clutch hydraulics - Rennlist - Porsche Discussion Forums

Notices
924/931/944/951/968 Forum
Sponsored by:
Sponsored by:

clutch hydraulics

 
Old 03-07-2019, 07:48 PM
  #1  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default clutch hydraulics

I pieced my car together and for the life of me can't solve my clutch problems. I replaced everything on the clutch (disc, throw out bearing needle bearing, the bearings in the fork, and resurfaced the flywheel). I bled the clutch 3 different ways, pressure bled, used a 200ml mightyvac to force fluid from the bottom, and the method from another member to push the fork in and then pump the fluid.

The problem i experience is that the clutch pedal sticks to the floor. The best results come from pushing the fork in reverse and pumping the pedal, but as soon as i engage a gear and push too deeply on the clutch pedal it doesn't come back unless i coax it back. If i drive for 30 minutes or so, it's weird it's like resistance builds in the pedal, and there are times when it works great, then randomly sinks again.

I have a new master cylinder, new soft/hard line, new slave cylinder and i pressurized via the brake reservoir up to 20psi and no leaks. Anybody have any ideas? I think the slave might have failed internally though it was new (FTE unit). When i press the clutch, i can hear a squeeking noise as the clutch is pressed off the flywheel.
azerite is offline  
Old 03-07-2019, 07:58 PM
  #2  
Dan Martinic
Addict
Rennlist Member
 
Dan Martinic's Avatar
 
Join Date: Aug 2017
Location: Toronto, Ontario, Canada
Posts: 1,540
Default

Did you somehow remove the spring on the pedal? What happens at the inspection window in the bellhousing? Are you certain of the slave rod adjustment?
Dan Martinic is offline  
Old 03-07-2019, 08:12 PM
  #3  
MAGK944
Addict
Rennlist Member
 
MAGK944's Avatar
 
Join Date: Jun 2007
Location: Palm Beach, Florida
Posts: 5,215
Default

Clutch pedal to the floor means you still have air in the system. It’s good practice to replace all four components when you open up the system, master, slave, pipe between master & slave and the blue pipe at reservoir.
MAGK944 is online now  
Old 03-07-2019, 09:03 PM
  #4  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default

Originally Posted by MAGK944 View Post
Clutch pedal to the floor means you still have air in the system. It’s good practice to replace all four components when you open up the system, master, slave, pipe between master & slave and the blue pipe at reservoir.
I did all 4. The problem isn't so much that the pedal sinks, it's that it's not returning of it's own force.
azerite is offline  
Old 03-07-2019, 09:07 PM
  #5  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default

Originally Posted by Dan Martinic View Post
Did you somehow remove the spring on the pedal? What happens at the inspection window in the bellhousing? Are you certain of the slave rod adjustment?
The spring on the pedal (the big blue one) is still there and acts as the cantilever. If i look at the bell housing when i press the pedal, it moves the rod on the slave cylinder. The rod is adjusted to the same length as removal.
Is it possible it's the bearings that hold the fork and that those don't easily move? The clutch when depressed moves the rod in the slave, but the pedal doesn't readily pop back. I can drive the car if i press the clutch and keep my foot on it and gently the pedal will come back, but not quickly. Something is definitely stuck in the system, just can't figure out what. I don't think it's air per se, unless it's sucking in air somewhere on the return stroke (master/slave cylinders).

Could the seal be blown on one of the cylinders on a new unit?
azerite is offline  
Old 03-07-2019, 10:06 PM
  #6  
951and944S
Super User
 
951and944S's Avatar
 
Join Date: Dec 2001
Location: New Orleans/Baton Rouge
Posts: 3,382
Default

Originally Posted by azerite View Post
The spring on the pedal (the big blue one) is still there and acts as the cantilever. If i look at the bell housing when i press the pedal, it moves the rod on the slave cylinder. The rod is adjusted to the same length as removal.
Is it possible it's the bearings that hold the fork and that those don't easily move? The clutch when depressed moves the rod in the slave, but the pedal doesn't readily pop back. I can drive the car if i press the clutch and keep my foot on it and gently the pedal will come back, but not quickly. Something is definitely stuck in the system, just can't figure out what. I don't think it's air per se, unless it's sucking in air somewhere on the return stroke (master/slave cylinders).

Could the seal be blown on one of the cylinders on a new unit?
With Fluid in brake reservoir well past the minimum level that will cover the feed hose to the clutch master, raise pedal by hand to normal height,
lay under car with a large flat screwdriver with your body positioned where you are looking at the inspection hole/lever/slave pin.
Place the blade between the fork and the casting and pry the fork opposite it's direction that normally releases the clutch.
Release pressure and allow fork to return slowly.
Repeat several times.
Report back,

T
951and944S is online now  
Old 03-07-2019, 10:37 PM
  #7  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default

Originally Posted by 951and944S View Post
With Fluid in brake reservoir well past the minimum level that will cover the feed hose to the clutch master, raise pedal by hand to normal height,
lay under car with a large flat screwdriver with your body positioned where you are looking at the inspection hole/lever/slave pin.
Place the blade between the fork and the casting and pry the fork opposite it's direction that normally releases the clutch.
Release pressure and allow fork to return slowly.
Repeat several times.
Report back,

T
haha you’re the user I was referring to. I did exactly this and it worked all the air out, but the pedal still sticks. I have no idea why it’s intermittent.
azerite is offline  
Old 03-07-2019, 11:02 PM
  #8  
MAGK944
Addict
Rennlist Member
 
MAGK944's Avatar
 
Join Date: Jun 2007
Location: Palm Beach, Florida
Posts: 5,215
Default

Originally Posted by azerite View Post
I did all 4. The problem isn't so much that the pedal sinks, it's that it's not returning of it's own force.
Not what you want to hear I understand, but pedal not returning is also air still in the system.
MAGK944 is online now  
Old 03-08-2019, 08:23 AM
  #9  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default Rod

I have one quick question. Does the piston lay flush with the position of the fork? When I removed the old slave it wasn’t centered, the pushing piston tip was slanted sideways. Did they make clutch forks of different lengths.
azerite is offline  
Old 03-08-2019, 09:06 AM
  #10  
951and944S
Super User
 
951and944S's Avatar
 
Join Date: Dec 2001
Location: New Orleans/Baton Rouge
Posts: 3,382
Default

Originally Posted by azerite View Post
I have one quick question. Does the piston lay flush with the position of the fork? When I removed the old slave it wasn’t centered, the pushing piston tip was slanted sideways. Did they make clutch forks of different lengths.
No, should line up.

I have seen one instance where a racer so frustrated with trying to bleed pedal to not load up and go home from a long road trip (Sebring) that he asked me to try the method I described.

It worked for a lap or two but the throw out bearing lock ring was broken on the pressure plate, the resulting vibration would just re-aerate the fluid within 5 minutes.

You have to perform the procedure I described until you don't have any more "swooshing" sound of bubbles/air.

Is your metal tube/rubber hose new....?

I have seen the interior wall of the rubber section peel away internally which caused a one way check valve in the line.

Good luck.

T
951and944S is online now  
Old 03-08-2019, 10:09 AM
  #11  
kirkandorules
Addict
Rennlist Member
 
Join Date: Jun 2017
Location: Madison, WI
Posts: 121
Default

I had trouble getting mine bled properly when pressurizing the reservoir at 20psi, the tank dipped below the top (blue? can't remember) tube too quickly. Had much better luck with my Motive set at 10psi or so.
kirkandorules is online now  
Old 03-08-2019, 10:34 AM
  #12  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default

Originally Posted by 951and944S View Post
No, should line up.

I have seen one instance where a racer so frustrated with trying to bleed pedal to not load up and go home from a long road trip (Sebring) that he asked me to try the method I described.

It worked for a lap or two but the throw out bearing lock ring was broken on the pressure plate, the resulting vibration would just re-aerate the fluid within 5 minutes.

You have to perform the procedure I described until you don't have any more "swooshing" sound of bubbles/air.

Is your metal tube/rubber hose new....?

I have seen the interior wall of the rubber section peel away internally which caused a one way check valve in the line.

Good luck.

T
yes the soft line is new as well. The only thing i didn't change on the entire system is the hard line that goes to the slave (which should be ok since it's metal anyway?)

That's what originally led me to do the work (soft line), the original was bulged out and i couldn't shift. I think it may be the fork. I pressed in the slave piston a few times, and the swoosh i was referring to was liquid. If i press it back fast and hard with a small prybar, you can only hear liquid. I think the problem is the fork, it's not exactly center on the entire travel path, and as a result it pulls the piston slightly and creates resistance on the way back? I know it sounds like a tinfoil hat idea. The lock ring on the throw out bearing is new, and i don't feel any vibration except when i engage the clutch (the clutch is spring type so there is some vibration in the pedal when i press it in to engage).

The only tell tale sign is a squeaking. After i lift the car, press the piston in like T suggested, there is squeaking, can't figure out if it's the slave, or something else.
I'll bleed again just in case.

azerite is offline  
Old 03-08-2019, 10:52 AM
  #13  
Dan Martinic
Addict
Rennlist Member
 
Dan Martinic's Avatar
 
Join Date: Aug 2017
Location: Toronto, Ontario, Canada
Posts: 1,540
Default

I didn't get a proper bleed until I used my Motive (at the recommended 15psi) and had my son press the pedal while the system was pressurized and I was cracking the bleed bolt. Only when I did it this way did the pedal fully return.

That fork action does sound funny though. I can't see why a fork wouldn't travel straight? It would have to be loose on its bearings or the pin loose in the bore; either way, you'd have a loose fork, no?
Dan Martinic is offline  
Old 03-08-2019, 11:06 AM
  #14  
951and944S
Super User
 
951and944S's Avatar
 
Join Date: Dec 2001
Location: New Orleans/Baton Rouge
Posts: 3,382
Default

Originally Posted by azerite View Post
yes the soft line is new as well. The only thing i didn't change on the entire system is the hard line that goes to the slave (which should be ok since it's metal anyway?)

That's what originally led me to do the work (soft line), the original was bulged out and i couldn't shift. I think it may be the fork. I pressed in the slave piston a few times, and the swoosh i was referring to was liquid. If i press it back fast and hard with a small prybar, you can only hear liquid. I think the problem is the fork, it's not exactly center on the entire travel path, and as a result it pulls the piston slightly and creates resistance on the way back? I know it sounds like a tinfoil hat idea. The lock ring on the throw out bearing is new, and i don't feel any vibration except when i engage the clutch (the clutch is spring type so there is some vibration in the pedal when i press it in to engage).

The only tell tale sign is a squeaking. After i lift the car, press the piston in like T suggested, there is squeaking, can't figure out if it's the slave, or something else.
I'll bleed again just in case.
So after that's done, did you use your hand, just manually lift the pedal and pump with your hand about 1 inch travel only.
About every 4-5 times, take the pedal to the top one pump and go back to pumping the 1 inch stroke.
Do that a few times after the stroking of the fork like you already did.

As long as fluid is above the blue feed hose, I can't see you having air in the system.

I have never bled a clutch on a system similar to 944 in the conventional way described here in 25 years.

I have flushed by opening the bleeder, but never touched a bleeder for air in system.

T
951and944S is online now  
Old 03-08-2019, 03:00 PM
  #15  
azerite
User
Thread Starter
 
Join Date: May 2015
Posts: 40
Default

Originally Posted by Dan Martinic View Post
I didn't get a proper bleed until I used my Motive (at the recommended 15psi) and had my son press the pedal while the system was pressurized and I was cracking the bleed bolt. Only when I did it this way did the pedal fully return.

That fork action does sound funny though. I can't see why a fork wouldn't travel straight? It would have to be loose on its bearings or the pin loose in the bore; either way, you'd have a loose fork, no?
I had to do the exact same thing to flush the entire line out. I held at 15, and then manually pumped in order to pressurize when bleeding. It worked, but not quite. I had to do what T suggested and do the 1 inch pumps at the bottom then full strokes etc. That really firmed up the pedal. That only lasted for about a day though. The next day as soon as i took it out, the pedal stuck. It didn't fall, you could feel it actuate, but it didn't pop back up. Then after a 20 minute drive, the pedal started working like there was nothing in the line. That's why i can't pinpoint, it's not a consistent symptom.
azerite is offline  

Thread Tools
Search this Thread

Contact Us About Us Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: