Front disc wearing more at the outer edge...

1981 XJ650 Maxim:
I tore down the brake system and cleaned everything, replaced the lines with braided steel, got new (nos) pads (which looked a little thin). I cleaned everything. I put in a new seal kit. Had the rotor turned a little but still within spec. I put it all back together and did a couple of fluid flushes...

After putting all back together, I have a much firmer feel at the handle (I attribute that to the steel lines and replacing rusty water with clean brake fluid...) But, the brakes only stop marginally better and I notice that the pads are only contacting the disc at the very outer edge. I'm considering putting the old pads back on but I thought I'd ask here first. Why am I not getting full pad contact on the disk? I only have about 100 miles on that setup. Should I just let it wear in more. I get the pivoting caliper and angled pads part. They do retract. I don't think they're getting stuck. I think some angle is wrong.

The pads I got were:
EBC BRAKE PADS
PART# FA61
FRONT

FITS ALL 1980-1983 YAMAHA XJ650 MAXIM & XJ650 MIDNIGHT MOTORCYCLES...FRONT ONLY


Any ideas?

 

Possibilities:

You got the pads in "transposed."

The caliper isn't doing its "pivoting thing" like it should.

 

The pads seem to only go on one way. There's the hole for the pin in the bottom. If they were on the wrong way they'd be back to back I think. Am I missing something?

The caliper was pivoting really easily when the wheel was off -- I mean really easily. But, that is something interesting to check.

Would you recommend trying the old pads or is that always a dumbass thing to do.

 

Lay a straight edge against the rotor to make sure that it wasn't worn unevenly by the old pads.

 

OK bigFitz52, with your 20K posts I wanted to make sure I was being very careful in my responses...

I pulled the pads. The caliper pivots like new. The pads on my model do indeed only go on one way. I used a round file to slightly widen the pin hole and a flat mill file to deburr the tangs that go into the pad retainer slots at the top and rear of the caliper. I greased the pin, reassembled, and test drove. The disc was warmer. Bike still seems to stop the same. I'll give it a week or so and see where it's at.

Now onto the more anal part of the analysis (note you can't spell the latter without the former ). If I take two new pads or two old pads and put them together -- pad material to pad material and holes aligned -- the metal plates are parallel. But, if I take one old pad and one new pad (with the pads "wedging" in opposite directions of course and the pin holes aligned), those mounting plates are slightly out of parallel. That means the bevel angle on the new pads is slightly different from the wear in-angle on the old pads. I can't figure out why -- maybe some part on the axle was changed to reposition the lateral position of the disk or a part is missing, etc. Either way, wearing in the new pads to that angle or going back to the old ones seems to be the only way I'll get even wear on that disc.

And, of course, thanks for such a fast response bigFitz52.

 

k-moe (love your avatar BTW). One of my all time favorites...
The disk was just turned. I was thinking of a way that that process could have left the disc tapered one way or another, but I can't see how that lathe could have done that on purpose unless the cutters evenly loosened -- perfectly symmetrically -- on every single cut. Not sure that would happen so easily.

However....
Since the dude abides, I went out and checked it with my most trusted straightedge and it is slightly dished. On the outside, with a straightedge going from about 8 'o clock to 4 'o clock, I can slip a 1.5 thou feeler under the straightedge at the inner-most part of the braking surface. That's the opposite of the angle of the evolving wear pattern. So, good call on that. I'm sure 1.5 thou on both sides (can't measure inside because my straightedges are too thick) would make for no wear on most of the disc until the pads wear to that angle.

Fascinating. Thanks k-moe.

 

Because the caliper pivots and there is a piston on only one side several factors come into play:

The thickness of the rotor will affect how squarely the pads set down.

Any side to side variation in the rotor will affect how squarely the pads set down (double check your wheel and rotor installations).

Frankly, I'd be surprised if any of them sit flat until they've worn a little. Get someone to grab the brake while you dive in with a feeler gauge. If I couldn't get a 0.010" gauge in on the "loose" side I'd move on to something else.

 

Great response MiCarl.
I'm definitely not at 10 thou. I can see that by eye. Plus, with all the other factors everyone mentioned, the'll never be right out of the box. What brake manufacturer is going to have sub-thou pad material cutting accuracy.

And, there are plenty of things to move on to -- like do I spend the cost of the bike to have my carbs rebuilt and when I remove them are those intakes going to crack so bad I need to replace them for like 200-250 (half the cost of the bike). You know, stuff like that...

Actually... I think I figured it out -- not that it matters... Cast iron is brutal on cutting tools. The guy did 3 or 4 passes on the lathe. So, if the tips of the cutters wore ever so slightly with each pass, I'd have a dished cut. And, the lathe would sound the same throughout the entire pass. OK, now onto other stuff like MiCarl told me to...

 

MiCarl,
Is the bike in your avatar pic an old Yamaha 50 or a Premier or somethin else?

 

Umm...

In regard to "turning" the disc. If it was simply "turned" using a brake lathe, there's at least part of the problem. And your rotor is now scrap (sorry.)

Your original disc is stainless steel. In order to "turn" them, they need to be sent to somebody who can Blanchard grind them simultaneously on both sides; and remove very little metal in the process. There are some (not a lot of) shops that can do this; myself and a few other members have had it done correctly. The shops that can accomplish properly resurfacing the rotors are usually in the business of doing race car brakes. The place I used specializes in brakes for Formula V (VW chassis-based) race cars. If you call around and people tell you you're nuts or pooh-pooh the idea, then they don't know what they're talking about. It can be done right; and the people who can do it right will have the right answers. Or just upgrade it.

You can eBay another rotor; or get an EBC floating-rotor replacement (Chacal has them.) Biggs has them on his Seca; see this thread: http://xjbikes.com/Forums/viewtopic/t=46285.html

I have an EBC rotor on my '83 also, but I painted my hub.

Here's a pic of the stock rotor I had Blanchard ground and drilled:

 

I bought one from China and had to return it (to China) because it was too small. Do people on the site have good luck with the right size ones from China?

Both the stock and the Chinese one were supposed to be stainless but they held a magnet. Not sure if that matters. When I watched the turning, it looked like steel (with twisty swarf) laminated on top of cast iron (dust swarf).

 

Stainless steel is still a ferrous alloy, of course it will attract a magnet.

"The turning" is the issue. Just out of curiosity, put a mic on it and see what you were left with, thickness-wise.

A Blanchard grinder is a vertical-axis surface grinder. The proper rig to grind our rotors involves TWO heads, one on each side of the rotor, grinding at the same time. Even most shops that do Blanchard grinding are usually only equipped to do one side at a time. But like I said, there are a few that can do it right.

People on the site have good luck with quality parts; I've bought Chinese rotors for a car that were warped in the box. False economy. Lesson learned.

Either upgrade to an EBC (highly recommended by all those who have done so, right Biggs?) or eBay a decent used rotor and if it needs to be resurfaced send it to a qualified shop that can do it right.

Dude. Your life depends on your brakes. Don't "cheap out." Fix it right and be done with it.

Plus floating rotors are sexy.

F* China. PM Chacal.

 

So, who is the shop who did your grinding and how much did they charge?
300.00 for a rotor is still just freaking me out, but maybe I'll get over it.

I measured 7.5mm which is min operating as per manual. I don't get why we can't turn if the system in operation is doing something similar. But, your idea of two sided blanchard grinding does make sense.

 

Barry; It's not "my idea." It's the only way to effectively resurface thin stainless steel rotors without screwing them up. I don't make stuff up; I'm here to provide technical assistance. If I didn't know from whence I speak I wouldn't. It truly is the only way to do it right.

When I had the one done I posted the pic of, about 4 years ago, it ran a whopping $75 plus shipping.

I'll have to do some digging to find the guy again; but somebody else on the forum had similar work done recently as well. Maybe he'll chime in.

Meanwhile you'll need a different rotor.

And you didn't PM Chacal did you? http://xjbikes.com/Forums/viewtopic/t=44636.html

Quoting now:

"HCP4133 Aftermarket oem-replacement front DISC BRAKE ROTOR, left side, spiral drilled cooling holes with a fully-floating, riveted hub design, fits all XJ650 Maxim and Midnight Maxim models, XJ1100 models, and XS1100 models. $ 229.95"

That was December, last. I doubt they've gone up $70 in the interim.

 

Austenitic stainless is non magnetic. Most stainless production is of austenitic alloys. My father always used to refer to it as "the good stuff."
Quick rule of thumb if you're trolling the scrapyard for stock: the less the magnet sticks, the more corrosion resistant the stainless is.

Barry, Fitz speaks the truth about how to resurface stainless rotors. They are remarkably easy to screw up if the incorrect method is used.

 

I'm not disagreeing. I just wish someone would explain why? Especially why turning on a lathe is so different from brake pad wear. I would just like to understand more.

 

I just would like to understand more about why turning them is so different from brake pad wear?

 

Usually when a rotor has to be turned, a significant amount of metal will be removed. With a bike, the rotors aren't very thick to begin with. I love having all the metal I can, it takes longer to heat up.

 

Oh, I guess I didn't really answer the question. Brake pad wear on a disk is rarely even. Usually one side will wear slightly more than the other. The purpose of turning it is to give it a fresh surface for new pads, as long as the thickness tolerances are in spec before AND after.

In the automotive world, a lot of people like to "pad slap". Ignore the rotor and throw new pads at it, and then complain that their brakes have worn fast. The new contact point has to wear down quicker to eventually conform to the wear pattern of the old pads.

If you can afford it, do it all correctly the first time with quality products. If you can't afford it, park your bike until you can. I'd rather be able to stop fast than accelerate fast.

 

I'm not a very aggressive rider and I have engine braking and rear brake in case my front rotor spontaneously shatters... I just dont see it happening. It's still within spec. No one's answering the metallurgical question (which is fine based on scope of forum) and I'm working with Chacal to get the right rotor on the bike.

Not thrilled about pulling the front wheel again, but at least now I can do it in my sleep.

I'm just freakin because the issues with bike rotors are so new to me. I'm with you with the "more metal the better" from the car world. But, car rotors cost 50.00 for the good ones.

I would never put new pads on anything without turning or replacing rotors.

 

Sorry for the "lack of why."

When you "turn" a rotor on a brake lathe, you remove some serious metal, and only from ONE side at a time. This causes uneven heating in the metal and will cause uneven expansion, resulting in what you got when you had yours turned.

When you apply your brakes, the pads are in contact with both sides of the rotor, so the rotor heats up evenly.

Blanchard grinding is a fine, surface-finishing process that removes very little metal if done correctly. Blanchard-grinding BOTH sides simultaneously doesn't cause uneven heating in the rotor and allows a nice smooth non-directional finish to be achieved with the removal of very little metal.

Car rotors only cost $50 because they're cast iron, not an expensive stainless alloy; and also because there's a heck of a lot more demand for them. A large percentage of motorcyclists never put enough miles on a bike to actually wear them out.

 

Thanks bigFitz. This lathe was one that simultaneously cuts on both sides at the same point. I had to remove a lot of metal because the warping was so bad that my headlight bobbed when I came to a slow stop. I do a lot of metalworking. I would agree that double sided grinding would provide the best, most even, and smoothest finish possible and I've never seen a two axis grinder in my life so they must indeed be very special shops that have these rigs.

P.S. Original owner of Norton Commando 850? Sweet (even though this is an XJ650 site).

 

Honda Mini Trail 50.

 

Cute.

 

So, just called my local "blanchard grinding shop..."

Seems that a blanchard grinder is a one sided, very accurate grinder on which it would be tough to do both sides of our rotors (take a look on youtube). What was described above and which would work could be some setup with a dual axis "regular" grinder which they call "double axis grinding" Two disks, spinning perpendicular to the cutting surface and which can be adjusted towards or away from each other. Even this setup with a holder for our offset rotors would be rare. I think the Blanchard system could be used one side at a time with some fixture to hold the rotor flat while cutting the left side. Both rigs would use flood coolant so they would be cutting so cool you could touch it. With that, cutting one side at a time should be fine and the accuracy of these systems is so tight that it would not be an issue.

If someone knows of a shop that can do this dual axis or blanchard grinding on our offset rotors and the cross drilling like BigFitz had done, I'd love a referral on that.

 

I will dig back through my records this weekend and see if I can locate the guy that did mine.

All I can remember for sure is that it was a race-car brake shop that specializes in Formula-Vee cars.

 

Thanks BigFitz. Not a hurry. Plus, the race shops are setup for the pretty drilling which is also nice-to-have.

 

you said the rotor is at min. thickness so if you do anything else , it's under size.
throw it away.
you or anyone else cant turn a warped rotor no matter what kind of machine they have.
if the rotors warped and you make it true the thickness will vary, that's just as bad as warped. so just.
throw it away

 

Correct on the min thickness and nice job attending to detail. I'm going to get another one and start from scratch and use the race shop service, or get an EBC replacement (which is thinner than min thickness of our rotors).

I don't agree with your statement about varying thickness. If I take all the warp out of disc on both sides I will have disc with consistent thickness by definition.

 

think about it for awhile. if it's warped and you grind it true the thickness will have to vary. ain't no two ways about it

 

That's only if I grind only one side true. Absolutely. If I simultaneously grind both true, I re-even the thickness. If I do one side and then the other and my rig is not setup just right, I could create a wedge. But, most industrial grinders are sub-thou accurate.

Let's use the example of just working on a lathe. I want to make a spinning top with an even disk in the middle. I turn one side (the one with the top handle) and then I turn it around and chuck the handle. Then I turn the other side. If my lathe's on the money (and mine's 75 years old so probably not), then the disc will be of even thickness.

 

confusion, first your cutting one side at a time, now we grind both sides at once. so this must just be theoretical.
so if you grind both sides you will get a even thickness. but you get a even thinner disk
are they really warped or just dished ? and did you measure the thick part or the thin part

 

Uncle.