Soft Brakes on W115 - PeachParts Mercedes-Benz Forum

purplecomputer · #1 02-21-2022, 05:31 PM

Hey guys,

Currently in the process of "restoring" an 72 220D w115. I've gone ahead and redid the entire brake system

* replaced all rubber brakes lines
* replaced all calipers
* replaced pads and rotors
* replaced Master cylinder
* ran new steel lines for front driver an passenger (left alone the rear steel lines)

I have bled and bled and bled. Started at the master, worked my way down to the back of the car. Even got one of those mighty vac clones from HF (the $12 one) I still have soft squishy brakes. I get fluid in all tires and its new because I was previously getting some very dark fluid initially.

I vaguely remember when I had my W123, it was something with the vacuum pump, but is there any way to test that before I take that thing apart. I remember it being a PIA to get all back together.

Anything else I can check?

Should I also start a thread on my progress(?)

Sugar Bear · #2 02-21-2022, 05:56 PM

How was the pedal before this work?

The master cylinder should be bench bled, installed and then each wheel starting with the farthest from the master working back toward the master sequentially. I prefer pressure bleeding vs vacuum bleeding as vacuum at the bleeder screws can pull air in past the threads.

Good luck!!!

purplecomputer · #3 02-21-2022, 10:50 PM

Quote:

Originally Posted by Sugar Bear

How was the pedal before this work?

The master cylinder should be bench bled, installed and then each wheel starting with the farthest from the master working back toward the master sequentially. I prefer pressure bleeding vs vacuum bleeding as vacuum at the bleeder screws can pull air in past the threads.

Good luck!!!

Pedal on the car was also horrendous when I got it. I assumed if I just replaced everything, which was probably a good idea in the long run anyway, it probably would have gotten fixed.

Let me look into pressure bleeding and see if thats something that can help

Sugar Bear · #4 02-21-2022, 10:59 PM

Good call on replacing everything due to its age. A Motive Bleeder, has worked well for many years. I bleed the farthest wheel first. Some build a pressure bleeder out of a hardware store pump liquid sprayer.

Good luck!!!

purplecomputer · #5 02-28-2022, 12:14 PM

Quote:

Originally Posted by Sugar Bear

Good call on replacing everything due to its age. A Motive Bleeder, has worked well for many years. I bleed the farthest wheel first. Some build a pressure bleeder out of a hardware store pump liquid sprayer.

Good luck!!!

wasnt able to find a pressure bleeder locally, so I picked up one of these

I thought I was doing something wrong as nothing but air was coming out, making a distinct gurgling sound, so after a while of making sure things were clogged, etc I just let it run as said "heck it"

after a while, I started to see fluid in the bleed hose. Did this process for all four wheels. Effectively, I flushed the whole system. There was a large amount of debris in the lines and the fluid was black

Once I was confident I had bled the lines I tested it. It was good for the first 10 seconds, but then the brakes went soft again.

I bled the rear again and there was a large amount of air. Check the front, and not as much air.

My theory, the T fitting connecting the rear wheels must have a leak, or the steel line from the master cylinder to the T in the rear might also have a hole sucking in air.

Sugar Bear · #6 02-28-2022, 02:19 PM

Confirm 100% for certain that the REAR section of the master cylinder fluid reservoir is full and stays full throughout the bleeding process. There is a small dam in the reservoir that overflows slower than the pressure bleeder pushes it out. This is a common issue that lets air back in.

Good luck!!!

purplecomputer · #7 04-11-2022, 09:23 AM

I bled this thing another time before going on vacation and I was pulling in fresh fluid on all corners and didnt see any air.

I tried to think back about my old W123 and decided that I should probably inspect the Vaccum pump. I ordered all the parts Just in case I needed them. Since I dont have a proper tool to test the vaccum (and if I did, I just dont know how to use it, because I am not a very smart man)

Pulled the pump yesterday; someone was recently in there and everything was brand new. I should probably just replace everything with the new stuff I got, but the only thing Im thinking is the check valves were reversed?

I should probably buy a repair manual at this point :^p

vwnate1 · #8 04-13-2022, 10:02 AM

Have you checked the length of the M/C push rod ? .

If it's too long it will slightly hold the M/C piston in a bit and cause just this problem .

I personally prefer the hand pump typ of pressure bleeder, I've seen too much pressure added too many times .

indybenz · #9 04-13-2022, 01:48 PM

This might sound stupid, but did you mount the rear calipers with the bleed valve at the top or the bottom? They can go on either way (at least on the W123) and I did this recently. Air is trapped in there and I bled and bled and bled after replacing everything, as you have...and then I realized the calipers had been mounted upside down/left on the right and right on the left. Hope this helps.

indybenz · #10 04-13-2022, 01:58 PM

Here is a picture of them on the wrong sides

purplecomputer · #11 04-19-2022, 04:41 AM

Quick Update:

my FIL came to visit so I finally had an extra set of hands so we can just bleed the lines old school style.

There was still air in the lines that these "one man" tools just couldnt get out.

Took it for a test drive and its working superb

Good thing I guess, I did rebuild the vaccum pump and everything brake related is brand new and ready to go. I also flushed the whole system so I now have 100% brand new fluid through the whole system.