I'm about to replace the rear pads so I opened the bleeder valve and compressed the caliper piston back. A good amount of fluid came out but once the piston was all the way in, no more fluid would come out by gravity like they did at the front. Do I need a scan tool to bleed the rears?

 

n/a

 

No, this is the W204 forum. It's for a C300.

 

You need to pressure bleed, I had the same problem after replacing a damaged caliper, I tried every way I could possibly think of, the scan tool had the feature for other cars but not the Mercedes, after a few phone calls, I was told that pressure bleed was the only way.
I was fortunate enough to use a friends machine that ads fluid while pressurising the system, was all done in a matter of minutes.

By the way, if you are only replacing pads you dont need to open the bleed screw, you just have to push the pistons back in.

 

But then you send dirty fluid back into the reservoir which I had just removed and cleaned.

 

Which is now why you have introduced air into the system, so what is worse?, now you need the right equipment to do the job properly.
You could have removed the fluid from the reservoir after the pistons were pushed back, then have someone help you flush / bleed the system as normal, but the way you have done it has now caused more problems than it was worth.

 

it sounds like you don’t know what your doing. Like just said. You possibly caused a lot more problems for yourself for not looking into how to do the repair enough.

 

Haven't introduced any air into the system at all. There are no lines between the reservoir and master cylinder.

 

Check this thread, post #8.

https://mbworld.org/forums/c-class-w...ce-thread.html

Purchase one of those units and pressure bleed the brakes as someone has already suggested.

 

The second you opened the bleed nipple you let air in, even when you pushed the pistons back, you let air in, there is now air in the system and the only way to bleed it properly is to pressure bleed the system.
Just listen to the advice you have been given, we are not typing it just to see the typing?

 

How so? When I pushed the piston back, fluid came out the bleed nipple. How would that let air in and from where?

 

Hi atikovi,
You have successfully completed stage 1, getting the pistons pushed back and bleed nipples closed.
Now install the new pads.

This step is 2 people required.
Top up the brake fluid.
One person pumps the brakes and then holds the brake pedal down - while it is held down you open the nipple bleed fluid out----closed the nipple ----- let the pedal up and repeat this 4to5 times should be enough.
Top up the brake fluid level
Repeat this bleeding procedure on the other side rear brake.

No fancy tools required, no scanner tool required.

 

Already got it done with vac tool but why would you need 2 people doing it your way? Why not just open the nipple and step on the brake a few times? That's how the WIS says to do it.

 

Because air will go back into the system when you release the brake pedal while the bleeder is open.

 

But there are check valves in the master cylinder to prevent that. The WIS says to open the bleeder and pump the pedal. Section 5.1 4th paragraph says the bleeder can remain open during the entire pumping procedure:

 

And what happened when you followed the WIS?

 

So when you cracked the brake nipple, you had a bleed tool connected ?, if not, you would have let air in, unless you are superman and nipped up the bleed nipple the millisecond the fluid stopped flowing.

Still dont understand?, get a straw, dip it in water and put your finger over the end to hold the water, still holding your finger over the end, squeeze the straw to let some water out, now you will see that there is air in the straw, does that make sense?

 

Only If you have a bleed tool connected to the bleed nipple, if you did not have the tool connected when you opened the nipple and pushed the pistons back you would have already introduced air, also if you emptied the reservoir and removed it to clean, when reinstalling and refilling you could have introduced some air and then pumping has moved it further into the system, which will require a pressure bleed.

Just go to your local indy that does European cars and get them to do a pressure flush, as somewhere along the line you have done something not right, we dont know the exact sequence of you attempting your own brakes and can only guess what you have done.

 

Maybe you didn't read the page I posted. Regardless, all done and pedal is firm. I've done the same thing for probably 30 years since cars started having plastic reservoirs. No indy on the planet will bother to clean the reservoir like I always do.

 

Did read your page you posted, Have also been doing my own and customers brakes for over 30 years, never once have I ever cracked a brake nipple to push pistons back, have also cleaned thousands of reservoirs, but have re bled the master cylinder to make sure I have not introduced air.

Remember you came here with the problem, it sounded very amateurish to open the bleed nipple to push pistons back, I for one when hearing what you did and how you did it was glad I didnt drive on any roads anywhere near you, but there is no law against people working on their own cars, except when it contributes to a fatality.

Anyway Im glad you are satisfied with your job now go and enjoy your new firm brake pedal.

 

Then you are doing your customers a disservice and potentially damaging the ABS system by forcing dirty fluid back into the ABS module. I understand not wanting to bother taking the time to do it properly but it could cost your customers in the long run. Most manufacturers suggest doing it as I mentioned and just because you don't, doesn't make it right. Plenty of literature to support this: http://my.cardone.com/techdocs/PT%2012-0001.pdf

 

So you think you have now successfully done your brakes and your a brake mechanic now? lol

The dirty fluid was already there.

 

Hi I am glad you have fixed your car.
You did ask advice and if you don't have very much experience which is what it sounded like to me and please take not offence we all start somewhere or a high level of understanding how the brake master cylinder works with regards to the reservoir port and at what point during the brake pedal/master cylinder piston movement covers the port then please take good advise and follow instructions two people as others said to hold down the pedal until the bleeder is shut stops air entering the brake nipple.

Valves in the master cylinder are not designed for the convenience of bleeding the brakes.

 

that “literature” is full of fail. Here’s a few. First off, if you didn’t open the bleeder this debris or contaminates wouldn’t enter the system as it is a closed system except per say the reservoir, but even the reservoir can be considered outside as the hydronic systems function starts at the master cylinder pistons going back to the caliper bleeder that is closed. Second, and a MAJOR fail, is that literature tells you to pinch the brake hose to keep fluid from going back. I don’t ever remember that being an accepted practice, even if replacing the caliper! That’s called a “hack” and Great way to collapse and damage the brake hose lining and possibly cause a driving concern. About cleaning the reservoir. It makes sense though that is only if you bleed out the system with new fluid with a pressure bleeder which is largely the accepted practice for flushing the brake fluid. Just having new fluid in the reservoir that is cleaned does absolutely nothing if even remotely marginal benefit to the hydrolic system as the fluid “in” the system is still dirty. You need to source repair information from more accurate sources.

I’m not trying to talk you down or be demeaning but you need to try and be more up to date on your info.

 

This is the problem with literature and Utube videos, it makes people think that they are now armed with the knowledge to tackle a task that should really as a legal stand point be left to the experts.

We all know that manufacturer recommendations are made to assist with the servicing dealers making money and has its place with the people who have deep pockets