W202 brake fluid bleed

[DRBC43AMG]

I have done plenty of brake bleeds in several type of "older" cars (Porsche 911, 968, MB W124, etc.) with no problems or hassles.
Changed my discs and pads on the four corners on my C240T and did the classic 2 man bleed method to flush the old fluid and get the new stuff in all the four corners. Some air came out of the front calipers. Tried three separate times but never managed to get a decent hard feeling pedal, despite using nearly 1lt of brake fluid. I finally gave up and drove down to my trusty mechanic who uses the pressure bleed method. He told me there was still air in the system.
Can someone tell me if W202's have to be bled the pressure method only?? What did I do wrong? Perhaps I'll have to do some small investments in the future for a pressure bleed tool.

 

[Alex Crow]

The W202 can be bled 'the old way', although it is not recommended.

Possibly you got air in the rear brake lines, the reservoir for the rear is small, and will only top up once the reservior for the front overflows into it.

So it's easy not to see that it empties quickly, leaving plenty of fluid showing in the chamber of the reservoir beneath the filler cap.....

 

[DRBC43AMG]

Weird, as more air came out of the front brakes than the rear. I'll talk to my mechanic tonight when I get the car back and see if he saw something special.

 

[vijilants]

I presume, you first syringed out any fluid from the resevoir, toped it up with new fluid, and then started bleeding whilst occasionally topping up the fluid ? (Not allowing the resevoir to run dry).

Ive used this method on several cars including my W202 and have never had any issues.

What did make a difference on the pedal hardness on my W202 was when I replaced all four flexible pipes.

 

[Dieselman]

Either you allowed the fluid to get too low, the master cylinder seals are leaking on return or you used an automatic one way bleed valve or air was allowed to enter the calipers after the down stroke.

The best method of manual bleeding is to pressurise the system before the bleed nipple is cracked free, then when the pedal is at the bottom of the stroke, lock off and lift, then re-pressurise before cracking free.
This guarantees a proper bleed and any entrained air will be ejected under pressure.

 

[horgantrevor]

i have had this happen a few times on a w202 but now i use a pressure kit to bleed the brakes now and its perfect every time

rear breaks first then front ones finishing with the one closest to the brake master cylinder


it sounds like the master cylinder fluid level was let go low

 

[DRBC43AMG]

Thanks for all the comments.
Yes I used a syringe to remove a large quantity of the old fluid from the reservoir without getting it empty and checking that the level never gets too low, so in principle no air got in that way. I open the bleed valve only after my "assistant" has pumped fully several times (not too fast) and holds the pressure on the pedal when I open the bleed valve, not releasing until the valve is closed.
My mechanic bled the brakes perfectly now using the pressure kit system. So, I must have stuck out with some bad luck. Hopefully the bleed of my 43 will work out well after I change the brakes soon

 

[DRBC43AMG]

Decided to purchase a pressure bleeder European Bleeder 0100 -- Motive Products Online Store so I should be prepared for future brake bleeds

 

[horgantrevor]

perfect for the job dont over tighten the cover when using the kit just nip it hand tight

 

[DRBC43AMG]

Thanks for the tip