Rotating Front Brake Pads

[bigbore2]

Perhaps I was unclear here, angle grinder with 4 1/2 inch plastic pad attachment one attaches pre-cut round sanding paper made for the plastic attachment for the purpose of finishing metal. NOT a grinding wheel, that would be impossible, I believe.

[ribbert]

Perhaps I was unclear here, angle grinder with 4 1/2 inch plastic pad attachment one attaches pre-cut round sanding paper made for the plastic attachment for the purpose of finishing metal. NOT a grinding wheel, that would be impossible, I believe.

I wasn't suggesting YOU used a cut-off wheel, my point was, in the absence of detailed instructions, someone else reading the post might.

Impossible to use a grinding wheel you say? I've been a mechanic for 40 years, you would not believe what people do armed with little experience on the tools they're using, no understanding of the parts they're working on and just enough self confidence to have a go.

And, even a plastic mounting pad, as opposed to a rubber one (which is what I assumed you used), is pretty harsh and likely to gouge the metal.

I just have a problem with brake rotors and angle grinder in the same sentence.

A point we differ on and likely to remain so.

That's what's great about the forum, we are all entitled to state our views, even the pink stripers and ambulance drivers.

Noel

[bigbore2]

My point is that with the use of a grinding wheel, it would be impossible to get a flat, smooth surface on the disc, I believe. I am sure someone might try a grinding wheel, like you say, its amazing what people will try.
 They no longer make a rubber pad at the store I bought my parts, only a plastic one.  It is a little stiffer than I wanted, but it still flexed enough to satisfy me and get the surface finish I was looking for. I only wish I had a camera to do a photo of this work.  I decided that if one cannot get a disc turned, this may well work as an cheap alternative to buying 3 rotors. We shall see how it turns out. Hope to have my shock mod. completed this weekend so I can put some miles on and see.

[Arnie]

Maybe there's a good reason these disks are not allowed to be turned.  They start out pretty thin and turning them may make them under-spec and subject to warping.  What is the disk thickness now that you've 'sanded' them flat & smooth?

Arnie

I decided that if one cannot get a disc turned, this may well work as an cheap alternative to buying 3 rotors. We shall see how it turns out.

[SlowOldGuy]

Unless they are horribly warped, I NEVER turn a disc.  I stopped turning them on cars about 20 years ago.  Usually the idiot running the machine just screwes them up.  Haven't had any brake problems since then; bike or car.

DavidR.

[ribbert]

Maybe there's a good reason these disks are not allowed to be turned.  They start out pretty thin and turning them may make them under-spec and subject to warping.  What is the disk thickness now that you've 'sanded' them flat & smooth?

Arnie

I decided that if one cannot get a disc turned, this may well work as an cheap alternative to buying 3 rotors. We shall see how it turns out.

New bike discs are only about 1mm thicker than min spec.  No meat for turning.

I'm with David, turning modern car discs, which are now rubbish, is a waste of money and only makes them thinner and even more likely to warp.

Car discs are now made from crap metal (I know this) and are throw away parts, they have become consumables.
There  was a time when you could expect discs to last the life of the car, our last car was getting new fronts yearly, and you can't even buy good ones if you're prepared to pay.

Porsche, for example, include rotor replacement at certain service intervals, regardless of condition.

I'm all for trying to eke out a few more K's from components but that doesn't include taking a handheld power tool to your discs.

I have never found the grooving that rotors develop over time reduces brake performance anyway, so there's nothing to be achieved.

Noel

[bigbore2]

Let's start with some technical data, here.      84-1100 with 34,000 mi.
[all info from 84-89 service manual]
Appendix lists new disc at 7.5mm
My before prep on rear disc was 7.38mm
Prepped disc is 7.34mm

In the chassis section, on page 5-5, min disc thickness is listed at 6.5mm      however on page 5-13 in the exploded view, brake disc wear limit is shown as 7mm. I believe the 6.5mm the correct value as I read somewhere there is 1mm of total wear availble.


I am suprised that with 100 grit paper, I only removed .04mm, however as I was working the metal, I could tell it was VERY hard metal. I guess the grooving was not as deep as I thought it was. Also even though I started out with 100 grit, the paper wears down quickly and I finished with much smoother grit.  
 I am doing a rear shock mod. and could not get front discs measurement yet as back of bike is all torn apart and I did not think it a good idea to try and balance bike with rear wheel and front wheel off bike.
Hope to have mod done this weekend and will get that measurement first thing next week.  FJMonkey- will follow your advice and watch wear on pads as they break in. It may be necessary to re-refinish with a finer grit.

[bigbore2]

It took about 300 mi to break in the pads.  I just got back from a 3300 mi. trip and brakes are excellent. No pulsing. I put in stock Yamaha pads. Wish I had a camera to have posted this rebuild. All this for $28 as I had to rent a 4 1/2 in. die grinder and buy the disc adapter and the paper.  Harbor Freight 4 /1/2 die grinder is less than $20.  New Makita is $40.