How to flush old brake fluid from 1991 560SEL? - PeachParts Mercedes-Benz Forum

HuskyMan · #1 10-20-2016, 06:39 PM

OK, I have the new rotors, pads and brake hoses installed and am ready to bleed the brakes. I'm going to use a pressure bleeder. I going to replace the old brake fluid with Amsoil synthetic DOT4 brake fluid.

I am using a twin chamber brake fluid capture bottle which has a clear hose to catch the old brake fluid. I'm assuming that I perform the bleeding procedure using the following steps:

1. Fill the pressure bleeder with approx 1 litre of new Amsoil DOT4 brake fluid.

2. Pump up the pressure bleeder to approx 10 - 15 PSI then open the bleeder valve starting with the right rear wheel allowing the old brake fluid to bleed out.

3. Keep the bleeder valve open until the fluid runs clear.

Is only one liter of new fluid in the pressure bleeder going to be enough? I'm thinking I'll need to refill the pressure bleeder with another liter of new DOT4 brake fluid for each wheel?

nulu · #2 10-20-2016, 07:38 PM

2 litres would be best

HuskyMan · #3 10-20-2016, 08:35 PM

OK, I'll try two liters. I'm assuming that I simply look for the fluid to go from a dark brown to clear which signifies the new fluid has entered the lines?

Ferdman · #4 10-21-2016, 07:00 AM

Husky Man, I presume you know the proper bleeding sequence is right rear, left rear, right front, left front.

Stretch · #5 10-21-2016, 09:44 AM

Definitely have two litres - the thing that might happen with fitting a pressure bleeder to the reservoir is that the fluid leaks out of the sensors on the top / or the connection to the reservoir.

So be prepared with lots of cloths - pre-wrap the master cylinder area as brake fluid when spilt is an effective paint stripper (strangely when you try to strip paint with brake cleaner it seems to know that you want the paint gone and then it doesn't work! Brake fluid: The first known form of artificial intelligence)

To try and stop this from happening try a low pressure first^^^

If the reservoir caps leak you are probably better off using a vacuum bleeder kit sucking from the bleed screws. This also is not with out problems as air often gets drawn from the side of the bleed screw giving the impression it "still" isn't bled yet.

If you still want to use the power bleeder (but the reservoir cap / sensors leak) you can do "reverse bleeding" by fitting the pressure bleeder to the bleed screw and push fluid up into the reservoir.

Reverse bleeding is advantageous to stubborn lines that don't bleed well like a Mercedes hydraulic clutch as air gets pushed up (which is easier than pulling air down). The disadvantages with pushing fluid "up" is that you need to keep an eye on the level in the reservoir to make sure it doesn't over flow. Also if you haven't pre-drained the muck out of the system (that collects in calipers at the bottom of the system) you end up pushing the crap back up into the system and potentially into the master cylinder causing trouble in the future.

Reverse bleeding is much like those pumps that suck oil out of sumps - the crap gets left behind / remains / hangs about in the system. A good drain is always the best way of removing crud (well a total strip down is even better but not everyone has the time to do that)

HuskyMan · #6 10-21-2016, 03:17 PM

Yes, I know the proper bleeding sequence. I'd rather be at the swimming pool today watching bikinis today but instead I'm getting to screw around with Mr. Big Benz.....the 300D is "little benz".

The next project is to get the suspension ironed out so that it gets back to its normal silky smooth ride. I'm going to be looking at accumulators and front and rear shocks. Fun.

After all this it will be time to burn up some concrete by taking a serious (over 1000 mile) road trip. I mean, what's the use in having a land jet if you don't get out and burn up some highway?

There's been a couple of times out on the freeway that the braking and handling of this bad boy saved my bacon. Seems these semi tractor trucks like to ride your a** at 90+MPH which can involve some quick maneuvering to avoid an accident.

Mercedes Benz Forever, Forever Mercedes Benz. (can you tell I'm an addict???)

optimusprime · #7 10-22-2016, 06:24 AM

Get a set of auto bleed niples .Screw them in to all 4 calipers .Undo them one at a time.Bleed them screw them up .Job done..

Duke2.6 · #8 10-22-2016, 11:13 AM

Quote:

Originally Posted by Ferdman

Husky Man, I presume you know the proper bleeding sequence is right rear, left rear, right front, left front.

That's old school single master cylinder advice, but it wasn't even that good decades ago. With either a split or single system the quickest way to expel old fluid or get new fluid into a dry system from the M/C to the junction block is the shortest route, which is usually left front and left rear for most split systems and left front for single systems. Then go to the next shortest line, and you'll need to make the complete circuit about three times.

But the bottom line is that it doesn't really make much difference where you start. You'll eventually get the system bled and filled.

If manually bleeding be careful not to let the rear reservoir go dry, or you are essentially starting over. On my 201 it's tough to see the rear level, and I think other contemporaneous models are similar. The rear level can only be seen on the inside side, extreme rear of the reservoir.

When the rear res. gets low, fill the res. then wiggle it back and forth to get the fluid over the baffle that separates the front and rear section until the rear level is equal to the front and continue bleeding.

Duke