Twinpot Brake upgrade on 78 Skunk

[limeex2]

I used a 84-86 GS550E rear brake disc. They bolt right up. I did use different caliper and spacers though. The bolt pattern was the same, not sure about offset.

[Adi]

Hey Chuck78, really appreciate the advise and I definitely think losing the rear disk for weight alone would be a huge benefit and worth the effort but if I can also get a more mellow rear brake by doing this and avoiding swapping out the caliper that is a bonus. I will post some feedback on results once I have finished making a mess.
I did consider the 310mm Blackbird disk but I was trying to max out the front brake strength with the largest disk possible, you live and learn I guess.
Thank you again for the guidance.
A.

[Chuck78]

This got me thinking about the rear caliper and particularly the weight of it and the fact that it is way over powered.

Does anyone have any suggestions regarding rear brake replacements / upgrades?

275mm katana front right swap to GS rear:

https://www.ebay.com/itm/263409313238

The holes are 10 mm or so to accommodate the special very large shoulder bolts originally on that year of katana. I just drill a new hole pattern with 8 millimeter holes in between those holes, but I suppose you could figure out a way to use the katana shoulder bolts if the thread size is the same, which I believe it is. Spacers would need to be fabricated though, so you may as well fabricate a top hat spacer to reduce the size of the hole to 8mm, or else just redrill.

The reason your rear "caliper" is so overpowering is because 1977 GS 750 use a single disc 295 mm rotor up front, and also a single disc 295mm rotor in the rear, same rotor... it is the rotor diameter, NOT the caliper, which causes the overpowering rear brake...
In 1978, the Suzuki engineers switched to a 275 mm rear rotor. This was not overpowering, but the rotor was still very heavy as all of that day are. This late 80's/early 90's Katana rotor is the same diameter, same deep 23mm offset, but has floating rivets, and is SIGNIFICANTLY lighter. You can then use a rear disc caliper hanger off of a 1978 or newer GS with 275 mm rotors to upgrade a 77 monster rear brake to a reasonable and useable size, and then bolt a slightly lighter gs650 caliper to it if you wish (not a significant difference in caliper, but DEFINITELY in rotor weight).

I have been playing around with single disk set up on one of my GS750’s. I picked up an Aprilia Tuono 320mm disk and drilled out the disk holes to 9mm to make it fit, though considering remaKing the holes in between the original holes with your spacer as 8mm holes in exactly the right position seem a better idea!

The sticking point at the moment is the disk offset as it is only about 8mm..., but about 21mm on the original disk, but I am thinking I can double up the spacers behind the disk and replace the original bolts for slightly longer ones to compensate.

Would this seem plausible?

Also, 320 mm rotors do not really work with the bracket configuration for calipers that are used for this modification, You won't be utilizing the outer 5mm of the disc friction surface and that area will be extremely close to rubbing the caliper or caliper pins.
BUT...a 310 mm rotor does work for the GS single-disc forks from bikes that used a 295 mm factory disc. I would abandon your 320 mm plans and just find a Honda 310mm rotor. Honda CB1 (20mm offset?), Honda CBR1100XX Blackbird for a couple years in the 90's (17.5mm offset), and 98-99 CBR900RR (23mm offset). All will need the holes very precisely aligned and drilled in a drill press from 6mm to 8mm. This will work pretty darn well.

[Adi]

Hi Dan
The brake bracket kit you sent through is excellent, thank you so much. I intend to use it on a twin disk front end with 296mm CBR disks etc as advised, but I have been playing around with single disk set up on one of my GS750’s. I picked up an Aprilia Tuono 320mm disk and drilled out the disk holes to 9mm to make it fit, though considering remaKing the holes in between the original holes with your spacer as 8mm holes in exactly the right position seem a better idea!

The sticking point at the moment is the disk offset as it is only about 8mm on the Aprilia 320mm disk and, as I measured it, about 21mm on the original disk, but I am thinking I can double up the spacers behind the disk and replace the original bolts for slightly longer ones to compensate.

Would this seem plausible?

I added an bandit 600 master cylinder with stainless hoses and it all seems far more effective and significantly lighter.

This got me thinking about the rear caliper and particularly the weight of it and the fact that it is way over powered.

Does anyone have any suggestions regarding rear brake replacements / upgrades? I have put this out as a separate thread question but thought I would ask here!

Regards
Adi

[salty_monk]

Yep, one back today. I should be able to ship them out tomorrow if all goes to plan

cool! can ya send me a set please? i'll message you!

[salty_monk]

One back at ya... Those Disks & Zephyr Calipers look like the right ones.

I have brackets on the shelf. Powdercoated black as normal. Henry Ford Model!

[Joegs1100gk]

Hi Dan, PM sent regarding bracket set. Cheers

bought some guaranteed genuine Honda items for an extra tenner they are 296mm dia so they should be ok also got some ZR 550 Zephyr calipers from Germany all i need now are some brackets

https://www.ebay.co.uk/itm/173329296890?ul_noapp=true

[Chuck78]

I don't recognize the looks of those rotor centers, I think they are aftermarket. Not sure if they are EBC though, but they are unfamiliar looking. If they fit the model stated, then they should work.

hi Dan you got any brackets in stock for the brake upgrade? for my 1978 GS750?

https://www.ebay.co.uk/itm/112894361898?ViewItem=&item=112894361898&fromMakeTrack=true

these discs correct?

cheers bud! looks like im going to have to spend some time on this!!!

[Chuck78]

Your pictures will not enlarge, not sure how you posted them, but zooming in to the very fuzzy thumbnail pictures, they look like opposed-piston 4-pot calipers, which will not work so well for this because the vintage wheels are wider in the spoke area. Also, those calipers are not the style that the brackets being sold in this thread are designed for.

They must have the reversible steel mounting bracket with the lightening holes drilled into it, and two pistons on one side of the caliper only, one larger than the other. Look up a 1989-1996 or maybe 1999/2001 Suzuki GS500 caliper.... if a caliper looks just like that, then it will fit. The GS500 will only give you one side, you need dual disc. So look for a Concours Kawasaki, some ZX 1100 ninjas, some zx600 Ninja if I recall, or a GSX 1100 G Suzuki. There should be a fairly comprehensive list somewhere in this thread that tells you what donor bikes are good to get the calipers off of. If hunting single calipers, early EX500 ninjas have a left caliper, later EX500 ninjas have a right caliper, or vice versa.

[johnod]

Dunno , pics don't open.


If you, like send me your email address and I'll send you the list of parts that should fit.