Friends hello! This time we're gonna be talking about disc breaks and how to skim
them or resurface them when either they warp or their unevenly worn and have groves in, and so on.
[Intro Music]
[impact wrench noises]
let's get started with this then. So first thing to do is get the disc brake
off the car. I'm going to assume that most people can do this otherwise just
look it up. There's like a million YouTube videos on removing the calipers,
changing the pads, changing the discs and all that. In this case we don't want
to change the discs! We want to reuse the old discs. They are a big chunk of metal,
they're almost always cast-iron and it seems a big waste, just throw them away
each time. They're even designed with resurfacing in mind. it's kind of
unfortunate that commercial garages treat them as disposable items these
days, almost changing them as regularly as the pads themselves, if there's any
kind of pitting or grooving the kind of thing that you could really easily get
out in a resurface operation. So I'm going to take you through how to do this. The
first thing to do is really wire brush most of the mess off. Clean them up a
bit get the abrasive disc brake particles off as much as you can. This
inside bit's really important to get clean, because that's what we're going to
be mounting to. I had the caliper seize up so the brake pad wasn't retracting properly and so constantly
rubbed on the disc and that caused overheat, and the disc best to warp slightly.
So one of the first things you're going to need to do is work out if you have
enough thickness to resurface the disc. Do a google or even go to one of the
places that does the car part- a replacement disc - and normally in the
stats for it it'll tell you a minimum thickness. I had a good couple of
millimeters or millimeter and a half to play with, which is plenty to resurface the disk.
So it is conceivably possible to resurface the disks in a four jaw chuck using a
dial indicator. This is really difficult though, because to make the surfaces
exactly parallel it takes a lot of fiddling about. This is what I read and
that's mirrored my experience. So the main part of this video is actually
going to be making the adaptor- arbour fixture type thing to mount the disk in the lathe.
EEEch. I dont know what kind of pipe it was, but it definitely had a thick layer of gunge in there.
Not very nice...
The disc break fixture is gonna be made from that pipe you just saw me turning up and
this big scrap lump of steel I'm not sure exactly what kind of steel it is. It
turns rather well. The basic premise here is that the disk brake will
eventually clamp to this Disk of Steel, which is going to make the fixture and
before each time you use the fixture you'll take a small skim off the plate
and that'll ensure complete concentricity. I've got a small section of high tensile
steel 16 millimeter threaded rod that I want to use for clamping and I'm just
turning that down so it fits nicely in the hole you saw me drilling in that
steel disc just a moment ago.
[click, click, click of turning dial]
The welder is on, you can hear that in the background. I've got my ground clamp here. I'm gonna
weld round here first and then flip it over to do the other side. It's on quite a
high setting so hopefully the wire will plunge right in, and we will get good
penetration.
[loud sparking/welding]
The way I'm doing this is with opposing welds to try and minimize the amount of distortion that's gonna
be. There's always gonna be some warpage doing a hefty weld like this in such thick material.
Going by eye [chuckle]
Plonking a weight on top...
Here's that pipe you saw me turning earlier. It's got a nice big 45 degree chamfer on
it which provides plenty of room for a deep weld fillet. Again firstly I'm just
making some opposing tack welds to hold the part sturdily and in place. Once I've
done that, then I can take my time with some nice inch long sort of seen welds, both
inside and outside of that pipe. Mainly angling the gun so it's going down into
the big steel disc as that's the much more massive of the two. So here it is
cooled down and chucked up. The pipes now chucked in the three jaw and you can see
there's a reasonable amount of warpage occurred during the welding. That's
entirely expected when you weld something like this. The idea now is that
that won't move from the three jaw chuck until I finish all four of the brake discs of the van.
[Sped up hacksaw noise]
[Vacuuming noise]
With everything else set I can come to this ultimate final skim of the clamping
surface that will be mating with the disc break. This is a very fine finishing
cut with a sharp new bit of carbide.
With that done we're about finished with the fixture so we can put the first disc
on. And it goes on as if mounting onto the axle of the car - so we want that same
surface to meet, and just like when you put the disc on a car, it's really
crucial to make sure there's no foreign debris in between the two surfaces are
being clamped together. So no specks of rust that can really put it out of
alignment and mean that you end up with unacceptable amount of run out in your
final disc. So this doesn't need to be ridiculously tight because it will be
turning in a direction where it would kind of self tighten anyway but
something decent... and then we need to clock up and check that we've got this
on roughly right and it's nice just to see quite how warped the disc is or how
true it's running to that inner surface that would be meeting on the axle. With
an idea of the high and low spots and the difference between them we can gauge
what kind of roughing cuts we need to take and get started with the actual
turning. For this lathe at least, the disc brakes about at the limit of what it
could turn without creating a gap in the bed and doing all kinds of extra
fettling, which probably would make the project not worth doing. So if you're
following along I guess it's best you check the disc will actually fit on your
lathe before starting any of this project, assuming you have a lathe and
you're not just watching out of interest of course. Once the outsides been turned,
we then need to take the finest of skims off this part of the disc brake. This is
the part that the wheel will clamp on to when it's on
the car and we need to make this exactly parallel to the inner surface that we're
clamping to and often corrosion means that it's not so with the finest of skim
off that, we can then flip the whole disc and clamp it back onto our fixture and
we know we have the surface completely parallel and I just verify that by
clocking off the.. what is now, back surface, the one that was skimmed before
starting even the braking surface on this side.
You're not going to be able to see it, you will have to take my word for it.
Yep. So I know that's parallel with
that edge which is also parallel with that face and the back face and that's pretty much got me covered.
So I think it probably is important to state the obvious, which is you do need to use a
dial indicator to... to confirm that all the surfaces are parallel and true. With
that done this could be taken off and put on the car now. First though, I'm just gonna
quickly rebuild the caliper. This is the seized one. I'm not going to go into the
details of this, but it basically needed polishing up and all corrosion cleaned off. It
seized because the seal had broken and so dirt was getting in there.
You can get new seal rebuild kits which is a good way of doing it, I think because
it means you can reuse the the meat of the caliper. So I really like this whole
process because it means you can almost double if not more the lifespan of your
typical disc brake. Once you set up and going with your lathe fixture it's not
too time-consuming either. I do feel though that I should give some words of
caution here. If you're not confident with any of this process, or competent
for that matter, then it's probably best avoided because it really is a safety
critical item! I feel a bit foolish just stating the obvious there, but better safe
than sorry, I guess. One other thing to note is that the disc always need
redoing in pairs whether that's replacing or resurfacing. You'd probably
notice I didn't use any coolant during the cutting and that's because it's cast
iron so it should self lubricate and another note on the cast iron is that
it can be really abrasive. It creates very small particles not like turning
steel, so it's well worth protecting your ways and being very vigilant like
hoovering up all the dust. Well friends that's about it, do let me know in the
comments below if you found that useful or if you think it's a load rubbish and
you've got a better way of doing it. It'd be great to hear from you! Thanks for
keeping me company and I'll see you next time!