Bleeding a 993 C2 with ABD
 

I am replacing pads and rotors on my 95 993, with LSD/ABD. I was planning to flush the fluid, using a standard Motive pressure bleeder. I have now read where the ABD require special techniques including use of Bosch hammer. Can anybody point me to the definitive procedure? I do not want a garage full of DOT 4.

It does not require a hammer, simply the Motive to flush. The DIY that I started with years ago is still available on p-car.com.

It's amazing how easy it is to change pads and flush the brakes on a 993 C2. While I think I took 3-4 hours my first time (going very slow and triple checking the DIY instructions), you can do it in under an hour - and that includes the time it takes to jack the car up and take it down.

Tom, did your 993 have M220, lsd/abd?

w/ an M220 system and the normal brake part of the system can certainly be bled w/o a 9288 or similar tester

but

According to the shop manual, a "hammer" is required for abd bleed

No, my car does not have abd. My understanding was to bleed the abd internals you may need a hammer, but you can still bleed the rest of the system without issue.

That’s my understanding as well. You can do the typical bleed with a pressure bleeder, just like any other car. Some of the fluid in the ABD or even the ABS system won’t get flushed.

There are various valves and lines in both the ABS and ABD systems that are not typically open. You need the hammer to open/close these various valves to do a complete flush.

On the other hand, it’s kind of like an oil change. Not every drop of oil gets changed with an oil change. If you do regular oil changes, the leftover oil is not an issue. If you do regular brake fluid changes, the left over fluid is not an issue.

Ok, so how about if you change the proportioning valves? I'm about to do that, and wondering if I'll need a hammer to get any air bubbles out.

Not a problem, the p/v(s) (2 on M220 cars) are inserted in the rear line(s) and can be bled the normal way w/ a pressure bleeder.

The p/v need ~30x the pressure that bleeding uses to do anything

Thanks Bill!

Well, I completed the fluid flush using my Motive pressure bleeder. Got it all done including slave with exactly 1 bottle. Bleeding the slave, while awkward is not as tough as I was led to believe from all the reading. You just need to find the right position. Only problem is now the clutch pedal is balkier than before. I had the problem of last 2 inches hanging up before. That did not go away, but now the pedal seems to bind a little all the way up and down. I will lubricate the piston up front, or maybe I left air in the clutch. When I have some more energy I might bleed it again.

Mark,
The first time I performed a complete brake/clutch flush on my early '95, the same thing happened. The clutch pedal action became 'crunchy'. After talking to numerous people about this, I concluded that the new fluid (Super Blue) reacted with the old seals in thhe slave, causing it to stick while moving. The solution was to replace the rubber line and slave. The clutch pedal action became super smooth again and I've never had an issue again. It's been more than two years and I've performed at least three complete flushes since.


Andreas