2012 XC60 New Discs & Pads Fitted - Braking Gone To Mush

[macdoni93]

Evening,
I've just spent an exciting(!) couple of days changing the offside driveshaft (never believe a Haynes manual) and all the discs and pads on my 2012 D3.

The braking performance is worse than before, and I've acquired what sounds like an asthmatic exhale from behind the dashboard when I push the pedal with the engine running. If I stop the engine and work the pedal, the sound can be heard for a couple of pumps and then it stops, and the pedal travel stiffens up considerably.

No errors showing up in VIDA (I thought it might be an ABS problem with changing the driveshaft). I pushed the caliper pistons back using a G Clamp (slowly, and removing the excess from the reservoir with a pipette), but I'm wondering if this has caused a problem in the system?

I've still got braking, so I'm hoping the master cylinder is ok, but the Haynes makes mention of a vacuum servo unit. Any ideas?

[macdoni93]

Ok - so after a night on the internet I now know more about vacuum brake servos than I ever thought I'd ever have to.....
Before I start pulling the front of the car off, and potentially spend a fortune on a new brake booster, I'm going to go back over the new disc/pad install. However before I got to that, I took a look at the old discs/pads. One of the old front discs has no wear over 10mm of the outer, and the pad has a corresponding groove (shown in pics). The other front is worn right to the edge.
I've had the car for 45,000 miles and never touched the brakes (2 main dealer services and no mention from them), but this looks odd. Could it be a twisted caliper? I'm wondering if this could be causing the excess travel (and hopefully the wheeze from the servo)

[kenny]

It is not unusual to have strange spongy feeling after replacing discs and pads on a diesel. It is well known phenomenon that usually settles back to normal in a couple of hundred miles.
The ridge issue could have been caused by a sticking pad. If you cleaned everything properly and applied brake mounting paste this should have sorted that issue.
Not sure what would cause the noise though. Sounds like you may have disturbed a seal somewhere.

[macdoni93]

Originally Posted by kenny

It is not unusual to have strange spongy feeling after replacing discs and pads on a diesel. It is well known phenomenon that usually settles back to normal in a couple of hundred miles.
The ridge issue could have been caused by a sticking pad. If you cleaned everything properly and applied brake mounting paste this should have sorted that issue.
Not sure what would cause the noise though. Sounds like you may have disturbed a seal somewhere.

Thanks for getting back. I've stripped everything and it is all aligned and spot on. The weird wear looks like some numpty has fitted a wrong sized pad in the past (the swept worn area is smaller at the outer and the inner edge of the disc, and different to the worn area on the flip side of the same disc), and then at some stage fitted the right sized pad (pad I removed is stepped at outer and inner edges). That must have taken some bedding in!

I've just bled the fronts, and a sliver of rubber about 5mm long has come out after pulling a fair bit of fresh fluid through. I'm worried I've damaged a seal in the master cylinder when pushing the pistons back. Never had this happen before, although I've read warnings about it online.

The noise is coming from behind the dashboard, where the vacuum servo sits. I haven't been anywhere near it so not sure how it could have been disturbed, unless pushing the piston back caused the master cylinder to push backwards and affect the diaphragm?

Interesting on the bedding in. They're genuine Volvo pads and discs and it doesn't really feel safe enough to drive if I had to hammer on the anchors. I'll take it out and do a few gentle stops to see if it gets any better.

Cheers!

[kenny]

If a bit of rubber has come out there is damage. 99% from your master cylinder. The noise will more than likely be the servo but will probably be from the damaged seal perhaps just making it work harder. Fixing the damaged seal will more than likely sort that. Start with stripping the master cylinder, it’s the most likely and easiest. If not that then you are going to have to check the whole braking system until you find it.

[johnnyoro]

Hi sit in the drivers seat with the engine off and pump the brake pedal several times this should exhaust the vacuum in the servo, and the pedal should be rock hard hold it down hard and it should not sink any further. with the pedal still held start the engine and the pedal should sink about 25-40%and then go hard again.
If with the engine off you cannot get a solid brake pedal ie it sinks to the floor then this indicates a problem with the hydraulics and probably air in the system.
If the pedal stays hard and does not sink (with the eng off) then it would seem that the brakes would be ok and just require a bit of bedding in
As for the bit of rubber I don't think it would be possible for it to come from the master cylinder through the system past the abs valves in the unit although I may well be wrong on that.