if the master cylinder bore is out of round from wear, then the seals do not stop all the fluid ans some escapes past the seal as the pedel is pushed down, the worn spot ( By passes ) and as such the travel needed for the slave to compleatly extend the clutch plate and disengage the disc from the flywheel is not going to happen -- it causes the unit to act as if you only depress the clutch 3/4 of the way -- jz

I realize that. But 3/4 +3/4 push = 1 1/2 push so the slave should operate on two quick pumps.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

That does happen sometimes but its a maybe

and it really dont matter the cylinder bore is an alloy and the piston is normally stainless so wear and seal / seal comes into play

on the back stroke it is causing bubbles it pulls air in to itself from the open end BOOT location and its like soapy water so a solid like you think might happen does not because of the introduction of air - jz

You guys are gonna love this one....

I appreciate any advice, Steve-o, and I never take umbrage when helpful people ask me questions to which I may already know the answer. And it was more careful examination of the "most likely cause" scenario that you were asking about that lead to the solution here.

So my brake fluid resevoir was full to the top, and that was indeed the first thing I checked a week ago. So in prep to really get in there and diagnose the problem, I rechecked the resevoir- still full. But I was bothered by the fact that I couldn't see the fluid level in the clutch resevoir and had to assume it was full without verifying. So expecting to get messy, I cracked the line off the bottom of the clutch resevoir so I could just make sure there was fluid in there, and lo and behold, exactly squat came out of the resevoir and the line was bone dry! Eureka- made me feel stupid, but at least it was going to be an easy fix.

So now you're thinking either "what a dork" or "how was it that the clutch resevoir was dry when the brake resevoir was full? They're connected." Both thoughts that occurred to me immediately, too. So I take a look at the nipple onto which the clutch fluid line attaches, and I'm greeted by... a solid piece of plastic, factory sealed! And then it all comes back to me.....

When I bought the car and was preparing to drive it acorss country, I had to redo pretty much the entire break system, which included replacing the fluid resevoir. Got a new dry one from some boneyard, yanked off the old one, put the new one on, replaced the clutch fluid line on the nipple, then filled with fluid. Hunky-dory, everything works fine.

Until I start having the shifting issues 8 months later, whereupon it occurs to me that the new brake fluid resevoir (which I'd completely forgotten I'd swapped out) almost certainly came off a Benz with an automatic transmission that had no need of clutch fluid. Apparently for some models, Mercedes decided to use the same brake fluid resevoir (i.e., with attached clutch fluid resevoir) for both manual and automatic trans models, but just didn't slice off the end of the plastic clutch fluid nipple for automatics. So assuming that my clutch fluid resevoir was attached to my clutch master cylinder, I've been driving this thing for 8 months with the 8 tablespoons of brake fluid that was left in the line between the resevoir and the master cylinder, and it took those 8 months for the car to develop severe shifting problems.

I sliced off the nipple with a dremel cut-off wheel whereupon the full resevoir began to drain into the line, and voila! the car immediately shifts like I just drove it off the lot. Didn't even have to bleed the lines! Just hope I didn't grind anything important off the transmission in the last week....

Thanks for the suggestions, all of you who offered advice- the MS forum rocks.

randy

Wow, thats a new one on me, glad you got it sorted out.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

That's one hell of a story. Wonder how many hours and how much $$$ it would have cost had you taken it to the dealership with those symptoms.

There is an important lesson to be learned here. MB designed these hydraulic systems with the clutch feeding off the brake master cylinder reservoir higher than the brake feed so that the clutch would fail before the brakes do should the fluid run out. So, if you are loousing fluid and brakes and still want to drive the car home, we now know we could pinch off the clutch master feed line with a pair of vice grips before it takes a gulp of air, and continue to have a functioning clutch without the necessity of functioning brakes.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

yeah, I had the same thought after figuring it out- and it gave me the heebie-jeebies.