Hi. Sorry for interrupting but I have a question about the ABS unit. What will happen if A valve is stuck open? Then the same sensation will be like a soft brake pedal because fluide will escape through that valve. Also when a wheel speed sensor is bad, the car thinks that the wheel is keeping blocking and the ABS releases the pressure and the pedal feels soft during it. I ask because I have an e91 and my car stops in waves like the road it's uneven.

yeah. unless Gareth is sick. I thought he looked healthy at his old weight.

Make sure you also look into the recall Mercedes has issued for the X164 and V251 brake boosters! You may be entitled to a dealer fix, and it's a high-priority one.

@@danny_playswithcars Thanks for letting me know about that. I thought I saw something about that online. But Mercedes didn't send me a letter. I'm in Canada so maybe it's just the US? I'll look into it further. Thanks

@@cuzimadapapushkian799 Yes, it is an open recall for US market specifically though I'm not sure about up North. I'd definitely recommend contacting your local dealer to give it a shot and verify whether or not you may be covered. The issue stems from corrosion around the booster, so it's possible you're experiencing a similar failure to the cars seeing issues down here. For reference and if it's helpful, our NHTSA ID in the US is "22V315" and may have helpful info for you. Regardless of the cause, best of luck tracking down your issue!

@@danny_playswithcars Thanks so much for all that info Danny. I really appreciate it.

Remove the plastic panel forward of the left rear tire. Give that hard line a good inspection. The line on my 164 popped in that spot, pedal went right to the floor.

Thank you kindly.

That is a common one on the 8P generation and others - Good luck on finding the cause of your lean condition.

I’m trouble shooting the same problem on my A3 8P. I purchased the car last year and since purchasing the brake pedal never felt 100%, more like 80%. 1. The brake booster itself had a leak so I replaced it. You could hear the leak from inside the cabin. 2. I bled the brakes with two people, one person pumping and the other loosening and tightening. 3. Recently I replaced the rear calipers because the pistons weren’t retracting freely. 4. I performed a brake bleed using the Motive bleeder and VCDS. Followed by the traditional bleed method but only by myself, not two people. During the first start up and 30min drive the brakes felt solid, 100%. When driving back home the pedal felt soft again. I will check for a vacuum leak at the hose but I’m thinking the soft pedal is due to air still in the system or damaged seals in the master cylinder.

Check the calliper pins,if they re stuck, then it will brake only on one pad,not both. Check to see if the brake bads are worn evenly,if they re not its the calliper pins. If this is not the case, then check the ABS unit

You DO need to bench bleed the master cylinder before you install it. Google it. And here's the wub....a slowly sinking to the floor brake pedal is always the master cylinder..it's the only place where fluid leaks around the seals don't actually show up on the floor. If a seal leaks on a slave cylinder, you'll get fluid on the floor.

It's subtle, but ..... if you have air in the system, the pedal force will still have some increasing force with travel relationship. But if you have a leak internal to the MC, the pedal will slowly sink down under a constant force. If you make one quick, spike apply, and the travel is short - that is also a sign of an internal leak.

Hey where you able to solve your issue? I just replaced a MC on a 2000 m5 after a soft pedal and it was okay for about 30 mins of driving on the way back home it felt as if fluid leaked and I had the soft pedal again. Checked for leaks and saw nothing. I will bleed system again tomorrow but I’m not sure what’s the issue is. I’m thinking possibly abs problem?

I have not. The E38 is not my daily driver so I am not driving it much because of the silly brake issue. Really want my brakes to be like they used to be.....am actually considering taking it to a local Indy....which is weird for me since I've done EVERYTHING on this car since getting it in 2008. My current theory is something is wrong with the pre-charge pump or the ABS block...somewhere fluid is getting past a check-valve or something. I'm not sure if the ABS block or pre-charge pump has rubber seals that could have failed or not. @@imOmar909

I'm not familiar with that exact ABS unit, but often times you need a specific procedure to bleed an ABS. In the factory, there is a special program to cycle the solenoid valves on and off. But sometimes, ABS units are 'prefilled', to avoid that need. May be worth checking in your case.

@@gregreed2713 I've used VIDA (Volvo's factory diagnostics and service software) to cycle the ABS unit's pump and solenoids while bleeding, no change unfortunately. Perhaps it's just a stubborn pocket of air trapped in a high point in the hard lines. There's one section that I'm suspecting that crosses from one side of the tunnel to the other over the top of the driveshaft/exhaust just aft of the front subframe. I'm going to give it another go with my Motive pressure bleeder and the key in pos. II so the aux vacuum pump can provide assist to the booster, that way I can get a ton of pressure behind it and hopefully blast that pocket down and through to the caliper. I have decent stopping power (probably more the fact that they're upgraded factory Brembos) but the pedal just isn't there - it feels like I stepping on stack of kitchen sponges where braking effect only starts occurring in the second half of the pedal's travel. A recent bit of work on someone else's car (unrelated to brakes) that required me to do a post-work test drive made me jealous of the pedal feel... it was a Pontiac Vibe! :/ Appreciate the suggestion all the same!

@xyphur did you ever figure it out I have the same issue out of no where after some spirited driving my pedal when soft as well. Exactly like in this video. Replaced the master and fixed it for a second but my problem was intermittent anyways but now o started my car up and the soft pedal is back.

Are your brake pads worn evenly? If not then it may be from something else

@@alinnimeni3789 yes, they're evenly worn. This issue was present from the time the pads were installed new into freshly rebuilt calipers. It was also present before the caliper rebuild, so it isn't related to the rebuild either. Part of me is convinced that it's partially to blame on the pads themselves just having poor initial bite and requiring way more effort to achieve a given amount of friction... They are Akebono 'performance' ceramic pads. I'm not impressed with them aside from the fact that they last a long time and don't cause any dust. Their initial bite is non-existent, and max pedal pressure often doesn't engage ABS, which tells me I'm not getting sufficient friction to maximize the grip available at the tires for braking. They will be going back to FCP for a refund when I've decided what pad to replace them with. It is apparent I'm going to have to give up on clean wheels and go back to a semi-metallic pad material. Ceramics are apparently (just barely) sufficient for a daily grocery getter. Anything else and they're useless. I have yet to try another reverse bleed using a fluid syringe. Hoping that doing so will shove whatever air that's in the lines - if any - back uphill to the master, which should be easier to accomplish than trying to force it down against its natural tendency to float. Also going to try removing calipers one by one during bleed and holding sideways in case there's an air bubble getting caught between the caliper halves in the crossover (where the o-ring is). Appreciate you trying to help!

Yes. That can also cause same symptoms. This happened to my Ford Edge. ABS hydraulic unit was bad. Master cylinder was fine.

That for sure is a leaking vacuum booster, definitely should replace!

Yea. I figured and I think the master is gone too. Doesn't firm up til you floor. Just gonna replace both. In for a penny. In for a pound!

@@Conquerred512 Good luck. If I recall, 3 series was always Conti-Teves business, not TRW, so yeah, more likely it all failed 😂

@@gregreed2713 ouch. Ate so yea. Conti... It's fine 160k miles. And track abused. Worth it.

Did it solve your problem?

Your brake booster push rod probably needs adjusted, the tool is $15 on Amazon and it's easy to do, did you bleed the master cylinder before putting it on, and did bleed the system after replacing those