The brake hose question is answered by the link in post# 6.

Caliper rebuild:

* If the caliper piston is weeping/leaking = rebuild needed.

* If the piston dust boots are damaged = rebuild needed.

* If a caliper piston is stiff returning = rebuild needed.

* If a caliper piston is seized (not moving) = rebuild needed.

* If the caliper half joint is leaking = The seal rings do NOT come in a rebuild kit..

Danger:
If the brake caliper piston is found to be pitted on the seal surface = it is junk = get a rebuilt caliper..

Also, I am still wondering about a bad booster; braking is very hard, I have to push down real hard to brake car, the stopping power comes when pedal is pushed down hard towards the pedal limit. A light to medium touch on the pedal does not do any braking.

The pedal sensitivity is not there as in my 1993 W124 abs brakes. Is this just how it is on an old 1984 non abs car?

fyi, I read about calipers, so I think they are ok; no leaks or sticking. No leaks or smells.

__________________
1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

609 Certification

Stop, before going to the booster..
What is your vacuum supply reading?

When you say hard pedal:

* Do you mean it feels good/correct with the engine off?

* With the engine running, does the pedal suddenly feel rock hard/very difficult to depress?

Vacuum supply is good at 26-30 going into booster.

Pedal feels ok with engine off, pumps up. Not rock hard but ok when engine is running. When test driving, the braking response is slow, hard towards the end of pedal travel, car goes a few feet before stopping. Have to press down hard to get car to stop.

__________________
1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

609 Certification

Tested at lunch, pedal is feeling better. Has a slight softness that gets harder as you pump with engine/key off. Driveway test braking is a little better.

Three things I plan to do;

1)replace front two rubber brake lines (on principal since never done since I owned the car for 8 years)

2) inspect and clean calipers

3)flush, then rebleed system with quality ATE dot 4 fluid (used Oreilly dot 4 quarts) to save money until bled right.

__________________
1993 Mercedes Benz 300D 2.5 205K (ex wife's)
1984 Mercedes Benz 300SD 320K (SOLD)
2004 Mercedes Benz C240 75K
1995 GMC Sierra 2WD 5.7L 188K
1983 Mercedes Benz 300SD 239K (SOLD)
1987 BMW 325i 220K (SOLD FOR SALVAGE)

609 Certification

The two man method on most MB's is only effective with the engine running.

I have a 1983 and a 1984 300SD and there are TWO CHAMBERS to the master cylinder!

I drained my master cylinder and then added new fluid about half way, then started pumping brake fluid out of my rear calipers, only to drain about 100cc and then only got air after that. The master cylinder LOOKED full, but it was the chamber for the FRONT calipers (the half closest to the brake booster). The master cylinder has an interior wall (separating the two chambers) with a small hole for fluid to flow from one chamber to the other.

There's a smaller chamber (toward the front of the vehicle) that only got filled once I filled the master cylinder to the top (almost spilling out). It seeped down after a second and then I kept filling it to the top until it stopped going back down.

I also found that it's much easier to do the brake fluid flush by putting the car up on ramps, jacking the rear (putting jackstands parallel to where the rear differential is mounted), opening a caliper bleeder, connecting it to my mityvac tube w/reservoir, and then turning the car to ON (NOT START) for the booster to turn on and then just pumping the brake maybe 20 times to get it to fill close to the 80cc. I then used the mityvac to pump a little more.

After I filled the cylinder to the brim and noticed it filling into the front chamber, the rear bleeding went much easier.

This is all factually incorrect for the W-126.

The master cylinder reservoir is divided into two sections............the forward section is for the front calipers and the rear section is for the rear calipers. The forward section is much larger and is the section to which fluid is added.

When the forward section is almost filled to the brim, the fluid will spillover into the rear section.

Accordingly, it is counter-productive to put the car on ramps in the rear. This raises the rear section and makes it that much more difficult to effect the spillover.

I'm not sure where you're getting your info from, but I had bled the rear brakes DRY and the main cylinder which had the fluid (where the cap goes) was still full, and it was the rear half of the cylinder. There are two 'MIN' marks on the cylinder, one for each chamber, one in the front, one in the back, and the front one was DRY (as the rear brake lines were empty). If you take the screen off the hole, you can see there is a wall on the front-end, with a small hole in it. I just changed it this morning and distinctly remember that layout. There may have been a second part to the rear calipers' chamber, closer to the rear of the cylinder, but there most definitely is (at least) part of master cylinder at the front that is blocked off from the main hole until it gets filled to a certain level.


Having the car level on jacks worked just fine for me, and made it that much easier to get under the rear of the car to bleed the calipers without having to take the wheels off. More room to maneuver when the car is 2 feet in the air. There really wasn't a problem getting the cylinder filled once I realized that there were two chambers and I needed to fill it to the top. I'm pretty sure a pro shop would just keep the car level on a hoist when they do their work.

But I think people should be given options on how they want to go about things and figure out what works best for them through trial and error.

It was the front half of the reservoir.



It's your vehicle...........do what you want.

It's our task to prevent others from following erroneous advice...........which is exactly what you posted here.

I may have observed the reservoir incorrectly, but the only 'advice' I gave was to fill it to the top since there are multiple chambers.

Upon closer observation, just now, there seem to be THREE chambers - one for the fluid to flow into (where the cap is), one for the front wheels, one for the rear wheels. The main chamber flows into the other two chambers to fill each of them, and if it's not high enough (and maybe if the vehicle is tilted, etc) then it simply won't go into the other chamber. Maybe the main chamber automatically goes into the front's, and won't go into the back until it's almost full. Maybe that's a safety design so that the front wheels get preferred brake fluid versus the rear wheels, in case fluid is low, etc.

Either way, I do know that there are two walls inside the reservoir, approximately where the brake level sensors are. Maybe it flows more freely into the one designated for the front brakes. All I know from my own legitimate observation was that the rear brakes were dry on my car and also the chamber on the left was dry also. How it's actually routed and what goes to what I don't know, I'm not taking it apart to find out. I do know what I saw, though.




If you look at the picture, you'll see two white lines coming down from the cap to the sides, which is where the chambers are separated from the main chamber.

Maybe what I observed was that the main chamber was half full and the front chamber was empty. Maybe the rear chamber was empty also, I dunno. All I know was that the rear bleeders was getting nothing but air because something in the reservoir wasn't filled all the way.

If you could clarify what erroneous 'advice' I gave, that could harm a vehicle or cause a mistake in a repair, let me know, because as far as I can tell, all I may have given was erroneous 'information', a mixup/confusion/misunderstanding (which section of the reservoir is for what) that either way did not make a difference to how someone remedies the problem (just fill the reservoir), nor could cause damage to a vehicle.

Other than that, I've read probably a half dozen different ways to bleed the brakes and I'm sure all work fine for different people. If you want to comment that my approach isn't gonna work, then fine. I figured I'd share why I spent 2 hours trying to bleed the rear brakes with no success, and what I eventually figured out on my own, which almost nobody else seems to have illuminated upon.

That is the reservoir.

You now have contradicted yourself, as I expected:

You are absolutely correct in that the person who never searched on here as to the layout of that reservoir will certainly get it wrong. The front chamber extends all the way to the rear wall of the reservoir if you look from the left side of the vehicle. This chamber only provides fluid for the front calipers.

If you look from the right side of the vehicle, you will now see the significantly lower level in the rear reservoir that is not filled unless you get spillover from the front reservoir. This reservoir only provides fluid for the rear calipers.

You have edited your post to completely eliminate the previous content and have derailed the continuity.

My last and final statement on the matter is as follows:

The reservoir has two chambers.

The front chamber is directly under the cap.

The rear chamber will not fill until there is spillover from the front chamber.

The front chamber serves the front brakes.

The rear chamber serves the rear brakes.



All of your erroneous statements regarding filling of the rear chamber and "three chambers" are factually incorrect.

You really ought to stop posting on here with information that is erroneous and will lead others to greater mistakes.

Brian,

Honestly, I really don't think the details matter. Fill the fluid to the top.

I was just stating my own repeated observation. Rear brakes were dry, left cavity (where left sensor is in picture) was empty. Front brakes were bled, main cavity (where cap is) was empty, but this did NOT include the area with the left-most sensor (in the provided picture). Took the screen off and saw two walls on the inside, one in the left corner, one in the right bottom corner, immediately surrounding the sensors. I'm sorry, but that's what I saw, I don't particularly think it will change (I'll let you know, though) and I by no means am trying to give people bad advice. Only advice is to fill the fluid to the top.

I'm just saying what I saw. After two experiments and several observations, I'm still wrong. Hey, maybe you're right too, but I don't think I'll notice anything differently tomorrow. Either way, none of it really matters!

I'm not by any means trying to give out bad advice. Just stating my consistent observations. I would just like other readers to consider that either one of us may be wrong. Or we may both be wrong. Or both be right. The logistics of why a problem is happening really doesn't matter if the solution is all the same.

This is where we fundamentally differ.

It absolutely matters to those who read these threads and act on the information that they get.

Accordingly, it's the responsibility of those that post to be concise and accurate and not ramble on about things for which they know nothing about. If you don't know what the hell you are doing, come here and ask for advice. But, don't post factually incorrect information on topics that you barely understand.

The alternative is unacceptable.