Rebuilt Brake Caliper and...Pedal goes to the floor? Options

[atomix8]

Have been battling this problem myself for a few weeks...and realizing I just missed the annual Northeast meet up, and am about to miss 2 more car shows... I think I have finally tried everything I can personally think of -- I need help!

Long story short, I hope: Front right caliper was dragging a little bit, figured I'd rebuild before it got worse. Took the caliper off and lost a bit of fluid, still plenty in the master cylinder. Had trouble getting the pistons out, so ended up using the "grease gun trick", not recommended but it worked. Cleaned up the caliper with tons of brake clean, put in new seals, pressed pistons back in, indexed them and bolted it back up. Then the saga of bleeding:
1. Did the "two man" brake bleeding method at first on just the rebuilt caliper...and couldn't get a hard pedal.
2. Did "2 man" on all 4 calipers -- pedal still soft.
3. Put on the Motive power bleeder, burst a hose on the motive...cleaned up a fountain of brake fluid
4. Actually bled all 4 with the Motive (new hose) -- pedal still soft.
5. Drove around the block, had to pump the brakes like heck to stop -- no change.
6. Had a friend 'pump up' the brakes and then 2 man bled the fronts -- no change.

Other relevant facts:
A. Before I started this adventure, I had a great hard pedal.
B. Brake fluid squirts out of all calipers when I bleed, so I don't suspect a master cylinder issue (should I?)
C. Rear brake pads are worn on one side, but seems unrelated...again pedal was great.

So, what the heck am I forgetting?? (IMG:style_emoticons/default/confused24.gif)

[stugray]

I have read MANY of these threads and just went through completely disassembling my brake system.
What many people fail to realize is that a car sitting on jackstands will not dislodge all of the bubbles in the system.

I bleed the system as best I can, then tap on all of the calipers with a hammer.
Then I DRIVE THE CAR HARD.
Do you have any railroad tracks?

Then I bleed again - rinse & repeat.

In my experience I could NEVER get a firm pedal just sitting in the garage.

[Mikey914]

Also the URO master cylinders are $hit. I did the same thing. Took me many hours to realize the MC had actually failed. It was new, so the last thing I suspected.
Sounds like you have not replaced it recently but if you have one id be suspect.

[Cuda911]

Hmmmm.... just had brakes redone in my '73 a week or two ago. Had the same... pedal was sinking to floor, before having the brake work done.

New master cylinder, rotors, pads, rebuilt calipers, etc. The work was not done by me, I took it to MRD in Vista.

I'm 100% certain they didn't need to drive the car hard or over railroad tracks. Brakes work great now.

My only point is, there must be air in the line somewhere, but I think it should be able to be adequately addressed without having to aggressively drive a car that has poor brake response.

[atomix8]

Appreciate the quick replies guys.

I had heard the "drive it hard" theory a few times here, but heck, I can barely stop...I'm not looking forward to going more than 20 mph! I will re-try banging all the calipers with a hammer...time to get it back in the sky on 4 jack stands I suppose. Are you recommending 2 man or pressure bleeding??

Mike (Cuda911) -- I tend to agree with ya...never had this much trouble bleeding brakes, but that's a famous 914 line as well.

RE: the master cylinder, it is old, but is some OEM brand, not URO. Trying to avoid replacing that as part of trouble shooting.

[GeorgeRud]

I will also attest to the bumpy ride then bleed again theory. When I installed my PMB rebuilt calipers I couldn't get a good firm pedal until I did the bumpy drive step. Then, after one last pressure bleeding, I have a wonderfully firm pedal.

[Bartlett 914]

Appreciate the quick replies guys.

I had heard the "drive it hard" theory a few times here, but heck, I can barely stop...I'm not looking forward to going more than 20 mph! I will re-try banging all the calipers with a hammer...time to get it back in the sky on 4 jack stands I suppose. Are you recommending 2 man or pressure bleeding??

Mike (Cuda911) -- I tend to agree with ya...never had this much trouble bleeding brakes, but that's a famous 914 line as well.

RE: the master cylinder, it is old, but is some OEM brand, not URO. Trying to avoid replacing that as part of trouble shooting.

I have never had this problem with a master cylinder but I have read that pushing the pedal to the floor can damage the master cylinder. Normally this never happens. When the fluid is changed and you press to the floor the seal in the MC gets into a place it normally doesn't go and the seal could be damaged. I think you still have air in the lines however.
When bleeding I like to connect a clear tube and run it vertical as much as possible. This makes it easier to see bubbles. I also press the pedal quickly. This helps move air down the line better

[stugray]

Another common error is putting the calipers on the wrong sides and having the bleeders at the bottom of the calipers.

You are bleeding from bleeders at the TOP of each caliper?
Some calipers have both top & bottom and people bleed from the first one they see.

[914pipe]

Once I have a hard time bleeding the clutch line, from a turbo 944 (the fluid comes from the same place as the brakes), and found that many people solve their problem by reverse bleeding (pumping brake fluid from the caliper to the master cylinder). In this case was from the slave cylinder to the master cylinder, used this technique in the 944 and worked great.
Here is a link for an example. http://www.brakebleeder.com/videos/reverse...bleeder-videos/

Some people used a cheap hand oil pump. That’s what I used that time and it did the work.
I have done the same in other cars and worked great.
The down side is that if your lines are dirty, you will push all that trash into the master cylinder and might clog the master cylinder. So assure that your lines are clean before doing this.

[mgp4591]

I thought I'd mention this because I haven't seen a comment on this- did you happen to run the M/C down to empty in the process? Even if you didn't, it's not a bad idea to bleed the master at the lines then start at the furthest point from the M/C, the right rear then left rear, right front then left front. You've probably done all of that so pardon my comment but if not, give it a try...and good luck!

[Chris H.]

Another common error is putting the calipers on the wrong sides and having the bleeders at the bottom of the calipers.

You are bleeding from bleeders at the TOP of each caliper?
Some calipers have both top & bottom and people bleed from the first one they see.

I did this once. Bled ONLY the bottom rears for DAYS. Once I found the TOP REARS and bled those I had the firmest pedal ever.

[VaccaRabite]

Chris and Stu are on the ball.
Check to make sure that your calipers have the bleeders on TOP not on BOTTOM. And if they have bleeders on both, make sure you are bleeding from the top. Otherwise you still have huge pockets of air trapped in the top of the calipers.

Zach

[atomix8]

Thanks again for all the advice. Will climb under the teener ... in a few days here when I can get a willing brake bleeding companion.

I do have the bleeders all on the top...damn I wish it were that easy.

Forgot in my sequence of frustration that I did reverse bleed from the rebuilt caliper w/ an oil pump. That's an old trick that's usually served me well.

Anyhow, I'll whack the cylinders, bleed from the top of the master, and say a prayer or two.

Slave cylinder on the truck is at least almost fixed...hydraulics are my least favorite project.

[Jeffs9146]

Thanks again for all the advice. Will climb under the teener ... in a few days here when I can get a willing brake bleeding companion.

I do have the bleeders all on the top...damn I wish it were that easy.

Forgot in my sequence of frustration that I did reverse bleed from the rebuilt caliper w/ an oil pump. That's an old trick that's usually served me well.

Anyhow, I'll whack the cylinders, bleed from the top of the master, and say a prayer or two.

Slave cylinder on the truck is at least almost fixed...hydraulics are my least favorite project.

Go down to the local auto parts store and get a pressure bleeder! Then you can pressurize the system and crack lines and bleed at each point without driving the car.

I did this on my complete refresh and had firm breaks on the first try!

[atomix8]

Well, did everything I promised.

Bled the lines at the top of the master cylinder, no air came out. Whacked all the calipers before I bled, whacked the proportioning valve, whacked the master cylinder a bit. Had a friend pump the brake pedal several times before I cracked each bleeder to get a lot of pressure, no change.

Still have a soft pedal. I'm starting to suspect the master cylinder. If you press the pedal once, a small amount of fluid comes out. When my friend 'pumped up' the brakes, a LOT more fluid came out of the bleeders. Is that normal? (never tried it!)

The master cylinder is certainly old, the PO put on a 19mm unit about 15 years ago now, and I'm sure it was stroked to the bottom while bleeding. My first assistant was...well...you can't disagree with the wife.

[cwpeden]

You don't suppose one of the hoses could be ballooning and its just coincidental? Don't see if you replaced them.