Bleeding the brakes of a W123
 

When we bought our '85 Calif 300D, I attempted to flush the brake fluid with my pressure bleeder, but was able to move fluid only through the driver's side front caliper. From the other three calipers, I got not a drop. Since the brakes seemed to work fine, I moved on to other projects. A year ago, I replaced the pads on all four corners and again tried to flush the system, with the same results, or lack of results.

Yesterday, when I replaced the master cylinder, which had been leaking, I again tried to flush the system because a little air had been introduced in the changing of the master cylinder. Fortunately, I had bled the master cylinder before installation, or I would have been in serious trouble, because, as before, I could move fluid only out of the driver's side front caliper. I should note that I've blown out all of the bleeder screws, so I know they're clear.

A mechanic I spoke with said that sometimes a pressure bleeder causes air to cavitate, thus defeating the pressure. He said that sometimes he opens the bleeder on the right rear caliper and allows gravity to slowly move the fluid through and the air out. Have any of you ever heard such a suggestion?
I have a MityVac also ... should I give that a try?

Right now, except for a very little air in the system, the brakes work great, better than with the old master cylinder.

Phil

'85 Calif 300D
'84 Euro 300D

Somebody on this board (PEH?), after replacing the fluid in the master cylinder, just opens up the bleed screws and lets it sit overnight to let the old fluid move thru. Sounds simple and effective to me.

..........in less than two hours, the rear reservoir will be totally empty and you will be very :mad:

Ok, leave them open for half an hour.
I could have sworn the post said overnight.

Phil...Bring it over if you want, shops empty. You eather are not giving it enough pressure (I use 15+-lbs) or your hoses are bad. The mity vac is no good for bleeding brakes.

Something is not right if you can't get the fluid out. Either your setup or your lines/calipers have a problem. As long as you have normal brakes you can drive the car. But what damage is occurring and what will it cost to repair.
I have used all the different methods to bleed a W123 body. All work, some are just easier and a one man job. More than likely, since the brakes are working fine, It is internal to the caliper.
First try the tried and true method. Get someone to press on the brake pedal and open the bleed screw. If this works then it is your setup. If not, then try another bleed screw. If the 3 bad units are still bad then!!!!
Try the following.
Disconnect the lines from the master cylinder to the calipers and blow them out with compressed air. Are they clear? if not then try the opposite direction. If they are clear then try the compressed air thru the caliper with the bleed screw open. See if you can get the system to bleed this way.
Note this method will commit you to fixing the brake system. Putting all that air in the system, you will have to bleed the brakes, or replace the faulty part/s.

Dave

Grab a friend, have said friend sit in the car. Now you go around to the calipers, crack the bleed screw and put a clear hose on the bleed screw. Place the end of the hose in a bottle to collect the fluid.


Have your friend pump the pedal as you collect the old fluid, keep pumping until the fluid that comes out is clean.

Start on the right rear wheel, then move to the left rear, then to the right front and then to the left front.

Takes about 45 minutes, inspect the suspension while you are under their and have the wheels off.

I did it in the dark, on the freezing concrete floor, in our small garage, on all four wheels of the 83, with the tires on, worked fine, but was NOT a pleasant experience (very cramped and cold). I didn't spill a single drop, using the power bleeder + tubing from the bleeder screws to the container I had worked great. :D

if i had one that wouldnt bleed
 

i would take a small piece of wire and try to clear the area the bleed valve screws into.

in 40 years of car hobbying i have never failed to be able to bleed the old fashoned way. i have used the power bleeders. i once had one come apart and spray brake fluid all over the front of my most valuable collector car. it also was dripping off the ceiling and light fixtures. i think that about cured me of any desire to ever use a power bleeder again.

you should have seen me scurrying around mopping up and cleaning it off. also it really tastes nasty.

tom w

Get an assistant to help do a two man bleed job and do it with the engine running to take advantage of the booster. You will be able to get fluid to flow then.

Good luck,

I have had success using a Mityvac with a collection reservoir to bleed brakes. Works fine just don't pull too much vacuum or air can be pulled past the piston seals in the calipers/cylinders and enter the system. I find keeping under 15hg is just fine.
The gravity method also works well. I just changed my rear brakes hoses on the 300D. Just installed the new hoses, cracked the bleeders and let it drip for 10-15 minutes. I rapped on the calipers every couple of minutes to break loose any bubbles that may be trapped. Worked great, no problems.
The old standby is two person bleeding. Its important that it is done correctly but it works very well.
If your brakes are not bleeding correctly then you have a problem that should be corrected for safety sake.
RT