240D. Slave and master are not leaking, replaced slave anyway since I couldn't see internal.

Same issues. Press in clutch, can shift through all gears, in and out, hold in clutch as long as I want, no issues.

As soon as I let out clutch, car is stuck in gear and pedal will go to floor and stay there.

Thought I may have a hydraulic issue so oil can back flushed from slave until just fluid was coming out of brake master (which it did right off, no bubbles, but I did a pint of brake fluid anyway). No change.

Went back in with a good flashlight and looked all over clutch master, no leakage, and I haven't been losing any brake fluid.

What's left?? Seems really odd that it's fine holding clutch down, going through gears while standing, repeating as many times as I care, but first actual engagement it's tits up. Wild things like pressure plates are going through my mind but never had one do this.

Help!!!

__________________
Eric, CPO, Submarines, retired.
Here's a sig line...
Mine: '68 Corvette LS1/4L65E, 83 240D, 2000 GMC 4x4, 08 FLSTC Anniv
Hers: '72 Corvette 454/4spd, '99 MB SLK, '93 Metro vert, 78 240D, '92 Silverado, '65 Fjord Rustang, '59 Fjord Fairlane, '17 Slingshot.

1) With the engine off, can you repeatedly move the clutch pedal through its full release/engage stroke, and feel what would be considered normal resistance?
2) Again, with the engine off, can you place the gearbox in any gear, and be able to release the clutch such that the car can be rolled?
3) Is it possible that the pressure plate diaphragm spring has become very weak, and is being overridden by the pedal overcenter spring when the pedal is down?

Yes to all. With engine on or off. Issue only occurs when clutch pedal is let up in gear, then it has no resistance for a re-engagement and car has to be stalled to stop movement. I can let it up in gear with engine off and no issue, I have to actually let it up in gear with engine running for the issue to happen. Oddest darn thing.

Only thing I do note, is that when I re-oil can reverse bled the clutch again a few mins ago and the bleed screw 'leaks'. Even just off shut, it drips, so when I'm pressurizing I'm dripping out of there too. Don't know if it can get air in there while I'm reversebleeding, seems to be a constant outflow until I shut bleeder again.

__________________
Eric, CPO, Submarines, retired.
Here's a sig line...
Mine: '68 Corvette LS1/4L65E, 83 240D, 2000 GMC 4x4, 08 FLSTC Anniv
Hers: '72 Corvette 454/4spd, '99 MB SLK, '93 Metro vert, 78 240D, '92 Silverado, '65 Fjord Rustang, '59 Fjord Fairlane, '17 Slingshot.

Consider this a rather long-shot possibility: the gearbox input shaft bearing and/or bearing retainer has considerable fore/aft play; the drive gear-thrust is forward when under load, moving the input shaft into contact with the pilot bearing, locking the input shaft to the engine, and carrying the release bearing forward against the fingers of the pressure plate, hence, a dead pedal.

How about a history of the car? It is not listed in your signature (Yowzers! A "water buffalo"?) Have you ever driven the car or did you inherit this problem?

Time to pull the transmission out I am afraid. Could be anything from a seized throw-out bearing (doubtful), scored/broken input housing, seized pilot bearing, shredded pressure plate "fingers", trashed internals, etc., etc.

Never mind, I see the 240D listed. The history would still be helpful.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Pull the tranny and see what's going on with the throwout bearing and such.

I had a problem years ago on my 82 240d. The car wouldn't disengage the clutch. Up to then it hadn't slipped. I did the slave and master cyl replacement. Still no clutch disengagement.

Kind of the opposite of your problem.

I pulled the tranny. The throwout bearing was gone. The clutch still had meat but the little coil springs had broken and were bouncing around in the bell housing.

So I say pull it. It's a light unit and easy to get out. Find out what is going on in there.

Forgot to mention, I recall a problem on a Lexus where a swollen brake line would inflate under pressure and move the brake calipers but then collapse down again after the master cylinder would release pressure. This would seal in some residual pressure in the caliper and drag the brakes. I vaguely recall a rubber hose on my clutch. Just a longshot, maybe you can crack the line and look in the hose before dropping the trans.

Nah. This doesn't make sense. I thought the clutch pedal not popping up was the clue. I cannot recall what pops the slave cylinder back. Is it the clutch spring or is there a coil spring in the slave? May be a good idea to start taking things apart in steps and checking.

Good luck.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

A swollen hose could certainly trap fluid in the slave, which would keep it from returning to normal height. But why only when the gear is engaged? How do you get the gear to disengage?

Seems likely that there's some problem with the clutch fouling the throwout bearing. In gear, there's stress on the mainshaft bearing, which may be failing.

The clutch pedal does have a spring IIRC. When its stuck in the down position can you bring it back up with your foot or does that not have any effect? The leaking bleeder screw on the slave sounds like its also a cause of your issues.

Operation of the hydraulic clutch system should be the same regardless of whether or not the engine is running. It's also the same whether you're just pumping the petal and not selecting gears or moving between gears.

Perhaps you have an issue internally within the master. Where for example it allows you pressurize the system with the initial push of the pedal, but cannot maintain a seal on the release stroke of the master.

The situation is odd as you experience no feeling of pressure leak down in the system while the clutch is depressed the first time.

I had the issue on my 240d where the push rod on the slave actually wore a hole through the clutch fork at 304,000 miles. I had some clutch disengagement when the rod would catch on the fork then eventually clutch would stay to the floor.

I'd probably replace the master and the line with the rubber portion before pulling the trans.

__________________
--------------------------------------------
Old Blue - 83 240D 6 speed manual trans, OM648
Green Machine - 2001 Europa G500
87 300SDL Bought on Peachparts. Low-ish miles..?

Family Truckster - 2012 VW Touareg TDI

Patchouli Wagon - 2004 E500 - SOLD
333k mile 97 BMW 750il V12. - SOLD
The Californian - 85 300TD - SOLD
Daily Super Sedan - 03 Audi S8 -SOLD

Thanks for all the inputs.

History. Have had this one several years, no issues. Guess is about 400k miles but previous owners changed out instrument consoles (I found 3 in the trunk), likely due to the famous odo issues on these cars.

We let the car sit for about a year as I had a pretty big brain tumor, surgery/recovery were a long time.

Pulled it out and it started right up, but pedal would 'sometimes' stick on floor. Did a pressure bleed up but no real change. Problem continued to get worse over about 200 miles.

Finally it went to failure after every release, even after a few more squirt can pressure bleeds. I replaced the slave pretty much from a 'toss parts at it', as I couldn't find any evidence of leak. No change in behavior.

Master is completely dry, as is the one rubber line (which is unpressurized fill line from reservoir to m/c). Pulled the rubber bellows off master and also dry in there.

Agree that the running behavior should match the engine off behavior. Letting the clutch up in gear running or not should yield the 'stuck to the floor issue' but it doesn't. Only happens when running. This indicates what folks have said about internal issue with fork/pressure plate/throwout.

Anyone have an idea of transmission weight? I have the car up on lift so access is easy, but wondering if I need a transmission jack for it.

__________________
Eric, CPO, Submarines, retired.
Here's a sig line...
Mine: '68 Corvette LS1/4L65E, 83 240D, 2000 GMC 4x4, 08 FLSTC Anniv
Hers: '72 Corvette 454/4spd, '99 MB SLK, '93 Metro vert, 78 240D, '92 Silverado, '65 Fjord Rustang, '59 Fjord Fairlane, '17 Slingshot.

The aluminum case one is light. My guess is around 100 lbs.

But I'd still use a jack.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Just curious, when you say "stuck in gear", is it the same gear or does the transmission actually switch gears (1st, reverse, etc.)?

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Before you pull the transmission, remove the clutch fan unless you are using an engine cradle to support the engine. This will eliminate the possibility of interference between the fan blades and the shroud/radiator fins.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

The Getrag (aluminum case from a 240D) 4 speed in my Mutt the Race Truck only weighs about 60 lbs. I was amazed at how light it was so I actually weighed it.

As I'm not using the Mercedes clutch master my system is pretty different from yours so I can only guess but somehow I'm thinking it has something to do with the shared master cylinder reservoir for the clutch master. When the engine starts so does the vacuum that acts on the brake master and I wonder if it's moving the brake master piston a bit and "steeling" fluid from the clutch. If you have a GoPro or some such you could take a vid of the master cylinder reservoir at start-up and see what you see. SOMETHING is changing when you start the engine and that's the point where the clutch system and a running/not running engine come together. It's a WAG, for sure.

Also, there IS a flexible line at the bottom of the bell housing that allows the engine to rock. I replaced mine with braided stainless w/teflon core but functionally it's the same. Remember, the master is hooked to the body and the clutch slave is hooked to the engine/trans assembly and engines DO move when under load so they have to allow for that. Still, it doesn't make sense that the hose condition would change as a result of starting the engine.

Dan

I didn't test properly so brought in a bit of a red herring.

When engine is running, clutch is released slowly and going on and off lift isn't released all the way.

With engine not running, I just dumped the clutch in gear and wasn't releasing slowly or part way.

So...treating the non-started engine just like I was driving the car, the same problem occurs. Let up on clutch slowly, and it'll come halfway up, and if I make believe I'm approaching the lift (a little clutch up and then down again), it's all the way stuck on the floor, engine off.

The clutch does act the same, running or not, it was just the loose nut behind the wheel not testing the same.

I mentioned that it became worse over 200 miles, it became even worse after replacing slave, as it's now every single instance. I can't really say that was cause and effect because it had degraded so much it was almost as bad pre-slave change. I pulled new clutch slave today and checked for shaft leak (since I can't see that). None, but I pulled the shaft out and it was shorter than my original shaft. I swapped the shaft thinking I had found a problem but nope...no change.

I'm putting in a new master today just...because it's easier than pulling a trans and I have one on the shelf, I have a lift trans jack on order, my old one is a floor style, not good for 5.5 feet in the air.

It's 'acting' like hydraulics, so I'm a bit stumped still even with the good suggestions. I'll check the rubber line as well but as the poster mentioned, odd that a rubber line would give good feel then and then fade after engagement.

Oh, and for the gent that noticed the suzuki kettle, I need to update my sig. I went a bit bonkers after surviving a dicey surgery and now have 3 kettles, a GT550, GT250, and a C5 Vette .

__________________
Eric, CPO, Submarines, retired.
Here's a sig line...
Mine: '68 Corvette LS1/4L65E, 83 240D, 2000 GMC 4x4, 08 FLSTC Anniv
Hers: '72 Corvette 454/4spd, '99 MB SLK, '93 Metro vert, 78 240D, '92 Silverado, '65 Fjord Rustang, '59 Fjord Fairlane, '17 Slingshot.