Have brake issues please help

[Aaron_West]

So we have a 66 porsche 912 and we have replaced the master cylinder, rotors, brake lines, brake fluid and all 4 calipers. We have bled the brakes and are getting fluid from each of them. However, there is more coming from the back wheels then the front. We drove the car for the first time tonight and when I went to press the brakes the pedal went to the floor. I quickly let off and pressed it again and it felt like normal and stopped the car. We then waited about 10 seconds and pressed the brake again and it went to the floor again. We bled the brakes and are still getting fluid out of all of them. What could be causing the pedal to go to the floor on the first pump? There are no leak's and we cannot figure out what the problem could be.

Any help is appreciated.

Thanks,
Aaron

[volken65]

What method of brake bleeding are you using?

-JT

[Aaron_West]

I am in the car pumping the brake a few times then holding it while my dad, who starts with the rear passenger tire, then moves to driver rear then passenger front then driver front, opens up the caliper bleeder and fluid is pushed out as the pedal goes to the floor.

We use this same method for all of our vehicles and this is the first issue we have ever had of a soft pedal that requires pumps to get it to work.

[WRGREENER]

sounds like a faulty pedal depressor to me. it should be replaced. besides the elder abuse. you should put your dad on the pedal, he probably has many more years of the depression needed to handle the delicacy and control of constant need of pressure better. one you replace the faulty depressor you might want to do the rubber tube into the bottle with fluid to mitigate the back-flow. other than that it sound like you just need to go thru it again. or buy the harbor freight bleeder tool..

[Jim Chambers]

Go here 912 Help and do a search. I had the same problem. The caliper pistons retract too far (there is a scientific term which I can't recall). The effect is to require two pumps to get proper pressure on the pads. The solution is to remove the pads and place thinner pieces of wood (or very worn pads) between the caliper and the disc. Then bleed the brakes. This allows the piston to extend farther when bleeding. Do it at all four corners. There is a far better explanation on the 912bbs. Do the search there.

[Jim Chambers]

Start with this thread Brake bleeding problem, need ideas

Then search "hysteresis"

[Aaron_West]

We took out the new brake pads and put in quarter inch steel plates so that the calipers could extend. After bleeding the brakes a few times the pedal started to feel a little better. We then put the new pads back in. As we pushed the piston out we bled the brakes as well. With all 4 corners bled and brake pads put in the pedal feels much better.

Thanks for everyone's help!
-Aaron

[kennzo5150]

Good info here, I'll try in the spring. I'm just chasin my tail on my brakes. Hopefully some this info works.

[Aaron_West]

Ok so the problem we had was not actually fixed. We bleed the brakes pedal feels great while bleeding. I take my foot off the pedal and wait 10 seconds. Then the pedal goes to the floor. I pump it up 2 or 3 times and it feels good then I take my foot off for a minute. All the way to the floor.
We have all new brake hoses, rebuilt MC, new Dot 3 brake fluid. And have bled the brakes multiple times not getting any air

Need help thanks

[Jim Chambers]

Still sounds like "hysteresis". Pistons are retracting too far and then it requires more than one pump to get them out far enough.

[djdsc]

Are all the calipers positioned with the bleeders on top?

There can also be air trapped in the MC. Have a go at bleeding it separately from the entire system.

[JT912]

To help narrow things down, does it have the original single circuit master cylinder? Would want to make sure there is no mix-and-match problems going on here.

As djdsc stated it is very important that the bleeders are on top. In other words: did you change left and right calipers? I once made that mistake ...

Also mportant is the gap or play before the brake pedal push rod touches the master brake cilinder. It should be about 1 mm at the push rod. The total free play of the brake pedal will be around 50 mm (2") when the brakes are correctly adjusted.

A single circuit is more critical than a double circuit.

Otto

[WFBowen]

If you've checked the things above and still have the problem, consider 'bench bleeding' the MC (as suggested by djdsc.) You can first try to bleed the MC in place by using the pump and hold method at the pedal while using the brake line to MC attaching point as a bleeder, loosening it slightly to allow fluid/air out of the MC. I've had a few MC's over the years that needed this.
Also, are you sure your MC is really good? Was it actually rebuilt (honed cylinder) or did it just get some new seals? Your problem really sounds like a faulty MC, since you're not getting any external leaks, etc.

[Aaron_West]

Thanks everyone for the responses. They are great and have checked and done all of them. We are using a single circuit MC and we bought a rebuild kit but the kit was made wrong and the Mc does not hold pressure. However, we came up with a solution after scratching our heads for a day or two. We had the rear brakes on correctly with the bleeder on the top. I read that bleeding the inside bleeder on the rear brakes is necessary as well. We did that and it did not get any better.

So we took off the rear brakes and flipped them upside down and put them back on. This put the inside bleeder on the top. We let it sit then bled it and a great deal of air came out on both sides that would not bleed out with the bleeder on the bottom if put on correctly. We then took the brakes off and put them on correctly again and now we have a firm pedal on the first push.
The brake pedal still sinks slowly because of the bad MC which we have ordered a brand new one which should be arriving later this week.
Thanks for the help everyone and I hope are solution of flipping the rear brakes can help others down the road.

[Peter Graham]

Your last post makes it sound like the rear calipers have one bleeder on top and one on the bottom (although that's just not possible on my '68 which has the crossover hard line between the caliper halves; earlier models have an internal crossover??). If this is true, the rear calipers have been assembled incorrectly: both bleeders have to be on top or all the air can never be bled out...

Peter

[Aaron_West]

The best way for me to explain will have to be with pictures. I will do that tonight. Sorry for the confusion.

[Aaron_West]

We basically rotated the brakes until the bleeder on the top was on the bottom and bled the crossover tube which was towards the top now and air could escape.