 by carrera mike

[ar38070]

The problem when you did this is that the ABS circuit (valves, whatever) has air in it. Supposedly you cannot get the air out of this part of the circuit without a Porsche computer (the computer manually opens all of the valves). I suppose you could take the car out on the street, ABS the car, and that would release the air. Then come back in and bleed the system again.