Power Bleeder Question...

KNS · 09-30-2005, 08:16 AM

I did a search and learned all I could about my first use of the Power Bleeder. The first caliper (I bled them in the correct order) had many bubbles but eventually ran clear, the other three very few or no bubbles and then clear. I bled the first one again to be safe but no bubbles. My brake pedal has some intial sponginess upon application - an inch or two - then is firm. I am thinking there is still some air in the lines. The whole pressure bleed process went fine with one question: When you first start to pump up the bleeder, there is some air in the pump hose until fluid works it's way towards the reservoir. If I bleed the system again, you just reintroduce air into the system that way. How can you be sure that that air isn't somewhere between the MC and the caliper? All total I bled about 16-18 oz of old/new mix of brake fluid.
Sorry if it's a dumb question, TIA

arcsine · 09-30-2005, 08:23 AM

If you replaced pads or rebuilt the caliper, the problem may be the pistons are too far back in the bore. When this happens, the stiction between the piston, seal and bore is such that the piston does not slide easily and gets pulled back in to the bore by the elasticity of the seal. The solution is to make sure the piston is moved out far enough so that pad is in contact with the rotor when you put it all together.

Jeff · 09-30-2005, 08:29 AM

Kurt, I initially had the same questions along with "how do you clean this thing without contaminating future bleeds". So, what I did is filled the MC resivoir, pumped the jug up to just under 15 psi and bled the brakes while keeping a close eye on the fluid level.

KFC911 · 09-30-2005, 08:29 AM

In your search, you should have find some threads where many of us have posted about using the power bleeder 'dry' (i.e.. no fluid in the bleeder itself). You might try that approach, and see if that helps...

KNS · 09-30-2005, 08:29 AM

Thanks for the reply. The only brake work was the bleed.

Jeff · 09-30-2005, 08:33 AM

And if I remember correctly, I had a slightly softer pedal after the bleed (I rebuilt the calipers, new brake lines, pads, etc.). I then took some high speed hard stops to bed the brake pads and bled the system again, which resulted in a firm brake pedal.

Hope this helps.

KNS · 09-30-2005, 08:45 AM

Thanks for the replies guys. Keith, Jeff, I think I might try the 'dry' approach as it seems to keep the air out - as long as the MC stays full of course. I did take it for a drive after the work and no change.
I noticed this mentioned in my search: Use a new piece of hose to block off the overflow line. I am going to do this the second time around because my 25 year old hose seaped a little at the MC fitting. I didn't go past 14psi as stated in the Bentley Manual but I still got a little wetness.

KNS · 09-30-2005, 09:45 AM

SoCal911SC, I don't get it either and perhaps that's not the source of my problem.

jthwan22 · 09-30-2005, 10:49 AM

I would suck out the old fulid out of the reservoir first. I use a little soft soap pump to do that. No need to fill the reservoir with new fulid. As long as you have new fulid in the Motive can, the reservoir is self filling. Do pinch off the over flow hose. Don't ask me how I know.

Breeang · 09-30-2005, 11:00 AM

bump

livi · 09-30-2005, 11:17 AM

Hey Kurt,

You got a proud avatar name !
At least from a medical point of view. KNS stands for Koagulase Negative Staphylococci. They are a world wide type of skin bacteria thats feared in medical institutions since they are resistant to virtually every antibiotic except a few bordering to poison...

vash · vash's Garage

i have two cans of the gold stuff ready to sacrifice in my next bleed. i feel better sucking it through, but so far so good with my power bleeder. KNS, i would redo it, and use more stuff. that stuff is not good just sitting half empty on the shelf anyways, just send it thru to the recycle can.

Dan in Pasadena · Dan in Pasadena's Garage

In Wayne's 101 Projects book, I thought he mentioned you want to go around the last time and still do the old fashioned pump-the-pedal-by-an-assistant method? I have to re-read that proejct to make sure, but I have only EVER bled brakes that way. Sure, it is more labor intensive and takes two people. But it has always worked in the past....on Hondas, Toyotas, Fords and Chevies of course. Guess I'll find out when I do a full brake job on my 911.

vash · vash's Garage

dan, i destroyed a MC by pumping much to enthusiatically. it may have been on the way out, but i definately gave it the final blow. i messed up the seals by pushing too far. so i got a power bleeder

Dan in Pasadena · Dan in Pasadena's Garage

Really, hmmm? Never had that problem, but then again I didn't go native pumping the pedal, just 4-5 steady pumps and hold it down. Of course, this has never been after a full system tear out, MC, wheel cylinders, etc. I'm sure that introduces a ton of air into the system. But I think I'd still want to use the old fashioned method as a last step. Of course I'd bench bleed the MC and the wheel cylinders before putting it back together and then use the power bleeder.

But why is it that 911's seem to have SUCH an air sensitive system as opposed to almost all other makes? Air is air, you'd think when the fluid is pressurized it would move toward the "end of the line" fairly consistently. What's the big secret?

KNS · 09-30-2005, 12:47 PM

Well, I went two more times around and I think it feels better(?). It seems about the same way as before I bled but I may just be being paranoid. I might swing by my wrench and get another opinion.
Livi,
I don't think I'll take any pride in the reference, had I left out the 'N' and just had KS then you would have associated me with Kaposi's sarcoma. No thank you!!

livi · 09-30-2005, 12:57 PM

I am sorry Kurt - occupational jargon. No offense - really !

KNS · 09-30-2005, 02:03 PM

Livi, No worries, just joking!
Thanks everyone for your suggestions, I tried the 'dry' method when I went around the second and third time and I did get some air bubbles out of one caliper. I asked a friend of mine who has owned several Porsches what he thought and he said it was fine. I'm pretty confident that it feels the same as before I started the whole process.