I am going to be removing the MC to replace the MC to booster seal on my W123. Ive never done any brake work before...

What is the size of the 'plug' that needs to go into the MC steel line receptacles?

Better have them now than to have to test fit a bunch with paint eating brake fluid spilling everywhere :-)

Thanks,
dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

I got a plastic nipple for bench bleeding at the auto parts store
by begging they donot sell or stock them
but inc then in the new/rebuilt master's
comes with a short plastic line to loop back to the rez
so that should work
no idea the exact size

Ok. In doing this job you WILL spill brake fluid so plan for it. Get a turkey baster ( stealing your wifes is not acceptable, buy a new on e give it to her and then ask for the old one.) Tools you will need are a set of metric flare wrenches. A regular set of metric wrenches. A plastic sheet ( a garbage bag is good ). The new Oring ( which is flat ). Some new brake fluid DOT3.
Consider painting under the booster Master Cylinder (MC) with POR15 or any polyurethane paint for future brake system leaks.
Place the garbage bag under the MC and booster. Tape it in position so it does not move.
Using the turkey baster remove as much of the brake fluid as possible. Disconnect the hard lines with the flare wrenches ( normal threads "lefty lousy") some fluid will drip.
After they are removed, remove the 2 bolts holding the MC to the booster.
Carefully pull the MC away form the booster and try not to spill any brake fluid. ( placing the cover on the MC reservoir is a good idea) remove and replace the Oring. Now I would consider replacing the orings between the MC and the reservoir. They do get old and leak. You of course will need a new set. To do this you slowly rock the reservoir left and right while pulling it up off the MC. Don' be to hard on the plastic reservoir. Then when off insert the new orings and lubricate the orings with brake fluid and press the reservoir back in the way you took it out. Slowly rocking it and pressing into position.
Reinstall the MC with the new Oring and attach the hard lines. I would bleed the system to get any possible air out and to change the fluid out. You should change your brake fluid at least ever 3 years if not sooner.

If you need instructions on bleeding the brakes let us know

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Dave, thank you! Perfect, now to beg for a turkey baster.

dd

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Dave,

I am about to do your above procedure. I am replacing the o-ring as a last ditch since my vac booster is leaking.

Do I need to fill the MC and bleed the brakes to check if the new o-ring allows the booster to hold vacuum?

dd

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car