New disc brakes, new problems

#1

I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? Any advice much appreciated.

#2

In an earlier contribution to this discussion,
Skonnie <iamthefritobandito (AT) gmail (DOT) com> wrote:

Quote:

I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? Any advice much appreciated.

I'm not quite sure what you're saying is happening. Are you saying that
there's metel to metal contact between calliper and disc - or simply that
the pads are binding and not releasing properly after you've applied the
brakes?

Do the callipers each have two pistons - one per side - or is there only
one, and a mechanism which allows the calliper to move sideways to balance
pad wear? If the latter, I would suggest that you may not have re-fitted the
callipers correctly, thus preventing this sliding from taking place.

Whatever the cause, I can't see how bleeding the brakes would help.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

#3

On Jul 28, 4:14*am, "Roger Mills" <watt.ty... (AT) googlemail (DOT) com> wrote:

Quote:

In an earlier contribution to this discussion,

Skonnie <iamthefritoband... (AT) gmail (DOT) com> *wrote:
I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. *I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. *Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? *Any advice much appreciated.

I'm not quite sure what you're saying is happening. Are you saying that
there's metel to metal contact between calliper and disc - or simply that
the pads are binding and not releasing properly after you've applied the
brakes?

Do the callipers each have two pistons - one per side - or is there only
one, and a mechanism which allows the calliper to move sideways to balance
pad wear? If the latter, I would suggest that you may not have re-fitted the
callipers correctly, thus preventing this sliding from taking place.

Whatever the cause, I can't see how bleeding the brakes would help.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

No metal to metal contact, the brake pads are not significantly worn.
There is one piston per caliper. I believe I refitted the calipers
properly, its just that the new discs are obviously thicker than the
old, worn ones. In manuals I have, the c-clamp method method of
depressing the pistons is used when replacing brake pads, but there's
no mention of this when replacing the discs. Should I try this, or is
there another solution? Thanks for the advice.

#4

Use the "C" clamp to depress the caliper piston.

Or, as I did, go buy a tool specifically designed for this purpose.

#5

Roger Mills wrote:

Quote:

In an earlier contribution to this discussion,
Skonnie <iamthefritobandito (AT) gmail (DOT) com> wrote:

I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? Any advice much appreciated.

I'm not quite sure what you're saying is happening. Are you saying
that there's metel to metal contact between calliper and disc

Strange question.
If he's competent to replace the callipers, I can't see why remembering to
refit the pads would present significant difficulties.

- or

Quote:

simply that the pads are binding and not releasing properly after
you've applied the brakes?

Do the callipers each have two pistons - one per side - or is there
only one, and a mechanism which allows the calliper to move sideways
to balance pad wear? If the latter, I would suggest that you may not
have re-fitted the callipers correctly, thus preventing this sliding
from taking place.
Whatever the cause, I can't see how bleeding the brakes would help.

#6

If the pistons aren't retracting normally, you've either refitted the pads
wrongly or the pistons themselves are starting to seize.
Difficult to imagine that if they were working normally before, they'd
suddenly seize up - which only leaves a correct calliper/correct fitment
issue.

Roger Mills wrote:

Quote:

In an earlier contribution to this discussion,
Skonnie <iamthefritobandito (AT) gmail (DOT) com> wrote:

I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? Any advice much appreciated.

I'm not quite sure what you're saying is happening. Are you saying
that there's metel to metal contact between calliper and disc - or
simply that the pads are binding and not releasing properly after
you've applied the brakes?

Do the callipers each have two pistons - one per side - or is there
only one, and a mechanism which allows the calliper to move sideways
to balance pad wear? If the latter, I would suggest that you may not
have re-fitted the callipers correctly, thus preventing this sliding
from taking place.
Whatever the cause, I can't see how bleeding the brakes would help.

#7

Skonnie wrote:

Quote:

I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? Any advice much appreciated.

Disks drag. That's a fact of life.
The only reason you'd need to use the C clamp to push the pistons back
is if you couldn't get the calipers over the rotors... which obviously
wasn't a problem.

If the rotors were 'warped and worn down' then the pucks would have
groves and stuff matching the old rotors. Not the best situation for
good stopping with new rotors.
They may wear in over time, or you could pull the pucks and file them
flat, or you could put new ones in and do the job right.

One has to wonder what the cost savings vs extra labor to not put new
pucks in the same time as the new rotors..?

#8

Hi Leftie,

I think your contribution may have "hit the nail on the head".
I recently experienced this failure to get the piston to retract all the
way, in order to insert new pads. It was on a Honda motor cycle, not our
Volvo.
Crud and corrosion had accumulated near the outermost portion of the piston
due to its long exposure to the elements with worn pads. (When the pads are
worn the piston remains further out to maintain near contact with the
thinner worn pads.) Instead of replacing the caliper I was able to remove
this stuff by rubbing the piston carefully with very fine steel wool and
cleaning with "brake clean". The piston was then pushed in all the way with
no trouble, the new pads inserted, and the brake has worked perfectly since.
No leakage.

Andy I.

"Leftie" <No (AT) Thanks (DOT) net> wrote

: Pistons on calipers often get 'habituated' to a certain extension,
: and don't want to retract enough to install brand new pads (or rotors).
: This is usually because some rust has formed on the slides and/or
: pistons, near the tops. I remember thinking I had the wrong pads for my
: 122S back in the day, because of this. If you can't get the pistons to
: retract with some careful application of force and slide lubricant, you
: need to replace the calipers.
:

#9

Centre Parting wrote:

Quote:

If the pistons aren't retracting normally, you've either refitted the pads
wrongly or the pistons themselves are starting to seize.
Difficult to imagine that if they were working normally before, they'd
suddenly seize up - which only leaves a correct calliper/correct fitment
issue.

Pistons on calipers often get 'habituated' to a certain extension,
and don't want to retract enough to install brand new pads (or rotors).
This is usually because some rust has formed on the slides and/or
pistons, near the tops. I remember thinking I had the wrong pads for my
122S back in the day, because of this. If you can't get the pistons to
retract with some careful application of force and slide lubricant, you
need to replace the calipers.

Quote:

Roger Mills wrote:
In an earlier contribution to this discussion,
Skonnie <iamthefritobandito (AT) gmail (DOT) com> wrote:

I just replaced the front brake discs on my '90 740 Turbo, as the old
ones were warped and worn down. I thought the pads would adjust to
the new, thicker discs, but a test drive after the reinstall shows
that the calipers are binding on the new discs. Should I use a c-
clamp to depress the pistons, or bleed the brakes to relieve the
pressure on the new discs? Any advice much appreciated.
I'm not quite sure what you're saying is happening. Are you saying
that there's metel to metal contact between calliper and disc - or
simply that the pads are binding and not releasing properly after
you've applied the brakes?

Do the callipers each have two pistons - one per side - or is there
only one, and a mechanism which allows the calliper to move sideways
to balance pad wear? If the latter, I would suggest that you may not
have re-fitted the callipers correctly, thus preventing this sliding
from taking place.
Whatever the cause, I can't see how bleeding the brakes would help.

#10

Andy wrote:

Quote:

Hi Leftie,

I think your contribution may have "hit the nail on the head".
I recently experienced this failure to get the piston to retract all the
way, in order to insert new pads. It was on a Honda motor cycle, not our
Volvo.
Crud and corrosion had accumulated near the outermost portion of the piston
due to its long exposure to the elements with worn pads. (When the pads are
worn the piston remains further out to maintain near contact with the
thinner worn pads.) Instead of replacing the caliper I was able to remove
this stuff by rubbing the piston carefully with very fine steel wool and
cleaning with "brake clean". The piston was then pushed in all the way with
no trouble, the new pads inserted, and the brake has worked perfectly since.
No leakage.

Andy I.

I should have mentioned the option of cleaning the pistons, but I
thought it unlikely that you could get them smooth enough to not damage
the seals as they retracted. Looks like I was wrong!

Quote:

"Leftie" <No (AT) Thanks (DOT) net> wrote in message
news:wUwjk.4292$tg.3006 (AT) fe119 (DOT) usenetserver.com...
: Pistons on calipers often get 'habituated' to a certain extension,
: and don't want to retract enough to install brand new pads (or rotors).
: This is usually because some rust has formed on the slides and/or
: pistons, near the tops. I remember thinking I had the wrong pads for my
: 122S back in the day, because of this. If you can't get the pistons to
: retract with some careful application of force and slide lubricant, you
: need to replace the calipers.
: