Warped Disks.

If you stick a car brake disk on a flat surface, & by pressing down on
one side can get a 0.013mm feeler guage under t'other side, is it
warped enough to need replacing?

I've replaced the (completely fucked) wheel bearing on that corner, &
rubuit the calliper, but there's a rubbing sound & the disk's getting
much hotter than t'other side. I'm wondering if the seizing wheel
bearing caused the hub to get hot enough to warp the disk.

 

Not sure what the runout spec is but I'm pretty sure it'll be more than
that.

Could be. The piston seemed to move ok but the sliding half was very
stiff.

 

There isn't a heat shield that could be making slight contact is there?
I had that on the Mazda 6 after the front end work. Took it back and it
was "adjusted". That created a rubbing sound, but I never checked the
disk temperature.


--
+-------------------------------------------------------------------+
| Pete Fisher at Home: |
| Aprilia Shiver Yamaha WR250Z/Supermoto "Old Gimmer's Hillclimber" |
| Gilera GFR * 2 Moto Morini 2C/375 |
+-------------------------------------------------------------------+

 

Surely there's a 'run out' specification for the disk that could be used
here?

Or maybe a sticky caliper?

 

Ah! I had a Citroen BX like that. It would eat a set of pads on one
wheel in about a month (2k miles or so). More to the point it would eat
one pad because the slider wasn't sliding properly and it was easier to
put half of a six-quid set of pads in than fix the issue.

Fixed it eventually.

 

No, checked that.

 

I'd have said not, but f you can get a 0.013" feeler under it then
it's knackered.

Swap discs and see if the disc gets hot when it's running in a
different caliper.

 

Except it's only 0.5 thou.

 

Bad form excused by a quick "doh".

 

You've got a 0.0005" feeler? My guess is that he'd either misplaced the
decimal point and meant 0.13mm or it was really warped and he'd got a
0.013" feeler under it. It he really has only managed to find half a
thou of distortion then I'll be very surprised.

 

I'd be very surprised if it could generate enough heat to warp the disc,
or even rub the disc unevenly.

 

That'd be my first port of call.

And that would be my second.

 

So are you getting any of the following:

juddery brakes;
Steering pulling to one side;
pulsing brake pedal;
uneven tyre wear on that wheel?

If not and the disc's just getting abnormally warm then make sure the
caliper's free.

Was the bearing itself running hot, though? If the wheel was wobbling in
a regular pattern then maybe the pads were rubbing intermittently on the
disc. I dunno if this is also a possibility, but as an alternative
theory, maybe a binding brake caused the entire hub to run hot and that
caused the bearing failure.

 

No - but they do make a rubbing noise if they are making contact.
--
+-------------------------------------------------------------------+
| Pete Fisher at Home: |
| Aprilia Shiver Yamaha WR250Z/Supermoto "Old Gimmer's Hillclimber" |
| Gilera GFR * 2 Moto Morini 2C/375 |
+-------------------------------------------------------------------+

 

Not done enough miles to tell yet.

It is. As I said, I rebuilt it. Well I actually said I 'rubuit' it,
cos I'm a mong.

The old one was judging by the state of it, & the tortured screeching
noise.

That had occured to me, but the brake wasn't sticking enough to be
noticeable so it seems unlikely.

 

That's actually a damn good idea.

 

You've made me go & check now you git. And you're right - kinda.
Previously unused 'kinked' guages I bought for the somewhat tricky
Outlander inlet valves, & they've got both metric & imperial sizes
stamped on, which I hadn't noticed. It's 0.33mm (0.013 in old money).

 

Try swapping discs but I'd say that it's new disc time because that
amount of distortion is going to cause problems.

If you actually want to get a true measurement you need to get three
old roller bearings, balance it on them then shim the low one to find
the distortion. Repeat in a couple of different places and you've got
it.

 

It's buggered, as may also be the case with the hub.
Not easy to check unless you can get a dial gauge on the disk mounting
flange.
I'd try a new disk[1], and hope for the best.

[1]probably sold in pairs.

 

I've come to that conclusion too, especially as they're only 55 quid
for a pair. New disks on the way.