So I was out for a cruise around the neighborhood the other day and things were going great until the brake pedal went to the floor. I was able to pump it a few times and restore pressure and crawled home in a low gear. Each time I used the brakes the pedal would go to the floor until I pumped it a few times. Scary!

Once home I looked under the car and inspected the soft lines at each caliper but they looked fine and no leaks. The brake fluid reservoir is still full. I'm not sure where the problem is.

What should I be looking for?

Master cylinder

Look for fluid under the pedal assembly in the car.

if no leaks at the MC underneath, look under pedals, this just happened to me this year but the last one i had fail i could get some pressure like you did after a few pumps of the pedal but will not maintain pressure, if that is the case you may not have any leaking but just failed seal internally and you still are in need for a new one.

one of my least favorite jobs to do

Phil

I haven't had time to lift the car up to be able to easily see what's going on with the master cylinder yet, but I'll check that next.

I did find a really nice youtube video from a member who installed the 19mm master cylinder upgrade from 914rubber. Unfortunately it looks like the "easy install" version isn't available right now.

Replacing the master cylinder looked fairly straightforward, what makes it your least favorite job?

if the MC leaked on the pedals
make sure you rebuild them with the bronze bushings...

the nylon will swell once they have been wet with brake fluid and cause binding a month after the fact.

When was the last time you replaced your brake fluid?

If there is any condensation at all in the fluid it will make the fluid compressible and will fail to transfer pedal force to the brake calipers.

If you are not finding any obvious failure at any of the other point in the system then almost certainly a seal in your MC has failed. This is consistent with a sudden brake failure. In my experience a slow buildup of condensation will cause more gradual symptoms, such as a progressively worsening spongy feel to the brake pedal. As Phil pointed out you may not see any leaking of the MC with an internal failure, but you also might find fluid around the pedal assembly. Brake fluid is nasty stuff and it was astute of @brant to recommend refurbishing the pedal assembly if it has become fouled with brake fluid. Because it's easy for me to spend your money, I also recommend you get a Motive pressure bleeder. You've already seen Ian's @iankarr video on replacing the MC and he also has one on bleeding the brakes with the Motive. You need to order the one that comes with the European adaptor (0100 I believe). This is also one of my least favorite jobs as it does require some contortion to get things hooked up and I HATE working with brake fluid. If it has been a while it's also a good time to replace all of the rubber hoses and fully flush the system. If you didn't already know it, you've just discovered how important your brakes are to your safety and this is one of those jobs that you just have to do before it becomes a problem. As you can see a failure of one component of the braking system should lead you to consider refurbishing the whole system. Again, easy for me to spend your money AND time! Wear gloves, safety glasses, and keep lots of rags handy.

Glad you made it home safely!!!!

laying on my back with no lift just on jack stands trying get the freaking line pushed into place and to seat- not much room to work, sometimes it goes easy- the last one i did the “easy” install one from 914rubber. still took all day to pull out old one install and bleed lines, etc. i don’t have a power bleeder,
pro tip- loosen the reservoir and attach the lines at the mc before bolting it in tight and also bench bleed the mc will help too.
don’t forget the washer it’s traditional hose attachment will leak without those washers, i found that out the hard way too

What are folks thoughts on the original 17mm vs 19mm master cylinders?

Would you guys recommend waiting until the "easy install" 19mm master cylinder becomes available again? Is it really that much easier to install than the non-easy version?

Edit: Here's the link - https://914rubber.com/easy-install-19-mm-master-cylinder

RE; the non-easy install MC version; You can get a good grip on those lines if you use the block from a flaring tool to hold the line while you pull it in.

IIRC... the 17mm master cylinder is NLA.

Im pretty sure I have the 19mm easy install version still in a box. I can check tomorrow when I’m get home. PM me if you are interested.

Check me on this - the only difference between regular and easy is how the lines from the reservoir fit/are located into the master cylinder, correct?

The regular version requires you to push the hard lines into the rubber grommets, right?

Yes.

I asked Bob Russo how he does it. He was the crew chief for the Holbert 962 race team among other Porsche experiences. He said he wrestles them in. There is no real trick. I was told it's way easier to assemble the MC to the lines on a bench and then feed everything up from the bottom. Fuel tank has to come out but sometimes that would be easier.

that certainly would make it easier, both having the tank out and bench installing the lines. This was one of the first jobs i did on my 914 after purchasing it. First time i left the washer out and found out the hard way it was necessary, but once done correctly , was leak free about 8 years. The next failure was back last winter right before going to Amelia island, puddle on the floor inside under the pedal cluster. remembering my previous experience i ordered the new 19mm easy install one from 914 rubber.
being i have no lift and therefore limited space under the car, it was still very difficult to attach the lines and tighten the clamps.
If i had to do it again(Lord i hope not ever!) i would do exactly like Mark and Bob Russo suggest if you can, and do that part on the bench. .

Let us know how your experience goes.

Phil

When I did mine I installed on a bench, just the lines not the reservoir, then connected the rest up top. It was really pretty straightforward but I forget if I had the tank in or not.

grommets on the line first, then push the line/grommet assembly into place after verifying the washer is there.

Never forget the washers. They are 100% mandatory. It’s fine to reuse the old ones out of a failed mc. I got a couple extra from my local Porsche dealer. They are ~ a dollar each.

I installed the 17MM in my stock '76. I didn't want a change in the pedal feel after driving it for 44 years!

An easy way to install the "hard install" reservoir fill lines is to disconnect the reservoir completely from is mount in the frunk and pull everything up a little bit. Install the new MC then pull the lines back down to insert in the rubber grommets on top of the MC. I had no problems at all using this method. Of course I emptied the reservoir first to avoid getting fluid all over the place.

Dave

I'll throw out another possibility....

One day while while driving the 6 conversion in my avatar, I came up to a stop and much to my chagrin I discovered I had virtually no brakes. Fortunately, my emergency brakes worked quite well and I was able to stop. (BTW...when driving my older cars I ALWAYS slow down early and give the brakes a little test tap. It's a habit I developed early in life when driving another car that experienced brake failure.)

Anyway, as I sat waiting over an hour for a AAA tow for some reason I hit the brake pedal. I had brakes! I drove the short distance home and as I walked around the car I could feel the heat coming off the right front wheel. The right front caliper was dragging so badly that the fluid was boiling ..causing a loss of braking. I replaced the rubber brake hoses (in case they were collapsed) and with a set of rebuilt calipers a few days later I was back in business!

That may not be your problem. But, worth a check especially if you aren't seeing any fluid loss.

The difference between the 17mm and the 19mm is only pedal feel and travel. You need a bit more foot to push in the 19mm piston. Some like that, some don't. Stopping power isn't different, but you have less travel with the 19mm so brake modulation will be a little different too. Bigger piston pushes more fluid...

If you can find one, I'd stick with a 17mm if your brakes are stock. That said I have a 19mm on mine (at the time I thought it was an "upgrade") and I'm used to it now.

Zach

Any idea how to check for this without going out for another scary drive? This sounds like a possibility since the brakes went out about 15 minutes into my leisurely drive. I checked the pedals for fluid yesterday and the brake pedal had pressure (and no fluid leaking)...

That one is easy.
Look at your pads and see if one pair is wearing WAY FASTER then the other. The four front pads should be similar, and the 4 rear pads should be similar. Also, if pads are stuck on the rotor, the rotor is probably also worn more too, if not scored and warped.

Zach

Did you pull the carpet and the pedal plywood and stick your hand around the pedal assembly. Mine wasn't much but it was wet. Nothing under the car or on the ground.

I pulled back the carpet but didn't remove the plywood. I'll check that today.

Update: Getting that board out is impossible! Feels like I'm playing one of those puzzle games trying to figure out the right angle to get it out. I'll have to do some research to see what else needs removing before it will come out. I was able to pull it back far enough to take a picture and get my hand back there though. The pedals are dry as a bone.

pull the rod off the bottom of the gas pedal and the board should wiggle out.

I did this a few months ago. I used this advice by McMark from another post:

1. Pop the throttle pedal off of the pushrod, so it can be pulled towards the rear of the car.
2. Depress the clutch pedal about 1/3 to 1/2 of the way down.
3. Route the board over both the clutch pedal and the brake pedal in the same motion (or close enough)

It takes awhile to figure out. But once you've done it a few times the 'right' way it becomes pretty easy. ...end quote

...hope this helps...worked for me.

Well it looks like the caliper is the culprit. Brake pressure felt normal when I backed the car out of the garage. I pulled both front tires and found the driver side caliper was seized and the pads were tight against the rotor like billh1963 described.

I think I'm going to replace both front calipers/pads/soft lines. I will also take a look at the rear calipers and make sure they're still functioning correctly.

@mburkhart
post='2850680' date='Sep 12 2020, 01:57 PM']
Well it looks like the caliper is the culprit. Brake pressure felt normal when I backed the car out of the garage. I pulled both front tires and found the driver side caliper was seized and the pads were tight against the rotor like billh1963 described.

I think I'm going to replace both front calipers/pads/soft lines. I will also take a look at the rear calipers and make sure they're still functioning correctly.
[/quote]

A siezed caliper would not explain the pedal going to the floor. I say it is still the master if no other external leak can be found.

I know we are making more now and may be able to locate a straggler. Call the office Monday and Kinzie will be able to tell you if I found one (I'll be at the day job shortly for a few days. I'll hit the shop on the way out).

As far as failure. If there are not any apparent leaks, it's an internal failure. Also when you install don;t pump the pedal all the way to the floor until you have pressure (then you shouldn't be able to). Doing so can damage the internal seal.

"The right front caliper was dragging so badly "

This was my first thought. I have had it happen to me.
A dragging caliper will overheat the brake fluid, boiling it and creating a big "Air Bubble" in the lines.

[quote name='bdstone914' date='Sep 12 2020, 06:50 PM' post='2850730']
@mburkhart
post='2850680' date='Sep 12 2020, 01:57 PM']
Well it looks like the caliper is the culprit. Brake pressure felt normal when I backed the car out of the garage. I pulled both front tires and found the driver side caliper was seized and the pads were tight against the rotor like billh1963 described.

I think I'm going to replace both front calipers/pads/soft lines. I will also take a look at the rear calipers and make sure they're still functioning correctly.
[/quote]

A siezed caliper would not explain the pedal going to the floor. I say it is still the master if no other external leak can be found.
[/quote]


"A siezed caliper would not explain the pedal going to the floor. "

Sorry, but this is false.
A dragging caliper will overheat that caliper and boil the brake fluid creating a large "air" bubble in the lines.

It has happened to me more than once.

This is usually not the caliper's fault, but the flex lies to the caliper.
They "swell" internally blocking flow and not letting the caliper release.

Old brake fluid increases the diagnoses..

As far as failure. If there are not any apparent leaks, it's an internal failure. Also when you install don;t pump the pedal all the way to the floor until you have pressure (then you shouldn't be able to). Doing so can damage the internal seal.
[/quote]

most likely the fluid is leaking past the seals in the m/c,had this happen years ago with a air-cooled beetle m/c ...took a while to work out,fitted a NOS ATE kit to it and all was good,I wouldn't normally do this on a road car but it was on my fun offroader.
Sounds like the OP is up for some brake work.