auzivision

After a lengthy suspension and caliper restoration project, I’ve manage to get everything put back together (almost, but not related). I have bled the brakes twice using the motive pressure bleeder. First I used clear and bled till they ran clear starting at the far corner and working my way back. Then I used blue and repeated till they ran blue. That’s the short story, now for the long version (skip to the end if you have read enough).

As part of the caliper refinish project I pushed all the pistons back as far as they would go. Using 12 to 14 psi on the Motive wasn’t pushing all the piston back out. So mid brake bleed (rears only) I pumped the brake pedal a few times to close the gaps.

There was plenty of fluid in the tank and while watching the filler hose, I notice air bubble coming out of the reservoir and back in the bleeder. Thinking getting the air out is good, I kept doing this until I couldn’t get any more bubble out the MC end. I also tapped on the MC and lower the pressure to only a couple pounds and worked it till there were no bubbles coming out that end.

I finished the front until they ran clear and worked the pedal, but it wasn’t a firm as it used to be. So I repeated the entire bleed process with blue. At no times did any more air bubbles come out of either ends (calipers or MC).

The brakes work, but don’t instill confidence. Before (which was just after replacing the MC last year) with the engine off I could pump the pedal several times and it would become rock hard with little to no travel. Now the best I get is half brake travel engine off and maybe ¾ travels with it running. At no time can I get them all the way to the floor.

I’ve checked for leaks and haven’t found any. I’m suspect I still have some air trapped in the system and am looking for help getting them out. Being that parts of the system sat ‘dry’ for 6 months (mainly calipers and the ends of the lines), what would you try next?

Leon Speed

Lot's of threads on this topic, but to experience is the best way. I've found that hands down the best way is to have a helper to push down on the brake paddle while you fill the resevour and bleed the brakes. I am assuming you do bleed both sides of the caliper right?

jcorenman

+1, what Aryan said ^^^

It's all about buoyancy, and velocity.

An air bubble in the system is buoyant, and wants to rise. If there happens to be an open bleeder right where it rises to, then it is gone. But more likely it will find a nice spot and just sit there. The fluid velocity with just the Motive bleeder pushing fluid through an open bleeder will not be enough to overcome the buoyancy of the bubble and get it to move.

If you close the bleeder, and then have a helper push the pedal, then two good things happen: the bubbles get much smaller, microscopic if you push hard, and most of their buoyancy is gone. And when you crack open the bleeder, the high pressure creates a much higher velocity which will sweep the now-tiny bubbles out of the system.

Don't open the bleeder very far, you want to maintain high pressure as the pedal goes down, in order to keep the bubbles small. But you also want pretty quick flow.

I think it will also work to crack open the bleeder a bit and just leave it open, and then pump repeatedly. This would allow you to do it yourself, but it will take some fiddling to get the bleeder valve opened just right-- there should be quite a bit of resistance to pushing the pedal, but be able to be pushed all the way down in 1 to 2 seconds.

And this is where the Motive bleeder comes in: By maintaining a few PSI on the system, there is no tendency for air to re-enter from the cracked-open bleeder valve, or via the MC. And it keeps the reservoir full.

Bill Ball

So, are you saying you didn't plug the lines when you detached the calipers and left them hanging for a month? Nicole had this problem when she did that and the brake system largely drained itself. We went through HELL to get the air out - regular bleeds, power bleeds, reverse bleeds, new master cylinder, cracked ABS fittings to bleed that, service tech replaced the proportioning valve and bled some more, we elevated the tail of the car high in the air to help move air along the rear lines while bleeding, a local electronics expert built an ABS pump and valve trigger device to purge the pump reservoir, Greg Brown bled it some more and adjusted the brake pedal rod to reduce pedal travel (shouldn't have needed that, but whatever works). It's better but it's not as firm as my brakes.

Lizard928

I found that pumping the pedal about three times fast seemed to help compress the air slightly more, and then get it out. My brakes are always rock solid.

Nicole

I'm so sorry to hear of another case like this. It's been a nightmare, and even though it's pretty good now, I don't think it's entirely over.

I have learned a lot in the meantime, including never to let the whole system go dry, not using aftermarket pads - particularly in the rear - the various bleeding techniques, etc. And I've spent a lot of money - more than $2k along the way.

Despite all the improvements we achieved over time, the brakes still don't feel as firm as those on Bill's 928 or on my Saab. However, it is now at a point where I can live with it. I'm considering having the almost new Porsche flexible brake lines replaced with braided ones, in order to get a firmer pedal feel again.

auzivision

I did do some searching and read a couple threads before posting since I didn’t find much I hadn’t tried.
I do recall someone saying something about the old pump the pedal method with a helper (aka Hans) might work better. I also, thought I remember someone mentioning to bleed the MC… that piece I need to research further. I did bleed the calipers inside and out both times.
I hope this isn’t a live and learn lesson, but yes I left the lines unplugged for several months. I elevated them to a higher position so they would keep leaking. So the system wasn't completely dry. A lot of original blue fluid came out on the initial bleed with intermixed pockets of air.

I’m going to drive it around slowly to help ‘vibrate’ the bubbles hoping they will float to the top while settling the suspension so I can start messing with the ride height. I need to get a couple measurements for that aspect before I put the car back on stands.

Fingers crossed the old two man pump the pedal method works for me.

123

Every single car in the world with a hydraulic brake system was built with it dry, and then filled. How was the system initially filled at the factory?

Nicole

Supposedly, they put a very strong vacuum on the complete brake system, and then let the system suck-in the fluid. The person who told me that says the bleeder nipples are not opened in the process.

I have not been able to verify this, though, and have my doubt you could get all air out before you let the fluid in.

In other words: I don't know how they REALLY do it.

jpitman2

I worked in a brake shop once, and it was well known that for some systems just pushing the pedal with the bleeder open worked fine, but others needed a different approach - crack the bleeder and STAMP on the pedal - like your life depended on it. This is like the process mentioned above, where you need fast moving fluid to suck out small bubbles of air. Having said that, I flushed the fluid in mine last year with a Motive, and had no issues at all getting a good pedal.
jp 83 Euro S AT 53k

Bill Ball

Flushing has never been a problem for me either, but a drained system is different. The factory uses a tool we don't have to fill a dry system. Several experts, including Greg Brown, have worked on Nicole's system after we bled it over 20 times with various usually successful techniques and followed everyone's advice here. Her brakes worked but were soft and had 2-3 inches of pedal play even after our 20 bleeding episodes while they were fine prior to the caliper removal. We did nothing to change the pedal play, so I hadn't planned on adjusting the brake booster rod, but Greg did that to restore reasonable play. Anyway, good luck. I can't say pedal pushing is any more effective than whatever other method you could use. I have a Motiv pressure bleeder, MityVac suction system, reverse bleeder system (excellent for clutch slave cylinders) and used them all on Nicole's brakes.

Lizard928

Well, I have changed the ABS pump on a 89 before. I replaced it with a completely dry 87 unit (had to change the electrics on top of the pump). I was able to restore the car to a completely firm pedal.

I have to admit, I would still like to get my hands on Nicoles car and take a look at it.

BC

This is my point. People redo brake systems all the time. Dry lines, dry calipers, etc. There has to be something missing.

Mrmerlin

something to consider when using the push the pedal to the floor is how old is your MC,
if it has say more than 10 years in position then there is a very good chance that it has corrosion in the bore ,
and as soon as the pedal is put full stroke the seals will run into the corroded section quickly cutting them and thus causing a failure. in the MC.

The other thing to consider is using synthetic fluids as they may not be compatible with the previous fluid,
this will over time cause the MC seals to swell thus causing a sticking issue in the MC.

Thats why I suggest to use ATE super Blue and then you can swap it out with Gold ATE Fluid,
changes must be done frequently to remove entrained water.
The other thing that can be done is to cover the MC cap with some type of cover,
to prevent water from dripping onto it and thus getting into the MC reservoir

jej3

My 12 year old got alot of exercise in his right leg when I pulled the calipers for paint (not so great) and swapped over to Roger's stainless lines.

I think we went through too much brake fluid but after the pump - open - close routine 4 or 5 times on every corner we found success. I used the vac to try and do it initially but I think that's more suitable for flushes versus dry fills.

Find an eager helper with a strong leg and put them on the brake pedal. I bled from the furthest point to the closest (Passenger rear, driver rear, passenger front, driver front) I forgot to do the master cylinder and that may be why it took me longer.

Brakes feel great now....and my son can now kick the stuffing out of a ball . It also caused him to understand AND appreciate hydraulic systems.

Good luck!