Brakes: Strange Brake Issues

[daveystoat]

Hi All, I need to tap into the collected wisdom on here.
I decided to get the XC70 I have advertised on here up together and MOT'd.
Part of which included sorting the brakes out. This means that it's now had new brake flexi hoses all round (fronts were a fail, rears an advisory), plus pads and discs on the rear, a new handbrake cable, new handbrake shoes, and a new brake pipe at the front (from the ABS unit to the flexi hose on the n/s). All of which has meant the brakes needed bleeding.
I used a brake pressure bleeder (the type you pump up). Started at the furthest wheel away from the master cylinder (I have since found out it's apparently best to start at the nearest wheel to the mc on these)
Bled them the first time, pedal was still spongy.
Bled them a second time, a load more air came out. No fluid leaks anywhere.
Pressed on the brake pedal last week, seemed firm at first, then went slowly to the floor. Came back up, and did the same. Not had chance to look at it again before today. Tried it this morning, pedal seems firm.
Had a chat to a neighbour who is a mechanic, he suggested it was the seals in the master cylinder, which I am not sure about as they have been fine up to now. Also had it suggested that I use DicE/VIDA to open up the valves in the ABS unit, and then re-bleed (if so, how would I do this? I do have access to DiCE/VIDA).

I want to get it MOT'd, but am a bit wary of driving it if I can't trust the brakes.

Any thoughts?

[SnineT]

The neighbour is correct and that's where I'd be.

[daveystoat]

Ok, thanks. I have checked it again this afternoon, and the pedal isn't going all the way down now, though is a little spongy, and fluid seems a little low. So I will try bleeding again.

[VOLVOBOY]

The Master Cylinder seals will only be an issue if you bleed by pressing the brake pedal and by the sounds of it , you haven`t . The thing here is not to press the pedal all the way down but only half-way or so .
Volvo say to bleed a RHD car from N/S/F to O/S/F and the rears in any order .
Also , you won`t need VIDA to fire the solenoids . When switching on the ignition the diagnostic test activates the solenoids . So just crack open the bleed valve and then switch on the ign. for as long as the diagnostics take to cycle and then switch off . Do this a couple of times for N/S/F and O/S/F and Twice for the first rear wheel you select. That should be enough to purge the ABS. Just watch that your pressure bleeder doesn`t run away with the fluid.
(usefull to have a second pair of hands)

[SnineT]

Originally Posted by daveystoat

Ok, thanks. I have checked it again this afternoon, and the pedal isn't going all the way down now, though is a little spongy, and fluid seems a little low. So I will try bleeding again.

Pump the pedal and hold it down, start the engine and it should sink a little bit probably about halfway down as the servo assist kicks in, if it's different you have a problem elsewhere.

I did have this on an old Cavalier in the 80's, new pads, disc's master cylinder and bled properly and the pedal was still spongy, it actually sorted itself out after a few hundred miles, that or i got used to it anyway.

[daveystoat]

Originally Posted by VOLVOBOY

The Master Cylinder seals will only be an issue if you bleed by pressing the brake pedal and by the sounds of it , you haven`t . The thing here is not to press the pedal all the way down but only half-way or so .
Volvo say to bleed a RHD car from N/S/F to O/S/F and the rears in any order .
Also , you won`t need VIDA to fire the solenoids . When switching on the ignition the diagnostic test activates the solenoids . So just crack open the bleed valve and then switch on the ign. for as long as the diagnostics take to cycle and then switch off . Do this a couple of times for N/S/F and O/S/F and Twice for the first rear wheel you select. That should be enough to purge the ABS. Just watch that your pressure bleeder doesn`t run away with the fluid.
(usefull to have a second pair of hands)

Thanks, that is useful. No, I haven't bled using the pedal. I only used it when I tried pressing it later, and it gradually went to the floor.
I have heard differing information on the bleeding order - mechanic neighbour (and other places) said do the furthest wheel away from the reservoir first, and work towards the reservoir, so Rear Left, Rear Right, Front Left, then Front Right. Found online on another Volvo site that it should be Right Front, Left Front, Right Rear, Left Rear, and in other places it says a different order or it doesn't matter.

I will have another look, but it won't be for a few days.

[daveystoat]

Originally Posted by SnineT

Pump the pedal and hold it down, start the engine and it should sink a little bit probably about halfway down as the servo assist kicks in, if it's different you have a problem elsewhere.

I did have this on an old Cavalier in the 80's, new pads, disc's master cylinder and bled properly and the pedal was still spongy, it actually sorted itself out after a few hundred miles, that or i got used to it anyway.

I will try this today, thanks

[Roy V70 850]

Had a similar problem after changing the pads a few months ago. When I first tried the brakes, the peddle went pretty much Down to the floor. Tried it a few times and it improved slightly. Took it out on the road and it seemed to get better where it was acceptable and over a few months the brakes worked fine.

I'd sheared the bleed n1pple on one of the calipers in doing this, so I installed new calipers. I changed the way I bled the brakes and used the gravity bleed method. No jars, pipes, just a bucket. Tried the brakes for the first time and I couldn't believe the difference.

I'd initially suspected the seals on the master cylinder, but you have to ask yourself, why would the seals go just as you've bled the brakes when everything was fine just beforehand.

Have a look at this video from A1 Auto :-

https://m.youtube.com/watch?v=HjREU-ag7zk


Oh, and one thing I did differently, was not to push the brake down at all but to allow the fluid to flow into the cylinder and out through the bleed n1pple until all the bubbles had gone.

[daveystoat]

Thanks Roy, it is exactly why I am not convinced that it is the master cylinder seals - I would have noticed something not right before (presumably the pedal would have been a little soft and getting slowly worse)?

[VOLVOBOY]

but you have to ask yourself, why would the seals go just as you've bled the brakes when everything was fine just beforehand.

The problem is that you can press the pedal down further when bleeding than when the brakes were under normal use .
If a wear ridge has formed on the Master Cylinder Piston Rod there have been instances where the Seal Lip has either been scored or reversed itself .