Theory on why clutch bleed can be difficult
 

I changed out all the hydraulic components on my 240D clutch this weekend, and spent a fruitless afternoon trying to bleed the system. I'm not the first to have this problem, judging from the number of frustrated postings!

I'm familiar with the oil can video, and I was attempting to do a bottom-up bleed with something similar: what I did was drill holes in the lid of a peanut butter jar, mount some barbed fittings in the lid using epoxy, and then hook this up to an air pressure source (a dry garden sprayer, if you're curious). The idea is similar to the oil can: the jar was filled half full of brake fluid, and there was a pickup hose going through the lid such that as air pressure was introduced to the jar it would push fluid out a hose. This hose was connected to the clutch bleed nipple. So, pumping the air pump pushed air into jar, air in jar pushed fluid into clutch system. Or so goes the theory.

In practice, I just couldn't get fluid to go into the system at all! It leaked from the slave cylinder nipple, even after I introduced a hose clamp onto the hose to hold it more securely onto the nipple. It was as if there was something blocking the circuit that should be free going all the up to the reservoir when the clutch pedal is not pressed. I checked the eccentric shaft at the top of the clutch master cylinder; it was set to the position that should push the rod into the cylinder the least.

Finally today it hit me: I recalled that when I bolted the master cylinder into place, I had to force the rod down a little bit to get the the bolt at the end of the rod to line up. I'm guessing that the little bit of movement on the rod closes off the inlet port on the master cylinder so that now the master cylinder barrel and the slave cylinder barrel are a closed system - no place for air or fluid to go!

So, the master cylinder came with two rod lengths. I chose the rod length that I thought most closely matched the one I took out, but I wonder if that was the longer of the two rods... I probably need to try the other, shorter rod length.

Kurt

I would love to hear about the end result of trying a shorter rod.

Ok, this is getting ridiculous... like everybody who has ever tried to bleed a W123 clutch, I'm still having problems. I've got bottom end pressure bleeder setup made from a garden sprayer and a peanut butter jar half-filled with brake fluid. I literally can't force fluid into the system. First I put the shorter master cylinder push rod on in place of the longer one I had originally. When that didn't work I took the rid off completely; still no joy!

In desperation I undid the pressure line connection at the master cylinder - now there is just the slave cylinder and the hard line, and fluid still won't go into it! Is it possible I have a bad slave cylinder?!?

Kurt

Have you made sure the slave bleed nipple is not plugged? Since it is in the lowest part of the system crud can collect there.

I cant understand why you guys have so much trouble. IIRC i first bled a clutch when I was 12 or 13. An old beater on the farm.
Its important to get the MC full of fluid first.
Then with a long piece of clear tube on the slave nipple, that goes into a jar with some fluid in it, loosen the nipple.
Push the peddle to the floor gently & before you release the peddle, have some one tighten the nipple.
Repeat 4 or 5 times.
You will be able to see how much air is still in the system by looking for bubbles in the clear tube.
Once there are little or no bubbles its done.
Often there will still be a little air in the system that will work its way out after a few days of use.

I've always bled the clutch on my 240D from below as a last step when I pressure bleed the brakes.

I think I'll try this externally next time, I have all the pieces out for a 5 speed swap. I could try the slave alone, to see if something wrong with the newer bleed screws or something, then work my way up adding components to the system, until I find whatever is blocking it.

When you do as you describe you are flushing the clutch system, not "bleeding" air out. That is if I understand, you have the pressure bleeder pressurizing the brake reservoir then open the clutch bleeder.

Are you saying you bleed the clutch just like the brakes? You haven't bleed an MB system down on the farm, it doesn't work like that. You must go from the bottom up to get the air out.

You can go from the bottom up with brakes as well if you wish.
Unless a MB clutch has some unique system & looking at the FSM it dont. You can bleed as you please.

I must concur with the bottom up method...I tried for days to do bleed normally and also with a vacuum on the bottom. It just isn’t possible in these MB systems to get it all out via a normal bleeding process. Though it was possible to build clutch pressure, I needed to bleed from the bottom up [pressured] to get ALL the bubbles out.

Alas, bleeding is difficult...for that reason many people just choose to neglect the system. Have a look at this(last page describes the procedure):

http://www.vintagetest.net/chassis/enis73/V2I736040.pdf

Maybe is does work from the top down where you are, I've heard hurricanes rotate in the "other" direction as does water going down the drain plus you folks are upside down as proven by looking at a map of the earth. Therefor "from the bottom up" to us would be from the top down to you.:D There, problem solved, we are both right.

Correct, the pressure bleeder is on the reservoir just like it is for the brakes. I have seen/felt no downside to my doing it this way. Clutch still feels fine afterwards and the clutch bleeder screw always produces the dirtiest fluid of them all. I don't think I would want to push that dirty fluid back up into the reservoir? Does not the pressure force out any air if there was some just as with the brakes?

In this thread Beagle describes a different approach:

http://www.peachparts.com/shopforum/diesel-discussion/273153-bleeding-clutch-slave-cyl-without-tears.html

Another by Beagle:
http://www.peachparts.com/shopforum/2495520-post8.html

You Tuve Video:
BMW, VW, Porsche Clutch Bleeding - YouTube

This is a single post from 2003, where Autozen describes the oil can method:
http://www.peachparts.com/shopforum/487380-post19.html

Single post:
http://www.peachparts.com/shopforum/2785439-post21.html

This is from Numbercruncher in the UK:
http://www.peachparts.com/shopforum/2496827-post17.html

Another method by Dirtkurt:
http://www.peachparts.com/shopforum/2785514-post22.html

I remember seeing these brake fluid pumps when I was a kid, think every gas station had one.

OK, last one.:rolleyes:

This is from the famous Jimmyl, a good pictorial:
http://www.peachparts.com/shopforum/diesel-discussion/215891-replace-clutch-slave-cylinder-bleed-clutch.html

When doing the Factory method as outlined in the FSM, going from the R/F brake caliper to the Slave cylinder, to first power flush the brake system and the clutch to blow out any and all contaminates.

Maybe first use your wife`s Turkey baseter to suck out as much of the old fluid first. :D

When I swapped the 4-spd into our 85 300D, I power flushed the clutch with my Motive. I blew enouth fluid through it, there couldn`t possibly be any air in the system. still no clutch.

Used the FSM method, still nothing.

Used the oil can method, still nothing.

Even tried to gravity bleed it, but nothing would drip out.:confused: I read where Gavin Leslie did this, and all was good.

Finally out of frustration, had my wife pump the clutch peddle, hold, open slave bleeder a few times, and it worked. what the.... :confused:
although the peddle was down lower that I would have liked it, it worked and if it works, don`t further mess with it. :rolleyes:

Since then I removed the transmission etc..... and am back to the bleeding problem. that was 19 months ago and the car has sat since then. but since the 240 drives..................... do need to flush the 240, so need to get at least one working back up car.

Charlie

Flushing the clutch system along with the brakes is a good idea and probably hardly ever gets done. I found my clutch slave bleed nipple completely plugged when I did my 79 a few years ago. This procedure is not to be confused with clutch "bleeding". If you have air in the system flushing wont get rid of it.

I almost spilt my coffee reading this. :D

Charlie

Well, I've progressed a little... it turns out that it takes quite a bit of pressure to push fluid up into the system. There is only a tiny orifice in the bleeder, and you also have to pressurize against the weight of the column of fluid that you're pushing uphill. The upshot is that my peanut butter jar reservoir just simply wasn't up to the task, and air was leaking around the rim.

So, I invested the time to find a suitable oil can (originally, I couldn't find one with a small enough tip to fit over the same tubing that goes over the bleed nipple). Now, with the oil can I can see that fluid is able to enter the system. I'm taking a break right now from pumping; the squeezing gets hard!

By the way, I also taped the bleeder screw with Teflon tape, as I saw suggested on an earlier thread.

Kurt

[QUOTE=

Since then I removed the transmission etc..... and am back to the bleeding problem. that was 19 months ago and the car has sat since then. but since the 240 drives..................... do need to flush the 240, so need to get at least one working back up car.

Charlie[/QUOTE]

I cant believe your having so much trouble. Something must be amiss somewhere. Did you check to see your slave nipple was clear? When you push fluid up directly from the slave up through to the master then to the reservoir what can go wrong? You might over flow the reservoir if your not careful but I cant see where there can be a problem. Theres no pumping the brake pedal or different sizes hoses to deal with. If your system is in order the oil can method is simple and should be fool proof.:confused:

Oh yah, Finding a suitable oil squirt can does present a problem. The HF one I tried first was a joke.

The system was working just fine, only had 22K miles on it, and decided to swap in a different transmission. get it it all bled and working. after driving it for a while realise there is a bearing in 3rd gear (or seem like it is) so decide to swap in the first one. then the shaft wouldn`t line up with the clutch, I pushed and beat one the damn thing. had it out to see what was wrong, back in and more beating and pushing etc...was getting late so closed up shop for the night.

Next morning decide to remove PP and clutch. remove it and pilot bearing fell out. so guess it dropped out when I removed the trans. then put clutch back in and hear the Disk rattling.:confused: had 2 broken springs, the 2 large one`s of the 6. order a new one and button things back up.

Now this time around, the clutch just won`t bleed. the slave and MC were new 22K miles befor and also bled ok about 2 monthts before when swappin in the second trans..

I just got to the point, I`ll get to it later, and threw a tarp over the car.

I now have the 617 FW to install, so back to pulling the trans etc...

Since summer is back and either get it going or plant flowers in it for a yard ornament. :D.

I bought one of those HF pump oil cans, maybe that`s my problem, need to blame it on something.

Charlie

Well, I think I finally got it bled, with the oil can method. It seemed to take about six ounces to fill and bleed a totally dry system, if anyone is interested.

I'll pass along another tip: I marked the eccentric nut at the top of master cylinder piston so that when it was shortest the side facing the viewer in the footwell showed a zero. Then the two faces on either side of that nut face were marked 1, etc. That way I could tell easily when the piston was at its shortest adjustment point.

Kurt

Kurt

And Charlie: when I'm down in July I would help you with your bleeding or install!

Kurt

The best way I have found to bleed up through the slave is to use the brake pedal by connecting a tight fiitting hose from the closest front brake bleeder to the clutch slave.

Stevo,
I thought you believed the world was flat !!!:P
Just remember that we are so far in front here that we have done the days work before you guys even get to waking up! :D
I have never had to bleed a clutch bottom up. not even when I lived on your side of the pond.
Always put the slave & MC back in pre-filled with fluid. If you press the slave back right in, the volume of fluid in it displaced is often more than the volume needed in the line.
An old dodge truck a friend had needed the MC internals to be filled with a syringe as the hole from the reservoir was so small.
Good luck with your bleeding!!!;)

I know the worlds not flat because I've been out there and haven't fallen off the edge, However its still a mystery why people below 40 or 50N dont fall off .:D

Yes, pre filling the slave and MS is the way to go but you should still be able to bleed the system should your brake fluid get low and she takes a gulp of air.

Kurt, be looking for you.:) the 240 should make the trip now.

Charlie

W123 clutch master slave bleed
 

I read it on this forum I think
Beat my brains out until i did this, then, instant success.

run clear plastic tube from RF wheel bleed nipple to clutch slave bleed nipple. Make sure that tube is full of fluid. Speed bleeder on RF bleed nipple is good too.

you must use a small hose clamp on both ends. Those clamps are manditory.

open both nipples, slowly depress the brake pedal several times. You will hear the fluid bubbles rising thru the system pushing fluid back to the reservoir. Clearly bubbles are not driven to the bottom of the circuit easily, but do rise back to the reservoir.

Instant success

Honestly, I think the OP didn't bench bleed his MC (unless I missed it).

Also, curious necropost. What lead you to revive this thread? I always wonder when I see an old thread reappear.

Lots of old threads pop up when you search the entire WWW for "W123 clutch master slave bleed" not using the board's search function. I assume people reply without regard to or even taking not of the date(s) of the previous posts.