Never realized there was so much controversy over brake bleeding! Might as well add my fuel to the fire. First, a disclaimer: I have not yet used this procedure on my Mercedes, I've only had it 6 months and the pads are still good, but I haven't had a problem with anything else in the last 15 years. That said, I'm a fan of gravity bleeding. No pumping, just let if flow. The theory is that if the system won't flow well enough to gravity bleed, there is another problem. If I don't get a nice steady drip at each bleeder, I start looking for that problem. I learned this method from a professional mechanic, and it has worked for me.

As always, when in doubt follow your FSM, kids! Just 'cause some hack on the internet says it works for him is no guarantee! (...says some hack on the internet)

__________________
'82 300SD - Somewhere over 220k - Becoming reliable...

yup.
I covered gravity bleeding too. first choice in post #26
it does work.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

We do all of ours with the Mityvac at each bleeder with a catch bottle, a helper behind the wheel to pump the pedal, and a person opening and closing the bleeder. Put pressure on the pedal, open bleeder, close bleeder, release pedal, repeat. Just like vstech said on his #2 on the list.

Works every time for us.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

I'm still a huge fan of the motive, moreso on cars with neglected brake fluid. You can develop a lot of flow with the unit pumped up and a helper stomping on the pedal, which helps to blow chunks of crap out of the system.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Resurrecting a decade old thread because I have the same issue as OP, or a little worse. Brakes won't bleed, at all, at the front. I've tried both vacuum and pressure based (Motive) and can't get a drop out of my new front caliper.
So now I've got new front lines on order in case there's a blockage. If that doesn't fix it, what's the logical next step? Master cylinder?
Also, I'm mainly a Jeep person, though I've also worked on some Porsche (928) and very new VW (never had to touch brakes) and a lot of Japanese stuff. Can't say I remember coming across the little pushbutton pumps on top of the master cylinder. They seem to move... something when pressed. What is the point of them?

(vehicle is an '83 240D)

Why did you change the caliper? Brake hose is closed internally? Possible bleeder passage obstructed. Very rare are but it is something.


Could be rubber in the master is not coming back enough to fill the space ahead of the piston with fluid. The fill port is blocked. That is probably about all the possibilities.


Tests. Loosen front brake line fitting at master. Fluid comes out as master drains down a little. The rear portion of the master. If it does tighten it. loosen brake hose at caliper. Fluid comes out? If not your brake hose is closed internally.

Thanks for the reply, Barry.

I had the whole front suspension apart for refresh (tie rods, ball joints, wheel bearings) and the car has been on stands for a year or so. (Third project car blues.) Before it was raised there were no severe brake issues that we noticed.
Since I was doing the bearings anyway I got new rotors. New rotors+new pads are a tight fit and when pushing back the caliper it was was not wanting to retract even with excessive force.
So I was at a "rebuild or replace" moment with the caliper and they are cheap enough that it was worth my time to replace. Got the new one on just fine, mounted and everything, then it wouldn't bleed. The line also didn't drip when swapping calipers, which was suspect, but I had the cap on at the time and hoped it was just really good vacuum effect (foolish, but such is the folly of a man on a garage floor.) I can see that the new bleeder is clear through (confirmed by dropping it in a bottle of brake fluid and sucking through it with the vacuum tool.) And I am trusting that the new caliper is not clogged, just full of air.

Now I have new lines waiting to go on. I see that there is no allowance for rotation on either fitting of the hose. So do you spin the line on at the body (and tighten it there, with wrench), then spin the caliper around to fasten the hose to that side (finishing with a wrench to tighten of course)?

Just a note about your observation about the line not dripping when switching the caliper over, not a folly at all. It is a common practice on older 911's to hold the brake pedal down ~3/4" with a dowel rod to keep the lines from dripping when you disconnect the caliper. For those who don't know, it is necessary to disconnect the hard line on 911's to pull the calipers to change rotors. I had to do this once and was surprised this method of holding the brake pedal down just a little worked, not a drip came out. I understand it blocks the reservoir port internal to the master cylinder and there is enough "vacuum" created to keep it from dripping.
Given this, I would say if the new hoses don't work, you might want to look inside the master reservoir for crud that might be blocking the port.
Just a thought...

My hose was bad. Opened the line at the master, it weeped. Opened it at the body mount, it weeped.
Got new lines and calipers on. Brake line fitting at body is the only fitting that allows rotation, so get the line on the caliper while it's loose, then tighten at the body side. Looking at it before I took it apart I didn't realize the body-side bracket wasn't all one piece... 40 years of crud build up - it's a brake line with a normal brake line fitting that just slides inside a bracket. But it looked like a monolithic thing when it was gunked up.

useful for the next guy:
11mm brake fittings, 17mm old hose, 14mm new hose, 9mm bleed screw.

Once I got the bad line swapped it bled like any other hydraulic brake system (my god, this thread). I know the hose took the weight of the caliper at least once momentarily while it was apart (due to the random bad luck of a system apart for a year) so I suspect that's what killed it.

Now I need an alignment and to address the dozen other issues it has (hard shifting, no stopping motor, etc etc)

This is an old thread but I'm hoping someone is still out there. I am having this same issue with the front calipers not bleeding on my '83 300d. Replaced the master cylinder and bled the rear brakes the conventional 2 person way. Got to the front, can't get anything, crack open the bleeder and the pedal doesn't move, no fluid flow, my head spinning. I saw that the starter of this thread managed to get theirs to work, I am desperate for help!

Did you replace the hoses?

Post #6. has important information.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

can't spell good does it have propo
rtion valve?

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

There is no isolated proportion valve.

Front / rear split system, the master cylinder is the proportion control.

Majority stopping power is roughly 75% FRONT brakes.

Alert: Brake pedal height is 75% REAR, and stopping power roughly 25% rear brakes.

For Safety: Always bleed front brakes first = 75%, then rear 25% + pedal height.

FYI: Critical functions = STEERING + BRAKES, everything else is inconvenient irritating or frustrating.

Have a great day.

.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

There is a divider wall between the front and back inside of the master brake fluid tank. Sometimes people don't put enough brake fluid in to fill both chambers inside of brake fluid tank.

Remove the bleeder screw and see if the passage inside of the screw is plugged with rust or dirt.

__________________
84 300D, 82 Volvo 244Gl Diesel

Aren’t you supposed to bench bleed before installation?

If you didn’t, you may have trapped air and no ability to force it out.

I use a pressure bleeder. Far superior to two person jobs. It may be the ticket.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)