Clutch bleeding me dry - PeachParts Mercedes-Benz Forum

origamitect · #1 04-09-2006, 10:54 AM

Hi all,
I just replaced my clutch master cylinder yesterday. (was leaking from the bottom) We bled that thing at least 3 different ways twice each, and I have great pedal pressure, but pressing the pedal has no effect.

The three ways we have tried to bleed:
1) traditional two man one at the pedal one at the slave bleeder, topping off the fluid. No result on pedal pressure
2) pushing fluid with a "suction gun" (can suck or push fluid) through the slave bleeder until fluid overflows from reservoir. Good pedal pressure.
3) passenger side brake bleeder to slave bleeder using the brake pedal to push. Still good pedal pressure.

It seems like at least one of those methods should work. After 8 solid hours of bleeding, and a veritable brake fluid bath, I am confounded that I have great clutch pedal pressure, but I can't shift into any gears. Is it possible I blew out my slave in the process? Or am I just missing something dreadfully obvious? Please help! Thanks in advance.

t walgamuth · #2 04-09-2006, 11:07 AM

like it would be very likely. but you could have gotten a bad one from your supplier. not often but it happens.

and you have tried all the ways to bleed that i know of. you must have missed something along the way. they are a b*tch to bleed for sure.

i used the method of forcing the fluid up thru the slave bleeder on my saab 99 many years ago. i used a long clear plastic tube, sucking the fluid up to near my mouth then putting it on the open bleed vavle and blowing it up into the system. i just did this a couple of times and voila, it was bled.

the system is essentially identical on a benz clutch so it would work on them too.

tom w

Ralph69220d · #3 04-09-2006, 11:59 AM

I don't know the percentage of clutch pedal pressure that comes from the pushing of hydraulic fluid in master & slave versus the power of the return spring for the pedal. So, I'm not sure if the hydraulics could not be working at all, but to be fooled by the heavy return spring. As Tom said, it's rare, but occasionally you get a bad unit from the manufacturer or rebuilder. If you had a fitting to close off the tubing that goes to the slave, that would tell you if the master cylinder is good.

origamitect · #4 04-09-2006, 12:19 PM

After the first attempt at bleeding, we loosened the fluid union at the bottom of the clutch master (connects the master --> slave hard line to bottom of master). Fluid oozed out slowly when the pedal was released, but gushed out when the pedal was pressed. Am I correct in thinking this indicates the clutch master is working? I know very little about hydraulics so please explain if this is not the case.

Stevo · #5 04-09-2006, 02:47 PM

[QUOTE=3) passenger side brake bleeder to slave bleeder using the brake pedal to push. Still good pedal pressure.

brake fluid bath,

If you connect the brake & clutch slaves using hose clamps on the hose you wont get a b/f bath. Since they are different size its hard to find hose that fits. Put the box end wrench (7mm on clutch & 9 on the brake slave) on first then the hose. make sure the pedel is up (no spring), Open them both and pump like crazy. If no pedal yet do it again. This is not a diffacult job if you use hose clamps. It is possable that the part is faulty, but I'de want to make sure before I crawled under the dash again, grooon

origamitect · #6 04-09-2006, 03:03 PM

going to buy a slave cyl - it sounds like its possible if the piston is bad there that I'd get pedal pressure but no action. Will do the brake bleeder to slave bleeder bleed + hose clamps. Thanks! BTW - the return spring is not enough on my car to return the pedal by itself.

Stevo · #7 04-09-2006, 03:22 PM

Quote:

Originally Posted by origamitect

BTW - the return spring is not enough on my car to return the pedal by itself.

I think there is no return spring, they will all stay on the floor

On the clamps I use a 1/4" drive socket w/ long extension after several b/f showers ,

73MB280SEL · #8 04-09-2006, 03:57 PM

Howdy,

I replaced my slave cylinder on my W201 190d 2.2 a couple of years ago. On my car, if you pump the clutch pedal vigorously, the master cylinder will self bleed after about 50-100 pumps. I did not have a problem getting the clutch pedal to return prior to bleeding--it just took alot of effort.

Once the master was bled, I finished the bleeding of the slave cylinder by using a reverse bleeder without any problems.

Also: Before I put the new slave cylinder in, I bench bled it so that there was very little air in it when it came time to put it in the car. Ditto for the brake master cylinder and calipers--bench bleed them first and it will make your life easier.

Sholin

janko · #9 04-09-2006, 03:58 PM

clutch hydraulics baffel village idiot

t walgamuth · #10 04-09-2006, 10:03 PM

it should run out on the ground.
if it is the master clutch it wont run out.

or air in the lines.

tom w

origamitect · #11 04-10-2006, 09:00 AM

Well, not really. Pulled the slave (what a PITA!). The front piston seal was completely separated from the piston body.

And the arm that seats onto the clutch spring was completely deformed at the head. I think it was safe to say that puppy wasn't moving any fluid in a meaningful way. Replaced with a new unit, reverse bled with the giant syringe thing (once!) and voila! I can shift again. Its a little stiff, but I think I need to adjust the pedal travel since I replaced the master. Thanks for all your help.

Ken300D · #12 04-10-2006, 11:26 AM

I recently did a master cylinder, slave cylinder and a portion of hyraulic line on my 240D's manual clutch system.

I found the end of the metal rod on the slave cylinder that fits into the transmission was significantly worn away, but the cylinder itself was probably good.

The master cylinder was probably causing the issues that I saw, mainly not being able to fully release the clutch. The interior of the master cylinder had some rust.

After replacing all the components and reverse bleeding with a power bleeder, my clutch returned to operation. However, it was still just about all the way to the floor to release the clutch.

There was a significant improvement overnight, and a further improvement when I parked the car nose downhill the next night. My theory is this allowed bubbles to rise out of the slave and master cylinder that were still in there after the bleeding. Those bubbles really kill the action of a hydraulic system because they are compressible - while the hydraulic fluid is not compressible. There's not much operational margin on this system for the presence of air bubbles. And these air bubbles are hard to completely get out even with reverse power bleeding because the slave cylinder is angled downward slightly at the rear, where the hydraulic line is connected.

So, give the system time to clear some air bubbles, and help the process along by parking the car nose downhill.

Ken300D

dieseldiehard · #13 04-10-2006, 12:25 PM

I have had bubbles in a new clutch master cylinder even after pre-filling with fluid before installation. Makes for no shifting. I finally used a Mityvac and put suction on the slave and with some pumping cleared the air out of it. Its a PITA. Oh! this reminds me

its time to flush the fluid on my 220! This is one of the most overlooked maintenance items on a car with manual trans.

origamitect · #14 04-10-2006, 01:25 PM

Yup - next weekend I'm going to swap out my transmission fluid to the Amsoil ATF that seems to be recommended. Also going to do the diff oil w/ Amsoil. Hoping that will cut down a little on what I think is diff noise. AND! If I'm really energetic I'll do a diesel purge and ALDA cleanout per Diesel Giant's page. Thanks again for everyone's tips. I never could have done most of what has been done to this car without this forum.

t walgamuth · #15 04-10-2006, 06:45 PM

if you have a lot of wear on the linkage parts of the clutch it could be changing your leverage and making the force higher to engage it.

tom w