Yesterday, my buddy's mini Big Red project came to a conclusion. Powder coating came out great, new dust seals went on ok and caliper reinstall went pretty smoothly.

When we removed the calipers, I didn't know about blocking off the m/c, so the fluid ran low. We just put plastic bottles on the ends of the brake lines. Anyway, yesterday there was a wee bit of ATE Gold still in the m/c resevoir. I used my Motive power bleeder and put in 1.5 cans of ATE Blue. Bleed went well. Then I had him fire up the car and test the pedal, which got soft pretty quickly. Car was still on jackstands. So I went around and bled a little more. Pressure bleeder was still on and my buddy pumped the pedal a little too.

I had to get home and couldn't go for a test drive, but he reported back to me today that the pedal had gotten a little soft again. I know that R&R'ing calipers sometimes requires multiple bleeds before it's all done. But how do I know if I need to have the ABS professionally bled? Should I try one more bleed and then take it to a shop, or will it have to go to the shop no matter what? Thanks.

 

Anyone? Buehler?

 

I've read here that whenever you do something major like that, you need to take it somewhere with a Bosche Hammer or similar system. It can get air bubbles out that have gotten trapped. Do a search on Hammer, since I barely know what I'm talking about...

 

You don't say whether it's a C2 (vacuum brake booster) or a C4 (hydraulic brake booster). If it's a C4, recommend you bring it into a shop that knows these cars; the total system bleed needs some special tools (Bosch "Hammer").

Now, assumng it's a C2 vacuum boost system: if you didn't totally drain the reservoir, you shouldn't have pulled air into the system. I've replaced front calipers without bleeding problems, and one time I screwed up and forgot to check the reservoir level and blew all the fluid out of it. I was able to bleed the system successfully using only my Motive Bleeder.

Some ideas:

- when bleeding the calipers, I developed a T-fitting clear plastic tubing arrangement, so I could attach the bleed tubing/hose to both bleed fittings on one caliper. I then bleed both ports simultaneously.

- I watch the tubing and ensure that all air bubbles have disappeared.

- I start at the right rear, then do LR, RF, and LF sequentially.

- While bleeding, I tap the calipers with a dead blow hammer (plastic-face hammer like a rubber mallet).

Your words of "buddy pumped the pedal" scares me, if the pedal went to the floor and was pumped several times. Ages ago, I used to bleed my '76 911s brakes by the old fashioned "pump and hold" method. Well, I went through 2 master cylinders in a little over a year. This method forces the master cylinder piston seals past their normal travel point. Dismantling the master cylinder proved this to me; the normal travel path of the pistons could be seen. Switching to a vaccuum bleed then a pressure bleed cured my master cylinder problems.

How can you tell if the master cylinder is bad? As I remember, first pump was soft; follow-ones were firm. Also, the degree of pedal softness might vary on each brake application.

First thought would be try another bleeding. If unsuccessful, bring it into a shop.

 

Rick,

Bleed the living daylights out of it. You should bleed each corner until you see no more (air) bubbles coming out.

BTW, I'm assuming you let all the fluid out. When i did the mini-red project on my car I twist-tied the line back onto itself and pointed it up. So I didn't dump all my fluid. Nevertheless, I had a ton of air bubbles in the system and it took a while to bleed them out.

Should be pretty easy though with the power bleeder...

Cheers,
Boris

 

Forgot to add it's a '95 C2 cab. If bleeding is all it takes, then that's good news. I don't want to have to take it to a shop. I guess we'll try the mallet tap technique and rebleed.

 

BTW, I know about the m/c damage that can occur when the pedal goes too far down. While I was not the one pumping the pedal, I did tell him to not push it more than about 1/4-1/2 way down. Dunno whether he did or not, but another bleed is in order anyway.

 

Rick,

If the car has LS-ABD and air was allowed into the ABS pump then may have real problems. When this happens, the pump usually has to be replaced. If no LS-ABD and air did get into the ABS pump then the only way to bleed the system properly is at the dealership or at a shop that has the Porsche System Tester II. You cannot perform the bleed sequence manually. If no air was allowed past the master cylinder, then keep bleeding!

Hank

 

But Hank, how can I tell if I got air past the m/c? What can I do now?

 

Rick,
One suggestion is to bleed, then drive the car and really use the brakes, even get into the ABS. Then bleed again until everything feels good.

I goofed up one time while bleeding my brakes. The pressure bleeder turned over and I ran the reservoir dry. I had to use my mechanics "hammer" but even then it took a couple times to get all the air out of the system. I would go on track for a session and re-bleed afterwards.

The car could have a bad m/c also.

 

Rick, same thing happened to me last year when I did my calipers (powder coated, etc...). I completely drained all brake fluid, forgeting about the m/c issue.

After my first bleed, brakes were mushy. I also looked at the possibility that I screwed something up and would need professional assistance (I have a 95 coupe), but fortunately I didn't.

Try this: Prepare to use a few cans of ATE fluid (I think I used 3). Drain rear passenger, rear driver. Stop and turn on engine for one minute (lets fluid circulate). Kill engine and do fronts. Repeat.

After I did this, I swear my brakes were better than they ever were before! They are tight and firm (are still talking about brakes ) and rock solid!

Try this before you panic (I sure panicked when I went thru this last year).

Good luck and report back to us.

 

Here's a lot less expensive way I learned from another Rennlister when I got air in my ABS system by completely draining it:

Bleed one wheel cylinder. turn on the ignition until the ABS pump stops; repeat on each wheel. They do it again all around the car. Be careful not to let the master cylinder run dry. It worked for me, no Hammer required. This is for a C2S.