300D Premature Clutch Master Failure
 

Good news: I found out where my brake fluid is going. Bad news: My clutch master cylinder is leaking.

The car is a federal '83 300D which was converted to manual transmission using a '77 240D as a donor. The conversion was done in 2010 and the master cylinder was replaced at that time. The car has only done 17,000 miles since the conversion. The brand on the master cylinder is FTE.

Should I just slap another one on, or is there something I should be looking at that may be responsible for the failure? The brake master cylinder failed and was replaced a few months ago, in case that may be connected in some way.

I've used FTE without any problems for some time. What I would do is replace the M/S and use a pressure bleeder to bleed the whole system. Bleed the clutch slave just like the brake slaves making sure you run plenty of brake fluid through the system (dot 4). The clutch slave is the lowest point of the system so thats where gunk will collect and most folks with manual trannies never include the clutch when bleeding the hydraulic system. The clutch hydraulic parts from the "77" should be compatible with your car so I would suspect crud in the system.

New master cylinder is on order. I found a local parts house that offers one considerably cheaper than this site. I've never heard of the brand, but that FTE only lasted 17,000 miles, so it would be tough to do worse. I will be flushing and bleeding with fresh DOT4 when I change it. I've changed brake fluid a couple times since the tranny swap, but I never thought to do the clutch part of the system.

Before you replace the master, how is the line that runs from the brake resoivor to the master cylinder? This is typically a cloth covered hose, if its the original one....there's a good chance it is rotted and cracking....thus fluid is leaking down onto the master, causing you to think that is the issue..

Hose is new from the conversion in 2010. I got down and looked. It's leaking from the MC.

New master cylinder is in, but I ran out of daylight before I could get it bled.

Make sure it gets bled with clean fluid, if it gets dirty fluid in there it can cause the seals to go prematurely

Stupid clutch won't bleed.

I tried vacuum bleeding. I sucked out about 100 cc of fluid, but got no clutch pedal. Then I tried the method where you connect the RF caliper to the slave cylinder bleed screw. Then I went to Harbor Freight and got a squeeze oil bottle to push fluid in through the bleed screw. Being a $3 piece of Harbor Freight equipment, all I got was a hand and arm covered in brake fluid. I'll go looking for a real oil can tomorrow. Any idea who sells them?

To push brake fluid up through the system you do need a good squirt can. Since the clutch slave is the lowest point of the system the bleed nipple can get plugged, are you sure its clear? The one in my 79 was plugged when I flushed the system.

I managed to get quite a bit of fluid out when I was trying to vacuum bleed, so it's not plugged, but I am a little unsure how far to unscrew it to get good flow without it leaking around the threads.

Not sure if it matters or not....but the caliper bleeding method worked great for me....I made sure the clutch peddle was pushed down...then I pumped the break peddle slowly.....once the clutch peddle came back up....I knew it was bleed....I also made sure the cap was off the brake fluid reservoir

What I do is remove most of the fluid from the brake master cylinder (turkey baster), put the 7mm box wrench on the clutch slave nipple THEN the squirt can hose, open the nipple till it starts to leak then close it down a little and pump the squirt can and close the nipple. The clutch pedal is up while I do this. That should be it. That should be it for you if you use a good squirt can.

Resolution:

I tried all methods described here. After about six hours total I ran out of time to work on it and needed it back on the road quickly, as I got in a motorcycle wreck and my bike is now missing two turn signals (on order-will be here...) and has a hole in the coolant reservoir (also on order). So I gave up and limped it to a shop. They only charged me a little over 50 bucks, but the manager said they had a hard time with it. Clutch effort with the new MC is higher than with the old one, but not alarmingly so. The car also needs a wash, but that isn't happening today. I also thought I was getting some funny noises I wasn't getting before, but then realized that the driver's floor mat, which is very thick, is still in the trunk, and I still have the old MC rolling around on the floor. Will correct those before I take the car to work.

Glad too hear your back on the road.