Air in the brake master cylinder..easy to flush out?

[AylmerQc]

Due to apparent discolouration of the brake fluid and somewhat sponginess of the brakes, I did a brake fluid flush and while I was at it, I replaced all the calipers on my 2007 XC70.

When finished bleeding the lines, with no more apparent air bubbles showing up through the clear bleed hose, I started the car up and tried the brakes but the pedal pretty much hit dead bottom without any resistance. I pumped it a few times and it eventually seemed to pump fluid.
I can move the car a few feet and brake but I won't dare take it on the road until I sort this out.
I have the pressure tank kit I'm using to bleed the brakes.
Do I just need to keep bleeding air fluid out to remove the trapped air or is there something else I should know or need to do..?

[scot850]

You may have got an air lock in the ABS unit, they can be hard to move without the pressure bleeder. I would start at the furthest point (RR) caliper and use the pressure bleeder to try and get that air lock out. I'm sure you did, but monitor the level of fluid in the header tank as it is easy to overlook and let air into the system.

Neil.

[AylmerQc]

Thanks..
I'm watching a YT video where a mechanic is using an Autel scanner to activate the ABS module valves so as to flush out the air, as far as I can understand it.
Would I need to do this as well with VIDA?

[scot850]

I have never tried to be honest. Didn't now it was a thing on a P2. I know of it on newer models but not tried looking into it. Maybe someone else can chip in?

Neil

[jonesg]

Due to apparent discolouration of the brake fluid and somewhat sponginess of the brakes, I did a brake fluid flush and while I was at it, I replaced all the calipers on my 2007 XC70.

When finished bleeding the lines, with no more apparent air bubbles showing up through the clear bleed hose, I started the car up and tried the brakes but the pedal pretty much hit dead bottom without any resistance. I pumped it a few times and it eventually seemed to pump fluid.
I can move the car a few feet and brake but I won't dare take it on the road until I sort this out.
I have the pressure tank kit I'm using to bleed the brakes.
Do I just need to keep bleeding air fluid out to remove the trapped air or is there something else I should know or need to do..?

if you didn't operate the system with the ignition on , running the elec vac pump, there shouldn't be any air in the abs.
Its more likely theres air in the master cyl, it gets trapped in the end, the usual fix is to bench bleed it.
but it can be done without removing , buy a bench bleed kit from amazon.

Remove the engine cross brace.
Fill with fluid and place a piece of plastic bag over the reservoir opening, reinstall the cap to hold the plastic in place, this prevents fluid from flooding out when the system is cracked open.
Crack the fitting on the end of the master cyl, remove and install one of the threaded nylon fittings (snug) with clear plastic hose that comes in the kit, put hose into small bottle with brake fluid. insert one of the small plastic plugs in the brake line.
Just bleed like a caliper.

https://www.amazon.com/Enhon-Cylinder-R ... 199&sr=8-3

[AylmerQc]

"if you didn't operate the system with the ignition on , running the elec vac pump, there shouldn't be any air in the abs.."

I did start the car after I was finished and tested the brakes...would that would that count as "operating the system with the ignition on"?
I'm guessing that's not what you meant but rather you meant having the ignition on with the cap off the master cylinder...
From what you're saying as well, there's an electric vacuum pump in the brake system?
I've seen somewhere that some are doing the bleeding with the engine running...does that make any sense or any change in purging air out of the lines?

I'm wondering if I may have messed up also by releasing the pressure on my pressure tank while it was still hooked up to the master cylinder instead of disconnecting it via the quick disconnect at the end of the hose that fits on the cap...?
When I did this it created a suction that seemed to draw a fair amount of fluid back. That's just a suspicion I have but in any case, what's done is done...
I'll look at that bench testing kit...thanks for the help...
"Modern" cars, even if this is a 2007 P2, sure are a different thing than the old 70s 240 models I used to own and work on back in the 90s...

[MoVolvos]

.
It is always best to bench bleed the Master Cylinder and afterwards have the car started and just push the brake pedal all the way down while someone loose and tighten the bleeder screw.

Since the late 70's I have never used a device from the top to force fluid through the system. Always did the pump 3 times and release and tighten the screw as the pedal goes down to let the fluid out. Within the last year or two gone with having the engine on and the system purge the fluid so no manual foot pumping.
.

[AylmerQc]

I'd never heard of bench bleeding (prior to seeing it on a video today) the master cylinder, but then again, a lot has changed since I took auto mechanics in HS decades ago.
So you recommend taking the MC out of the car? I've ordered the bleeder kit mentioned above and was thinking of bleeding it still in the car...
And then running the engine and letting the system self-purge without pressing the pedal...Works on most/all models?

[MoVolvos]

I'd never heard of bench bleeding (prior to seeing it on a video today) the master cylinder, but then again, a lot has changed since I took auto mechanics in HS decades ago.
So you recommend taking the MC out of the car? I've ordered the bleeder kit mentioned above and was thinking of bleeding it still in the car...
And then running the engine and letting the system self-purge without pressing the pedal...Works on most/all models?

.
If you have room in the car, using your foot is much easier than pushing the plunger manually for the bench bleeding but that will require two persons.

As for running the engine you still have to depress the pedal to push out the fluid. You just don't pump 3 times and hold. Just be sure to secure the bleeder screw before letting the foot off for the next pedal push. I usually run at least 2 quarts of brake fluid through the system to clear the old and of any bubbles in the lines. Start from the longest then to the shortest line from the MC. If you feel the fluid has changed color and the system feel normal you don't have to go through all 2 quarts.
.

[jonesg]

"if you didn't operate the system with the ignition on , running the elec vac pump, there shouldn't be any air in the abs.."

I did start the car after I was finished and tested the brakes...would that would that count as "operating the system with the ignition on"?
I'm guessing that's not what you meant but rather you meant having the ignition on with the cap off the master cylinder...
From what you're saying as well, there's an electric vacuum pump in the brake system?
I've seen somewhere that some are doing the bleeding with the engine running...does that make any sense or any change in purging air out of the lines?

I'm wondering if I may have messed up also by releasing the pressure on my pressure tank while it was still hooked up to the master cylinder instead of disconnecting it via the quick disconnect at the end of the hose that fits on the cap...?
When I did this it created a suction that seemed to draw a fair amount of fluid back. That's just a suspicion I have but in any case, what's done is done...
I'll look at that bench testing kit...thanks for the help...
"Modern" cars, even if this is a 2007 P2, sure are a different thing than the old 70s 240 models I used to own and work on back in the 90s...

bench bleeding is always done for a new master cyl because you have it in your hands. it makes sense.
But it can be done in the car too.
the air bubble is stuck at the end of the cyl because its angled up.