Bleeding brake woes - PeachParts Mercedes-Benz Forum

earl orchard · #1 09-16-2020, 01:40 PM

Hi all
I just replaced my rotors/ pads/brake lines And installed speed bleeders on my 1992 w124 300d everything Worked fine before I did any of this but I can’t seem to get the air out if the system, I get fluid out of all four wheels, I followed the instructions on the speed bleeders
Which were to open the bleeder 1/4 1/2 open pump the brakes, close the bleeder. Do I need to bleed the master cylinder? If so how do I do this? Do I need to bleed the abs if so how do I do this ?
Thanks
Ken Willmann

Diesel911 · #2 09-16-2020, 02:12 PM

Different year and Model but one of our new members got air into the system because he did not realize there was a wall inside of the mastery cylinder tank that after the fluid reached a certain depth divided the sections of the tank.
He ran one of the sections dry and got air into the system.

If you got air into the Master Cylinder you would need to get it out of the Master Cylinder. However, either way you are going to have to bleed all the way back to the calipers.

I had what I thought was trouble bleeding the brakes which I did many times over a 3 month period and finally decided it was the Master Cylinder. And it was the master cylinder.

On my W123 if you wait the calipers will bleed by way of gravity.

Diesel911 · #3 09-16-2020, 02:26 PM

I had to do a google image search to look at the speed bleeders.

The are a good idea on rebuilt brake calipers that are clean inside but I don't think they valve would seat well if the fluid is dirty/rusty.

earl orchard · #4 09-16-2020, 02:46 PM

My fluid is new and will flow from the calipers but I can’t get a firm pedal, cant seem to find anything on bleeding the abs/master cylinder

imgolden · #5 09-16-2020, 03:12 PM

Hi there, I just bled my 82' 300D brakes for the first time a few months ago, and ran into some issues and wasted a lot of time. Hopefully my mistakes can help you:

-The fluid reservoir needs to be super, super full. I am the one Diesel911 mentioned that didn't realize there is a partition inside that will not fill until it's almost completely full.

-I was using a Mity Vac at each caliper (not speed bleeders), so this may not apply to you, but I could NOT bleed each caliper until I had put a good amount of grease around the base of the bleeding nipple. Only then could I get a good seal. A good way to know if the bleeder screw is leaking air is to look at the bubbles. If they are small and consistent, the air is coming in from the bleeder screw.

Hope that helps.

earl orchard · #6 09-16-2020, 04:12 PM

Yes I saw that thread about the master cylinder needs to be super full and did that and got fluid to come out of the rear brakes i an gonna try the grease trick to see if i can get a better seal, I have a harbor freight vacuum brake bleeder I have been using but I think iam sucking air through the outside of the bleeder screw as it’s real foamy. Getting off work in an hour and gonna start back at it.

imgolden · #7 09-16-2020, 06:01 PM

Quote:

Originally Posted by earl orchard

Yes I saw that thread about the master cylinder needs to be super full and did that and got fluid to come out of the rear brakes i an gonna try the grease trick to see if i can get a better seal, I have a harbor freight vacuum brake bleeder I have been using but I think iam sucking air through the outside of the bleeder screw as it’s real foamy. Getting off work in an hour and gonna start back at it.

That was my exact problem too. I ended up having to use yellow thread tape AND grease.
Thread tape is frowned upon, but it's the only way I could bleed.
Good luck!

Diesel911 · #8 09-16-2020, 08:30 PM

Quote:

Originally Posted by earl orchard

Yes I saw that thread about the master cylinder needs to be super full and did that and got fluid to come out of the rear brakes i an gonna try the grease trick to see if i can get a better seal, I have a harbor freight vacuum brake bleeder I have been using but I think iam sucking air through the outside of the bleeder screw as it’s real foamy. Getting off work in an hour and gonna start back at it.

The pictures on the internet I saw showed that the speedy bleeders had valves in them. I a not sure a vacuum bleeder would displace the valve.

I would assume that the idea of the speedy bleeders is that you install them open one and you should be able start the engine and every time you depress the pedal fluid or air is going to come out and when you release the pedal the valve in the speedy bleeder closes preventing air from being sucked in from that end.
It indeed out to bleed fast that way. Then tighten it and move on to the next caliper and repeat.

Of course you need to keep the master cylinder full.

This site has a gif of the valve action.
Speed Bleeder Main Page

BWhitmore · #9 09-16-2020, 10:56 PM

A good thing to remember about bleeding brakes. Begin the bleeding procedure at the wheel farthest from the master cylinder (right rear), then left rear, right front, and finally left front.

optimusprime · #10 09-17-2020, 06:34 AM

Diesel so you have fitted the speed bleeders .Can i ask what size you sent for i am about to do the same thing .Its a job anyone can do on their own once you have them fitted .. I have the part numbers for mine.And i wonder if yours are the same type .You do need bleeders just for your calipers ,,they are not all the same fit . The taper must marry up to the seat angle on the caliper .May be your problem is the wrong speed bleeders for your car ? only a thought .

Diesel911 · #11 09-17-2020, 01:38 PM

Quote:

Originally Posted by optimusprime

Diesel so you have fitted the speed bleeders .Can i ask what size you sent for i am about to do the same thing .Its a job anyone can do on their own once you have them fitted .. I have the part numbers for mine.And i wonder if yours are the same type .You do need bleeders just for your calipers ,,they are not all the same fit . The taper must marry up to the seat angle on the caliper .May be your problem is the wrong speed bleeders for your car ? only a thought .

No I did not know they existed till I read about them in this thread. Then I did some searching.

At one time in some cheapie tool store I picked up a brake bleeding hose that worked the same way with a valve in it. The caliper end of the hose had a metal collar with fingers to keep the hose tight over the stock bleeder screw.

As I said in the other post you stepped on the brakes and the air or fluid went out the hose end and the valve at that end of the hose closed keeping air from being sucked back into the caliper, the master cylinder refilled when you released the brake pedal and you repeated till done keeping the master cylinder full of fluid.
That is pressure bleeding.

The next time I went to use it the Hose was soft and eaten away by the brake fluid. Again cheapie tool store.

I made a larger catch jar and use vaccum bleeding with my Actron mighty vac type tool.

If some air gets sucked in past the bleeder threads I don't care as long as fluid is coming out I don't care. When I am done I simply remove the hose and wait till fluid starts dripping steadily out of the bleeder screw indicating all the air is out.

Previous to making the catch jar I had also simply let gravity bleed the brakes. Takes a long time but not labor intensive.

Note that I have no idea if the bleed screws on ATE, Bendix, and Girlings are all the same size.

g300d · #12 09-17-2020, 08:18 AM

I replaced all my brake hoses and we got tired trying to get fluid to come out, my indy broke out a Motive power bleeder and that got fluid out of all the lines quick.

earl orchard · #13 09-17-2020, 10:02 AM

Do any of you know if I can rent a motive power bleeder from any of the auto parts stores? I did replace all four brake lines so I imagine I let a lot of air in there. I also gonna try the yellow tape grease thing tonight, by the time I get home from work it’s getting dark and hate trying to do stuff in the dark

Diesel911 · #14 09-17-2020, 01:31 PM

Quote:

Originally Posted by earl orchard

Do any of you know if I can rent a motive power bleeder from any of the auto parts stores? I did replace all four brake lines so I imagine I let a lot of air in there. I also gonna try the yellow tape grease thing tonight, by the time I get home from work it’s getting dark and hate trying to do stuff in the dark

For the power bleeder you would be best off with the special reservoir Cap they sell for that which is not so expensive.

There is I think 2 threads where they say how to make a power brake bleeder from a garden sprayer (like used to spray pesticides or liquid fertilizer).

earl orchard · #15 09-18-2020, 10:14 AM

Hi all
A friend is gonna to let me borrow his pressure bleeder, I am going to use yellow tape on the back bleeders( they seem to be sucking air while the front seem to have a good seal) and grease around the rear bleeders hopefully I will get to it this weekend. I just hope I haven’t ruined my master cylinder. I’ll let you guys know !