brake disc don't fit with new brake pads

[marp68]

Have a B -75... with 34 mm forks.

So, I bought a new pair of brake pads and they fit nicely in the caliber holes. But when putting back the wheel/rotor, there is not enough space between the pads for the rotor.

And no, it doesn't have to do with not squeezing the piston enough in. The pads are seated as much as they can.

And yes, the PO seemed to have swapped the forks, so the calibers ends up behind the fork instead of infront. If anyone thinks it look strange...

The rotor are 7 mm thick, the caliber the gap is only approx 11 mm wide and the brake pad is 8,8 mm thick (pad material is about 6,5). It seems that the rotor is too thick for this caliber.

EDIT: (BTW, the caliber on the image are fitted with the old brake pads. The new ones are on the other image, on the table.)

After searching info about discs etc. for xs650, it seems to exist also 5 mm. I only find 7 mm to be found for 77-84. Does anyone know which is the original disc thickness for a B -75? I can't believe it's 7 mm. Or could it be wrong calibers, maybe from another Yamaha? Or which other 5 mm discs from other models fit the wheel and caliber? Discs from SR500 and xs1100 seem to bolt right on, but does it fit correctly in the caliber?

And what would be the most easy and economical solution? To make an upgrade with new and better calibers or just grind off the existing rotors down to 5 mm or more? I have a local workshop near that may would be able to do it.

Cheers

 

[fredintoon]

Hi marp,
the 1976 XS650-C carried it's front disc caliper behind the fork, perhaps the bike's PO made that swap?
The SR500 & XS1100 discs are made all in one piece rather than a disc bolted to an inner support like yours and they have more offset too, so although they will bolt straight onto your wheel they won't line up with the slot in the caliper.
Did you completely dismantle the caliper and thoroughly clean it's interior?
Perhaps the caliper pistons are bottoming out on rings of interior corrosion that prevents them from backing all the way off?

 

[gggGary]

grind some thickness off the pads? Precautions dust etc.

look at the thread list below this post you may see some similar situations.

 

[TwoManyXS1Bs]

ReycleBill posted a lot of disc/brakepad info here that may help:

http://www.xs650.com/forum/showthread.php?t=22558

 

[marp68]

Thanks for the info

I've had other bikes before (i.e. a Ducati Monster, which i btw put spoked wheels on, and an older Honda) and know about the squeezing procedure of the pistons. But on this caliber the pad cannot be seated anymore, since the little T-shaped wing that is sticking out can't go deeper. If you know what I mean... But I will have another look.

And this caliber only uses one piston and the opposite pad rest on a shoulder and can't be pressed in more due to the T-shaped wing on the pad.

I couldn't even put both pads in the caliber. After putting one pad in, there was not enough room for sliding in the other one. To much pad material sticking out.

Grinding the pads off will be of no use, since they will look like the old ones.

But if you look at the image showing the rotor in the caliber, does that look correct? To me the rotor seems to close to the caliber walls. Also very close to the fork itself. I'm pretty sure the caliber is the correct one, but was 77 mm standard on the European dual disc B models?

I ended up mounting the old ones back, but will have another go.

 

[marp68]

Wow, that's a lot of info TwoMany.. Thanks

 

[gggGary]

And this caliber only uses one piston and the opposite pad rest on a shoulder and can't be pressed in more due to the T-shaped wing on the pad.
.

IMHO; there's the answer, this is a TWO piston caliper that's not a shelf, it's a stuck piston.

I'm a 'merikan single disk kinda guy there could be a, unknown to me, caliper used on one side, then again I doubt it because then that caliper would have to float. Marp68; don't worry, I think you are a chap of high caliber.

 

[650Skull]

Every thing changed from 77 and later, Caliper, disk, pads, and the SR500 XS1100 and some XS750/850 triples, calipers, disk, pads will interchange from 77 and later. Not for your model

XS650 had a 7mm disk on the early, 72-76, and later model, 77-83.

Your 75B had the forks changed over from the Yamaha factory. You will probably find there is a tab for the brake line facing forward as well as the one on the rear.

 

[5twins]

I think Gary nailed it, a stuck piston. I encountered this on an RD350, which basically uses the same caliper. The brake worked but not very good because, well, it was only half working, lol.

 

[fredintoon]

Hi marp,
you are working on just one of the two front brake calipers shown in your photo?
Like the punchline in the old joke about the single Celtic warrior claiming he could beat 5 Roman Legionaires, "Don't go, it's a trap, there's two of them!"
Because like Gary says, that caliper has two pistons.
Use the ol' grease gun trick to get the stuck piston out of there, eh?

 

[marp68]

Holy cow, one learn something new everyday.... CaliPer it is then..

And two pistons it is... I have the Clymer manual, but was so sure it was only one piston. Then perhaps, if both pads can be seated 1 mm more each, that may be enough. Didn't measure exactly while testing the new pads. Will do. It seems that i will go over the instructions I found earlier somewhere on the forum on how to repair calipers. BIG thanks, don't know what I would do without this place.

Another perhaps odd question. When changing brake pads on this model, does one normally have to remove the wheel/rotor to withdraw it from the caliper to be able to change pads? Or should it originally be possible to, after unscrewing the lower caliper bolt, fold the caliper upwards and off the rotor? As you can see on the image, the position of the metal brake line makes it impossible to fold the caliper upwards against the fork. Before withdrawing completely from the rotor, the brake line hits the fork. Did the PO put the brake line back incorrectly or should it look that way (beside the fork side swap)?

Maybe I should get rid of the metal brake line part, if it would make it possible to inspect or change caliper and pads without having to remove the fender, wheel etc.

 

[marp68]

And here's my old tribute to spoked wheels. And this was before those ugly retro Ducati appeared...

 

[gggGary]

These ARE a PITA to work on, even the single rotor US models are hard. If I was messing with one very much the stud would be gone and I'd use two bolts to hold the caliber to the fork leg.

 

[gggGary]

Well it might be a bit of a trick. Yeah wouldn't recommend it. Swap the forks, brakes etc.

 

[NONclow]

Some inventive folks use three bolts!

http://www.xs650.com/forum/showthread.php?t=39110

 

[marp68]

If I'm going to drain the system from brake fluid and take apart the whole caliper to repair it, then maybe it would be a good idea to get rid of the S-shaped metal tube part and replace the whole system with braided stainless hose all the way into the caliper.

The hoses has been changed with new rubber hoses which look okej to reuse.

I don't even understand the reason with the S-shaped metal brake line in the first place. Why not just a straight hose down into the caliper? With just rubber or braided stainless rubber hose. Like on many newer bikes...

And that's why I would like to know if my set up with the S-shaped metal tube is correct. And if someone knows if it's possible, without the metal brake line hitting the fork leg, to unscrew the lower bolt and just loosen the upper a bit, and then, sort of, just "turn" the caliper upward, around the loosened bolt, towards the fork leg to free the caliper from the rotor. Just to make it easier to change pads in the future. Or would the caliper first hit the rim before being free of the rotor. Sorry about my maybe a bit confusing English...

Or am I missing something here?

 

[marp68]

A repair question...

In all threads about removing the pistons, everyone seems to do it after draining the brake fluid and separating the two caliper halves. Is it not possible to first, before draining and separarting the halves, use the lever and brake fluid pressure to press out the pistons a bit?

EDIT: I of course mean to press them out a bit, maybe until they meet each other, then separate the halves and use some sort of grip to get them out the last bit. Has anyone tried that?

 

[gggGary]

Yes you can do that, it's actually a good way to get them freed up, but one piston will move the other will just sit there. you can put a piece of metal into the caliper slot to stop the moving piston and force the other one to start moving. Since you know the inner piston is stuck; place a used pad on the outer side, the chunk of metal in the slot, and start pumping, see if that will free up the inner. you will need to have a chunk of "stuff" in the other caliper as well.
When a piston is really stuck it helps to force it back with a c-clamp then pump it out again. do this a time or two.

 

[marp68]

Thanks for the advice. I will get right to it during the weekend. Will let you know how it proceeds.

What about the S-shaped metal tube part at the end? Okej to remove, if I decide to go for new braided stainless hose? Just saw that there is another metal tube part, more at the top, between the T-split and the upper rubber line.

 

[gggGary]

IT can be done without the metal tube but you may have to route the line around the outside of the fork tube, there just isn't enough room for a full size line where that metal tube is now. Sorry I have not done a metal tube removal on an early system "yet".