Learning something new...brakes

[DeltaBravo]

First, love this community and the cars. Great inspiration and help.

But...

I recently rebuilt my front calipers and replace brake pads and fluid on my 88' Cabriolet. Everything went well with no surprises (thanks to this forum and "how to" articles) until I got to the point of bleeding the brake system.

Before I get into that, I feel the need to disclose my abilities. I have been doing my own auto maintenance for the last 20 years. Starting from basic oil changes that progressed to rebuilding major components, like engines, trans, rear ends....etc. As well as as electrical, suspension, upholstery, and body work. I am by no means claiming any level of skill as I feel I am always on a steep learning curve, particularly since this work has been on several different makes/model autos. So, I haven't "mastered" any particular brand.

Which brings us to my 1988 Porsche Cab. When I hooked up my Motive brake bleeder set up and pressurizing the system with a few pumps, I began to hear a fluid sound cascading and hitting the garage floor. I immediately though I didn't tighten a brake line or bleeder screw and frantically looked underneath the car at all four corners looking for this water fall of brake fluid. What I discovered next is something I never experience in any brake system (this is my first), nor did I read about it in any "how to" or in my Porsche project book.

This is why I rebuild the calipers, dust shield were brittle and torn





Below are pictures of what was causing the brake fluid to push out of the system before I could crack a bleeder screw. The master brake reservoir has a small upper hose located on the top/driver side of the reservoir. This line goes through the drivers front fender towards the front and stops just behind and below the front bumper.

Below is the end of that line. I had to plug it with a 3/16 rivet (perfect fit).


After plugging that line, I was able to pressurize the system up to 10psi and bleed the brakes.

I hope this helps the next person that will use the pressure method of bleeding there brake system.

Cheers,

[zedsn]

Thanks for the heads up. Did you position the pistons in the same manner for which they were removed? They are suppose to be put back in a certain position from what I have read.

[manbridge 74]

The piston in above pic needs to be turned clockwise. Should be turned until first step is between bolt holes.

[kent olsen]

I use that overflow line from the master cylinder as the source to apply pressure from my home made pressure bleeder.

[pete3799]

[DeltaBravo]

I spent yesterday with some PCA members on a wonderful drive. Check out the pics.
https://www.facebook.com/PCA-Grand-Prix-Region-336827569682620/


Update on the Porsche brakes. THEY ARE FREAK'N AMAZING! I didn't realize how bad they were...what a difference.

A couple of things prior to this work raised red flags. First, is when I needed (wanted) to stop the car in a hurry one of tires (or two...no sure) would lock up. I new this characteristic wasn't efficient or safe, but I wasn't sure why it was happening at the time. The next red flag was more of a "possibility" of why one or more of my tires would lock up when braking hard and it was the brake dust...I'll explain. My rear brakes would develop a much heavier brake dust coating on the rear wheels than my front brakes would on the front wheels. This characteristic concerned me because it told me there where either two different pad compounds front to rear and/or my rear brakes were doing the majority of the stopping...which we no isn't good. Either way, it called for an investigation.

Yes, there were two different brake pads front to rear (don't know the brands), and yes there was a obvious visual problem with my front calipers. After rebuilding the front calipers, installing all new pads of the same brands and bleeding the system the car is a completely different car.

The new characteristic are; first, the brake pedal travel actually increased. Before, I couldn't rev-match during my deccel and braking because when I pushed on the brake peddle, it would only move an inch or two thus not allowing me to roll my foot over to "blip" the throttle. Now that the travel has increase, the total height of the pedal during hard braking is much closer to the height of the throttle thus allowing me to roll my foot over and "blip" the throttle.

And second, is the overall braking ability. I can push the pedal as hard as I want and there is no more lock up of a tire...the harder I push, the harder it stops...AMAZING, pulls the eyeballs out of the sockets!

As far as the installation of the pistons, I believe I did them correctly. I made the the tool from some aluminum sheet metal using some math to come up with the "20 degrees" needed to set the piston. My math isn't as fresh as it used to be, but that's what the internet is for...right? Either way, no brake noise.

[DeltaBravo]

Originally Posted by zedsn

Thanks for the heads up. Did you position the pistons in the same manner for which they were removed? They are suppose to be put back in a certain position from what I have read.

No problem, glad you found that useful. I find it kinda funny that this isn't mentioned in my Porsche books or did I read that in any of the "how to" articles. I would think that would be something very significant to mention...especially if you going to pressure bleed.

I though about just pinching the line with vise grips, but I didn't like that idea because I didn't want to damage the line at all...seemed a bit old.

I believe I installed the piston in the correct "clock" position. I understand the specific reason in that design is to reduce or eliminate brake squeal.....and I don't have any unwanted noise from the brakes.

[DeltaBravo]

Originally Posted by manbridge 74

The piston in above pic needs to be turned clockwise. Should be turned until first step is between bolt holes.

Thank you for replying.

That is a much easier way to "clock" the pistons without having to make a jig. I will keep that one in my pocket for next time.

Does that same method work for the rear calipers?

[DeltaBravo]

Originally Posted by kent olsen

I use that overflow line from the master cylinder as the source to apply pressure from my home made pressure bleeder.

That is interesting. Would love to see that set up.

[DeltaBravo]

That is what I used to make my jig for the correct angle. Maybe...due to my rusty math, I created a 30 degree jig

[2jmotorsports]

What is the size of that MC overflow line? Can a vacuum hose be used or does it need to be a small dia brake fluid resistant line?

[gazzerr]

What did you use to clean the corrosion off the pistons?

[HaroldMHedge]

The MC overflow line is N-020-361-2, 4 x 1.5 hose, 900 mm length for a left hand drive SC/Carrera.

This hose appears to be just normal vacuum hose since it is used in the fuel evaporation, intake vacuum and brake systems of various Porsches.

[2jmotorsports]

Thanks Harold!

[Flojo]

a most common "mistake" many DIYers make, they forget to plug the overflow line, reason of not fully reading the how-to articles...

Originally Posted by DeltaBravo

This line goes through the drivers front fender towards the front and stops just behind and below the front bumper.

Below is the end of that line. I had to plug it with a 3/16 rivet (perfect fit).


After plugging that line, I was able to pressurize the system up to 10psi and bleed the brakes.

I hope this helps the next person that will use the pressure method of bleeding there brake system.

Cheers,

['78 SC]

I use that overflow line from the master cylinder as the source to apply pressure from my home made pressure bleeder.
__________________
Kent Olsen

Like Kent, I pressure the reservoir through the overflow nipple. You do have to keep an eye on the reservoir level so no air goes into the system. I set the regulator for 5-10 PSIG and get good flow through the caliper. At the wheel, attach a hose to the caliper bleeder, route it upward for a few inches and then down to a catch can. That provides a liquid-filled section where you can see any bubbles and check the color of the fluid.

Pressuring the fluid gets it moving faster and does a better job of sweeping air bubbles from the system.



I bleed the brakes after every track event and this saves time and brake fluid.

[DeltaBravo]

Originally Posted by Flojo

a most common "mistake" many DIYers make, they forget to plug the overflow line, reason of not fully reading the how-to articles...

Hi Flojo...did you read all my post?

This was the exact reason I shared this issue.

I read all of the words in the how to articles on "911 Brake Bleeding" along with all of the words in my Porsche project books. Didn't see anything mentioning this...

And this always already mentioned in my initial post.

[DeltaBravo]

Originally Posted by gazzerr

What did you use to clean the corrosion off the pistons?

Green scuff pad with a little brake fluid for lube, then cleaned with brake clean. It didn't take much to get rid of the corrosion/dirt...couple of passes around the circumference of the piston.