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86 slabby brake upgrade questions

5K views 9 replies 6 participants last post by  Gixxerider86 
#1 ·
I want to make my 86 Slabby a bit more potent and I'm thinking to start with what I feel is the weakest part of the bike, namely the brakes. For now I plan to keep the original forks and 18" wheels, but later on they might be swapped too.

I want good braking bite but also feel, I do not want on/off light switch type of brakes. I testrode a 2018 GSX-S 1000 and the front brake was very twitchy, I did not like it at all, so I want to avoid that.

I have researched a lot and have come up with the following so far, but I still have some questions so I thought I would turn to this forum, as you guys have done every modification possible to these bikes and know what works and what doesn't.

For the brakes I was thinking to do the following (starting from top to bottom)
Master Cylinder
Stainless steel lines
EBC pads

Q1 Some say that the calipers are not the weakest part of the system, so will this be a good setup together with the original calipers? Or do they need changing as well? If so what do you recommend?

For the Master Cylinder:
1) GSX-R 750 Slingshot 1988/1989 MC
2) Bandit 1200 2001-2004, Hayabusa 1999-2007 (Same look as the original and direct fit)
3) R6 OEM Brembo Radial 16x18 MC
4) Brembo/Nissin 19x18 MC

Q2 Is there a difference in performance between #1 and #2? If so, what is the better option between them?
Q3 a) For #3 and #4, is it overkill and will it work with those small calipers? b) does it fit (fairing clearance)? c) Brake light cable connection?
 
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#2 ·
From further research:

MASTER CYLINDER BORE SIZE: 16mm / 5/8" (15.870-15.913mm). Piston diam. 15.827-15.854mm
GSX-R 750 1985-1987* (confirmed in owners manual)
GSX-R 750 1988-1989 (confirmed in owners manual)
Bandit 1200 2001-2004*
Hayabusa 1999-2007* (confirmed in owners manual)

I have concluded that they all use a 16mm (5/8) bore master cylinder.
I saw many recommend to use a MC from these models, but since they all have the same bore size as the original (even the same piston for Busa and Bandit), will they still be an improvement?



* Slabside, Bandit and Busa even have the same Piston and cup set product number: 5960045860. (MC product numbers are different though).
Source:
 
#3 · (Edited)
an addition to your list should be lightweight floating rotors. they reduce rotating mass allowing quicker stops, floating rotor allows more progressive braking feel. I think EBC still makes replacements, the steel alloy they use will have a better bite than the OEM stainless alloy. If you are not changing the MC/caliper bore ratio "feel" will not come from changing the MC alone unless you are changing from standard to radial MC, or adjustable lever to get the lever right where you want it, or a longer lever allowing for more leverage. here is a link to a MC/caliper bore ratio chart, if you are interested. Also i wouldn't dismiss the effect of tuning your forks will have on braking performance.

 
#5 ·
Service your calipers & master cylinder, have they ever been done before - look at: www.brake-masters.com
You will be surprised how much crap you will find behind the pistons - use the right tool to remove your pistons or get a kit including new pistons.
Its not that hard to do, just be aware of the hidden cir-clip you need to remove before pulling the master-cylinder piston and take note in which order it comes apart.
Replace discs & get a good set of EBC pads - look at: www.s3performance.com.au
 
#6 · (Edited)
Good call about the ratio! Any other 16mm MC will feel the same. I was thinking of going with the R1/R6 OEM Brembo 16mm MC, which is radial so will offer some improvement but it will still be more or less the same, but with everything else also upgraded it should do well. I fear that going with a 19mm would be overkill and produce a wooden lever.

I read some guidelines that stated that the

Ratio of BRAKE CALIPER TOTAL PISTON AREA to MC PISTON AREA should be around 22:1 to 28:1.
30:1 - soft feel
27:1 - sweet spot for design
23:1 - firm feel
20:1 - wooden feel


The stock calipers are 4 piston with a diameter of 32mm.
BRAKE CALIPER TOTAL PISTON AREA = 804,25mm^2 * 8 = 6433,98mm^2 = 6433,98mm^2

MC PISTON AREA
:
16mm MC = 201.07mm^2
19mm MC = 283.53mm^2

A 16mm MC would give me a ratio of 32 : 1
(6433,98 / 201.07 = 32.00)

A 19mm MC would give me a ratio of 22.7 : 1
(6433,98 / 283.53 = 22.69)
 
#7 ·
Digging further into this I found out that the R6 has smaller caliper pistons; 27mm and 30mm, which is why the 16mm MC works so well, because this combination gives it a ratio of 25.5 : 1

Some more digging and I calculated the ratios for two bikes that I think have great and not so great brakes, it seems it holds true.
Panigale 959 ratio of 28.5 : 1
SUZUKI GSX-S 1000 ratio of 22.7 : 1
 
#8 ·
The ratio of MC to Caliper is by far the most important aspect in "feel" IMHO. I have used that chart in selecting caliper/ MC combos on two bikes with complete custom brake setups and it has always led me to great results. Vintage brake has a lot of good information on their site.
 
#9 ·
all good advice, and i totally agree that the front rotors will need to be replaced with "floating" style. keep in mind that the first gen 1100 had semi-floating rotors, but they were larger, so the calipers were drilled differently.

besides all of the other advice, i'd keep this in mind. when making changes. fresh fluid, rebuild master and calipers, steel braided lines, and proper bleeding should help, though. it's all relative, and should provide decent braking for street use.
 
#10 ·
I know what you mean by "twitchy" brakes on modern bikes, thats why the levers are adjustable. I put them to the softest setting and it makes them much better. With that in mind, going with modern MC's will give you this option. I'm running a hayabusa complete front brake setup on my slabby and really like it
 
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