brake bleeder users vs old school
 

i've got a few questions:
1.with the power bleeders:do they suck out the fluid(ala topsider oilvacs) or push the fluid out of the bleed screws at each wheel
2.regardless of wether they suck or push,doesn't the master cylinder become dry and if it does is that a bad thing
3.if you go the gravity method do you have the key in the ignition to activate the pressure.hold on i guess the answer is no-that's why it's the gravity method.right?
4.my master cylinder appears to have two compartments- a forward and an aft one(why is that?).the front seems to be full yet the aft looks empty or real low.
5.why doesn't the front compartment leak into the rear to equalize the two?
i know i've asked alot and hopefully they're valid questions and will help others out as well so don't worry if you don't know all the answers,just comment on what you do know or have experienced.thanks everybody:) :) :) :)

1.with the power bleeders:do they suck out the fluid(ala topsider oilvacs) or push the fluid out of the bleed screws at each wheel

Normally you start by sucking out as much old stuff as possible, with whatever is clean and handy. A small turkey baster works good. Then top the resevoir with fresh fluid. The actual bleeding part pushes the fluid through the lines and out the bleeder whether doing a pressure or gravity bleed.

2.regardless of wether they suck or push,doesn't the master cylinder become dry and if it does is that a bad thing

Yes and yes again. When bleeding the brakes you have to make sure the resevoir does not run dry. If it does you are then pumping air in the system - exactly what you don't want to do. If pressure bleeding make sure the tank has plenty of fresh fluid before starting the next wheel. If manually pumping the brake then top off the resevior every second or third crack of the bleeder screw.

3.if you go the gravity method do you have the key in the ignition to activate the pressure.hold on i guess the answer is no-that's why it's the gravity method.right?

Correct. However some ABS systems won't gravity bleed worth a darn.

4.my master cylinder appears to have two compartments- a forward and an aft one(why is that?).the front seems to be full yet the aft looks empty or real low.

Actually I believe the resevoir has three chambers. Yes the rear ones will go dry on you when you aren't looking closely. The fluid only transfers from the front chamber when the fluid is at MAX level, just pour the fluid in very slowly while keeping an eye on the rear chambers, you'll see when they are full.

5.why doesn't the front compartment leak into the rear to equalize the two?

See above answer.

Hope this helps.

thanks for your time and efforts,mike.i had hoped to hear from some of the gurus that frequent this site but maybe it was too much of a post.thanks for all your help again,martin

Martin-

You have....Tangas is a great mechanic, and likely could be a successful full-time tech if he weren't chasing bad guys!

Perhaps he has more b@lls than brains, that Tangas-did you see the W126 job he tackled?:D

As to the topic, I've worked on auto & aircraft hydraulics for 15+ years, and I can add nothing to Tangas' post...very thorough. Perhaps this is why none of the full-time techs responded-nothing to add either?

Mikes response was right on. The only thing I would add is that I bought a pressure bleeder mail order from an ad in the Star magazine. It has a hand pump, a pressure guage, a vessel and an adapter for the MB master cylinder cap.

With this gizmo, you fill it with brake fluid, connect it to the master cylinder and pump it up. It maintains pressure AND it supplies fresh fluid as you bleed. This way you don't have to worry about letting the reservoir get low.

As Mike said, it's good to get a head start by emptying as much of the nasty stuff out of the reservoir before beginning the procedure.

My gizmo works great and I don't have to enlist help. Now that my son is off to college and my daughter has discovered boys and working and, of course, my wife never seems to be available to help with this chore, my one man solution is very convenient.

I can't remember the name of the gizmo, but it cost about $55 and was worth every penney. It is advertised in the Star.

Good luck,

i used my Ace Hardware (home brew) pressure bleeder for the first time last week. worked great except it was leaking a little bit at the pressure cap / valve stem fitting. i had even sealed around it with permatex right stuff. oh well - you get what you pay for...

down on bended knee,mike
 

iapologize mike if it seemed i wasn't thankful or sincere in my reply.by gurus i meant moderators or whatever they are who run the tech section.i must admit i don't know much about you other than when you've replied to posts that i also subscribed,in which your replies seemed always helpful.it seems your held in high regard by the others and i'm sure there is good reason.i'm just glad you were there for me.thankyou!:) ;) :)

No apology necessary as I am kinda thick skinned. In this internet world it's hard to know who's who or who knows what and I understand.

Once you've been here at the "Shop" a while longer you will find there are a few people here who only work on cars for fun and who are only one step below the Mercedes trained technicians in skill level. You will begin to trust their word too - those are the guys I look up to. Michael and Larry - Thanks :).

You might find that by reading as many of the posts as possible, rather than just subscribed posts, you will learn much, much more about your own car, even if the post doesn't pertain to your specific model. There are a lot of shared parts and equipment and a perticular problem may manifest itself in one model, and you can evaluate your problem or relate your experience to the problem model at hand.

As for pressure bleeders, they are great, I built my own for very little $$$. Try a search on "pressure bleeder" posted by "dlswinford", you'll find plans for your own. Great tool, load it with a quart of brake fluid, that coupled with the full resevoir of fresh fluid, you should have enough to bleed all four brakes with some left over.

Joe, if you are getting leaking at the valve stem on the resevoir cap, try easing off on the pressure a little, maybe 12 PSI.

Daddiojiggy,

Do you remember a guy named Newton? Remove the reservoir, empty it, and clean it thoroughly. Fill both compartments with fresh fluid, and open each bleed screw slightly until clean clear fluid comes through. You will almost always see bubbles, but that isn't air in the system. It is air being syphoned in by the open bleed screw. This won't work with drum brakes, but always works with discs. Some cars require a sequence of calipers, but not MB. The law of gravity is very simple, and no trial lawyers are needed. You can buy a bleeder if you are compelled to, but gravity has worked for me as a professional mechanic for three decades. Also, the reason for a split reservoir is safety. The front brakes on MB cars have been historically been supplied by the rear chamber, and the front chamber supplies the rear brakes. If you loose all the fluid in one circuit for some reason, you still have brakes in the front or back.

Good luck,
Peter