I was going to comment the same thing i was like what's a return pipe on the master cylinder 🙂

This is the proof that fixing safety equipments are not for everybody😮

Good to hear Jeffrey. I hope it works for you? Let me know how you get on.

Good result. 👍

Thanks Adrian 👍 The video is intended to stop people making the same mistake I did, and replacing an expensive master cylinder. It seems it might be working?

Good luck. I'd be interested to hear how you get on?

The part number on the black abs pump refers to the pump and the alloy valve block it is fixed to.

That is what I thought too. That's why I changed the master cylinder first, and it didn't fix the problem. After changing the abs unit, it cured the problem. For me, logic dictates that somehow, fluid was getting past a seal in it, and somehow returning to the master cylinder? The brake fluid level didn't change, and there are no leaks? Perhaps there is some sort of porting, or pressure differential relief in the brake master cylinder that allows that? My video is intended to get people to check the master cylinder first, by blanking it off, and check its OK before wasting time & money replacing it. I know it doesn't sit right with conventional understanding of how a dual circuit brake system works, but the results challenge that?

@@philcross7315That is correct logic, MC can be the issue if fluid bypass the fluid internally in result of soft pedal , the older system does have a return line from the abs back to the MC, but from the video shown it is looks like it is one of newer design which has an internal accumulator. What you are feeling is one of the solenoid bypassing fluid to the accumulator cause the soft pedal

@@carlosk2752 thanks for that 👍 I had no idea there was an accumulator inside the abs unit. Happy to be corrected, and have the knowledge passed on 👍 Hopefully, if anyone else has the same issue, it will give them a heads up?

@@philcross7315 I'm so glad I found this video, and particularly this comment thread. This is exactly what I've been scratching my head over on my '07 XC90 V8. For the longest time, I've thought "the brakes do work, but they don't feel very confidence-inspiring under the foot" what with it taking about half the pedal travel to attain decent braking force, and not much pedal travel left after that which makes attaining maximum brake force next to impossible before hitting the floor. Getting into ABS engagement is difficult/impossible unless I'm being a maniac and absolutely standing on the pedal, or braking hard on gravel/sand/ice/etc. Fast forward a few years since buying it, and I've now got S60R factory Brembo calipers fitted to the XC90, with HEL stainless braided lines. Yet, even after those upgrades, both of which should have contributed to a firmer pedal and more immediate, positive braking performance, the pedal still travels too far before brake engagement, initial bite is better but still not good, and in general the brakes can be characterized as 'weak, and gradual but not linear'. The pedal also slowly sinks away with constant moderate pressure - but only with the engine running, which I found slightly odd. Not thinking more deeply into this particular detail was my main mistake in troubleshooting and probably could've saved me a chunk of money. I've bled the system about a dozen times before and after swapping the Brembos, always trying to attain a firm pedal but never with any success. Manual two-person bleeding, vacuum bleeding, and pressure bleeding. Nothing changed. After going through 2L of fluid the last time, I had concluded it's something other than air in the system. Next, I swapped in a brand spanking new master cylinder, because conventional wisdom and prior experience told me that if it's not air in the system, and I don't have any external leaks anywhere, then the piston seals in the master cylinder are likely leaking internally causing pressure loss and the pedal to creep down slowly. The car has 266k KMs on it, so I figured "yeah, they're probably just worn out by now." At least I didn't pay retail to Volvo, and instead got the same OE (Ate brand) part from FCPEuro for a quarter the price... Interestingly, as mentioned above, it only does it (sinking away) when the engine is running, which I initially chalked up to the booster simply providing more force on the master cylinder than just my foot alone with the engine off and no vacuum assist. I didn't even consider the ABS block! Mainly because I didn't realize it has an internal accumulator - I thought it was simply an array of valves and a pump, not something that would allow fluid pressure to bleed off, at least not unless it was leaking externally, which would be obvious by a loss of fluid and a leak that would be visually apparent. Armed with this new knowledge, I'll be heading to the U-pull-it yard to grab a replacement ABS unit and hopefully resolve this issue and get a properly firm pedal for the first time since I bought this thing! You'd think that an internal leak would be something that could be assessed by a few sensors and a fault logged in the BCM. Clearly a design oversight on the part of Ate/Volvo. I wonder how many people have this issue, perhaps not as pronounced (yet?) and simply think it's normal behaviour. It's borderline unsafe. At any rate, thank you both very much, Phil Cross and Carlos K! It should be noted that the ABS unit/block/pump you show is the exact same design (different part number though) as in the XC90. It appears you may have a different model vehicle (and you're clearly across the pond, what with your pedals being in the passenger footwell ;) but it appears this same ABS block design was carried through multiple models and model years, so I won't be surprised if mine has developed the same internal fault.

I have the same exact issue on my Mazda 3, same sinking brake pedal. Changing the master cylinder and bleeding the system made no difference. The ABS valve block comes from Ford, so this issue spans several manufacturers. It’s very unsafe, and worse yet when the ABS comes on my brakes don’t work at all unless I pump the pedal a few times.

No special equipment needed, but we did use a pressure bleeder to do mine. If you haven't got access to one, just get an assistant to pump the brake pedal for you. Open the bleed nipple, press the brake pedal down, tighten the nipple, or just put your finger over the end, and release the pedal. Rinse/repeat... Good luck.

Something like this makes the job much easier though: DAYUAN 3L Hand Brake Fluid Bleeder Bleeding One Man Tool Kit www.amazon.co.uk/dp/B081HD3CNB/ref=cm_sw_r_cp_apan_glt_i_P0Z7AED62460FXE8WPC4?_encoding=UTF8&psc=1

@@philcross7315 Cheers Phil, that's good to know and I'll get one of those pressure bleeders before I start the job. It was just that I read somewhere that the ABS pump had to be activated to bleed it properly so I'm glad that's not the case. Thanks.

No. The brake lines run directly from the abs unit, to the calipers. Barring a burst pipe, or leaking hose, there's no way to lose pressure.

Thank you for your reply@@philcross7315

I used a pressure bleeder, but didn't have to do anything special for the abs. Just pumped it ip, and bled each corner twice.

@@philcross7315 Thank you so much Phil! I am planning to swap my ABS next week :) My right front wheel is locking. The pedal feels normal and all lines look good. Swapped brake line and caliper but didn't help. The brake gets released after opening the line at the ABS. I think the valve is stuck for this wheel at the ABS. Thank you again for the great videos.