After having some stubborn bubbles in my brake system after a caliper rebuild and m/c replacement I did a bit of reading. In both the German Factory manuel (non-translated version) and the Bently manuel there is, what seems to me, a different way to bleed by pressure. It goes as follows...roughly:
1) pressure system to 1 bar at m/c
2) have assistant press on brake pedal
3) open bleeder screw and have assistant pump the pedal slowly at least 12 times with the screw open (this is the new part to me)
4) on last pump with pedal in down position close bleeder screw.
5) repeat at other wheels in order

This seems to contradict what I have done in the past by pumping the brakes with the system open...with pressure will there be no air introduced in the system? Both manuels suggest that this is the best way to bleed. Any comments or some that have tried this technique?

 

What does no one have an opinion on this? Am I the only one who reads the manuels?

 

Oh yessir,...I have an opinion on this and yep, I DO read the manuals,...ROFLAMO.

One simply uses what is successful for them under a lot of varying conditions.

 

I KNOW your opinion on this Steve...LOL...
I guess what I wanted to ask is, will this work or is it a misprint? It seems to me that my pumping the brakes with the circuit open I will be introducing more air into the system. Or is this counteracted by having the m/c pressurized -- unlike manuel bleeding?
I seem to have some very stubborn bubbles in my system this time and am looking for new ways to bleed the system effectively. I am about to remove the calipers and do what I have done on S calipers and bench bleed them then set them on a vibrater for a while. Just for good measure, I have already bench bled the m/c and all calipers...although in replacing all the lines there was some air at the start.

 

Seems to me that this system would work, sort of, if the bleed valve on the caliper were immersed in brake fluid(not an easy thing to do...). This would only allow fluid in and still allow any trapped air bubbles in the system to escape. Having the bleed end of the system open to the atmosphere would do just as you suspect; suck air back into the line when the pressure was released.

 

DANGER!!!!!

With any pump technique you are putting your master cylinder piston in places it may not of been for years....in the corrosion zone. Entering this area may rip the boot. I'd use vacuum or straight pressure or place a 2x4 under pedal so you don't bottom out pedal.

 

Well, first off, I would hope you have a hose attached to the bleeder nipple and running to a container. It's just like bleeding other brake systems, put some fluid in the container and open, pump, close and repeat until you see clean fluid in the hose. That should stop you from getting air in the system. Some folks like the Mity-Vac and others use the Power Bleeder system. Either one of these will run about $50 and lets you do the bleed solo. Remember to start with the right rear caliper, move to the left, then the right front and finally left front. Then repeat. Basically you start at the caliper furthest away from the MC/Resoviour and move to the closest. I didn't see what year your car was so if you have a G50 model then you might want to hit the master and slave cylinders for the clutch.

Personally, I like the Speeder Bleeders that some of the vendors on the board sell with a Power Bleeder to supply fresh fluid & pressure.

Good luck!

 

I have used that method of bleeding brakes for about 25 years until I bought my Power Bleeder a couple of years ago (a good $45 invesment). They taught it that way in my high school automovite class in the late 60s... The only difference was that you made sure the MC reservoir is always near full so no air gets into the system (I guess there was no way to measure/pressure at that time at least for the home wrench?). It is a long process and required two people and you conintually had to keep checking the MC reservoir adding fluid to make sure no air entered system. Here's the process I used: Jack up car, find a helper, remove the reservoir cap, fill with fluid to max capacity, loosen bleeder valve but do not open, attach a hose to bleeder valve, fill a receiver bottle about a quarter full of fluid, run the hose from bleeder valve into bottle making sure it is submerged in fluid, have helper push in the brake pedal, hold down, open bleeder valve, pump until no air bubbles showed and the fluid was running clear, one final push to the floor, hold pedal to floor and tighten bleeder. Start with the furthest wheel from the MC, usually the right rear, then the left rear, then the right front, then the left front, then do it all over again to make sure, then do it one more time (yep they taught 3 times total to make absolutly sure all air was out). Wow, no wonder I didn't do it once a year, that was a pain...

I love the Power Bleeder. Takes about 15 min. for the entire process and I can do it by myself...

 

Yes Jim, I had done the same thing...the type you are explaining was called manuel bleeding -- I have not done this way since working on my dads cars in the 60s. We had the one person (dad) open the bleeder screw, another person(me) pump down, close screw, up and pump, open screw, pump down down, close screw, up and pump... etc until all fluid is clear. What I am explaining takes the best of this manuel bleeding(quality time with father adn son) and combines it with pressure bleeding(the best solo method). With this pressure bleeding you set your "power bleeder" or what ever device you have to presurize the master cylander to 1 bar (14.7 psi) --like a Motive power bleeder -- THEN have assistant pump the car. As a side note, I have heard that Porshce does not recommend vacuum bleeding eg mityvac. Also, for those of you who are pressure bleeding, I have heard that you should never pressuize above 14psi, and 9-10psi is preferable as the bubbles will not be as compressed and will be able to exit the system more easily.

(Marty916) I had not thought of the fact of having the hose submerged in the fliud will rid the system of air. That remedys my fears. Thanks
I have been bleeding brakes using a pressure system (like the power bleeder) with no problem for over 30 years and have not had this extra air problem before...think Ill try something different. Will report with my results. And in the words or Herr Steve Weiner, "...patience grasshopper...bleeding is an art only few can master."

 

I'm still wondering why you would want to pressurize the system if you have a consistantly full reservior. As long as there is no way for air to get into the system, I don't understand the benefit as when you push in the pedal, it pressurizes the system. Hmmm...

 

Im not sure why Jim...I guess since the all knowing Weissach engineers wrote it in stone in the factory manuel....
I figure it is worth trying.
I just have not been able to rid my system of air since I replaced all the components (m/c and calipers, pv, and lines) Although the proceedure seemed odd to me too, hence my starting this thread. I guess I need to just try it and then give a report. Thanks all

 

I'll be waiting to hear how it goes. Good luck and thanks for the insight!

 

You probably already know on higher mileage cars, using the pedal to pump the brakes is a sure fire way to, in the near future, install a new master cylinder. What happens is that over time, the MC seals smooth the bore they traverse, and corrosion occurs in the other sections. Pushing the brake pedal to the floor, as in what happens when bleeding, pushes the seals over the corroded areas, creating small rips in the seals. It might work fine on a factory new car, but on one with 100,000 miles, I can tell you from personal experience, it's not a good idea (unless you need an excuse to replace the master cylinder!)

 

Good point Bill, as you may have read this is on a new m/c so the possibility of corrosion should not be there. I guess I have not mentioned which car I am talking about either...89 Carrera Sport. 49K very enjoiable miles so far...except for this new brake problem.

 

Well all,
I did the bleeding last night. Hooked the pressure cap to the m/c and set it for 1 bar, had my trusty assistant get in the car, hooked my hose (my favorite is a clear flex tubing that is for O2 use--can be stolen from any old lady), filled about 1cm of new fluid in a clear/clean container (about a .5L size), made sure that the hose was UNDER the fluid at all times, opened the screw and had my assistant slowly pump the brake pedal 12 times. I was amazed that after about 8-9 pumps a few small bubbles were detected at each wheel -- even after a few small ones at first. The amount of fluid transfered is high. I was careful to use the large CLEAN container so I could re-use as it was new fluid to begin with. After repeating at all corners my pedal is as hard as ever. Has less than 3cm of travel with engine off, and about 5 cm of travel until hard when engine is running. Feels almost as hard as my early, non brake boosted cars. I think the reason this works is that one is essentially flushing out the system. By the time you have both pressure at the m/c and someone pumping the pedal 48 times, the fluid has all but recirculated throughout the lines and will not allow for any bubbles. This takes much less time than just power bleeding as I usually have to go around 3-5 times to make sure there are no bubbles whereas this is only a one lap affair. All in all maybe 15min were taken. Only drawback...finding the poor soul whom you trust to pump the brakes. I find the neighbor kids love to sit in "race cars"...