refurbing disc brakes

[aaroncarver]

Newbie working on my first bike, 79 xs400, and looking at the discs, they're grooved (and mildly rusty) so I'm going to have to do something about that. The groves are quite visible, but they don't feel that bad and I'm wondering if there is anything I can do to renovate them myself w/o paying to have them shaved. Is sanding stupid/dangerous? And can I use a regular ol' drill to drill holes in the discs? Maybe this is a really dumb question (sorry).

And regarding the pads: how do I know if they are worn out or not?

I'd like to go with totally new discs/calipers like some folks here (like Drewpy: Nice look btw!) but for my first build I want to keep the budget in check while I learn something about motorcycles.
thx in advance

 

[tonupNW]

You can try and scuff them up and get rid of some of the grooves/glaze by wet sanding with 600-800 grit and clean them off with brake clean. But I personally would get new rotors if they're pretty well grooved. As far as pads, if the friction material is thin (less than 2-3mm) and they looked glazed up, replace them. As far as drilling rotors, you can use a regular drill but I would recommend a drill press. Make up a template the size of the rotor, lay it on top and center punch your mark.

 

[hardtailed77]

Definitely going to need a HSS bit to do the rotors as well...

 

[tonupNW]

Yes hss or cobalt if you have the coin.

 

[hmusket]

New pads are about 1/4" thick. For me. if they are 1/8" or less, I replace them. Try some brake cleaner and a scotchbrite red on the discs and see what happens.

 

[aaroncarver]

I see several OEM rotors on ebay and I might go that route...but my fear is that when they come in the mail they'll be just as grooved as what I already have.

I don't want to have the attitude where I just throw money at the problem, but it seems that if I go with some aftermarket rotor then I'll have to go with an aftermarket caliper. And then I'll have to find someone to weld new caliper mounts...and that's throwing alot of money at the problem My chief concern is having a safe bike and I new enough at this where I'm not sure of the right answer.

 

[bcware]

A few points:

From my experience with cars, resurfacing a rotor is not terribly expensive; about $30-40 per rotor; never go to a dealer. However, unless your rotors are warped (i.e. not parallell; rare) or have deep gouges you probably don't need to resurface them.

Minor scoring of the rotor isn't going to do much. Smoothing the surface with sandpaper should be fine. Some rotors, slotted, are actually designed to shave off the pad material for high end applications.

Drilled rotors are bad; drilling yourself is not a great idea in my opinion. Drilled rotors crack the most and these are engineered rotors I am talking about, not home-brew. And yes, I know, most high end cars come with drilled rotors, not slotted. The books I've read on high end braking systems have me convinced slotted is superior.

 

[crush1776]

Rotors with concentric grooves, ie the direction of rotation WILL wear pads prematurely. In the brake industry just swapping out brake pads is called "pad stacking" and is a half arsed way to do a brake job.

BC: I believe the type of slots you are referring to are along the radius lines from the center to the edge and do aid in cooling, but grooves scored from worn pads are a no-no.

Drilling rotors is an old-school high performance trick to aid in cooling. Depending on who you believe it is either effective or it isn't on original rotors. It does structurally compromise original rotors that are not designed to be drilled, but all modern high performance rotors have reliefs in them of some sort. The metal on our bikes is in most cases 30+ years old remember.

I would not hand drill rotors, if I was going to take the risk I would want them as uniform as possible. I understand wanting that cool drilled look, but it may be a risk.

I had a rotor crack on a bike once, it had no noticeable effect on the braking. Scared me when I discovered it though. And if it shattered before I noticed it it could have killed me possibly maybe kinda.

 

[dO-bOy]

i'm gonna definitely say no to drilling your rotors. i've seen x-ray type photos of used drilled rotors online and cracks actually form from the holes. and this thing spins around not too far from your shins or your face even.

 

[aaroncarver]

I understand wanting that cool drilled look, but it may be a risk.

I guess it wasn't the aesthetic of the drilled discs that I was going after, but performance. But I hear you about the old rotors not being engineered for it. I guess I should just take them to somebody and get them resurfaced and then save up for the new rotors/calipers.

TONUP, you said "if the friction material is thin (less than 2-3mm)," I should replace the rotors. Well, the width of the disc on both is 4.5-5 mm so I should be good.

 

[OliverB]

I once had a car rotor "lightly touched up" instead of the full grind. Removed some of the irregularities. You will always get some small groves on older rotors, you just don't want deep grooves. I wouldn't allow them to take much off. I don't know how the industry feels about resurfacing cycle rotors - probably not too keen on it.

 

[tonupNW]

Ive got a rotor that ill sell you on the cheap if you want it. Its off my project, im gonna run a 320mm rotor so I dont need it. Its in good shape, has a few minor grooves, just enough to catch your fingernail on. Just scuffed it up to clean all the glaze off of it. Measures just under 5mm

 

[tonupNW]

And when refering to friction material I was refering to the pads. Should have clarified that.

 

[dO-bOy]

This is in relation to the calipers. I'm looking at the caliper rebuild kits available online and some of them appear to include the piston as well. Is that anyones experience? Yamaha rebuild kits only include the seals. My pistons might be useable but I'd rather not.

 

[tonupNW]

If you have any question wether it comes in the kit, just give the vendor a shout. If it was me I would replace the piston if I had any doubts. Stuff a rag in the caliper and use a blow gun and apply gradual pressure until the piston pops out. then clean the caliper really good, lube up the new piston and slide it home. Then drive in the new seal carefully and make sure to lube the lip slightly.

 

[hardtailed77]

^ "Slide it home"......"Lube the tip slightly".....wish my girlfriend talked more like that!!!

 

[tonupNW]

lol, dont we all.

 

[aaroncarver]

Tonup

Pm me. I'm interested in the rotor, depending on the price of shipping. I'm in Wisconsin, so the shipping might make it more feasible for me to look for one here.