Brake Fluid Change? - Page 2 - PeachParts Mercedes-Benz Forum

mpolli · #16 12-20-2004, 07:43 PM

Quote:

Originally Posted by LarryBible

Yes if you need to BLEED, then more pressure is better. The thread here, though, is talking about FLUSHING. For flushing, 15 or 20 PSI works great. If you have air in the system, then you need to BLEED and you will need to use the two man method or a higher pressure bleeder.

Merry Christmas,

So are you saying that low pressure flushing will introduce air into the system? If that is the case then why would anyone do it? Do you flush and then bleed?? How much do the professional units cost and what about the vacuum type?

DanielW · #17 12-20-2004, 09:06 PM

The idea is to move the fluid fast (w-high pressure) so that any trapped air, which would naturally be at high points in lines and cylinders, will be pushed on out. At a lower pressure (slower fluid speed) the trapped air may be able to stay at the high points and therefore contribute to a soft pedal feel.

OK to flush a perfectly working system with moderate pressure, but if components are replaced or if you have a soft pedal then you need higher bleed pressure to ensure that all air is pushed quickly on out.

I had to have 28-30 lbs even to flush-replace my 95 S420. At lesser pressure it would have been a painfully slow flow at the wheel bleed screws. I suspect there is something in the ABS braking system which requires this much pressure. Older cars w-o ABS may work with lesser pressures. I also remember reading somewhere that some new models may not work at all for the DIYer and require dealer procedure and special equipment.

DanielW

nglitz · #18 12-20-2004, 10:07 PM

And then, there's Mity Vac's version that pressure bleeds backwards, from the caliper bleeders back up to the master cylinder. I think they call it a power-shot or something similar. Their theory is that the ABS and other regulating devices slow down fluid going to the wheels, but allow free return. And, that's the way bubbles naturally travel, so less velocity is needed to sweep the system clean of air. Never tried it myself, but it sounds like a good idea. It might even be do-able with the homemade jobby. I can just see it now, a geyser of brake fluid spouting out of my m/c all over the fenders.

With a simple google search, you can find almost anything. Try it out.

DanielW · #19 12-21-2004, 10:27 AM

info available at http://www.speedbleeder.com , this would allow the high pressure (speed of fluid flow) of the power assisted brake system and a one man job. ( With engine idling so that power assist works.) I have never used them but think they make a lot of logic. One possible difficulty with them might be that the threaded sections must have an effective sealing compound applied. Since when cracked open, air could be pulled in around the threads if there was no compound on the threads. ? Am I thinking correctly ?

DanielW

#20 12-21-2004, 11:43 AM

DanielW,

GREAT POSTS!

I was formulating my answer to mpolli when I read your posts, but I could not have been more clear, or maybe as clear.

What I was trying to say that mpolli did not understand, was that flushing is just pushing fresh fluid through a properly bled system vs. getting air out of a system that had been opened up, or otherwise had air in it.

There is a difference in bleeding and flushing.

Merry Christmas,

pcmaher · #21 12-21-2004, 12:21 PM

Dear Larry,

Can you provide details of how to bleed the brakes on a 95 S600? I've bled brakes in old US cars, but never anything with ABS. I also don't have a reliable assistant to help, so I'm thinking of buying a power flusher kit.

mpolli · #22 12-21-2004, 01:00 PM

Many good options, and the Speedbleeders look very interesting.

Does anyone know exactly how the dealer does it, pressure, vacuum, or some other system?

Mike

#23 12-21-2004, 01:43 PM

pcmaher,

Again, lets define our terminology. Are you talking about BLEEDING brakes, meaning that for whatever reason, there is air that must come out or are you simply talking about FLUSHING a system to put in new fluid and there is currently no air in the system? Flushing is no problem with either a pressure bleeder or the two man method. On your car, however, if there is service work done and air must be removed, there are some specialized considerations that go beyond ABS brakes and have to do with the traction control system.

mpolli,

The service departments use a pressure bleeder. The speedbleeders are wonderful, but if you have as many cars as I do, it would be a considerable expense to equip them all.

Merry Christmas,

ctaylor738 · #24 12-21-2004, 01:44 PM

I bought a Motive power bleeder/flusher off eBay, and I believe I paid $54 or so with S/H. It came with a Mercedes cap, and has worked very well for me.

I also bought a "universal" cap with a chain and screw tensioner and I used that on an XKE.

My only complaint is that there needs to be a swivel connection where the cap meets the hose so that the hose would not twist when you put the cap on.

I have always used 20 psi.

pcmaher · #25 12-21-2004, 01:56 PM

Larry, I'm interested in both flushing and bleeding. I have no issues with my brakes at this time, but I would like to flush the the system in the near future. The ABS and Traction Control spook me...If I ever do need to replace a component, I would like to know how to bleed to remove any air that gets in.

#26 12-21-2004, 03:00 PM

pcmaher,

Okay, I understand. There are some issues with bleeding the high end traction control cars. You should consult the manual unless there is a tech reading the thread that is familiar with your particular system.

Flushing will be no problem, but when you need to bleed air I believe there will be a particular method necessary.

You should also do a search because I remember reading something about this on the forum.

Merry Christmas,

pcmaher · #27 12-21-2004, 03:36 PM

Thanks Larry. Happy Holidays!

Graham · #28 12-21-2004, 03:49 PM

I went through the brake flush bleed procedure recently, when replacing the pads/disks on our '98 E320.

I decide to make bleeder/flusher using a garden sprayer using the instructions available somewhere on-line as a guide. See picture below and for more pictures, see

http://home.cogeco.ca/~photos/Press_Bleed/

I can choose whatever pressure I want. I think that the sprayer can handle 20 or 30 psi. However, I am more comcerned about what pressure teh rubber grommets that hold the brake fluid resevoir can take. If I was using high pressure, I would use some type of device to hold the resevoir to the master cylinder- maybe just tie it down.

In my case, I had no real need to bleed, so I just flushed 2 pints of fluid through teh system - 1 wheel at a time. the old fluid was 100% clean and I could not see when I had flushed , so just used 1/2 pt per wheel.