Bleeding the clutch slave cyl. without tears! - PeachParts Mercedes-Benz Forum

Beagle · #1 03-10-2010, 11:55 AM

This, of course, only applies to those smart enough to have bought one of these cars with a stick shift!

What MB were thinking mating these 616/7 engines to an A/T box is beyond my ken.

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) The whole procedure is a time consuming P.I.T.A. and you need an assistant.

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-insall:

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 and then tighten pipe connection.
3) As the piston is pushed back as you bolt the slave back on any air in the pipe is pushed back thro the M/C.
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.

Stevo · #2 03-10-2010, 12:20 PM

Quote:

Originally Posted by Beagle

This, of course, only applies to those smart enough to have bought one of these cars with a stick shift!

What MB were thinking mating these 616/7 engines to an A/T box is beyond my ken.

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.

Your brake fluid shouldn't be dirty

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.

Humm that hasn't been a problem for me.

c) The whole procedure is a time consuming P.I.T.A. and you need an assistant.

If you have the hoses, clamps, and wrenches handy its not a bad job and you dont need an assistant except to get you a beer when your done

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-insall:

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 and then tighten pipe connection.
3) As the piston is pushed back as you bolt the slave back on any air in the pipe is pushed back thro the M/C.
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.

Your way to bleed the slave my work fine but your description of the "brake slave method", I dont agree with.

rs899 · #3 03-10-2010, 12:54 PM

I like it....but have you done it? Sounds promising in theory.

How is all the air in the M/C pipe to slave going to escape? Is there enough excess fluid in the fully extended slave to fill that whole length of pipe?

I would like to watch somebody do this on their car...

evb · #4 03-10-2010, 01:00 PM

Sounds like it could work.

But if one didn't want to flush all the contaminated fluid back into the reservoir they could disconnect the hose which goes from the reservoir to the clutch M/C, and allow it to drain into a separate container. They'd need to plug the nipple the hose connects too..

Stevo · #5 03-10-2010, 02:31 PM

The clutch slave is the lowest point in the system (brake/clutch) so many times the bleeder is plugged with crud so I pressure bleed the clutch slave when I change brake fluid. (not to be confused with bleeding air from the system).

Beagle · #6 03-10-2010, 10:14 PM

Quote:

Originally Posted by Stevo

Your brake fluid shouldn't be dirty

Changing the fluid,even if done the day before, does little or nothing to clear the crud that has accumulated over 25 years.

Quote:

Originally Posted by Stevo

The clutch slave is the lowest point in the system (brake/clutch) so many times the bleeder is plugged with crud so I pressure bleed the clutch slave when I change brake fluid. (not to be confused with bleeding air from the system).

Your bleeders will never plug up with crud if you replace the rubber caps!

And when you pressure bleed that crud is going into the slave and M/C.

Quote:

Originally Posted by rs899

I like it....but have you done it? Sounds promising in theory.

How is all the air in the M/C pipe to slave going to escape? Is there enough excess fluid in the fully extended slave to fill that whole length of pipe?

I would like to watch somebody do this on their car...

More than enough as the M/C and pipe are already full as you have capped the pipe end. Any air above the slave self bleeds into the res.

I have been using this method for many years and I can guarantee it works every time having run my car for over 28 years.

Quite simply if you fill the slave before reinstalling it there is no need to bleed at all.

JimmyL · #7 03-11-2010, 12:03 AM

I bled the clutch via the RF caliper and it worked easily the first time. And also was a one man job.
Not taking anything away from your method, though.....

Stevo · #8 03-11-2010, 12:50 AM

The bleeders can plug with crud from the inside as that is the lowest point in the system, but you are right about those caps. The clutch system can be FLUSHED the same as the brakes using the pressure bleeder. (not to be confused with bleeding air out)

I 'll try your slave replacement method as the air should work its way up, but for bleeding I'll stick with the R/F brake slave method.

Beagle · #9 03-11-2010, 01:17 AM

Quote:

Originally Posted by JimmyL

I bled the clutch via the RF caliper and it worked easily the first time. And also was a one man job.
Not taking anything away from your method, though.....

Yeah. you (and Steve) are quite correct it is a one man job! I replaced my first slave over 20 years ago by the caliper method and realized then I was wasting my time. I have replaced the slave 3 times since then - latest only last week which prompted me to write this post. The whole job took just under half an hour but I should admit I do have a pit in my garage!

rs899 · #10 03-11-2010, 06:37 AM

Quote:

How is all the air in the M/C pipe to slave going to escape? Is there enough excess fluid in the fully extended slave to fill that whole length of pipe?

More than enough as the M/C and pipe are already full as you have capped the pipe end. Any air above the slave self bleeds into the res.

OK- I guess I didn't comprehend this the first time. So, when you disconnect the slave at the pipe, some fluid will dribble out. You cap the pipe. Bench bleed the slave. Uncap the pipe. More fluid dribbles out, but that is replaced from the reservoir (?) and from excess in the slave when the piston is pushed home.

I'll give it a try next time ( I hope there is no next time).

I used the caliper to slave method once and it worked like a charm and then another time and I was within an ace of junking the car.

It is nice to have alternate methods. As I said in another post, they should have made hydraulics out of clear materials so we could see what we are doing.

Rick

fruitcakesa · #11 03-11-2010, 07:10 AM

Where was this post when I r&r'd my slave ?

It sounds good but no way in heck am I pulling the slave to bench bleed it now that it is installed.
I stll have to thoroughly bleed my system as the clutch pedal engagement point is so low.

Beagle · #12 03-11-2010, 07:24 AM

Quote:

Originally Posted by rs899

OK- I guess I didn't comprehend this the first time. So, when you disconnect the slave at the pipe, some fluid will dribble out. You cap the pipe. Bench bleed the slave. Uncap the pipe. More fluid dribbles out, but that is replaced from the reservoir (?) and from excess in the slave when the piston is pushed home.

Fluid is pouring out faster than air can rise so very little air enters the pipe and will quickly rise to the res. when you cap the pipe or reconnect to the slave.

Just BTW....................
This method and procedure works equally well on the brake hydraulic circuit.
IE - You can R & R the brake M/C or a caliper without having to open any bleed valves or re-bleed the whole system.

Stevo · #13 03-11-2010, 10:04 AM

Quote:

Originally Posted by Beagle

Just BTW....................
This method and procedure works equally well on the brake hydraulic circuit.
IE - You can R & R the brake M/C or a caliper without having to open any bleed valves or re-bleed the whole system.

The other day a project 240D I'm working on needed a BRAKE master cylinder so I pulled one from one of my parts cars, installed it, then needed my shop for something else and pulled out the project car and the brakes feel fine.

, without bleeding.

i'll try it with a clutch slave next time but I still think its a good idea to know (and have the right tools on hand) how to bleed the system with the brake slave should you do more than a clutch slave.

Beagle · #14 03-11-2010, 11:30 AM

Quote:

Originally Posted by Stevo

The other day a project 240D I'm working on needed a BRAKE master cylinder so I pulled one from one of my parts cars, installed it, then needed my shop for something else and pulled out the project car and the brakes feel fine.

, without bleeding.

i'll try it with a clutch slave next time but I still think its a good idea to know (and have the right tools on hand) how to bleed the system with the brake slave should you do more than a clutch slave.

For a 100% job you needed to push a caliper piston in 2-3mm on both front and one rear wheel to push the bubble in the loop of the pipe into the M/C. But I'm not surprised you got away with it.

Likewise with the caliper, bench bleed and pressure bleed using the caliper piston. Leave the piston on the bleeder side about 6mm out - but I guess you'd figure that

.

I personally prefer to treat the two systems as a separate entity for the reasons I mentioned.

Stevo · #15 03-11-2010, 12:18 PM

[QUOTE=Beagle;2423470]For a 100% job you needed to push a caliper piston in 2-3mm on both front and one rear wheel to push the bubble in the loop of the pipe into the M/C. But I'm not surprised you got away with it.

I'm not sure I got away with it

...yet, I cant drive the car around and see how the brakes are for a couple days, as I have the instrument cluster out, but they feel fine sitting in the shop.

Of course, "push a caliper piston in 2-3mm on both front and one rear wheel" never thought of it that way, I do allot of swapping parts around on manual 240s, I'll try it thanks.

EDIT I should say, I'll try it if you try the RFBC method again with the right tools and accessories