Twinpot Brake upgrade on 78 Skunk

[hannibal]

I know 10.9 steel hardware is recommended for the calipers and brackets. I need to source the bolts that hold the rotor to the wheel hub. Should I use 10.9 steel or stainless for these?

Edit: my bike has a thin plastic spacer between the hub and rotor (#16 in the diagram). I assume I ditch this and just use the metal spacer from the kit since the dual disc bikes don't have the plastic spacer. Correct?

Do you guys use the "washers" (#15) on the rotor bolts as well?

 

[johnod]

Re #15, I do , it locks the bolts in place.

 

[salty_monk]

G
The aftermarket now has cost effective alternatives for new rotors. Are there brand new (Asashi?) rotor, rotor carrier, and buttons that can be recommended that don't require drilling modifications? Part numbers would be helpful. Ebay is such a crap shoot.
Thank you for your time

Nope. All of them need drilling to some degree.

 

[salty_monk]

Entering comments in quote below with a ****

I know 10.9 steel hardware is recommended for the calipers and brackets. I need to source the bolts that hold the rotor to the wheel hub. Should I use 10.9 steel or stainless for these?

**** I have used Stainless before but made sure it was a decent A2-70 grade. 8.8 or 10.9 regular steel would be better.

Edit: my bike has a thin plastic spacer between the hub and rotor (#16 in the diagram). I assume I ditch this and just use the metal spacer from the kit since the dual disc bikes don't have the plastic spacer. Correct?

**** CORRECT

Do you guys use the "washers" (#15) on the rotor bolts as well?

**** YES

 

[hannibal]

Thanks for the answers.

One more question: is there any reason a Suzuki piston and seal rebuild kit (from a GS500 or GSX1100G) wouldn't work on a Kawasaki caliper? I tore down my Kawasaki calipers to inspect them and was planning to replace the seals and dust seals, but at least one of the pistons has some minor pitting. The Kawasaki piston and seal set is about $50 per piston ($100 per caliper), and the Suzuki set is under $40 per caliper. The calipers are identical (as far as I can tell), so the Suzuki kit should work in the Kawasaki caliper, right?

 

[Chuck78]

Should be identical parts...
Good to know the Kaw stuff is for rich people & Mr Suzuki prices parts for the common people, THANKS!

 

[johnod]

Why should they be identical?

 

[hannibal]

Thanks Chuck. Just wanted a sanity check.

Why should they be identical?

Tokico makes the calipers and Kawasaki and Suzuki both use them. The parts diagrams are identical. I assume the caliper components are made by Tokico (or likely a Tokico supplier) but Kawa and Suzuki package and price them differently.

 

[johnod]

I see, did not know that, good to know. Thanks.

 

[Guest]

I'm not sure if this has been discussed before in this thread but I have searched the best I can and can't find anything. Basically what I want to know is if there is any benefit to the twin-pot caliper on only one side? I'd kinda like to keep the look of the single rotor with spokes on the 78 Gs750 but would also like better braking performance. Common sense tells me that there should be some improvement with a larger swept area but is it worth it? If so how about MC size for a single caliper? Stock rotor or aftermarket?

 

[johnod]

I'm sure there will be a benefit even with just the one caliper.

 

[Chuck78]

Yes you will definitely benefit with just one side on a 750, as you will be getting twice the swept area and be going from 295 mm rotor up to 310mm. You need a 98 - 99 CBR900RR rotor to do this. And you just need the caliper bracket, you do not need the rotor spacer as that rotor already has 23 mm offset.

I would definitely recommend getting a good brand new set of pads and a stainless steel brake line if you are just going single-disc, you will want every bit of performance you can get. This setup is plenty adequate for a GS 550 which is about 50 pounds lighter than your 750. If you are riding a 750 really aggressively and on very twisty roads, or if you have a lot of big hills around, a dual disk would still be beneficial to keep them running cooler and not have to suffer from anywhere near the amount of brake fade when the rotor(s) get hot.
On a race bike, dual discs are also beneficial as then you have the fork twisting forces somewhat equalized since both fork legs are trying to twist under the braking force.

 

[Guest]

Yes you will definitely benefit with just one side on a 750, as you will be getting twice the swept area and be going from 295 mm rotor up to 310mm. You need a 98 - 99 CBR900RR rotor to do this. And you just need the caliper bracket, you do not need the rotor spacer as that rotor already has 23 mm offset.

I would definitely recommend getting a good brand new set of pads and a stainless steel brake line if you are just going single-disc, you will want every bit of performance you can get. This setup is plenty adequate for a GS 550 which is about 50 pounds lighter than your 750.

Thanks for the info, I think I'm going to go for it and see what happens. I already have a cool set of (very expensive) blue anodized stainless lines. I'm not really looking for all out performance at the moment since my exhaust limits my ground clearance anyway. I just want a little better brakes for an extra margin of safety and for the occasional spirited riding I do. Also I'm in florida so all the roads are all straight
How about MC bore size? I've got a 14mm aftermarket MC for the stock system. What is the piston volume of the Ninja caliper?

 

[salty_monk]

The Ninja MC is a 14mm (aka Ninja 250) if you use one or 5/8" (aka bigger ninja, concourse etc) if you use two...

 

[Chuck78]

I usually recommend using a ninja 250, GS500, or Bandit 400 master cylinder for the single disc setup, & I believe those are all 9/16"? It is basically the same as GS stock single and dual disc master cylinder bores. It was 5/8" for the dual. Funny thing is, despite being metric parts, the bore size i recall seeing cast into the parts in inch sizes on some of them! Sort of like inch sized tires worldwide, except for newer bicycles, & car/truck widths being in millimeters (but not rim diameters still, standard is in inches!)

 

[Guest]

The Ninja MC is a 14mm (aka Ninja 250) if you use one or 5/8" (aka bigger ninja, concourse etc) if you use two...

Does this Vintage Brake chart still make sense? http://www.vintagebrake.com/mastercylinder.htm


What is the master cylinder ratio for the single disk + 14mm Ninja 250 MC?

 

[Guest]

I see EBC offers their pro-lite rotors for the CBR900RR. Do aftermarkets fit the GS wheels also?

 

[salty_monk]

Does this Vintage Brake chart still make sense? http://www.vintagebrake.com/mastercylinder.htm


What is the master cylinder ratio for the single disk + 14mm Ninja 250 MC?

Without doing a lot of measuring I can't say... but the stock is 5/8" and the stock Kawasaki is 5/8" and both feel ok. The Stock 250 is 14mm (as is the twin piston KLR) and the stock Suzuki single is also 14mm.

 

[salty_monk]

I see EBC offers their pro-lite rotors for the CBR900RR. Do aftermarkets fit the GS wheels also?

They fit as much as the stock ones do... that's to say all of them need drilling / spacing correctly. I have fitted a few sets of EBC

 

[hannibal]

A question about clearances from the caliper bracket to rotor: How does this look? This is with a 40mm bolt on all three fork mount/bracket positions. Is this what you guys are running? In the first pic, I'm concerned about the lower fork mount to caliper bracket bolt shown without a nut. The second pic shows the same lower fork mount bolt without a nut and the caliper bracket bolts.