Brake system bleeding 78 911sc
 

I have searched for specific answer to my question, but find it difficult to find information on bleeding a dry brake system with power bleeder.

My 1978 sc Targa sat idle for 10 or more years. I have managed, with help of Tony, to get the thing running well. Now I want to make sure it will stop.

I decided to take the safe route and disassemble, clean, replace major components including brake master cylinder (replaced,) inspect brake booster, Calipers (rebuild,) and lines between body and calipers (replaced.) I have purchased the Schwaben power bleed from Pelican and am progressing toward getting everything back together. No major problems so far............I think I may have dodged a very expensive bullet on the brake booster: master cylinder may have been leaking as some paint on the booster was badly bubbled. Inspection of booster revealed no internal corrosion. I guess I will find out for sure, shortly.

My question is whether or not there are any considerations- not applicable to normal brake system bleeding/flushing- associated with refilling and bleeding a dry brake system with a power bleeder. All the information on power/pressure bleeding I am able to find has to do with bleeding and flushing a systems that is already full of brake fluid.

Any advise is appreciated.

Best,

Wayne

Yeah, stopping is pretty important. :eek:

Several recent threads here about how to bleed the brakes. Short version is to fill and bleed the MC on the bench before you install it in the car. After that, keep pumping brake fluid through the system (and frequently refilling the reservoir) until you don't get bubbles out the caliper bleeders. Then go drive the car vigorously, then bleed the calipers again. It may take several rounds.

I have heard up to, 10 times pump & bleed for the front brakes calipers and 14 for the rear.

It is not necessary to remove the master cylinder to bench bleed it if you don’t want to. There are (cheap) kits available with plastic tubing and fittings that you can screw into the brake line ports, then run the hoses into the reservoir.

Once there is fluid in the system I have not found it hard to bleed with a pressure bleeder. Though I did, once upon a time, have a firmer pedal than I have now, and after a fluid replacement about 6 years ago I’ve never been able to get the pedal that firm.

I guess my main question is, does the power bleeder, if used properly, eliminate the need for bench bleeding the master cylinder?

+1 for Otter74 suggestion. Buy the kit from Enhon bleeding kit from Amazon and bleed the MC.
For my '83 SC, I bled it on the bench. But, as Otter74 says, can be done installed in the car.

I went through this challenge about a year ago. Here's my thread for your reference: https://forums.pelicanparts.com/porsche-911-technical-forum/1166024-help-bleeding-brakes-83-sc-new-master-cylinder.html

So far I’ve never needed to bench bleed. Open the calipers and gravity will do its thing.

He already has the brake system out and disassembled. Bench bleeding it at this point is easy.

I just did this on my completely new system, all rebuilt, new lines everywhere, new MC, rebuilt Turbo calipers.

Just bled it with gravity.

Hoses on each bleeder long enough to go higher than the MC.

Fill the reservoir and lower the hose for a few minutes starting with the PS rear caliper.

Fluid will come out and after you have let it "flush" for a while, put the hose back up high again and off to the next wheel.

I think it took me an hour all in, no excitement, no pedal pressing (although I do swish it around a bit to help fill everything) on each corner.

Just keep the reservoir filled and its easy, peaceful and no problem

Been doing this way for years.

D.

+1 on the gravity bleed method.

I'm happy with the speed bleeders on my SC

Agreed, speed bleeders make it an easy one man job.

One time I experienced an extremely difficult to bleed motorcycle front master and single caliper.

A system so simple you couldn’t imagine that it would be the least bit difficult. But I just couldn’t get it to work correctly after doing all the standard DIY methods.
Because of this, I did research and ended up learning about how to fill a dry system the way they do it at the factory.

Basically, a factory fill from dry starts (and ends) with a connection to the master cylinder reservoir and nothing else.


Connect to the master reservoir with a short hose up to Y connection with two valves on each side of the Y.
One side of the Y will be the fluid supply, close that valve.
From the other side of the Y, pull a vacuum on the brake system. This is where a factory filling system would look for leaks.
Once the system is evacuated, close the valve to the vac pump and open the valve to the fluid source and watch the fluid gets pulled into the system. A factory filling system would verify the correct volume of fluid is sucked into the brake system.

Done.
No need to open bleeder valves, pump brakes or other techniques are used.
The system won’t have air to bleed out because all the air was removed before the fluid was introduced.

I’ve never seen one of these tools in person or used one, but I was able to use the concept and I’ve used this method on several occasions and had good results.

I imagine that the calipers and/or master could be bench bled with this method, but they don’t do that on an assembly line.

Clever!!! It's similar to how you have to fill some modern coolant systems. I had to use that method to refill the coolant on 2004 C4S. I didn't realize it was used for brake systems too.

Yes speed bleeders are great. Power bleeder is nice to make sure the reservoir does not run dry :eek:

Thanks for the great responses. Anxiety is gone. I can handle this.

Now I have to, somehow, stop looking for new sources of anxiety............Rebuild all the CV joints? :)

Working on this thing is starting to make me miss my old airhead BMW motorcycle.

I am struggling to get my 75 bled. A few things I learned.....

• Pressure bleeders should only be used under 10psi, preferably about 5psi. Unlike every other system I have bled, our 911's lines from the reservoir to the master only press into the master. As a result, too much pressure will just push fluid past the grommets, and not through the system (ask me how I know).
• Be careful of your bleeders. My newly refinished PBM calipers have at least 2 bleeders that, when opened enough to flow fluid, will give a stream of bubbles. If I push the bleed nipple down the bubbles stop. The calipers are all very old, and the coarse threads are not the greatest. While I don't think this will let air into the caliper because fluid is always flowing out, it is not ideal. I called PBM and they basically said it is what it is, they can send me another set of calipers if it's a problem, but I'm not sure that is my issue. Just be careful with your old, worn out, wobbly nipples. :eek:
• I did not bench bleed my master. So far I have been through 5 quarts and the system felt great when done. Then the car sat for a few days, and the pedal is completely soft again. We re-bled with the pressure bleeder, waited a few days, same issue. Nothing is leaking so it's a bit of a mystery.

Helpful tip I learned years ago for bleeding master cyl.

Look carefully at the orientation of the master cyl and how it sits naturally when installed in the car. Imagine you are an air bubble inside that cyl, where would you migrate to? Get an imaginary visual of where air would naturally sit.

Now, let us assume the cyl has the piston pump side at one end and the outlet line of the other end. And if this cyl sits tilted so that the piston side sits higher than the outlet you have a issue! No matter how many pumps you pump the piston you will never move ALL the air to the outlet! This is the single biggest mistake in achieving rock solid bleeding! Does not matter how you bleed, power bleeder, old school, ... if you do not orientate the air bubble so it's near the outlet you will leave some air in the master cyl!

How do you fix this? Simply jack the car up as need be to favor any air to move to the outlet(s) of the master cyl. You may need to jack the front or the rear higher and/or also jack the left side or right side higher. Bottom line is study the orientation of the master cyl and understand how/where air bubble will be sitting.

Thanks again. This is all beginning to seem like fun: As I rolled around under the car (QuickJack) and contemplated the great advice given here, as well as the general condition of the car, I resolved I need to buy my first pneumatic die grinder. Life will be different with a die grinder...........just like it became different after I purchased my sawzall.

I see no place for the sawzall in relation to this brake restoration project.

Best,

Wayne