Need some brake bleeding help...

[dieseldan44]

I am trying to bleed the front brakes on my 300D. I just replaced the vac booster. I successfully bench bled the MC and the rear brakes. All was going well.

Went to do the fronts last night and bled the passenger side fine. Went to drivers side and noticed a different bleeder screw. After one open-shut it broke off. To make a long story short, got the whole screw out, went the MB this AM and got a new bleeder screw.

Now when bleeding I cannot get the air out of the dirvers side front. Must have had my assistant pump it 20 times, and more air keeps coming out.

Can someone help walk me through what to do next?

thanks - im getting really frustrated on this car whenever I feel close to getting somewhere something like this happens!

dd

[sokoloff]

Make sure both chambers in the brake fluid reservoir are filled up to the top. When you pour fluid in, only one side fills up and that only serves one axle. You've got to fill that chamber up until the fluid pours over the dam into the other chamber. That's often been the problem when guys have trouble bleeding the brakes.

[dieseldan44]

Originally Posted by sokoloff

Make sure both chambers in the brake fluid reservoir are filled up to the top. When you pour fluid in, only one side fills up and that only serves one axle. You've got to fill that chamber up until the fluid pours over the dam into the other chamber. That's often been the problem when guys have trouble bleeding the brakes.

Thanks -this may be one of m problems.

I have the front wheels off and the front of the car raised while im bleeding, will this make any difference?

[Brian Carlton]

What's your bleed procedure?

I like to put the hose into a jar of fluid. Then, there is no chance of air going back into the system on the pedal upstroke. Also, you don't need to close the bleed screw on the upstroke........making the process a one man operation if you need to.

[dieseldan44]

Brian - thanks for the reply.

Im bleeding according to the Haynes manual's general procedure. My change is I have raised the car and removed the wheels to give me better access.

1.) Bench bleed MC on the bench. I have plugs that I used to do this.
2.) Install onto booster, attach steel lines.
3.) Open one steel line at a time, bleed until no air escapes.
4.) Raise rear, remove wheels.
5.) Open RR bleed valve. Put rubber hose over valve into small bottle of clean fluid. Open screw, push pedal down, close screw, release screw. Repeat until no air escapes. In my case I did ten repetitions to get junky fluid out.
6.) Repeat for LR.
7.) Put rear wheels on lower car, raise front, take front wheels off.
(i was fine to here)
8.) Bleed FR.
9.) Bleed FL.


The bleed screws in my front brakes were cheap aftermarket or generic ones. One of them snapped last night during the bleeding procedure. Got that sorted out and got one new one from MB this am (wish I had gotten two).

Tried the bleeding procedure again, messed up and sucked some air into the system. So, Im back to square one I guess. Ill start over, but do the bench bleed on the car.

Anything seem wrong with my approach?

[Brian Carlton]

Nope, you've got it covered.

There's no assurance that 10 pumps of the pedal will clear the air........usually it does.........but sometimes you might need 15.

Note that the rear chamber of the m/c can't make it for 15 presses of the pedal........it'll run out of fluid and you'll have to start all over again.

[dieseldan44]

Ill try the exercise again today and report back.

[vstech]

yeah, only thing I see wrong with that procedure, is each pedal press, (*maybe every other one...or so,) fill the mc reservoir back up. (both chambers) also, on these older cars with the awesome dual piston fixed calipers, it's not really necessary to pump the pedal. just take the top off the reservoir, and open up the bleed screw, close the bleed screw when the fluid flows clear.
be sure to keep the reservoir full! John

[Brian Carlton]

Originally Posted by vstech

yeah, only thing I see wrong with that procedure, is each pedal press, (*maybe every other one...or so,) fill the mc reservoir back up. (both chambers) also, on these older cars with the awesome dual piston fixed calipers, it's not really necessary to pump the pedal. just take the top off the reservoir, and open up the bleed screw, close the bleed screw when the fluid flows clear.
be sure to keep the reservoir full! John

I'm not convinced that such a procedure will fully clear all air. Since the flow is accomplished with almost no pressure (just the head of the m/c), I have a suspicion that the fluid can pass some air bubbles that might hide at the curves or within the slave cylinder. When the pedal is pressed, the system pressure climbs a bit and the speed of the fluid is increased dramatically, thereby forcing any air bubbles along.

Note that I have not proven this theorem and just don't fully trust it. The EZ-bleed works with a similar principle......with a bit of air pressure........and I'm not all that comfortable with it.

If I could be convinced that it works under all conditions, I'd use it because the risk of damage to the m/c seals is eliminated. I've lost my share of m/c's due to bleeding in the past..........

[vstech]

yeah, you're probably correct Brian, not the best way to bleed the air out, but it works GREAT for bleeding the dirty fluid out, and it is adequate for bleeding just a caliper change. on 4 of my MB's I have replaced calipers, and TOTAL solid pedal, no air "mushiness" at all. I have not tried it with a MC change, that would be more air intrusion to the system, possibly requiring pressure to get out all the air.
John

[Brian Carlton]

Originally Posted by vstech

yeah, you're probably correct Brian, not the best way to bleed the air out, but it works GREAT for bleeding the dirty fluid out, and it is adequate for bleeding just a caliper change. on 4 of my MB's I have replaced calipers, and TOTAL solid pedal, no air "mushiness" at all. I have not tried it with a MC change, that would be more air intrusion to the system, possibly requiring pressure to get out all the air.
John

I'll give it another whirl on a caliper change.

Speaking of caliper changes..........what do you use to plug the hose as a temporary measure while the caliper is off..........I still haven't found anything that works well. Maybe I've got to get a legit golf tee...........

[crashone]

Brian when I did my brakes I used a piece of old hose cut in half to judge the pessure from a pair of long nose vise grips. I piched with just enough pressure to close the hose. With the old hose I could see how much pressure was needed without causing damage. Hope that helps.

[vstech]

well, ... on all of mine, I just let the fluid drip out with the mc sealed, during the swap. I loosened the fitting, got the new caliper ready, and only unhooked the line when the swap was ready to go. then of course, I liberally sprayed brake cleaner on all the undercarriage stuff that got dripped on. I would think even a golf tee would allow drippage, so a fast swap sounded best to me.
then I opened up the mc, opened up the bleed screw, and out came all the air. cool design.
I wish american cars worked this way...
John

[Brian Carlton]

Originally Posted by crashone

Brian when I did my brakes I used a piece of old hose cut in half to judge the pessure from a pair of long nose vise grips. I piched with just enough pressure to close the hose. With the old hose I could see how much pressure was needed without causing damage. Hope that helps.

Don't wish to crush the hose with vice-grips. That's simply an invitation to future problems at that location.

I want to find a golf tee or similar to fit the opening in the fitting.

[Brian Carlton]

Originally Posted by vstech

well, ... on all of mine, I just let the fluid drip out with the mc sealed, during the swap. I loosened the fitting, got the new caliper ready, and only unhooked the line when the swap was ready to go. then of course, I liberally sprayed brake cleaner on all the undercarriage stuff that got dripped on. I would think even a golf tee would allow drippage, so a fast swap sounded best to me.
then I opened up the mc, opened up the bleed screw, and out came all the air. cool design.
I wish american cars worked this way...
John

Naturally, a fast swap is the best. But, I'm going to have the SD apart for awhile and a fast swap is impossible.........especially if you're going to rebuild a caliper. I typically lose all the fluid from the m/c in such situations and I'd really like to avoid it.