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  #1  
Old 07-25-2018, 06:04 PM
E300d 1995
 
Join Date: Jun 2017
Location: Near Lake Texoma
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1995 E300D, Brake fluid flush with pressure attachment at master cylinder cap

I need/plan to replace two front rotors and replace all pads soon. I've read several writeups and watched videos about 'pressure bleeding'.

Question 1: Some people mention a pressure around 29 lbs is required to open & flush the Mercedes ABS mechanism. Is the plastic master cylinder reservoir able to handle this pressure?

2. If not, how to flush the ABS without going to a professional shop?
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Old 07-25-2018, 06:23 PM
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I have a pressure bleeder unit that takes its air pressure from the spare tire , meant to be used at 15 psi but I use less in fact its about 10 psi or less .
It still gets the job done and at a nice slower pace.
I use less because to much can blow the connection at master cylinder if your not carefull and brake fluid will blow everywhere.
Personally I would go the other way and use say a Sealey engine oil vacuum pump and connect to bleed nipple at caliper and pull fluid through.
Not sure if it needs to be done when bleeding but I do put ignition on for abs
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Old 07-25-2018, 07:01 PM
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Personally I’ve never used either. Especially on a 124, the fronts are a snap to do by pumping the pedal a few times. Attach a hose to the bleed nipple, route it to a bottle part filled with fluid, pump until the air is gone.
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Old 07-25-2018, 07:06 PM
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As long as you don't pump the pedal to the floor, that will work. Putting it to the floor puts the piston seals in an area of the cylinder where they usually don't go. May damage the seals (had this happen once a long time ago). Master cylinders don't cost a mint but its a major inconvenience.
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Old 07-25-2018, 07:11 PM
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Won’t happen.
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Old 07-25-2018, 07:37 PM
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Quote:
Originally Posted by Texasgeezer View Post
Question 1: Some people mention a pressure around 29 lbs is required to open & flush the Mercedes ABS mechanism. Is the plastic master cylinder reservoir able to handle this pressure?
The reservoir will hold. If your reservoir has vent caps (black mushrooms), make sure they’re in good shape or brake fluid will spray.

I suppose pumping the pedal is fine for bleeding. For flushing, I find it easier to watch for a steady stream of effluent, rather than pulses, to run clear and not worry about the reservoir running dry.

Sixto
98 E320s sedan and wagon
02 C320 wagon
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Old 07-25-2018, 07:39 PM
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If bleeding the brakes trashes your MC, it was junk anyway. What happens in a panic brake situation? Pedal goes to the floor. ABS kicks on? Pedal goes much lower than usual or to the floor. If using the MC the way it was designed destroys the seal, it was on borrowed time.
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Old 07-25-2018, 09:14 PM
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The Motive pressure bleeder makes the every-two-years brake flush and fill an easy peasy one-person job.

Using suction at the bleeder screws sort of works but you can still suck air in past the bleeder screw threads.

Using the two-person fill and pump method is hazardous to your marriage.
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Old 07-26-2018, 05:16 AM
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Trevor Hadlington
 
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No need to bleed the brakes after rotor and pad change .
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Old 07-26-2018, 11:10 AM
E300d 1995
 
Join Date: Jun 2017
Location: Near Lake Texoma
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Thanks for the comments, especially the warning about spraying brake fluid due to pressure. I'll probably cover the master cylinder with a towel to prevent damage to exterior paint.

I think the only reason not to change fluid along with the rotor and pad would be if the fluid had been changed in the past few months. The non silicone brake fluid is touted to 'suck' moisture out of the air so quickly that it should be changed at least about every two years. It is this corrosive moisture in the fluid that makes me want to flush the ABS unit.

About 58 years ago I started using the pump & bleed method, worked ok but required two people. Then I discovered gravity bleed ( just open all caliper bleeders ) & keep topping up the reservoir with new fluid until they all run clear. That has sufficed in keeping clean fluid in the master cylinder & brake calipers. I'm now more concerned about the ABS mechanism that supposedly can be flushed with a pressure flusher like the Motive. I also like the idea of having pressure on the fluid ( maybe a pressure flow will clean sediment better than gravity flow ).

Any opinions on how to flush ABS mechanism? I'm guessing I've lucked out in the past & never have had any ABS failures due to old fluid. I would like to flush the ABS if the pressure type method will do so or any other method that I can do myself.
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Old 07-26-2018, 04:18 PM
E300d 1995
 
Join Date: Jun 2017
Location: Near Lake Texoma
Posts: 194
I've been searching for more info on pressure bleeding. The following provide possibly useful information.

https://www.benzworld.org/forums/w202-c-class/1395045-photo-diy-brake-bleeding-using-power.html

Further searching has not provided anymore useful information. Will probably search more over the weekend.
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Old 07-26-2018, 05:39 PM
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Again, put a tight fitting plastic hose on the bleed nipple, lead it to a bottle with some fluid in the bottom, and pump and bleed is a simple one man job. You won’t ruin the cylinder, and there’s no advantage to a stream over the pump until clear method.

Why I think pressure bleeding is a bad idea. With a pressure bleed, you pretty much have to force fluid against the piston cups, which IS potentially damaging. You run the risk of spraying paint-removing fluid everywhere if a fitting leaks. You achieve no savings in time or efficiency. You have another clumsy tool to store, and you’d better keep it away from any painted object. But it’s new and cool, that I understand.
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Old 07-26-2018, 07:59 PM
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This is strange I am asking this with all my years of experience, but I have never done the pressure bleed method. Does anybody have a link to a pressure bleeder kit to buy that will do a good job?
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Old 07-26-2018, 08:39 PM
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How things have changed. When I was a kid, we just pumped the brake, opened the pitcock, and let it squirt on the ground until the air bubbles were gone.

But we did use paper straws.
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Old 07-26-2018, 10:38 PM
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Quote:
Originally Posted by MB140300SD View Post
Does anybody have a link to a pressure bleeder kit to buy that will do a good job?
https://www.pelicanparts.com/catalog/shopcart/TOOL/POR_TOOL_BLEEDR-detail.htm

Sixto
98 E320s sedan and wagon
02 C320 wagon
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