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After a nightmare trip to France, where my brake fluid was leaking from a corroded brake pipe and I had to get the car trailered back (I live near London), I had a quote to replace my brake pipes from Mercedes.
So I decided to not pay the £2950 quid and try myself.
I've replaced all the pipes and all the brake hoses, bleed the system 4 times, both manually and from a pressure bleed kit (20 psi) and unfortunately I'm left with a strange brake pedal.
Nothing seems to happen for a couple of inches and then it feels weak but works. (I can get the abs activating etc).
After reading loads of threads I decided to replace brake master cylinder (£250 quid), bleed the entire system twice more to find -- it made no difference.
Any advice on what I'm doing wrong, or suggestions to try I would greatly appreciate it.
I'd like to know how you replaced the brake lines, my rear passenger side is looking like I should replace it.
I have only done the regular brake line bleeding with a pressure bleeder so dont have much experience.
When i was reading some of the instructions I noticed it mentions depressing the brake pedal as the system is being bleed if work was done to the brake system. Mentions this for 6 piston brakes but I dont see why it wouldnt apply for them all.
Thank you for the replies. its greatly appreciated.
I tried bleeding the brakes again today, but at 30psi (2 bar) and pumping the brake pedal slowly whilst the bleed nipple was undone.
I started at the passenger rear then Drivers Rear, passenger front, Drivers front.
Some bubbles were seen on the rear passenger. Everywhere else seemed fine.
Glad to say that after the 2 inches of pedal travel, the brakes do feel more confident. Thank you for the advice !!!
I'm not quite sure what I can do about the 2 inches of travel before the brakes start to work. - any suggestions ?
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TimC300 - changing the brake pipes was awkward but okay. Both front flexy hoses had to be chopped.
I spoke to Mercedes (cheeky I know) and they now have a joiner/coupler inline with the brake pipe going over the diff. The joiner is located under the plastic cover that's under the drivers side sill. It makes that run easier.
I used the rusty steel brake pipe as a guide for the new 90/10 Cu/Ni 4.75mm brake pipe. Bend it by hand and tape together as you go.
Its bubble flares for the pipe connections to the hoses and abs module. I used a single flare tool backwards (see youtube). It was quite easy once you had a few practices.
The only "dodgy" think I did was use a collet style coupler on the drivers side brake pipe. The brake pipe runs behind the engine, under the windscreen wipers. I tried to replace the whole pipe initially but its beyond my skills/patience.
I used this collet coupler because flaring a steel pipe is very tricky with hand tools. I removed the plastic coating and made sure that I protected the bare steel afterwards.
I'm purely speculating since I dont have that much experience with brake systems, but reading up on the subject it may seem air is in the abs. I've come across many threads on all types of vehicles where someone had a squishy brake pedal after they had there master cylinder run dry of fluid.
I think my Foxwell scanner has an option to run the abs pump.
Another option I have been seeing is drive on a gravel road fast and keep braking hard so the abs activates. Then bleed the brake lines again.
This is all stuff i've read, no idea if it really works.
I read online that the engine needs to be running during the bleeding procedure.
So:
30psi pressure bleed.
Start engine
Release the brake nipple on the caliper you are doing.
Press and release brake pedal.
Allow at last 0.5litres, ideally more through each caliper. (I did used 3 litres of brake fluid in the end !!!)
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by Ads_C350
Hi TimC300 and all.
Finally, success - I have a pedal !!!!
I read online that the engine needs to be running during the bleeding procedure.
So:
30psi pressure bleed.
Start engine
Release the brake nipple on the caliper you are doing.
Press and release brake pedal.
Allow at last 0.5litres, ideally more through each caliper. (I did used 3 litres of brake fluid in the end !!!)
Pedal is back !!!!
Thanks to all that replied, especially TimC300.
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Good find. I have never had the engine running when bleeding the brakes, but I have not replaced brake lines either. It makes sense since the brake vacuum is electromechanically operated by the vacuum pump, usually on the back of the engine near the master cylinder. But when normally bleeding the brakes, the positive pressure from the fluid pump is sufficient to force the fluid through the lines.
Do you have a link where you read that? I'm curious to read when to do that. I know according to the WIS, bleeding the brakes procedures make no mention of having the engine running.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Searching the internet as to whether the engine should be running or not, the answers are mixed. Some say yes, some say it doesn't matter, others say definitely not. If bleeding works with the engine off, I would keep doing it that way. Older Mercedes with SBC brake systems should only be bled following published procedures, which require activating the bleed procedure through a bi-directional scanner like XENTRY. SBC is very dangerous if you don't know what you are doing.
So soft pedal because air was in the brake system. That is true.
I also never ran the engine while bleeding brakes. With power bleeder + 15psi pressure, I just pay attention to the pressure and the fluid level after each wheel’s bleed.
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Brake Pedal - C350
