Replace clutch slave cylinder and bleed clutch - PeachParts Mercedes-Benz Forum

JimmyL · #1 03-09-2008, 12:12 AM

**Taken from one of my other threads. I hope it will aid in future searches**

Well, the reason for replacing the clutch slave was just a horrible hemorrhaging from the seam between the slave and the tranny bell housing. No problems at all with operation.
So, pulled the Squash into the garage and put the front up on ramps

Here is the slave on the passenger side of the tranny. You can see I think where it has been oozing down the side of the tranny. {oil under there too from oil filter housing gasket}

I'm not sure if this is advised, but first I clamped off the line from the brake reservoir.

Next is where I messed up a little bit. I removed both of the 13mm bolts holding the slave to the tranny.

**Notice gasket in between slave and tranny**

What I should have first done is loosen the 12mm fitting to the fitting on top of the slave. Doh! I was still able to get it loose, but it simply would have been better to break that fitting loose while still secured to tranny. Lesson learned.
Here are old and new slave cylinders, along with gasket. There is a rubber seal/bladder in the front of the slave, and the old one looked horrible compared to the new one.

JimmyL · #2 03-09-2008, 12:13 AM

I want to point something out about the gasket. I may be totally wrong about why, but notice there are 2 diagonal channels in the bottom end of the gasket {channels point down}. I believe this is so that if the slave develops a leak it gives the fluid a place to run out and not get all in the bell housing. Maybe not...... ***NOT*** As vox pointed out below it is a gap provided to slide in a tool for checking clutch wear. It just doubles as a runoff......

You can see the marks from this on the tranny bell housing

OK, back in with the new slave

Put your 2 13mm back in and tighten down.
Next took me quite a while, and you could so profoundly screw-the-pooch here if you aren't careful. You have to thread the 12mm fitting back onto the top of the slave. Be so very careful not to cross thread here. I spent almost 15 minutes trying to make sure I got this right. In the end I was a little hesitant to put the wrench to it as I sure couldn't hand tighten it very far, but it worked out fine thank goodness.

NOW, the dreaded clutch bleeding:

After reading about clutch bleeding over the last 4 years I certainly wasn't looking forward to this. I did a bunch of searching this morning on the various ways to go about this.
I thought about using my still-never used pressure bleeder and bleeding from the slave fitting up through to the brake reservoir, but there really isn't any way to control the flow. It is just "on" or not.
So, basically I did pretty much the same thing, only using the right front brake caliper and reverse bled.
Worked well for me.
First I went and bought 3 feet of 3/16 fuel line and some Dot 4 brake fluid. I filled the brake fluid reservoir to full and I removed the clamp on the line from said reservoir that I installed earlier. I attached the 3/16 fuel line to the slave bleed nipple and opened it some.

The thought was to maybe let some fluid run down from the reservoir then connect it to the RF brake caliper bleed nipple. And, that worked pretty well. When I got a little drip I connected to the caliper nipple and opened it up. {Uh, btw, I opened it a little too far and puked brake fluid out during pedal pumping. Just an fyi}

So, just to clarify at this point, the brake fluid reservoir is full,

3/16 hose is attached at the slave cylinder and at the RF brake caliper and both bleed nipples are loose.

Then you simply step into the car, with the hood open and leaned/standing out the driver's door so you can see the line coming into the brake fluid reservoir and pump on the brake pedal and watch for bubbles to start floating up. {Which they did!} Oh, and you do nothing with the clutch pedal during this.
Now, like I said, I first left the RF caliper bleed nipple too loose and it oozed quite a bit of fluid, so I tightened everything back, opened them up a tad and pumped the brakes some more. When no more bubbles came up, but I could tell fluid was entering I tightened both nipples, started the car and prayed it would shift into reverse with out grinding. {I chose reverse in case the car crammed into gear and wanted to "go". Better to shoot off the ramps than over them.

We'll see after I drive it awhile if I have to re-bleed. I'm hoping not.......

vox_incognita · #3 03-09-2008, 07:00 AM

Wonderful !!
The two diagonal channels in the slave cylinder gasket allow you to introduce the clutch wear checking gauge...
amb

15 $$ otherwise....

SW · #4 03-09-2008, 08:36 AM

Nice write up. One thing you should consider is to replace the clutch master at the same time. I replaced the slave on my long gone '81 240D once and within a week or so the master started leaking. I figured the old master just couldnt push the new slave and started leaking.

JimmyL · #5 03-09-2008, 10:08 AM

Quote:

Originally Posted by vox_incognita

Wonderful !!
The two diagonal channels in the slave cylinder gasket allow you to introduce the clutch wear checking gauge...

Doh! I remember reading that somewhere now. Thanks.

Quote:

Originally Posted by SW

Nice write up. One thing you should consider is to replace the clutch master at the same time. I replaced the slave on my long gone '81 240D once and within a week or so the master started leaking. I figured the old master just couldnt push the new slave and started leaking.

I had a master cylinder also and was planning to replace it, but the day was slipping away from me so I rolled the dice. I had them both as I've always heard to replace them as a set. Guess I may want to drive it for awhile without the carpet piece in there, just in case.
Time will tell......

JimmyL · #6 01-10-2012, 12:34 AM

I loved that car!!!!

SD300 · #7 01-13-2012, 04:02 AM

done changing the slave once,
when bleed the system took quite a while to build up pressure, u need patience.
u might think the system is not working!
after re-bleeding for a while the pressure or springyness start to build up, and u have clutch again soon.

My much dreaded job namely clutch master will need changing real soon, this is a 74 240d 115, the master develops leaking.

Beagle · #8 01-13-2012, 07:54 AM

Try this next time............unless you enjoy sufferance??

Quote:

Originally Posted by Beagle

The method of pressure bleeding from the front brake caliper is most unsatisfactory for a number of reasons:
a) You are filling the clutch system with dirty fluid from the caliper.

b) As the front of the slave is inclined upwards on level ground (much worse on ramps) an air bubble is trapped at the front of the cyl. not purged when bleeding and can remain there giving a soft low pedal.

c) This whole procedure is a time consuming P.I.T.A. and was ill conceived in the first place.

There is a much easier and quicker way to R & R and bleed the slave cyl.
1) Remove clutch feed pipe from brake M/C and drain reservoir. Replace feed pipe and refill to max with new fluid.

2) Remove pipe from slave cyl. and cap the pipe end with one of the bleed nipple rubber cups.

3) Undo bolts and remove slave.

To Re-install: (N.B. The slave bleed screw is not loosened at ANY time.)
1) Thoroughly bench-bleed the slave leaving the push rod fully extended. Ensure all bubbles are out and fluid is filled level with the top of the pipe connection.

2) Remove the rubber cup and let at least an egg-cup full of fluid drain down to replace old fluid in clutch M/C. Then replace and tighten the pipe connection.

3) Bolt on the slave. As the piston is pushed back in as you bolt the slave back on any air in the pipe is pushed back through to the M/C and reservoir.

4) Top up the reservoir and you’re done!

The system is self-bleeding anyway but the trick is to get all the air out of the slave piston before installation.

Stevo · #9 01-13-2012, 10:42 AM

Thanks, that sounds good. I have used that brake slave to clutch slave method many times and it is a pain. Last week I tried the oil can method and that was much easier but your method sounds even better.