I just finished replacing the rear calipers, pads and rotors on a 1989 420 SEL. I highly recommend flushing those brake lines annually. When I went to bleed the calipers, the fluid was dark grey . By the time I was finished, the fluid was a light yellow colour. I only needed 500 ml of brake fluid. It only took about a hundred pumps with the Mityvac!

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1989 420 SEL

I usually flush my brake fluid once every 2 years. I thought that was normal. What does Mercedes recommend?

My 18-year old 560 had, I'm sure, 18-year old brake fluid in it. No doubt, this led to the damage that required my replacing of all FOUR brake calipers (2 frozen, 2 looked close to it, pitted). The fluid looked like dirty, rusty milk.

After doing some extensive reading on the subject, 5+ year old brake fluid is almost as bad as using water. The boiling point goes down very quickly with just a small % increase of water in the fluid. The stuff (DOT3 and 4, anyway) is extremely hygroscopic and will attract moisture in even a "perfectly sealed" system.

I wore gloves when using my Mityvac to pump my system out - was worried about blisters! But the tool did the job, and it was inexpensive.

PS: The manuals I have say every 2 years, preferrably in the spring. If you can do this yourself, this seems cheaper than calipers.

I just did the brake flush on both MB's 2 weeks ago. I used a pressure bleeder running at 30psi but just barely got the rear calipers to dribble out, even at that pressure. Is there a trick involved? I'm wondering because if I ever have to bleed the lines due to replacement, I'll never be able to clear the air pocket with the rates the fluid was dribbling out.

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1995 E320 -171k-km
1995 S420 -333k-km

It is interesting thast you mention that you only got a dribble out of the rear calipers. There was a point where I too only got a dribble.

When I was bleeding the rear calipers with the Mityvac, at first there was lot of bubbles coming into the jar. Later, at one point I was barely getting anything, then I increased the vacuum to about 25, and slowly but surely the fluid would start moving again, then I got a big burst of bubbles, and then it resumed a normal flow. It seemed like there was blockage that moved as the vacuum increased.

I recommend that you try a Mityvac for bleeding the rear calipers. Alternatively, try the 2 person method.

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1989 420 SEL

"When I was bleeding the rear calipers with the Mityvac, at first there was lot of bubbles coming into the jar. Later, at one point I was barely getting anything, then I increased the vacuum to about 25, and slowly but surely the fluid would start moving again, then I got a big burst of bubbles, and then it resumed a normal flow. It seemed like there was blockage that moved as the vacuum increased."

When vacuum bleeding (as opposed to pressure bleding) it is common for air to come in around the threads of the bleeder valve.
While benign, it can be difficult to distinquish between air in the line, and air that comes in around the valve. The best solution I have found is to remove the bleeder valve, and apply teflon tape on the threads.

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1986 300E 5-Speed 240k mi.

When I rebuilt the front calipers on my 85 W126, I found jelly in them. Fortunately, there was no corrosion or pitting.

Don't want to get into a fight, but if you are applying suction to the brake line, the best you can do is one atmosphere, about 14.7 psi. The pressure method applied to the master cylinder allows more. I had the dial gauge showing 30psi and me constantly pumping once it got to 28psi. Still only a dribble at the rears. Put 4 lire (about a US gallon) through the first line (passenger rear). Saw no air bubbles and the brakes are solid. This happened on both the "S" and the "E". Is there some form of restricter in the system. The car was not level while doing the operation and I'm wondering if the brake system responds to the "not level" position differently. For the life of me, I can't see why though. Who wants partial brakes going down an incline?

Ron

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1995 E320 -171k-km
1995 S420 -333k-km

If you have a two chamber master cylinder make sure both chambers are full .this fooled me one time...........

William Rogers

Tower:

I'm not aware of any restrictor. How old are the brake hoses? The hoses decay from the inside out and could create a restriction.

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1989 420 SEL

Absolutely, I'd swap out all the brake hoses on any 10-year-old-car (I have seven of them, all with new brake hoses). They're like $10-$20 apiece. Spend the money on the right tool and use a pressure bleeder. ...but if you want to use a Mytivac to bleed brakes, remove the bleeder screw and jam one of the conical accessory fittings into the bleeder screw seat. As long as you maintain pressure, air leakage shouldn't be a significant problem

Pressure bleeding is preferred, though, and the Motive bleeder seems to be the tool of choice these days. Shop around and you should find new one for $45...maybe less. I can guarantee it works great on a W123 and W114 MB, Typ 85 Audi and E30 and E24 BMW.

Russ M.