New brake pads - uneven wear?

[RobBMW]

Changed the front pads on my daily Volvo V70 at the weekend.
Once finished I took it for a drive and had hardly any braking under the pedal as it almost went to the floor. Bled the system and this improved greatly, still felt a little spongy though but put this down to the new pads perhaps needing bedding in.

Anyway, 24hrs later and I've done about 50miles of driving and noticed that the inner section of the brake discs (at the front) is staying rusty, suggesting the pads are only wearing on the outer half of the discs.
I presume this would be why the pedal still feels a bit soft?

Is this normal for new pads? do i need more bedding in time? Bear in mind they're being used on the existing discs?

Had enough trouble with this car recently and sick of having to take it to garages to do things on it that I can't do at home. I thought changing brake pads would be easy enough apparently not

[Pica-Pica]

Are the calipers sliding effectively?

[Steven_RW]

Assuming brake pedal was ideal before the pad change, I can see no reason the system needed bled unless you made some sort of mistake or another issue occurred.

Open the brake res, push the pistons back into the brake caliper. Fit the new pads. Close up the res. During the exchange you can clean up the caliper and the slider.

Regarding the rusty disc area. Either the disc was a heavily worn disc and not a flat shape and the pads are yet to adapt, or the pad isn't sliding straight on to the disc. Usually that is because the caliper and the slider needed a good going over with a wire brush and a file so that the pad has a nice surface to move on.

Next step? Give the pads longer to bed in. Unless you experience some other strange sensations, the chances are they will mate and all will be well.

One final point, the reason the brake pedal probably went to the floor was the first few pumps of the pedal brought the piston out from fully returned position to the position where the pad is now touching the disc.

In future, press the brake pedal a few times when stationary and that will "pump" the caliper back out. Which means I don't think it needed bled, but I can understand why you thought it might have..

RW

Edited by Steven_RW on Monday 11th February 09:51

[RobBMW]

Thanks everyone.
I got air in the system as I was advised to open the bleed valves when pushing the pistons back to accommodate the new pads. Apparently not doing this can cause some issues of seals failings in the master cylinder which I didn't want.
Sort of wish I'd ignored that advise and risked it after the issues I had.

Anyway, that was my plan, give the pads a few hundred miles/couple of weeks to line up with the discs. If not, I'll take it apart again...

[steveo3002]

they always take a few hundred miles to bed in and touch the whole disc

[Steven_RW]

RobBMW said:

Thanks everyone.
I got air in the system as I was advised to open the bleed valves when pushing the pistons back to accommodate the new pads. Apparently not doing this can cause some issues of seals failings in the master cylinder which I didn't want.
Sort of wish I'd ignored that advise and risked it after the issues I had.

Anyway, that was my plan, give the pads a few hundred miles/couple of weeks to line up with the discs. If not, I'll take it apart again...

Lordy - having been messing around with cars for 25 years, I have not opened the bleed valves when returning pistons ever. I have opened the fluid reservoir to allow the fluid to move. Maybe different with your car.

Okay - been for a read up. I see some people do believe in opening the bleed nipples to make returning the piston easier. I see the logic. I just haven't had to ever do that. Nice steady pushing of the piston back into the caliper has worked fine. Opening the bleed nipples could make changing the pads a two person job due to needing assistance with the bleed after.

Your way forward sounds sensible.

RW

[Triumph Man]

Steven_RW said:

RobBMW said:

Thanks everyone.
I got air in the system as I was advised to open the bleed valves when pushing the pistons back to accommodate the new pads. Apparently not doing this can cause some issues of seals failings in the master cylinder which I didn't want.
Sort of wish I'd ignored that advise and risked it after the issues I had.

Anyway, that was my plan, give the pads a few hundred miles/couple of weeks to line up with the discs. If not, I'll take it apart again...

Lordy - having been messing around with cars for 25 years, I have not opened the bleed valves when returning pistons ever. I have opened the fluid reservoir to allow the fluid to move. Maybe different with your car.

Okay - been for a read up. I see some people do believe in opening the bleed nipples to make returning the piston easier. I see the logic. I just haven't had to ever do that. Nice steady pushing of the piston back into the caliper has worked fine. Opening the bleed nipples could make changing the pads a two person job due to needing assistance with the bleed after.

Your way forward sounds sensible.

RW

I think it's an issue when people try and attack the piston with the incorrect tool - I've never had an issue taking the top off the reservoir, and siphoning fluid, and pushing back with the correct push back tool. If it's too hard to push back you've arguably got a problem with your caliper anyway! A colleague of mine swears by slackening the bleed nipple - he came into the office with a right cob on one morning because he'd broken his bleed nipple off....

[ToothbrushMan]

ive had this. the outer disc surface on a rear brake was only getting swept by half the pad leaving the other half to rust slightly - I knew the caliper was new the sliders were all OK and the pads were free to move etc so I left it after reading on the net that other people had the same and it took varying amounts of miles/time before the new rogue pad had full contact.

on mine it was considerable circa 1000 miles I reckon before the full disc was being swept. I say rogue pad and hope thats what it was - the inner face of the disc was being swept fine from day 1 so it can either been the outer pad ever so slightly out of square or the carrier holding the outer pad was slightly twisted somehow (dunno how its iron) or the slider pins were maybe bent slightly putting that outer pad at an angle other than dead square to the disc face.

I have decided for now it was just the pad itself.

[it_be_like_that]

RobBMW said:

Changed the front pads on my daily Volvo V70 at the weekend.
Once finished I took it for a drive and had hardly any braking under the pedal as it almost went to the floor. Bled the system and this improved greatly, still felt a little spongy though but put this down to the new pads perhaps needing bedding in.

Anyway, 24hrs later and I've done about 50miles of driving and noticed that the inner section of the brake discs (at the front) is staying rusty, suggesting the pads are only wearing on the outer half of the discs.
I presume this would be why the pedal still feels a bit soft?

Is this normal for new pads? do i need more bedding in time? Bear in mind they're being used on the existing discs?

Had enough trouble with this car recently and sick of having to take it to garages to do things on it that I can't do at home. I thought changing brake pads would be easy enough apparently not

sounds like a caliper problem. with new pads you should be hardly touching your brake pedal to feel strong braking. the unevenness can be related to many things, including a warped rotor.

if you dont know what youre doing, i would recommed going to see a mechnic, brakes is not something you can afford to mess up...

[grumpy52]

You have a partially seized piston on your brake caliper .
It happens when the part of the piston that has got corroded is pushed back into the caliper after years of exposure to the elements.
Most often on the inner section of the caliper , out of sight etc .
Stripping , cleaning and polishing can sometimes rescue them but if the seals are damaged its time to replace the caliper .