MarcusF

I recently did the rear brakes and a fluid change on a CLK430. I own a Motive brake pressure bleeder, but have never been able to get it to work on the CLK.

This is the procedure:

• The cap for the master cylinder reservoir comes off
• Use a MityVac to drain the old brake fluid from the master cylinder reservoir
• Fill the master cylinder reservoir with fresh fluid.
• Dump a liter of brake fluid into the pressure bleeder
• Attach the cap with it's line from the pressure bleeder to the master cylinder reservoir.
• Pump up the pressure bleeder to 20 PSI.

At this point the brake system is pressurized to 20 PSI. When I open a bleeder nipple on the right/rear caliper, the 20 PSI should push the fluid from the lines and the caliper out. It doesn't. When I crack open a bleeder nipple on the CLK it just drips. The same thing happens at every bleeder nipple.

The pressure bleeder works fine on other cars, and will hold pressure while on the CLK, so I don't think the problem is with the bleeder. Since it would take forever to change the fluid using my pressure bleeder, the last two times I changed the fluid I used the "pump - pump - pump - hold" method.

I read something earlier this week that said on a Mercedes-Benz with ASR, a minimum of 2 Bar is required to pressure bleed the brakes.

Here's the question: Has anyone ever pressurized their brake fluid reservoir to 2+ Bar? It's not a problem on my pressure bleeder as it will easily hold 30 PSI. I'm trying to avoid blowing a hole in the master cylinder reservoir and spraying a liter paint eating brake fluid all over myself, the car, the garage, my wife's car, the garage fridge, and well, you get the point.

Thanks in advance

kjb55

I have the exact same bleeder and have used it on numerous vehicles, following the same method that you outlined above. I normally pressurize from 20 to 25 psi. I share your concerns with too much pressure. I would also believe that my C is more or less similar to your CLK.

How about loosening the bleeders more, my C bleeders have deep seats. Also, is your hose connected to the bleeder pulling or pressing the bleeder that would block the flow?

Some bleeding methods detail keeping the pedal depressed approximately 1/2" to 1" (a small block between the pedal and its stop). However, I'm unsure of the reason.

MarcusF

It doesn’t seem to matter how much I turn the bleeders, they still just drip – as if there’s not enough pressure. I’ve had the bleeders so loose that I can rock them in the threads, and it still just dribbles. This also occurs without a hose on the nipple.

The document I read regarding the pressure requirement on an ASR equipped car was in an MBCA technical publication (the name of which escapes me). At any rate, I’m going to assume that they’re correct and test it again with 30 PSI in the near future.

The block under the pedal is a technique used for the “pump and hold” method of bleeding the brakes. If I were to tell my wife to pump the brakes several times and then to hold them, and I opened the bleeder, I believe she would continue to push and the pedal would sink to the bottom. Having the pedal on the floorboard is a bad thing.

The brake master cylinder has a piston that moves back and forth in a bore. A normal wear pattern gets established in that bore. When the piston is allowed to extend past that normal wear area (like when the pedal is on the floorboard), it causes excess wear on the piston seal. This excess wear can result in early replacement of the master cylinder. Putting a block beneath the pedal while bleeding prevents the pedal from extending beyond what’s normal. This prevents the piston in the master cylinder from extending beyond it’s normal wear area.

Although I refer to it as the pump and hold method, that's not exactly what I do. I do a one man method where I run a line from the bleeder to a bleeder bottle. Motive sells bleeder bottles too, but I use another brand. I attach the line, loosen the nipple, pump the brakes (making sure no to let the MC reservoir run dry), and retighten the bleeder nipple. It's something like this:



I prefer the pressure bleeder though.

C240LEE

Try removing one of the bleeders completely to see if it still drips out of the caliper. Maybe the hole is blocked in the bleeder screw.