Having trouble with salty_monk brake upgrade

[salty_monk]

So the new fork legs are also 35mm and you are using the stock triple tree?

My best guess is that the donor bike triple trees would be wider than the single rotor model. Ordinarily you'd have about 9mm between braking surface and fork leg.

If you remove the spacer behind the rotor to give you the 9mm what happens? Does the caliper then interfere with the wheel spokes? Is the caliper center offset to the rotor braking surface center (viewed from the top) at that point?

When you use the GS550 rotors instead of the CBR the offset is a little bit off center but it doesn't seem to matter at all (other than making it more difficult to fit the calipers).

The measurement you need is what offset will center the braking surface in the middle of the caliper. We then just have to check for caliper to wheel spoke clearance as if you have bolt to rotor clearance now then that will only grow not shrink.

if you need thinner rotor spacers I can swap yours over. I have a couple of odd sets of thinner ones that should work.

Also just humor me and check rotor dia is 295mm just in case.

[MadCapsule]

So the new fork legs are also 35mm and you are using the stock triple tree?

My best guess is that the donor bike triple trees would be wider than the single rotor model. Ordinarily you'd have about 9mm between braking surface and fork leg.

If you remove the spacer behind the rotor to give you the 9mm what happens? Does the caliper then interfere with the wheel spokes? Is the caliper center offset to the rotor braking surface center (viewed from the top) at that point?

When you use the GS550 rotors instead of the CBR the offset is a little bit off center but it doesn't seem to matter at all (other than making it more difficult to fit the calipers).

The measurement you need is what offset will center the braking surface in the middle of the caliper. We then just have to check for caliper to wheel spoke clearance as if you have bolt to rotor clearance now then that will only grow not shrink.

if you need thinner rotor spacers I can swap yours over. I have a couple of odd sets of thinner ones that should work.

Also just humor me and check rotor dia is 295mm just in case.

Yep. The new fork legs are 35mm and the triple tree is stock, as far as I know. The lower triple was on the bike when I bought it. The top triple is from a '78-'79 750, to accommodate a new ignition switch.

I'll check the clearance without the spacers behind the CBR rotors and with the Suzuki rotors when I get home and get back to you on those. (I have two single-disc rotors from a 750, which are the same size as 550 rotors, correct?)

I'll also confirm that the CBR rotors are 295mm.

[MadCapsule]

OK, the CBR rotors are indeed 295mm (11 5/8").

I'm putting them back on without the spacers right now.

[salty_monk]

Ok good! Let me know what the results are!

[MadCapsule]

Strangest thing. It all seems to line up without the spacers on. There was some extra room between the fork leg and the caliper hanger as well as between the lower bracket hole and the spacer, but I took up the slack with a washer for each and it's fine.

There's now plenty of outer brake pad visible above the retaining clip.

I just need to cut a few threads into half of the rotor bolts. Six of them have the Suzuki S on the head, six do not. The six without the S have a shoulder that is slightly too tall and it butts up against the threads in the hub. Wasn't an issue with the rotor spacers installed.

[steve murdoch]

Did you get a chance to measure the offset when you had the rotors off?
Glad you got it sorted

[MadCapsule]

Did you get a chance to measure the offset when you had the rotors off?
Glad you got it sorted

No, but I'll measure it tonight when I put the rest of the rotor bolts in.

[salty_monk]

Those rotor bolts will be your original ones. The older bikes had those ones with a taller shoulder. Either that or they are from the rear.

Glad you got it sorted.

If a washer fixed it I don't think I have anything that thin that you could put behind the rotor as an alternative... I might have a set of 2mm ones somewhere but sounds like even they would be too thick!

[MadCapsule]

Yeah, it seems that this particular combo doesn't need the spacers. If remember correctly, the offset of these rotors measured about 20mm.

Thanks to everyone for all the help. The bike stops on a dime now! The new brakes combined with a set of Sonic fork springs and fresh fork oil has completely transformed this bike!

[salty_monk]

Nice! Maybe those rotors are a weird one.. it should be less than that.

Do you have a way to reasonably accurately measure centre to centre of your fork legs?

[MadCapsule]

Nice! Maybe those rotors are a weird one.. it should be less than that.

Do you have a way to reasonably accurately measure centre to centre of your fork legs?

It's also possible that I measured the offset incorrectly. I turned the rotor so that the outer braking surface was flat on the ground and use the depth gauge on a digital caliper to measure from the back of the carrier down to the ground.

I'm not sure how accurately I'll be able to measure center to center on the fork legs, but I'll see what I can do. What will that data help you determine?

[Guest]

It's also possible that I measured the offset incorrectly. I turned the rotor so that the outer braking surface was flat on the ground and use the depth gauge on a digital caliper to measure from the back of the carrier down to the ground.

Did you account for the thickness of the buttons that hold the rotor to the carrier? They stick out and would skew your measurements. Try laying the rotor with the mounting surface (the part up against the wheel) on a flat surface and measure up to the rotor face.

I'm not sure how accurately I'll be able to measure center to center on the fork legs, but I'll see what I can do. What will that data help you determine?

Measure outside-to-outside or inside-to-inside of the legs then add/subtract the leg diameter to get an accurate measurement of the tube spacing.


Mark