Prev: PCD - How critical?
Next: Are looking for buying car?
From: Duncan Wood on 20 May 2010 06:48
On Thu, 20 May 2010 11:21:29 +0100, The Other Mike
<rootpassword(a)somewhereorother.com> wrote:

> Thanks for all the advice, a follow up to my previous posting,
>
> Yes it was an independent garage, they do very little other vehicle
> work besides welding so nothing to gain from failing it on the brakes.
>
> I road tested it again and found a panic stop from 40mph caused the
> drivers side front wheel to lock up right at the end of the stop if I
> didn't modulate the pedal pressure. From speeds less than this there
> was no locking. There was certainly no evidence whatsoever of any
> pulling.
>
> So I removed the calipers from their mounts and exercised the
> hydraulics against a G clamp, the pistons moved ok and I checked that
> they returned with thumb pressure I couldn't find any seal kits
> locally so didn't bother disturbing the dust covers and hydraulic
> seals any more than looking under the dust seal - there was no
> corrosion.
>
> I removed the sliders and flushed them through to remove all traces of
> grease, no wear was evident, no damage to the sliders either so I
> relubed with copious amounts of CV joint grease, the sliders seemed a
> bit more free moving than before.
>
> I checked all areas of the caliper that the pads were bearing on and
> removed a small area of corrosion maybe the size of a drawing pin head
> and maybe 1/16" thick. Ran a smooth file over the metal bits of the
> end of the pads to remove any burrs. A few blobs of copper grease on
> the sliding areas and back out on the road to retest.
>
> It was still locking at the end of a panic stop but the road was now
> slightly damp so I'm not sure it was representative.
>
> In desperation we took it back for a retest (free) and it passed.
>
> The previous imbalance was 30%, the new imbalance is 17% (which I
> presume is still high?) In hindsight I might have tried using a
> rotary hone on the discs and rubbing the pads on some glass paper.
>
>

17% is down in the zone from the two tyres being worn differently & at
different pressures.
--
Duncan Wood
From: Chris Whelan on 20 May 2010 07:36
On Thu, 20 May 2010 11:21:29 +0100, The Other Mike wrote:

[...]

> The previous imbalance was 30%, the new imbalance is 17% (which I
> presume is still high?) In hindsight I might have tried using a rotary
> hone on the discs and rubbing the pads on some glass paper.

FYI, the maximum permitted imbalance on the steered wheels is 25%.

Where some testing stations are not being totally honest is how they
interpret MOT 3.7A 2c (and d):

"the braking efforts at the roadwheels do not increase (decrease)at about
the same rate..."

It's the "about" that allows too much unscrupulous tester discretion.

Chris

--
Remove prejudice to reply.
From: Mrcheerful on 20 May 2010 07:40
The Other Mike wrote:
> Thanks for all the advice, a follow up to my previous posting,
>
> Yes it was an independent garage, they do very little other vehicle
> work besides welding so nothing to gain from failing it on the brakes.
>
> I road tested it again and found a panic stop from 40mph caused the
> drivers side front wheel to lock up right at the end of the stop if I
> didn't modulate the pedal pressure. From speeds less than this there
> was no locking. There was certainly no evidence whatsoever of any
> pulling.
>
> So I removed the calipers from their mounts and exercised the
> hydraulics against a G clamp, the pistons moved ok and I checked that
> they returned with thumb pressure I couldn't find any seal kits
> locally so didn't bother disturbing the dust covers and hydraulic
> seals any more than looking under the dust seal - there was no
> corrosion.
>
> I removed the sliders and flushed them through to remove all traces of
> grease, no wear was evident, no damage to the sliders either so I
> relubed with copious amounts of CV joint grease, the sliders seemed a
> bit more free moving than before.
>
> I checked all areas of the caliper that the pads were bearing on and
> removed a small area of corrosion maybe the size of a drawing pin head
> and maybe 1/16" thick. Ran a smooth file over the metal bits of the
> end of the pads to remove any burrs. A few blobs of copper grease on
> the sliding areas and back out on the road to retest.
>
> It was still locking at the end of a panic stop but the road was now
> slightly damp so I'm not sure it was representative.
>
> In desperation we took it back for a retest (free) and it passed.
>
> The previous imbalance was 30%, the new imbalance is 17% (which I
> presume is still high?) In hindsight I might have tried using a
> rotary hone on the discs and rubbing the pads on some glass paper.

sometimes a fresh set of pads can cure imbalance, I believe this is probably
where one side has become a bit cooked from minor seizure that has gone
unnoticed for a while.


From: The Other Mike on 21 May 2010 08:13
On Thu, 20 May 2010 11:48:49 +0100, "Duncan Wood"
<nntptmp(a)dmx512.co.uk> wrote:

>17% is down in the zone from the two tyres being worn differently & at
>different pressures.

Surprised that could make such a huge difference but I can probably
eliminate those reasons too.

Tyre wear is pretty even (On the failed test there was a tyre with
slightly excessive inside edge wear which was an advisory so we
swapped it with the near new spare)

I checked all the tyre pressures just before the retest. They were
all a few pounds high 36vs30 front and 30vs28 back iirc having not
been reset after the car was used for towing a few weeks back.

--
From: Duncan Wood on 21 May 2010 08:17
On Fri, 21 May 2010 13:13:35 +0100, The Other Mike
<rootpassword(a)somewhereorother.com> wrote:

> On Thu, 20 May 2010 11:48:49 +0100, "Duncan Wood"
> <nntptmp(a)dmx512.co.uk> wrote:
>
>> 17% is down in the zone from the two tyres being worn differently & at
>> different pressures.
>
> Surprised that could make such a huge difference but I can probably
> eliminate those reasons too.
>
> Tyre wear is pretty even (On the failed test there was a tyre with
> slightly excessive inside edge wear which was an advisory so we
> swapped it with the near new spare)
>

If one sides new & one side is worn or a different make you'll get
imbalance.


> I checked all the tyre pressures just before the retest. They were
> all a few pounds high 36vs30 front and 30vs28 back iirc having not
> been reset after the car was used for towing a few weeks back.
>


--
Duncan Wood
First  |  Prev  | 
Pages: 1 2
Prev: PCD - How critical?
Next: Are looking for buying car?