Need help confirming if I have a bad clutch pressure plate

[roymil]

Hello, today I tried to go for a drive but I couldn't get my transmission into gear (original 4sp manual).  Just get grinding when trying to shift, so I didnt force it.  First thought was a clutch master/slave hydraulic issue, however fluid is fine, no leaks, and I can see the clutch fork move as expected on the side of the trany when my wife depressed the peddle.   Not sure exactly how far it should go, but it looks like it is moving the full travel, about as far as it could.  I think the slave cylinder is doing fine.

With engine off I can, with some difficulty, get it into gear, but if I then depress the clutch peddle and crank the starter, the car lurches, telling me that the clutch is definitely not disengaging the engine from the transmission.

It all worked just a week ago so I'm not thinking its anything like corrosion causing things to seize up someplace but wondering if there is way to verify that, or maybe get a borescope in to look.

I've also read that a failed shift fork or pressure plate might explain these symptoms so I'm looking for a definitive set of things to check and confirm this before I have to drop the transmission. 

Any ideas would be appreciated!  thank you, Mark

[DaveB]

There’s a small plate on the front of the bellhousing. If you remove that you might be able to get a borescope in for a look. Or maybe remove the starter and look in through there.
But as you said it sounds like the problem is internal and the transmission will have to come out. Do you get the normal resistance when you press the pedal?

[roymil]

Thanks, I had forgotten about that access plate, hopefully I can sneak a scope in past the fly wheel to get a look.   

I did measure the clutch slave travel at ~25mm and it feels completely normal when pressing the peddle.   I also put a vice grips on the clutch fork and can only move it another 5mm past the point the slave cylinder moves it and can feel the pressure plate springs as I would imagine they should feel like, although I've never done that before so cant be positive.  There were no strange noises or anything.   

It sure feels like the pressure plate is releasing force on the clutch disk, but there is just no question that the transmission is staying locked up to the engine.  If I put it in neutral then everything frees up so there isn't a question of the problem being somewhere else.

So something is binding the flywheel to the pressure plate, and even some pretty forceful rocking of the car back and forth, (while in gear with clutch peddle depressed), doesnt seem to budge it.   

I'm going to spend another day looking for answers and then have to make plans to drop the transmission.

Does anyone know exactly how high I need to get an SL to have room to slide the trany out from underneath?   How tall is it?
thanks

[Benz Dr.]

The 280SL have zero free play between the throw out bearing and the release fork. In other words, the throw out bearing is designed to turn at all times as opposed to the 230SL that only spins when the clutch pedal is depressed. 5 mm free play is far too much which could be a worn out disc. The 280SL is a self adjusting system until it runs out of adjustment.

If you end up having to replace the clutch disc, make sure you have the flywheel ground until the surface is smooth. The stepped surface must be ground the same amount or 19.4 mm. If the surface of your pressure plate shows any wear, hot spots, or cracking, replace it too. Replace the throw out bearing.

[roymil]

Thank you!  This is all starting to make sense now.   

I just had a bore scope up there and was able to watch the pressure plate springs moving so thats not the problem.    I was just assuming a worn out disk would manifest with slipping, not locking, but from what I gathered in reading many posts and BBB today, and then your post I think confirms, a worn out/thin disk could actually prevent the pressure plate from being able to release, resulting in my currently locked up engine/transmission.

I cant find new flywheels anyplace so thanks for the advice on the flywheel grinding, not machine, and I will plan to replace pressure plate, throwout, and pilot bearings. 

[Charles 230SL]

..I also put a vice grips on the clutch fork and can only move it another 5mm past the point the slave cylinder moves it..

I realize it's easier said than done but, were you able to check whether that additional 5mm was enough to release the clutch disc? If not, loosen the lock nut on the slave cylinder and extend the push rod out 5 - 10 mm and see if that's enough for the clutch pedal to release the disc.
I've never had a pressure plate go bad from normal driving - but I have replaced several clutch master cylinders over the years due to leaking seals.

[roymil]

Well, I pulled the clutch last night and found out why it was locked up to the flywheel.  You may not believe this so I took pictures.

The pressure plate looked clean and undamaged.  It came off easily and there is clearly good life left in the pad lining based on thickness, but the clutch pad itself was literally stuck hard to the flywheel.  It did not fall out as the manual warned might happen. I couldn't even pry it out with a sturdy plastic trim removal tool.   I had to get my biggest screw driver and pry it away from the flywheel face.  It finally "peeled" off like it had been glued on. .  So, the clutch was bound to the flywheel no matter what the pressure plate was doing, and believe me, before tearing into this I was pretty forceful rocking the car back and forth while in gear, with the clutch pressed fully in,  just in case I could break loose any corrosion as others had reported success with.

So, Nothing is broken or worn out at all, but it is all contaminated with a thick grease layer!  I mean a layer of that thick stiff black gooey pasty old grease like you would find around a 50yr old differential fill plug.  Very sticky, definitely not oil, even old oil.  I took a couple pictures of the saturated clutch disk where you can see moist beads of sticky black substance (just on the flywheel face) and on the flywheel can be seen a bead of black goo which I could smear with a lot of effort.  On another area I cleaned it off with alcohol to show the contrast.

I have never heard of this and hope some of the experienced folks on the forum might have and idea how it would happen.   I'm not aware of any path for contaminates like that to get into the flywheel housing area.   It's the only place I found grease too.  The rest of the housing and flywheel are pretty clean and there isn't any sign of build up or contaminates at the bottom.

All I can come up with is that this car has a history with grease.   My dad truly believed in maintenance, probably too much.  he would give each zert a pump of grease every time he changed the oil.  there were some nooks and crannys in the suspension arms where I scraped easily 1/2 inch of old grease.  The layer of grease on everything did a wonderful job preserving the car, no rust anywhere, but I'm wondering if somehow, some way, grease made it inside the clutch area.   I just don't see how, but thats all I got.

So I'm cleaning everything up today and then replacing all the usual parts with new ones, but would really like to know if there is something someplace to check for root cause of this? 

I already ordered a new pressure plate and clutch pad from Mercedes Classics, pretty good deal right now BTW, compared to some of the usual suppliers.

While I have it torn down I'd appreciate any advice or ideas of what to check or do while I'm in there.

last one is just another crappy picture of the eclipse that happened just as I was discovering this issue.  Maybe related ;-)
thanks!
Mark

[Charles 230SL]

hmmm, grease from the throw-out bearing or pilot bearing? I believe they're both sealed but one may have leaked and slung out grease   

[DaveB]

That's a strange one. I can't see how grease would get in there. Maybe it's oil leaking from the crankshaft onto the flywheel somehow then getting slung onto the clutch and baked into grease. There are some possible radial stains on the flywheel flange in you first pic but maybe they are just machining marks.
Or could oil leak from the transmission along the input shaft to the clutch?? Anyhow you better find the source before bolting in the new stuff!
The eclipse came far too late to have caused this problem, I suggest it occurred on the last full moon.

[DaveB]

hmmm, grease from the throw-out bearing or pilot bearing? I believe they're both sealed but one may have leaked and slung out grease

There do appear to be stains coming from the pilot bearing…seems unlikely that bearing could contain enough grease to stick the clutch plate though?

[roymil]

I haven't been able to get to the pilot bearing yet.  Those flywheel bolts are tight! and engine turns over when I try to loosen them.  Have to figure a way to lock it down without hurting anything so I can get my big bar on them.   

 I did feel a lot of grease around the outside of the case but I cant figure out how it would have entered, I don't see any vents or passages.