lcrain

Yesterday I attempted to do a brake flush on my 993 (my first with this car). I don't have the appropriate fitting for the motive power bleeder so I opted to go manually with my GF pumping the brakes. She has helped me with many other cars to great success.

It started out smooth. We were probably 20 pumps or more into the first caliper (passenger rear). I topped the reservoir off twice. After the second top off of the reservoir, my GF started commenting about a lack of pressure in the pedal. I was also noticing less fluid coming out, barely any at all.

I was stumped. Spoke with a friend who also has a 993 and his immediate thought was an issue with the master cylinder, potentially the piston stopping to travel and push fluid. From my understanding, a failed master cylinder is a pretty rare occurrence on a 993. Does the mind hive of Rennlist have any recommendations for me before I replace the master cylinder? Is it possible that a large pocket of air was introduced somehow leading to the soft pedal (I tried to be overly vigilant about checking the reservoir and topping it off as needed)? If so, how might I go about rectifying that?

paranoidandroid

Do you have a C2? C4? If you have a C4 you need to bleed the accumulator first.

lcrain

It is a C2.

paranoidandroid

No ABD either right? If you didn't feel spongy brakes before I wouldn't suspect a MC issue. It is easy for air to get into the system through the bleeder valve. How much did you back it off when bleeding?

lcrain

No abd. I did not feel a spongy brake pedal before. Always firm. Backed off ever so slightly, just enough to get the fluid moving.

71-3.0-911

First off, what is the pedal at? Is it now firm, spongy, or flat/no pressure? Second, if it's flat to the ground, that means you have an open somewhere. Spongy is air. I doubt it's firm as that would signal all is ok. Check all your connections and report back status. These systems are pretty simple.

-Scott

lcrain

right now it is spongy.

71-3.0-911

Definitely an air bubble then. Get the euro adapter for the master and use the motive. Repeat bleeding sequence and you'll get it all out. I never open the bleed valve much. Just enough to start flow. Use your catch can to make sure no bubbles are coming out.

Not knowing where your air bubble is, I'd bleed all 4 again. If you have the tool, it would be good to cycle the abs system and flush that as well. I haven't gotten there yet.

Good luck and report back. I've bled my c2 yearly since I've owned it. My daughter helps me and once you get the procedure down, it'll be easy day.

If you can't find the euro adapter, PM me. I'm not planning on using mine again until this winter maintenance cycle, I'll mail it to you to use.

-Scott

993.Coupe

Be careful, if yours is a 1995 you have to crimp the vent line....I recently purchased and used the motive bleeder via the dry method and it worked great.

pp000830

As said above the pressure bleeder is the way to go.
Be sure to bleed both bleeder screws on each caliper and tap on the caliper housing to release any bubbles clinging to the inside of the caliper casting. At one time DOT3/4 fluid came in more than one color so the fill of replacement fluid could be an alternate color. In this way one knows at the bleeder screw when that leg of the system is completely bled. Saves time and brake fluid if it is still available. I also found that if one takess a little clear nail polish and paints around the bleeder screw threads with it after bleeding the brakes the threads stay very clean and there is a complete absence of corrosion the next time the brakes are serviced. This is in addition to reseating the bleeder's rubber dust caps.

lcrain

Thanks everyone. I have ordered the motive adapter via amazon, which should arrive tomorrow.

paranoidandroid

Great, glad to hear. BTW - when you use the power bleeder, refrain from pumping the brakes while the system is under pressure. You'll likely damage the master cylinder if there is too much pressure. If I recall, 15-20lbs of pressure is adequate.

If nothing is coming out even when the system is under pressure, you may have some sludge in the lines. I've read some unscrew the bleeder valve completely, then use a small copper wire to dislodge sludge and try again.

Kein_Ersatz

Also be aware, this process does not flush old fluid from the ABS pump. At some point you will need to find an Indy shop with the proper Porsche electronic test tool to activate the ABS pump while bleeding the lines to refresh the 20+ year old fluid sitting in the ABS pump valve body. Ignoring this can result in wax build up in ABS pump and hampering it from working properly. Motive Bleed bottle is money well spent / headaches avoided.

helmet993

You can also use a rubber mallet to tap the caliper to encourage a waxy buildup to move or ensure any air bubbs are gone.

I have used both the motive and the vacuum bleeder and like them both. I use the motive system “dry” to prevent a mess just in case.

pp000830

Interestingly, my understanding is that this is just an issue with the C4 and Turbo with both ABS and Automatic Brake Differential (ABD). On the C2 cars, the pump gets flushed during the normal manual process without OBD ABS valve/pump actuation required.

May others here validate this for me?

Andy