ca993twin

My mechanic installed my Big Ruf brakes a few months ago, and I noticed the pedal was a little soft... quite a bit softer than with the stock big reds. Either this is because the Ruf brakes have huge pistons, and you must move more fluid before getting solid resistance, or... my mechanic doesn't know how to bleed brakes properly. Of course neither do I. Is the brake booster involved? Is the bleeding process different for the turbo than the NA cars? Are the 993s different than 964s?

He's a good mechanic, but a bit inexperienced, so any help would be appreciated.

911/Q45

There was a good thread not to long ago that addressed this. You need to bleed out the accumulator and the inner and outer bleeders on all the calipers. After you empty the accumulator you must turn on the ignition key to run the pump and fill the accumulator with fresh fluid(I did it several times to empty the old stuff out of the reservoir). Keep the reservoir topped off with fresh fluid all the time you are bleeding. The manual talks about using a hammer to cycle the ABS block during bleeding, but I've never done this and only had trouble when I forgot the inner caliper bleeders.

ca993twin

Don,

Thanks for the advice. Where is the bleed screw located for the accumulator. Is this different than the reservoir on the booster? As you can see, I'm scrambling up the terms.

PierreTT

Steve,
+1 Q45. I had the problem 2 weeks ago. Search on my previous posts. Rebleeding the brakes with the right procedure solved the problem. Our cars does require special attention when bleeding...
Pierre

911/Q45

The accumulator for the brakes is down next to the spare tire on the passenger side. The bleeder is right on it.

ca993twin

Don,

Muchas gracias me amigo. Can you clarify the terms I always misuse? The brake booster pump thingus with the reservoir... same as the accumulator? San Luis Obispo is only a 3 hour drive (2 by Porsche). Get your coveralls.

911/Q45

The booster pump is up front above the battery. The small inline lump is like a muffler that helps quiet the buzzing sound that the early cars had. The thingus is actually located right above the drivers seat cushion and varies greatly in size.

Ima2nr

thingus = old fartus emeritus

then where in the hell is the muffler bering located? (mine's getting noisy)

PierreTT

I think that 96 cars dont have the muffler thing... Maybe my car have a muffler bypass there too...

ca993twin

After careful review of Don's (911/Q45) post, I decided that was the thingus that need a good draining... a job best handled by my wife. I must say, it was good advice, and I feel a whole bunch better now. The pedal may still be soft, but I don't much care.

Droops83

Steve,

Your thought about the larger brake pistons causing the change in pedal feel could be right on; the laws of hydraulics state that the same master cylinder will take longer and more travel to build pressure if the pistons in the brakes are bigger. But, it is definitely worth rebleeding the system to make sure there is no air trapped in there, especially since they are new calipers.

Refer to this thread where I posted the complete procedure on how to bleed the 993tt/C4 brake system:

https://rennlist.com/forums/993-forum/295116-flushed-slave-cylinder-wow.html

Of course I posted the procedure for flushing the entire system, so disregard the part about sucking out the old fluid, etc. But definitely let the pump run and the stop on its own, and disconnect it (bottom connector, not the one for the green pressure switch on top!) before starting to bleed, so the pump doesn't try to turn on while you're bleeding.

The accumulator looks like a black plastic bomb, it is right above where the spare tire goes in the luggage compartment, on the passenger side. Bleed that first, but be careful since fluid comes out fast and at high pressure when you crack the screw loose; you'll have to hold the hose onto the bleeder screw so it doesn't pop off and make a mess. Eye protection may be a good idea here.

When bleeding the calipers, bleed the inner screw first to flush the line from the master cylinder to the caliper, THEN bleed the outer screw. Do it in the traditional order: RR, LR, RF, LF. Of course monitor the fluid level in the reservoir continuously as you bleed so it doesn't run dry.

And remember, when you're done, reconnect the pump and turn the key on to let it run, and then stop. Only after the pump has run can you accurately check the brake fluid level in the reservoir and correct if necessary.

Good luck and feel free to ask any other questions.

---Chris A.

ca993twin

Chris,

Thanks again for your always great advice. I've printed out the procedure you've outlined, and will see how offended the mechanic will be when I go over it with him. I may be wrong... maybe he knows all about the accumulator. But... I'm suspicious. I wish your shop was a bit closer to Moorpark... still... it may well be worth the extra drivie.

Droops83

Steve,

I would hope your mechanic would have the factory service manual, which has more detailed instructions than I posted (IE tells you exactly how many CCs of fluid to bleed from each bleeder screw, etc; I usually wait till I see clear new fluid if flushing the whole system, or till there are no more bubbles if bleeding) complete with pictures and everything. This is the procedure that I paraphrased, with a bit of additional insight from experience. So ask him that first before whipping out my procedure! Give him a second chance.

BTW I would love it if you brought your beautiful car in sometime, I saw it briefly last fall at the Porsche motorsports open house, would love to check it out!

---Chris A.

ca993twin

Chris,

My concern is that if you think you know how to bleed brakes... for almost every other "normal" car, you may not even think to look at the manual. But I'll try to be as gentle as possible.

I'd love to get my car up there... maybe the way to do it would be to take a day off of work and drive up with my wife and spend the day up there. We'll see. Thanks again.