Biovox

I am about to change the calipers on my '95 993 and hence will need to refill and bleed the brakes afterwards. My question is do I need to also bleed the ABS? Does it form part of the same circuit as the normal brakes or is it a closed system? I have a copy of the 993 WS manual but it only details what to do, not when to do it.

Any help greatly appreciated

Steve Weiner-Rennsport Systems

Biovox:

You do not need to bleed the ABS (need the Hammer for that) as long as you never let the brake fluid reservior go empty.

Since the ABS controller manages peak brake pressures, its part of the same circuit as the MC and all four calipers.

I'd strongly suggest you remove and replace one caliper at a time (to minumize fluid loss) and use a pressure bleeder to flush-bleed the system.

Rick Lee

Uh oh. Hey Steve, I helped a buddy remove all 4 of his calipers a few weeks ago, so he could send them out to be powder coated red. We just put water bottles around each brake line and let them drip. Are we gonna be in trouble when it comes time to reinstall?

Rezal

Ooooh, I hope that's not an issue. That's what I did when I put in the Big Reds. I've had the car with 'em for a few months now, covering around $3K and it seems ok.

Edit:
Correction. I just realized that I probably replaced the calipers one-by-one. Phew!

Greg Fishman

Rick,
You will probably just need to bleed the ABS system if the reservoir is dry.

Rick Lee

How does one bleed the ABS? I've flushed/bled brakes many many times. Dunno about ABS.

Greg Fishman

You have to have a "Hammer". Bleed as usually but then you will probably have to take it to the dealer or shop with the tool to finish the job.

Steve Weiner-Rennsport Systems

Greg is correct,....

If the reserviour drained out as the calipers were changed/replaced, the liklihood of the ABS controller getting an air bubble inside is very high.

The only way that unit can be properly bled is with the Bosch Hammer. It cycles all of the internal high-pressure valves to purge any air.

You do NOT need the Hammer to do a good job of bleeding/flushing the brakes as long as the reserviour is kept full.....

Rick: You should plan on a "Hammer" bleed job on your buddy's car....

Biovox

Thanks guys. I was planning to replace the brake hoses at the same time. Just have to be quick on the swapping and keep the reservoir topped up I guess.

'Preciate the advice - no substitute for experience

Rick Lee

Does every P-car shop have the Hammer? And how much does it cost to have done?

Greg Fishman

Most should. I can't imagine they would charge more than an hour of labor to bleed the brakes.

85Gold

A trick to use when changing calipers to prevent draining your master cylinder res. is to take a stick and put it between the seat and the brake pedal to hold it partly depressed when you disconnect the calipers. This moves the master cylinder piston past the fluid input hole from the res. and prevents it from draining. I have not tried it on a 993 but it works real well on a 911.

Peter

Jeff 993TT

I remember that being mentioned in the service manuals also. But there is the possibility of "pushing your master cylinder past it's normal travel" causing increased MC failure. There seems to be a lot of religion if this is really a problem or not.

What about just capping off the ends of the brake fluid lines? Take a small baggie and a nylon tie to make a tight seal?

85Gold

You don't need to push the pedal all the way to the floor, just enough to stop the flow of fluid past the piston. I would guess no more than an 1.5" or so.

Peter