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HomeTech Articles > 993 Technical Article:

Pelican Guest Technical Article
Permission to publish this article is provided generously by
Robin Sun at www.p-car.com
Be sure to visit his site for loads of 993 info!

How to flush the slave cylinder
(The following procedure was performed on a normal aspirated two wheel drive 993, the 993 twin turbo and the 4 wheel drive model cars have a different hydraulic circuit which is separate from the brake's hydraulic system, the procedures to bleed the slave cylinder maybe different)

The 993's clutch system is operated on a hydraulic system that require routine fluid change.  What makes this particular job difficult is that the clutch slave cylinder's bleeder valve is located in front of the clutch slave cylinder on top of the transmission.  In order to keep your eyes on the fluid flow and operate the wrench there is no way you can get to this part with both hands.  Unless you perform the process with another person's vision. 

The procedure itself is simple, but this is definitely an 1 hour job. 

(1). Jack the car up from the left rear jacking point, and place jack stand under the front jack point and rear suspension pivot point.  I did not rest the car on the jack stands, they were there strictly for protection.

(2). Remove the left rear wheel.

(3). Remove the engine and transmission pan

(4). Reach up to the slave cylinder area from under the car with your left hand while lying on the floor .  Pull off the protective rubber cap on the end of the bleeder valve, push on a 1/4" clear vinyl tubing onto the end of the bleeder valve with the other end in some sort of disposable bottle for catching all the old fluids.

(5).  Hook up a power bleeder unit, or some sort of pressure bleeder unit to the brake fluid reservoir. Prior to hooking up the unit make sure you first remove the white cylinder inside the brake fluid reservoir. 

(6).  Get back underneath the left rear of the car, and use a 7 mm open end wrench to unbolt the bleeder screw, since the limited maneuver area this will require at least two movement of the wrench before the fluid will be compressed out. 

(7).  It is always a good practice to change the to a different fluid color fluid when doing a hydraulic system flush, this way you will know when all the old fluids is completely flushed form the system when you notice the color change.

(8). Tighten the bleeder screw and install the rubber cap and the rest of the stuff.  Double check the brake reservoir level after you have lowered the car. 


Ray Calvo (pops) said that I am a RAT for not mentioning in this web site that 
I took this picture from the left rear wheel well opening of the car, so here it is :)
 
 

In case if you guys are interested in Ray Calvo's clutch slave bleeding experience please read on....  "It is funny :)"


Killed three birds with one stone (long)
Posted By: Ray Calvo <porsray@sgi.net>
Date: Saturday, 24 February 2001, at 9:19 a.m. 

Well, kinda. After work yesterday, I 

a) bled the clutch slave cylinder 

b) tested my Power Bleeder 

c) got some info off the Vertex front rotors 

CLUTCH BLEED: printed Robin's procedure for a laugh (read on), then went ahead with it. Generally followed Robin's directions, and agree accessing the bleed screw is a royal PITA. Definitely a touchy-feely job, you can't see a thing if your hand is up there trying to access the bleed screw. Tried both box and open end wrench; think I opened the screw with a box and closed it with open-end. The screw is very loose (well, mine was); I didn't even realize I had broken the screw loose till I reached up and found I could move the screw with my fingers. The screw is a lousy design - about 1" long, made up of about 1/4" of nipple end, 1/4" of hex wrench fitting, and 1/2" of smaller pipe end. This setup is just asking for trouble like being very difficult to position a wrench on the hex fittng and possibly overtightening and snapping off the bleed screw. 

AND ROBIN, YOU RAT!!!!!!! Your pretty picture on your web site? While working on the car, could not figure out where you shot that picture. Finally noticed it was shot from the left wheel well, looking in to the top of the tranny. ONLY YOU HAD TAKEN OUT YOUR SPRING/SHOCK!!!!!!! Let people know, will you? Also, you had a jack stand under the rear suspension mount? How you did this and still accessed the bleed screw is beyond me; anyplace I put a stand got in my way when tried to get to the screw. 

POWER BLEEDER: Followed the directions with the unit; will say it's nicely made and easily possible to get a airtight seal. Have to pump like crazy to pressurize the unit, but works as intended. I only filled it with about 1/2 liter of fluid; made it easy to tilt the unit when wanted to stop filling the master cylinder and vacate the fill tube and bring the reservoir level down to normal point. One thing I will say: place the bleeder below the reservoir, and run the fluid supply line so that the center is higher than the reservoir; makes it easier to vacate the supply line and lower the reservoir level to the desired value at the end of the job. 

Was all this worth it? I don't know. I pulled out about a pint of fluid; the first portion had the look of used engine oil; black and totally opaque. Quickly took on tint of clean fluid. Initial clutch trial and drive on crisp below freezing night seemed to indicate clutch was like new. After about 1/2 hour, noticed some clutch pedal hangup again. When pulled into the garage and worked the clutch with the engine off, could definitely hear a loud squeak from the clutch, and the pedal felt notchy when I was letting it up. So, might have more problems. 


Here are some comments from Jim Stover after his experience with the clutch slave 



               "James A. Stover" <jjs5@psu.edu>
         To:webmaster@p-car.com
         Subject:Brake fluid change
         Sent:Mon, 14 May 2001 10:49:22 -0400Robin:

As I mentioned some time ago, I was planning to replace the brake fluid in my 95 993 and would send you some comments on the experience in case they might be of general interest. I did it last weekend. Since my car has Option 224 (Active Brake Differential), I expected it to have the hydraulic pressure unit. I do not see how ABD could work without an independent pressure source. Nevertheless, I could not find the pressure unit or the accumulator tank in the car. So I just went ahead with the normal procedure.  The Motive pressure unit is a neat device; Ray's (?) idea of making a "T" todo both cylinders at once is the way to go. 

The only procedure I did that might be of general interest was the clutch cylinder bleeding. I'm not sure if it contributes anything new over what you have already covered on your web page, but below is a write up. Use it or not, any way you wish. It is actually quite easy to do.

"Put the car up on jackstands to a HEIGHT that allows you to easily maneuver your body underneath the car. Remove the left rear wheel. From below the brake disk, using a light, you can see the clutch cylinder resting atop the transmission in all its inaccessible glory. (See Robin's picture). Move around until you can find a hand position that provides enough strength to pull the rubber cover off the bleed nipple. Long, ape-like arms are an asset here. Maneuver a 7mm, 12-point box-end wrench over the bleed bolt and on up against the cylinder, where it will hang freely. Work your bleed tube over the nipple. Secure the bleed bottle out of the way so you won't kick it over. Pressurize the hydraulic system following the instructions for your unit. Maneuver yourself until you can get enough leverage on the wrench to loosen the bleed bolt. The bleed tube will prevent the wrench from falling off. Watch the fluid going through the clear bleed tube until it clears up. It is likely to be dark and grungy looking initially. (Maybe this stuff should be bled out at least once a year). When the exiting fluid is clear, snug the bleed bolt back closed and disconnect the system, covering the nipple with the rubber cap"

Thanks, Robin, for all the help and advice you have provided.

Jim

Comments and Suggestions:
Viper6 Comments: Manual says to depress the pedal for this procedure, but I don't see that mentioned above... which is it?
August 30, 2012
  Followup from the Pelican Staff: You don't have to if you are pressure bleeding. - Nick at Pelican Parts  
Breu Comments: Doh!! I should have read Floyd's comment before I tackled this job. I least now I know why my clutch pedal is on the floor.
June 10, 2012
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
floyd landis Comments: It should be noted that the inlet for the clutch system in the hydraulic fluid reservoir is above the brake inlet. If you let the level get below that point, you blow air into the clutch line even though the reservoir appears about half full. I guess this is a good idea in the event your clutch hydraulics go, you can still stop, but it was pretty agravating till I figured it out.
December 15, 2010
  Followup from the Pelican Staff: That's exactly it - if the fluid level drops too low, then your clutch will no longer work. Which means the car won't be moving, which means that your fluid won't get so low that your brakes stop working. - Wayne at Pelican Parts  

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