Go Back  Rennlist - Porsche Discussion Forums > Water Cooled Technical Discussion Areas > 928 Forum
Reload this Page >

Clutch pedal will not disengage transmission - update - fixed!!!!

Notices
928 Forum
Sponsored by:
Sponsored by: 928 Specialists

Clutch pedal will not disengage transmission - update - fixed!!!!

 
Old 09-27-2010, 01:15 PM
  #16  
WallyP

Rennlist Member
Rennlist Site Sponsor

 
Join Date: Jun 2001
Location: Acworth, GA
Posts: 6,469
Default

A maladjusted center plate will usually cause clutch drag, but will not lock up solidly. A stuck clutch plate will lock up solidly.

A quick check method also provides a brute force method for freeing a stuck plate...

Position the car so that there will be no damage or danger if the car lurches forward a few feet. Very securely chock the front wheels. Jack the rear wheels just off the ground, and securely support the car.

Put the transmission in fifth gear. Push the clutch pedal to the floor and hold it there. Do not apply the foot brake or the parking brake. Crank the engine - the rear wheels will spin. Accelerate until the speedometer reads about 20 mph, then stab the brake pedal. If the engine stalls, repeat a couple of times.

If the clutch doesn't break loose, its time to pull the bottom of the bell-housing and take a look.
WallyP is offline  
Old 09-27-2010, 07:29 PM
  #17  
jwillman
Addict
Rennlist Member
Thread Starter
 
jwillman's Avatar
 
Join Date: Jul 2009
Location: Austin, Texas
Posts: 1,842
Default

Originally Posted by Mrmerlin View Post
lets go back to the bushing on the top of the release arm with the aircleaner off and the clutch released can you move the arm on the ball??
any front to rear play??
the plastic bushing fits over the ball then the arm is pressed onto the bushing. if the bushing has failed then the arm will have too much play.
Originally Posted by Garth S View Post
If you have a '79, and the ball stud for the release arm was not updated ..... there is an excellent chance that it is broken: it may appear to be in place, but if the teflon ball cup in the release arm has degraded, the release arm works against the ball stud and it snaps - it has no place to go, so may still appear attached.
So I looked at the upper pivot ball and used a pry bar to push it back (slave still in stalled). The ball is intact and still threaded into the engine. The arm moves back with what i would judge to be pressure from the slave rod on the bottom end but there does not seem to be an insert holding the arm onto the ball. I would have expected it to be a snap on type fit but were it not for the slave being installed I would gues it would just slide off.

Seems like I need the new insert and I assume I pull the slave to allow enough room clear the ball joint. Not sure this is the sole problem but looks like it needs to be taken care of to work down the list.
Attached Images   
jwillman is offline  
Old 09-27-2010, 10:18 PM
  #18  
Garth S
Addict
Rennlist Member
 
Garth S's Avatar
 
Join Date: Oct 2003
Location: Nova Scotia
Posts: 7,203
Default

That looks to be it. Fortunately, it is limited to stage 1 of failure as Stan indicated ..... so all you need is a ball socket bushing 928 116 145 03: sometimes, enough of the bushing remains to allow the release arm to function ...... poorly. That can be short lived, as the early version of the ball stud then fails. That happened on my '80 in the early '90's.

Search the archives - I recall someone posting of replacing the bushing from the top side as pictured with no more dissassembly than removing the slave
Garth S is offline  
Old 10-02-2010, 11:00 AM
  #19  
jwillman
Addict
Rennlist Member
Thread Starter
 
jwillman's Avatar
 
Join Date: Jul 2009
Location: Austin, Texas
Posts: 1,842
Default

I have a new release arm upper bushing coming in hopefully this weekend.

I bleed the system again using the pressure bleeder from the top. The pedal seem to be soft the initial 1/2 " of travel and then hits some resistance. The soft area seemed to end aburptly like you were going past a stop so I started looking at the WSM and previous posts and looking at the pedal it self.

WSM shows a clutch spring at the pedal. It states that the space between the spring plate and center of bolt is 43mm but pic shows that demension with the pedal at rest while verbiage seems to indicate measurement is pedal fully depressed.

I have ~24mm at rest and ~29mm with pedal fully depressed. If I am reading the WSM correctly I need to turn the wing nut to copress the spring more to get 43mm with pedal fully depressed, correct?

Again this is my first 928 so I have no feel experience to go by. What issues are created by not having the proper clutch spring setting? Is it only a pedal force issue? I still need to check rod preload but based on the diagram below the spring adjustment should not impact that setting.

Thanks for the help.
Attached Images  
jwillman is offline  
Old 10-02-2010, 11:40 AM
  #20  
GlenL
Super User
 
GlenL's Avatar
 
Join Date: Jul 2003
Location: Minneapolis, Minnesota
Posts: 7,625
Default

I don't know about those measurements but I have adjusted a few.

Be careful about those instructions. They varied over time and models and I've had problems when pre-loading the rod.

My suggestion is to adjust the rod until it is firm and then back off (loosen) it one turn. This ensures the master will fill from the reservoir. Maybe you have too much play there.

Also note that you don't need to remove the clevis, just loosen the lock nut and turn the rod with your finger or small wrench.

Also, your description of the pedal action is in-line with other 928s: free motion at first but not fully disengaged until it's almost to the floor. A long engagement angle, too. So ya press it and it goes down a bit easily then it gets firm and the clutch slowly opens and isn't fully open until it gets to almost the floor.

I've been following along somewhat but have you dropped the clutch out and inspected everything? Might have clutch plates stuck on the intermediate shaft or wear there that prevents the plates from moving.
GlenL is offline  
Old 10-02-2010, 01:12 PM
  #21  
jwillman
Addict
Rennlist Member
Thread Starter
 
jwillman's Avatar
 
Join Date: Jul 2009
Location: Austin, Texas
Posts: 1,842
Default

Originally Posted by GlenL View Post
I don't know about those measurements but I have adjusted a few.

Be careful about those instructions. They varied over time and models and I've had problems when pre-loading the rod.

My suggestion is to adjust the rod until it is firm and then back off (loosen) it one turn. This ensures the master will fill from the reservoir. Maybe you have too much play there.

Also note that you don't need to remove the clevis, just loosen the lock nut and turn the rod with your finger or small wrench.

Also, your description of the pedal action is in-line with other 928s: free motion at first but not fully disengaged until it's almost to the floor. A long engagement angle, too. So ya press it and it goes down a bit easily then it gets firm and the clutch slowly opens and isn't fully open until it gets to almost the floor.

I've been following along somewhat but have you dropped the clutch out and inspected everything? Might have clutch plates stuck on the intermediate shaft or wear there that prevents the plates from moving.
Thanks Glen.

I have not had the bell housing open yet. Working through the easy stuff first. I am trying to do one thing at a time and then verify results so I know at what point the issue is resolved understanding that it maybe a culmination of many items contributing to the current problem.
jwillman is offline  
Old 10-17-2010, 04:15 PM
  #22  
jwillman
Addict
Rennlist Member
Thread Starter
 
jwillman's Avatar
 
Join Date: Jul 2009
Location: Austin, Texas
Posts: 1,842
Default

Originally Posted by WallyP View Post
A maladjusted center plate will usually cause clutch drag, but will not lock up solidly. A stuck clutch plate will lock up solidly.

A quick check method also provides a brute force method for freeing a stuck plate...

Position the car so that there will be no damage or danger if the car lurches forward a few feet. Very securely chock the front wheels. Jack the rear wheels just off the ground, and securely support the car.

Put the transmission in fifth gear. Push the clutch pedal to the floor and hold it there. Do not apply the foot brake or the parking brake. Crank the engine - the rear wheels will spin. Accelerate until the speedometer reads about 20 mph, then stab the brake pedal. If the engine stalls, repeat a couple of times.

If the clutch doesn't break loose, its time to pull the bottom of the bell-housing and take a look.
Okay, release arm ball joint insert is replaced. System bleed, pedal firm and slave rod travels per WSM. Still encounter grinding with engine running whenattempting to shift the car into reverse or 1st.

I attepmted the suggested procedure today without the hoped for results.

I jacked up the rear end to get the rear wheels just off the ground. Put the transmission into 5th depressed the clutch and started the car. Rear wheels were turning. I acceleratred until about 30MPH on speedo and then depressed the brake. Engine decelerated and then died accompanied by what sounded like an air brake releasing.

I attempted this 5 times with the same result. With the engine running and clutch pedal depressed the wheels begin to turn as I attempt to pull the shifter into 4th or 5th gear but I get no grinding.

What next?
jwillman is offline  
Old 10-17-2010, 04:35 PM
  #23  
Landseer
Addict
Rennlist Member
 
Landseer's Avatar
 
Join Date: Sep 2007
Location: Frederick, Maryland
Posts: 11,262
Default

I understand that slave rod travels the right distance. But is it the correct length?
Then, you could hook-up a comealong to the acuator arm and try a little extra motion to actuate (not much).


Beyond that confirmation, I'd pull bell housing, take it apart and measure.

You've seen the long comparison of parts in the WSM during these years that the clutch/trans was being massaged.

Worn actuating sleeve, discs frozen/corroded to intermediate splined shaft, discs stuck to flywheel and intermediate plate are possible. Also some wrong parts.

I'd probably write-off those clutch discs and star soaking the biatch with penetrating oil.

Just an amateur here, but that's what I'd do.
Landseer is offline  
Old 10-17-2010, 06:08 PM
  #24  
WallyP

Rennlist Member
Rennlist Site Sponsor

 
Join Date: Jun 2001
Location: Acworth, GA
Posts: 6,469
Default

"...then stab the brake pedal."
"...then depressed the brake."

The idea is to use the rotating inertia of the drive train and wheel assemblies to apply a sudden impact loading. "Depressing" the brake pedal implies a tentative application, which will have little or no effect.

At this point, it would be better to pull the bell-housing lower cover and take a look. That should take thirty minutes or so, including jacking the car.
WallyP is offline  
Old 10-17-2010, 06:21 PM
  #25  
jwillman
Addict
Rennlist Member
Thread Starter
 
jwillman's Avatar
 
Join Date: Jul 2009
Location: Austin, Texas
Posts: 1,842
Default

Originally Posted by WallyP View Post
"...then stab the brake pedal."
"...then depressed the brake."

The idea is to use the rotating inertia of the drive train and wheel assemblies to apply a sudden impact loading. "Depressing" the brake pedal implies a tentative application, which will have little or no effect.

At this point, it would be better to pull the bell-housing lower cover and take a look. That should take thirty minutes or so, including jacking the car.
Ah okay, there is a difference. I pressed and held the brake. I will try the stab approach a couple of times.

I had the bell housing off inorder to get the release arm out of the way enough to replace the bushing.

I have never worked with a clutch before so I am a deer in the headlights at this point. Not sure what to look at. Not sure if these photos are any help but at this point I am out of ideas and experience.
Attached Images   
jwillman is offline  
Old 10-18-2010, 01:25 AM
  #26  
WallyP

Rennlist Member
Rennlist Site Sponsor

 
Join Date: Jun 2001
Location: Acworth, GA
Posts: 6,469
Default

Remove the lower cover from the bell-housing, exposing the clutch from below.
Use a good flashlight or drop-light to examine the clutch.

You have, starting from the front:
- The flywheel surface, bolted to the crankshaft and turning with the engine.
- The forward clutch disk, squeezed between the flywheel surface and the front surface of the intermediate plate. The disk is splined to the clutch output shaft, which is bolted to the driveshaft inside the torque tube.
- The intermediate plate, which is connected to the pressure plate, and thus driven by the crankshaft.
- The rear clutch disk, squeezed between the rear surface of the intermediate plate and the pressure plate. This disk is splined to the output shaft, thus also bolted to the driveshaft inside the torque tube.
- The pressure plate, which is a heavy metal ring inside the stamped metal cover. The ring is strongly spring-loaded to clamp the two clutch disks and intermediate plate against the flywheel. The ring is pulled away by the release bearing, removing the clamping pressure.

When the clutch pedal is all the way up, the pressure plate is heavily spring-loaded against the rear clutch disk, thus tightly clamping the front clutch plate, the intermediate plate and the rear clutch disk between the flywheel and the pressure plate. The friction makes all parts turn together, driving the output shaft with the crankshaft.

When the clutch pedal is all the way down, the pressure plate pulls back, removing the clamping pressure, allowing the two clutch disks to float freely between the clamping surfaces, freeing the output shaft from the crankshaft/intermediate plate/pressure plate assembly, allowing the crankshaft to rotate without driving the output shaft.

What you are looking for is one or two of the clutch disk surfaces being rusted to one or two of the metal friction surfaces, OR you are looking for insufficient rearward movement of the pressure plate to release the clamping force on the clutch disks.



When the release arm pulls the throwout bearing against the pressure plate fingers (the segmented metal disk in the center), the fingers move the pressure plate to the rear, pulling it away from the rear clutch disk.

The rear clutch disk should slip back slightly, so that it floats freely between the pressure plate and the intermediate plate, transmitting no torque.

The removal of pressure should allow the intermediate plate to also move back slightly, releasing the pressure from the forward clutch disk.

The release of pressure on the forward disk should allow it to slip slightly to the rear, so that it floats freely between the intermediate plate and the flywheel, transmitting no torque.
WallyP is offline  
Old 10-18-2010, 08:49 AM
  #27  
tmpusfugit
User
 
tmpusfugit's Avatar
 
Join Date: Apr 2010
Location: Magnolia TX, just north of Houston, Red 1984 S
Posts: 654
Default

Hey Jim, I have the clutch plates, pressure plate, and flywheel setting here (out of Dogbert, an '81) The clutch and pressure plates are Sachs I think and marked with an '86 date as I best recall, and they appear to be in good condition. More than happy to ship them your direction if you want to try replacement as a solution...

Jim D
tmpusfugit is offline  
Old 10-18-2010, 09:15 AM
  #28  
theporscheguy
Addict
Rennlist Member
 
theporscheguy's Avatar
 
Join Date: Jan 2010
Location: Kansas City
Posts: 2,811
Default

When I originally purchased my 87 928 5 speed I had the exact problem after the slave cylinder was replaced. The sound of the tech grinding the gears was not good to say the least. I contacted a friend who is very good on 944's and 928's. We put my car on a lift and ten minutes later he had the problem solved. Send me a PM and I will forward you his contact information. Even though it has been a few years he will remember working on my car.
theporscheguy is offline  
Old 10-23-2010, 03:46 PM
  #29  
jwillman
Addict
Rennlist Member
Thread Starter
 
jwillman's Avatar
 
Join Date: Jul 2009
Location: Austin, Texas
Posts: 1,842
Default

So I have it fixed and she now shifts into all gears with engine running and moves under it's own power

I dropped the bell housing and used a ratchet strap to hold the release arm back per a recommednation from Mark Robinson.

I adjusted the h's/t's all the way back and the discs were still stuck to the plates. I added some tension and pulled the release arm back further and then used a flat tip screw driver to gently free the discs.

Thanks all for the help and advise. Your diagnosis was spot on!!!!
jwillman is offline  
Old 10-23-2010, 10:08 PM
  #30  
pcar928fan
Super User
 
pcar928fan's Avatar
 
Join Date: Apr 2008
Location: Austin, TX
Posts: 9,337
Default

YEE HA!!! I saw Blake today up at the dealership and he said you were able to taken him for a ride around the hood!! NICE! SO GLAD it is running! If you are not ready to take it to 3rd Coast in a couple of weeks just come get my '84, it is running SOOOO NICE right now!!! WOW! Sweet ride, I hate to sell it, but really do need to...
pcar928fan is offline  

Thread Tools
Search this Thread
Quick Reply: Clutch pedal will not disengage transmission - update - fixed!!!!


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: