Brake MC replacement today, how? - PeachParts Mercedes-Benz Forum

imagesinthewind · #1 11-06-2010, 01:57 PM

Okay, today mother nature has given me a nice day to do the job of replacing the master cylinder on the 78 SD.

So, whats the best way? Steps? anything I should know?

I plan on suctioning out the res of brake fluid, but then what? Should I loosen the rear brake screws so the fluid begins to drip out?

If the MC plug and play? Take the res off first or take the MC off as a unit?

Thanks for everything!

Ginny

benhogan · #2 11-06-2010, 02:04 PM

plug and play and bleed. each caliper has a bleed screw. bleeding the brakes is a two man (woman) job. one to pump and one to bleed the brake fluid from the calipers.

one big thing to watch for. be careful when you thread in the brass connectors to the new MC. they are very very easy to cross thread. i suggest you thread them in first THEN wiggle the MC onto the two studs.

I assume you have a shop manual to do this?

imagesinthewind · #3 11-06-2010, 02:08 PM

no. no shop manual. But I've done regular brake stuff and all my other repairs without it, so as long as there isn't a special tool, or the need to take the engine out, i'll be fine.

What would you do first? Do I need to remove the res first?

Hit Man X · #4 11-06-2010, 02:21 PM

Not sure about 'plug n play' ... I have always bench bled my MCs prior to install. Infact I am doing one on my SD today and my SDL today.

imagesinthewind · #5 11-06-2010, 02:41 PM

BTW, I am the inventory of the 'Noid, your picture.
I worked for Dominoes pizza in the mid 80s. Like 1983-1986.
My friends and I would call ourselves 'Dominoids' as employees.
The main man, owner of the whole thing, Tom, came to our store
as we were one of the top stores in Ohio and we were in a small
market so they came to find out how we did things.
I told Tom we called ourselves Dominoids and other pizza places should
avoid us 'Noids and three months later there were commercials with that
character in it. It's all me.

Anyway, I am going to take all the brake fluid out of the res; tape, label and remove the vacuum lines, take the entire unit off, put the new unit on, put the new res on, put all vac lines in their places and fill the res. Watch for leaks,and then open and bleed each line to the wheels. I have many helpers for this last part. I'll have one person watching and filling the res as the lines get new fluid, one in the car pressing the brakes and me at each wheel watching for air and new fluid.

Let me know if that's the wrong way to do it.

G

Stretch · #6 11-06-2010, 02:44 PM

Ginny don't forget to read your original thread - I think there was some advice there too!

However, if I were you I'd:-

1) stick the car up on axle stands
2) remove the wheels
3) Find and clean the bleed nipples
4) Get a bit of pipe to fit on the bleed nipples and just open up each nipple

DON'T FORGET / GET CONFUSED about which way is anti-clockwise!

If you snap off a bleed nipple in a caliper because you turned it the wrong way you'll be kicking yourself

5) Let the old fluid drain out - drain it into something that will allow you to safely move the old brake fluid AWAY from your paint work

6) Cover the area around the MC before disconnecting it - protect your paint work

7) Check your old thread for fitting advice

imagesinthewind · #7 11-06-2010, 05:20 PM

Okay, the swap went fine, easy and no problem.
The rear bleeds went fine, no air left and the color of the
fluid changed from pretty dark to kinda honey colored so I think all the old fluid is also out of the two rears. I even took off the wheels to do it so I could inspect the rear brake pads, which are both good.

The front are giving me fits.
I had a vacuum leak, the line that went all the way down to the engine
that came from a Y (went past the resevoir) had come off the engine side and I found it when Angel was pumping and I was adding fluid. I heard a strange sound and found the line was off and put it back. It kept coming off, or sliding nearly off so I put a hose clamp on it to fix that.
PROBLEM: I cannot get any fluid out of the front caliper bleed screws, the pedal goes to the floor and there is an alarm when the pedal is pushed.

What's the problem and how do I fix it?
Thanks!

EDIT: vacuum is not always a problem. If I turn off the car right after the car is started is fails to stop right away. If i allow the car to remain started for a few minutes the car shuts off right away with the key.

I know you're all doing stuff today but if you have any ideas, please let me know. it's now way worse, ie no brakes at all, than it was before I started. I can't figure out why only a few drops of fluid would come out of the two front bleed screws but I can feel air coming in and going out of the screws.

The MC didn't look worn at all from what I could see. i'm starting to think that is wasn't the MC. anyone. thanks.

tangofox007 · #8 11-06-2010, 06:19 PM

You probably allowed the chamber in the fluid reservoir that supplies the front brakes to go dry. The rear chamber (which supplies the front brakes) in the reservoir is hard to see. It fills from "overflow" from the front chamber, so you have to keep the reservoir fairly full.

Did you bench bleed the master cylinder before you installed it?

imagesinthewind · #9 11-06-2010, 06:29 PM

no, no bench bleed.
do I need to start over?

Do I need to take the res off and fill the MC on it's own?

Thanks

tangofox007 · #10 11-06-2010, 06:36 PM

Don't remove the reservoir. Do you have bench bleed fittings/lines?

http://www.youtube.com/watch?v=vOuDEiwiozQ

imagesinthewind · #11 11-06-2010, 06:42 PM

no, I don't have the ability to bench bleed.

how do I get around this? I can't go buy one.

Any ideas about the vacuum thing?

tangofox007 · #12 11-06-2010, 06:47 PM

Quote:

Originally Posted by imagesinthewind

no, I don't have the ability to bench bleed.

Then you may well have a different type of bleeding experience in your future.

imagesinthewind · #13 11-06-2010, 06:53 PM

So should I take off the res, fill the MC though the screw holes?

EDIT: okay, I know everyone has things to do and sitting by their computers in order to help me is not high on the list, so tomorrow I'm going to start over and try to fill the MC with fluid so this doesn't happen again.
I need to get the car running and don't have a bench bleeder.

vstech · #14 11-06-2010, 11:32 PM

bench bleeder is just clear hoses screwed into the line holes, and then you pump so no air can return through the hoses.
if you fill the MC, and loosen the nuts on the lines, let it drip onto the towel you should have under the MC the used MC should bleed itself ok.
I don't know why I didn't think to toss in a set of bench bleeder hoses when I shipped you the MC... sorry.
if you have access to an auto parts store, ask to see a MC, and ask if you can steal the bleed hoses from one.

imagesinthewind · #15 11-06-2010, 11:46 PM

Quote:

Originally Posted by vstech

bench bleeder is just clear hoses screwed into the line holes, and then you pump so no air can return through the hoses.
if you fill the MC, and loosen the nuts on the lines, let it drip onto the towel you should have under the MC the used MC should bleed itself ok.
I don't know why I didn't think to toss in a set of bench bleeder hoses when I shipped you the MC... sorry.
if you have access to an auto parts store, ask to see a MC, and ask if you can steal the bleed hoses from one.

Don't be sorry. You've done a lot for me already!
I'll take the res off, fill the MC and loosen all the line nuts and let them drip, filling the MC as they do, then put the res back on and re-bleed the brake lines.
It should be fine.
Thanks!