Brake Bleeding - Could Use Some Help

[bbarrington]

Once again I humbly come to the forum in desperate search of advice and understanding.

Here's my situation. I replaced both rear calipers on my '88 Carrera. Before I opened the lines, I depressed the brake pedal slightly with a 2x2 that I had in an attempt to keep the fluid in the lines. However, that didn't work at all as both rear lines emptied before I could install the new calipers.

Now I'm ready to bleed the lines, but the pedal sinks to the floor when foot (or hand) pressure is applied regardless of whether the bleed valve is open or closed. The reservoir is full. So I guess this means the master cylinder is completely empty (??). Any suggestions on how to proceed? Would a vacuum pump help? Do I have to prime the master cylinder somehow? I'm at a loss to understand what is going on and how to correct it. Any help is appreciated.

Thanks,
Bill
'88 Carrera Coupe

[GG Allin]

Are you using a pressure bleeder?

[75 911s]

You either need a pressure bleeder like the Motive setup sold here, or a second friend pumping the pedal.

Make sure the resevoir doesn't drop down too low while doing all this or new air will be introduced in the system.

It's soft because air is compressible. You are squeezing air instead of the hydraulic fluid moving the part. So clearly the rear calipers have a lot of air in them and the lines maybe a bit.

So bleed them using the normal procedure. A helpful tip is to tap the caliper all around with a soft rubber mallet while you bleed that caliper. That will get some of the stubborn air bubbles out.

You may have to go around several times using up quite a bit of fluid to do so.

[bbarrington]

I've tried with a friend pumping the pedal. Like I said, the pedal goes to the floor with the bleeder valve open or closed. There is absolutely no change in the level of fluid in the reservoir. Can you point to 'the Motive setup' that you mentioned? Would a vacuum pump work, too?

[fanaudical]

Pelican's page for the Motive products:

https://www.pelicanparts.com/catalog/shopcart/TOOL/POR_TOOL_BLEEDR-detail.htm

Something else to try:

- Connect hose to one rear bleeder and run that to a jar.

- Brake pedal all the way up; reservoir full

- Crack the rear bleeder screw

- Stand by the reservoir and wait; keep pouring fluid in to fill when it starts to get low

Sometimes you can get lucky and head pressure from the reservoir will slowly displace the air in that line. Once you see fluid in the bleeder hose, close that one and move to the next. This might get you "close enough" where you can then have a friend pump the pedal to bleed. (Similar to trying the vacuum pump at the bleeder approach, but you need somebody watching the reservoir in that case. I've never had much luck with vac pumps...)

Be sure to limit how far the pedal goes to the floor so as to not bottom out and trash the master cylinder seals.

[jlex]

Why don't you try a simple gravity feed? Fill the reservoir, open one of the bleed valves, then let the fluid displace the air naturally. Will take a bit of time and you need to watch the fluid level so it's not introducing more air if it goes too low.
I see you have an '88 that means G50 transmission and that means you have a hydraulic clutch. Did you know the clutch fluid also comes from the brake reservoir? If the fluid goes too low and someone happens to touch the clutch pedal you'll suck air in, then you'll have to bleed it at the slave cylinder...watch out for that.

[bbarrington]

Awesome. I employed my wife initially to help pump the brakes. She was pumping the clutch pedal to start. So that's probably what happened. Excellent.
Now what? I don't have the slightest idea how to verify that. And then how to take care of it if that's indeed what happened. If you could point me...
Looks like I've managed to do everything wrong on this one. Hooray!

Thanks for your reply.

BTW, I'm trying a gravity feed as we speak (or email). No joy.

[Cory M]

If you pressure bleed don't forget to clamp the overflow line on the master cylinder reservoir

[jlex]

Just worry about the brakes for now.... clutch may be okay if there was sufficient fluid in the reservoir to prevent air from being introduced. Clutch will feel funky if it needs to be bled, but that's another project. It may be okay. See if the gravity feed works for the brakes... IIRC, it should take about 30 min. per wheel. If you have enough know-how to replace the calipers, you should be able to knock the air out of the system one way or another.

[bbarrington]

Well, that makes me feel better, but the right rear has been sitting there with the bleeder valve open (hose from bleeder to jar) for over four hours now and there is no fluid moving at all. Filler cap on the reservoir is off.
I don't understand what is preventing it from flowing.

[jlex]

Give it a bit of a start by pushing the brake pedal... that should get things moving

[jlex]

Make sure the hose is in fluid to begin with if you pump the brake while the bleeder valve is open... you don't want air sucked back in from the bleeder hose.

[jlex]

When I overhauled my front calipers, I used gravity bleed to evacuate air from the lines.... was too lazy to break out my Mityvac vacuum power bleeder, compressor, etc. Worked great!

[bbarrington]

Well. Embarrassing, but mystery solved. The problem is that I can't see. Or I need a more brightly lit garage. What I thought was the fluid level in the reservoir turned out to just be a dark line. I've filled the reservoir now and I can see air bubbles occasionally flowing through the clear tube on the right rear. What a dumbass. I think I'm on the way now. But I may have to deal with the clutch. Maybe I'll get lucky. Also, how likely is it to trash the seals in the MC if the pedal goes down too far? Geez, I learned a lot, but most of it was too late.

Thanks very much for everyone's help. I'm very appreciative.

Bill

[jlex]

Ha... that's a good one, although I can see how that could happen. The fluid will discolor the reservoir making it look like it's full. Keep your fingers crossed that no air got into the clutch line.... can be a bit of a PITA to bleed, although if it hasn't been bled so far, it would be something you'll want to do anyway when you want more Porsche fun...

[tirwin]

It happens. I overfilled the coolant on my daughter’s Honda because of a horrible design that made it damn near impossible to read the level. I had to use a boroscope with a light to illuminate it enough.

Glad it was an easy fix.

[bbarrington]

LOL. I'm feeling a bit better. :-) Thanks. I will know the complete story tomorrow... [fingers crossed]

[John W.]

Don’t feel bad. Almost everyone here has made a dumb mistake at some point.
I screwed up big time at work once. When I told my boss he just said the only people who don’t make mistakes are the ones who don’t do anything and I don’t want them working for me. Keep wrenching.

[bbarrington]

Probably not the last time, either.
Good quote, BTW.

[911tracker85]

just about to do this on my 86 951, had to remove the MC and booster and disconnect the clutch line to replace the AC lines. when I have to bleed the clutch systems I force the fluid in from the bottom bleeder valve. I had read how hard it can be to get all the air out of the clutch system pushing fluid from the top as any bubbles keep wanting to go UP the line.

good luck.