NO BRAKES, pedal to floor!! Help solve my brake mystery

[kger]

Well I'm flummoxed:

I just finished a brake job that included new soft lines and rebuilding all 4 calipers (new rotors too). I flushed the whole system with a jug of new fluid using a Motiv power bleeder and got clean, bubble free fluid from each corner.

Then... I'm driving to the gas station and get a pedal to floor moment (but brakes hold at very low speed)!! I pull my foot off the brake and magically have pressure and brakes again, no problem.

When airing up my tires I inspect the lines/calipers and notice the front right caliper is leaking fluid from the bleed screw. Forgot to tighten it perhaps. I get home and re-bleed that corner with the helper's foot method and tighten down the bleed screw.

Go back out for a test, all feels good and pretty firm (not perfect) and I stop for about 30 seconds at a light. Light pressure on brakes, just enough to keep the car stopped on a very slight downhill... and PEDAL TO FLOOR out of no where. Release and press again, firmness and brakes no problem. The rest of my test ride around some empty back streets goes fine except one downhill the pedal gets soft.

When I get home I stand on the brake when stopped and sometimes can put it to the floor, sometimes can't. No leaking from the MC or booster or reservoir. Brake warning light is on. No more (noticeable) leaking from that bleed screw...

What is going on?? Do I just need to keep bleeding, or is there a more serious issue going on (MC, Booster, etc)?

Thanks in advance for the thoughts!

[shadowjack1]

when you reinstalled the cal did you put them back on with the bleed screw on top? Just aksing

[macssc911]

Sounds like you still have some air floating around in the system Get A Partner and do it the old fashioned way

[Bob Kontak]

Originally Posted by kger

What is going on?? Do I just need to keep bleeding, or is there a more serious issue going on (MC, Booster, etc)?

There is a rule to follow with respect to bleeding brakes with the traditional method with a friend. I never did and never had a problem. It has something to do with limiting the travel of the brake pedal so you don't move the actuating rod past where it normally travels inside the MC because you expose the seals to potentially skanky surfaces. Big downside being you damage the seal(s).

Your symptoms sound like a recent job I did on and old Dodge Durango. This one had pedal near the floor all the time AFTER repairs Gravity and pressure bled. Nuttin. Still wimpy. Friend method resulted in firm pedal on rare occasion then it would go away. We were stumped. Walked away, next day rolled the dice and sprung for a MC. Fixed.

Air is a stinker on old 911's. If all is well your pedal should go down about 2" and hit a wall. If you feel a little step in the pedal, you don't have the air out. You will feel this if your foot travels 3". Hard to describe.

[jjeffries]

Having first checked like Shadow suggested that the calipers are in the right positions and that all the other hydraulic connections are good, I'd let the car sit overnight then patiently re-bleed with the Motive. I've learned to be weary of pedal bleeding an older master cylinder. John in CT.

[jjeffries]

.....for the same reasons BobK spelled out.

[SalParadise]

Originally Posted by Bob Kontak

Air is a stinker on old 911's. If all is well your pedal should go down about 2" and hit a wall. If you feel a little step in the pedal, you don't have the air out. You will feel this if your foot travels 3". Hard to describe.

Bob is right here. You need to get that air out. It hides. It goes places and resurfaces at times. Hard to get it all out.

The only other time I had your problem was using a new URO master cylinder that almost killed me and my car. If it's a URO master, don't use it.

[kger]

Originally Posted by SalParadise

Bob is right here. You need to get that air out. It hides. It goes places and resurfaces at times. Hard to get it all out.

The only other time I had your problem was using a new URO master cylinder that almost killed me and my car. If it's a URO master, don't use it.

Not sure how to do multi-quotes yet, but I'll respond to all here:

Would air in the system create that scenario where all is good one minute and then the pedal drops to the floor randomly, or inconsistent pedal feel? In my past experience with brakes air just creates sponginess, but its consistently bad, not good one moment gone the next.

I initially pumped some fluid through the lines to the rear brakes before I bought the motive (Craigslist find), and am almost sure I pumped too far - nearly full travel. So maybe I damaged the MC, but again, would that create the pedal-feel grab bag I have?

And what's with the brake warning light being on (fluid is still full and brakes work).

Thanks again for all the help!

[Bob Kontak]

Originally Posted by kger

Not sure how to do multi-quotes yet, but I'll respond to all here:

Would air in the system create that scenario where all is good one minute and then the pedal drops to the floor randomly, or inconsistent pedal feel? In my past experience with brakes air just creates sponginess, but its consistently bad, not good one moment gone the next.

I initially pumped some fluid through the lines to the rear brakes before I bought the motive (Craigslist find), and am almost sure I pumped too far - nearly full travel. So maybe I damaged the MC, but again, would that create the pedal-feel grab bag I have?

And what's with the brake warning light being on (fluid is still full and brakes work).

Thanks again for all the help!

Air in the system creates a softer pedal all the time. If it's there it squishes when the pads should be squeezing.

I have never seen intermittent. My guess is MC.

Not sure but brake warning light might have to do with pedal traveling too far.

[kger]

Originally Posted by Bob Kontak

Air in the system creates a softer pedal all the time. If it's there it squishes when the pads should be squeezing.

I have never seen intermittent. My guess is MC.

Not sure but brake warning light might have to do with pedal traveling too far.

Thank you Bob. Yea the intermittent thing is strange... They feel pretty good and then standing still at a stop light, pedal goes soft and to floor and then recovers when you pump it once.

Any other ideas out there? Ways to track the issue by tests?

[fiminod]

has to be the MC

[kger]

Originally Posted by fiminod

has to be the MC

Thanks for chiming in fiminod - do you mind taking me through your thought process?

[chrismorse]

Bob is right.
With years of usage, small bits of corrosion and debris are pushed about in the master cylinder. The piston seal does a great job of moving this junk to the normal end of travel, where it sits, eventually forming a fairly solid nasty bit of debris. With a bit of moisture, this trash corrodes and sticks to the bore.
I was a service writer manager at a dealership for 10 years and got called on to be the foot in the bleeding process when the old power bleeder was acting up. Maybe 5 to 10 percent of the time, especially with older cars, we would have a master cylinder failure - brakes wouldn't bleed, very uneven pedal or it would just go to the floor.
If the mc is 10+ years old, perhaps not flushed annually, or bi-annually, and the brakes are manually bled, the seal is pushed over that rough, pernicious debris in the bore and the seal is "cut".
As Bob said, don't push the pedal further than it normally goes to avoid damaging the seal.
This is often hard to guestimate, so, a power or vacuum bleeder is the way to go.

To postpone or substantially reduce the risk, bleed annually, to ,avoid trash build up.

However, most of us have not owned the car since new, so, until you replace the MC and are diligent about cleanliness, don't manually bleed.

Good luck.
Chris

[GaryR]

My shop taught me a "trick" when I installed all brand new calipers on my SC race car and seemingly couldn't get a solid pedal after several Motiv bleedings. They use a set of pads worn down to the backing plate, pump the pedal to put them against the rotor, then force them all the way back using a spreader, doing this several times per caliper, bleeding afterwards. I think Dan called it "exercising the calipers". Can only assume air gets trapped in a bone-dry caliper and new pads only allow slight piston movement, but doing this worked for me..

[Targalid]

Unless you have the calipers upside down you have a bad master cylinder.

[kger]

Sounds pretty definitive, and I know that I and my helper each pushed too hard and far on the pedal when manually bleeding the first time. I know the MC hasn't been replaced in the last 10 (probably last 15) years so I guess it's time.

I'm out of free weekends for a while and am getting impatient for a driveable car so I may outsource this job... unless someone talks me into it being doable without too much pain and suffering in a couple of weeknights.

Thanks again for all the responses.

[kger]

Originally Posted by kger

I'm out of free weekends for a while and am getting impatient for a driveable car so I may outsource this job... unless someone talks me into it being doable without too much pain and suffering in a couple of weeknights.

Holy schnikies, just got quoted ~$900 bucks for the replacement job. I'll be DIY'ing this after all. Any words of encouragement would be appreciated http://forums.pelicanparts.com/ultimate/wink.gif

[Bob Kontak]

Originally Posted by kger

...........~$900 bucks ............. I'll be DIY'ing this after all. Any words of encouragement would be appreciated

The bare bones Motive power bleeder comes with a single adapter that fits your 911. $60-70 range. I just bought the adapter for that Durango I was talking of above and it was $30. So, just for your 911 and some other German/Euro cars the price is sweet.

There has to be a tech article here on how to replace. Lemmie look.

Edit: https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/52-Master_Cyl_Repl/52-Master_Cyl_Repl.htm

Article is not granular but gives you a flavor.

Also, Pelican has the Euro Motive bleeder for $51.

[Bob Kontak]

Originally Posted by kger

before I bought the motive

Oops. Sorry. Did not catch that point.

Another bleed option is one way bleeders.

Methods:
Gravity
Foot
Pressure
Suction

They all work and I do like Gary R's recommendation of worn out pads to get some serious travel out of the pistons.

Also, to eliminate a variable, pump your brakes until firm. Start car. Pedal should drop a wee bit when power brakes kick in. If not, vacuum issue. Just put this one to bed by checking.

[Zaz]

There's also the possibility that your master cylinder needs to be bench bled if it ran dry during your brake work. Regardless, if replacing the MC with new you must bench bleed it before install.