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Coeur d'Alene, Idaho
 
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New clutch, but slips when hot - help.

So I did a by the book careful replacement of the clutch on my 60k 1984 944 last summer about 1000 miles ago. Stock Sachs clutch kit with pressure plate, new main seal, pilot bearing, even new release tube, throwout, etc. When I got it all together the clutch pedal released when it was high off the floor and the clutch slipped once it was warm. So I adjusted it down a bit using the shaft adjustment barrel adjuster that goes into the master cylinder atop the clutch pedal. Still slipped. More downward. Slipped. More downward solved it. Only happens when the car is warm. Its fine for the first few miles.

Later that summer (maybe 300 miles into the 1000 miles I've put on the car) it started slipping again and I realized the pedal was again releasing high. So I installed a new clutch slave cylinder thinking it was somehow involved and was perhaps not releasing pressure on the clutch. Had a great summer driving the car then stored it all winter, putting about 700 miles on it happily.

A month ago I got it out of storage and have driven it about 50 miles. Yesterday it started slipping again. So in frustration I adjusted the pedal barrel adjuster way down to the floor, not wanting to screw around with a bunch of subtle adjustments and just wanted to ensure the clutch had no pressure on it to let it slip. Crikey. Still slips. Same as earlier where when the car is cold its fine. I'm confident I bled it correctly btw but plan to re-bleed when I can.

So. Am I not understanding the purpose of that adjustment? My other fear is that I over greased the pilot bearing and it's gotten to the clutch. However the fact that it operates normally when cold seems to rule out oil on the friction. I also have a leaking valve cover and the drops end up right on the black sheetmetal clutch guard so I wondered if the wind is carrying that up into the clutch to let it slip. However again it operates cold just fine so again questioning the contaminant angle.

Help!
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84 944, 87 Vanagon, 88 Mitsubishi Van Wagon, 88 Supra Targa, 1990 Audi 90 20V Quattro sedan, 1992 Lexus LS400, 1993 LandCruiser, 1997 LandCruiser, 2017 Subaru Outback.
Old 05-11-2019, 08:25 AM
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Hey Doug- thatís a bummer. I wonder if the clutch fork is binding. Did you replace those little bearings when you were in there? Just a guess, but check to see that you are getting full travel to release all tension. Also, try Loosening up the slave and see if the fork pushes back more when you do that (meaning slave is not fully releasing)?

Thatís all Iíve got. Good luck.
Old 05-11-2019, 09:34 AM
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Coeur d'Alene, Idaho
 
Join Date: Aug 2017
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Yeah, I was actually thinking of something similar to your suggestion. I was going to drive it till its hot/slips, then remove the clutch slave and take it for a drive without a clutch to 100% eliminate the hydraulics. If I can't make it slip without the hydraulics then something's amiss there. I'll also perhaps video the movement of the clutch fork through the little viewer window in the clutch/bell housing when its cold (paying attention to the resting position of the fork/slave). Then video this same movement when its hot before I remove the slave.

I did also put new fork bearings in. I literally set this girl up to run another 37 years. Or so I thought.
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Old 05-11-2019, 07:41 PM
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I know the answer, it is the clutch pedal free play adjustment. Check it when the clutch is hot!
Old 05-12-2019, 04:52 AM
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Coeur d'Alene, Idaho
 
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Thanks for providing the diagram!

So this is the frustrating part that makes no sense on that above diagram. The words under the title "CHECKING CLUTCH PLAY" make no sense at all. The ".5mm" play shown on the diagram and referenced in the text is not adjustable though it's implied that it is. That's essentially slack in the mechanism. Adjusting the rod as it says in the last sentence "correct play by adjusting rod" does nothing for that play. It simply makes the rod longer or shorter and the play/slack remains the same. Adjusting it moves the clutch pedal toward the carpet or away from the carpet. The slack remains the same *until* you lengthen the rod so much the clutch pedal has topped out and then obviously you are now reducing the slack by pushing against the topped out pedal. Keep lengthening the rod once the pedal is topped out and you'll eventually remove all the slack and then even start to disengage the clutch as you are now essentially beginning to push the master cylinder through its travel.

At all points of adjustment of this rod BESIDES when you've topped out the pedal, the slack is exactly the same, which belies Porsche's phrase "correct play by adjusting rod". As I've said, you cannot really do that unless you've topped out the clutch pedal and begin removing slack that way. I do have one take away however - to adjust it hot.

So I don't understand some aspects of this procedure. If I shorten the rod from fully lengthened/pedal topped out there is an amount of slack I'd judge to be correct. Shorten it more - same amount of slack. Shorten it a ridiculous amount - same amount of slack. All I'm doing with this huge adjustment is bringing the clutch pedal closer to the carpet, I am NOT adjusting the amount of slack.

Because of this confusion, it is playing with my head. Because Im having trouble with the clutch it makes me think either Porsche made an error in the instructions here, and I'm being led astray as to how to deal with this.

The other text above is to adjust the amount of help that spring provides in depressing the clutch pedal. That adjustment seems fine - the clutch pedal is not overboosted or hard to push.

So, any other thoughts?
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Old 05-14-2019, 04:54 AM
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I believe the "slack" is measured from where the pedal could be lifted up if the return spring was still strong enough. Try lubing up the clutch pedal return spring and pivot joint to make sure everything is moving easily & smoothly. Then shorten the rod as others suggest.

BTW, I don't think anyone gets the 3.0mm at the pedal anymore... too much wear in the system. 10-20mm is usually fine.

Last edited by theer; 05-14-2019 at 10:30 AM..
Old 05-14-2019, 10:28 AM
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Quote:
Originally Posted by 944 Ecology View Post
Shortening the length of the rod will fix your problem. If you don't believe djnolan, believe me.

It won't take much, perhaps two full turns...
Been there, done that, fixed that. Listen to what these guys have said.
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Old 05-14-2019, 01:57 PM
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You don't have to get super scientific about the 5mm measurement. If there is a little free play in the pedal when the car is hot it is adjusted right. You have to go by pedal feel as first there is the free play in the clutch linkage, and then the return spring kicks in later in the pedal travel. The clutch freeplay is the very first movement of the pedal.

However you have to be a contortionist to get in there to do the adjustment

Last edited by djnolan; 05-14-2019 at 02:51 PM..
Old 05-14-2019, 02:48 PM
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Coeur d'Alene, Idaho
 
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So, I've been out of town on business for a couple weeks and am getting back to this. In the above diagram, there is reference to two color coded springs on the clutch pedal. A green one and a blue one. When I look up there at mine, there is no color on the spring - it's plain black. So I'm wondering if someone could tell me how the springs are marked? If it's a single paint dab, I'll have to spin it to find it but it seems the color is crucial to the correct length. Thanks in advance.

EDIT: So I used a small dental mirror to thoroughly look over the spring and find no color dabs anywhere on it. I can see 95% of the surface, excepting the faces of the last coil on each end that are against the adjuster. So now there is the real possibility someone put a nonstock spring in there added to all the mystery. Anyone have input on where the "color" is?
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Last edited by IdahoDoug; 05-29-2019 at 08:19 PM..
Old 05-29-2019, 07:20 PM
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I adjusted the piston rod to get the 3mm pedal play and I did not bother with the spring measurement or adjustment. I have had a few instances of the clutch pedal not returning up, but I always thought it was related to a bleeding problem.
Old 05-30-2019, 12:46 AM
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Coeur d'Alene, Idaho
 
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Could someone agile (or self checking if you are) slide into their driver's footwell and see what color your clutch pedal spring is? It is on the rear surface of the pedal. Easiest way is to hold onto the A pillar as you slide under. Then to stand up, grab both straps of the driver's seatbelt up at the anchor point for a strong easy hand hold to get up. Thanks!

This is critical for me as if I have a nonstock clutch spring the adjustment in the manual is useless.
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Old 05-30-2019, 08:25 AM
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The cell phone camera is quicker than the eye...
Old 05-30-2019, 11:34 AM
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Coeur d'Alene, Idaho
 
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Well, I think I have resolution and the diagram above and its instructions are not worth a hill of beans. Very frustrating. Read all the text and you'll see for example the distance "A" is measured "from the edge of plate and bearing". Uh, what bearing? The end sits in a slot. So let's call that mating surface a "bearing" for fun. Now do I measure from where the tab and slot touch (that's the absolute tip of the "nipple" in the diagram)? Or where the top surface (above the slot) is - which the diagram clearly indicates IS the measure point. But that point is decidedly NOT the bearing which is about 5mm deeper in the slot where they actually touch. So that's one of Porsches "A" measurement explanations on the diagram above - giving you about a 10% error to start the whole process if your guess which point Porsche wants measured is wrong. Rough start on a project Porsche wants a precise measurement on, eh? But it gets worse.....

Now bring your attention to the text at the bottom where it clearly says to remove the spring and measure "A". Uh, really? Note it says measure "the spring", not measure "the spring and funny plastic thing they call a bearing in the diagram" the other end of which (metal part the plastic tip rests in) is not on your bench just as an aside - it's over in your car up under the dash. So apparently I measure the spring lets say at 60mm on the work bench. Then I put it back in and make sure I don't compress the spring to ensure that "A" when assembled remains at 60? Or do I somehow elongate the spring from the bench so it conforms to the added length to the "bearing". Obviously impossible. Not very helpful. Very confusing.

So here's what I did. I completely ignored all the instructions. I backed the bolts holding the slave onto the clutch out until only a couple threads remained (about a quarter inch). Then I opened the bleeder so ANY hydraulic pressure was dissipated. I even gently pried the clutch fork through the access hole against the slave to be sure no pressure on my clutch plate existed.

Then I pushed the Porsche out of the garage, started it in gear and drove off without touching the clutch pedal. I went up and down through the gears on steep local hills after it was fully warmed. For more than a half hour after warmup I tried to get it to slip in any gear at full throttle. Over and over. Nothing. Great news. My new Sachs clutch and all the bits were installed correctly and there is something amiss with the hydraulic clutch system and this was the only way I could confirm it.

Back home, I turned the slave bolts home with the bleeder open (this is all possible without removing the starter, btw - use a small 1/4" ratchet for the slave bolts and you''ll find limited swing). Then I ignored my Mighty brake bleeder which is always a pain and never seems to give me volume flow to remove bubbles. Instead I hooked up my oil suction system to the clutch slave bleeder and opened it wide. Massive flow of brake fluid satisfied me no bubble could possibly have withstood that. Shut bleeder. Topped off reservoir. Adjusted pedal travel to where I prefer it (the shaft to the master cylinder to me does NOTHING more than this - simply puts pedal travel at your preferred spot despite Porsches suggestion it "adjusts" amount of slack). Ignored the Porsche instructions that I'm adjusting slack with that rod going forward to the master cylinder as I am most assuredly NOT making any difference in that slack no matter where I put it. Went for a drive. Perfect. No slippage.

So for those who come across this thread in the future. Beware the ludicrously unhelpful Porsche clutch instructions. Simply hyper bleed the system if you're having troubles - because you're fighting bubbles in a two foot vertical column of brake fluid and a normal hand bleeder may not get the air all out as the bubbles immediately rise again when you stop for another pump. I've also tried having my son in the car pumping with the clutch pedal and apparently that didn't work because I have 45 years of brake bleeding under my belt and we did it twice and were still having the "clutch slippage" problem that spawned this thread and now appears to simply have been air in the line. So bleed the crap out of it, then make sure you check when the system is hot that you don't have the clutch pedal topped out up as far as it will go toward the dash and hitting the stopper. If you do, the heat expansion can place pressure on the master cylinder and slave cylinder and cause the clutch to slip.

Hopefully the end of the story. I feel I had air in the system and nothing more. Will update if it is not. In the meantime, I've enjoyed about 50 miles with our 944 running and shifting flawlessly over a stunning N. Idaho summer weekend!!

Thanks to all who contributed their thoughts, time and suggestions.

Doug
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Last edited by IdahoDoug; 06-03-2019 at 10:39 AM..
Old 06-03-2019, 10:30 AM
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Very innovative and thorough analysis. In my case the pedal was topping out and the clutch was slipping. This was after the slave cylinder was replaced. May have been air as suggested, however adjusting the free play cleared up the slipping.
Old 06-04-2019, 03:52 AM
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Coeur d'Alene, Idaho
 
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Thanks for your continued input, and for advising your clutch was topped out. That's the condition where adjusting the shaft (by shortening it) will stop slipping, so others should be aware if they've got that happening.

So it's been a long enough time and I've had the car out on the interstate, and put another 100 miles on it as well. My wife has taken it on errands, and its summer temps here - almost. All is well so far.

If it does this again, I'll immediately conclude the hydraulic line to the slave straight up and down has aged out and could be letting air in and replace it. Pelican has it for $44 which is very reasonable IMO.
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Old 06-11-2019, 05:24 PM
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